Throttle bodies, cold air intakes and headers

[Tnmustcobra]

I am wanting to get a little more out of this 4.6L 4V engine and have been looking at the aftermarket throttle bodies. I see that Accufab makes one and that BBK makes one. The Accufab is a 70mm whereas the BBK is 65mm. From the installation instructions for the Accufab I see that material has to be taken off the plenum in order for the Accufab butterfly to clear the plenum. The BBK throttle body requires no fabrication to install. I like the easy install, but from what I hear, the Accufab will deliver a little more horsepower than the BBK unit. I was wondering if the installation of a spacer between the throttle body and the plenum would solve this problem so the Accufab would have clearance without grinding the plenum. I also plan on getting another mass air sensor and a cold air intake. Most of the cold air intakes won't fit with the strut tower brace still on the car. I prefer to keep the strut tower brace on the car and wonder if anyone has a cold air intake that does not require removing the strut tower brace, other than maybe for installation. Also, planning on long tube headers or shorty headers and wanted to know what everyone is running on their Cobra.

Thanks,
David Morrison

1997 Mustang Cobra
1987 Porsche 944 (NA)
2004 Ford F-350 Dually
1988 Mustang AV8SS Unlimited race car (sold) :(

[cvalois1]

The JLT Carbon Fiber CAI fits with the Maximum Motorsports STB :thumbsup: The intake tubing is oval shaped from the TB down to the turn into the fender well, where it becomes round.
http://i126.photobucket.com/albums/p91/VNEMUS/IMG_2415.jpg http://i126.photobucket.com/albums/p91/VNEMUS/IMG_2417.jpg

http://i126.photobucket.com/albums/p91/VNEMUS/IMG_2416.jpg

http://i126.photobucket.com/albums/p91/VNEMUS/IMG_2418.jpg

http://i126.photobucket.com/albums/p91/VNEMUS/IMG_2414.jpg
There was some minor modifications made to the rubber elbow JLT supplied to make it fit nicely. The hp gains are minimal. A larger TB on a basic bolt-on NA set-up will also show minimal/negligble gains (not worth the money IMHO).

[Tnmustcobra]

Thanks for your info. The 4V motors are not easy to get any "good" HP from these bolt on parts. It seems the only way to gain decent HP is by adding a supercharger. My guess is adding Throttle body, Mass Air, Cold pipe and some headers may yield an additional 25 to 50 HP ...with an offroad H-Pipe. Sometimes I wished I had a 95 model with the 5.0L. I currently run an offroad H-Pipe, K&N air filter, 3:73 gears and chip. Just need extra HP to chase down 03' and 04' Cobra's down the straights and the 2000 thru 2004 ZO6 Vettes. Got the handling and brakes modified and can get up on their bumpers in the corners, only to have them pull better down the straights. Might change the rear to a 4:10 to help off the corners.

Any other thoughts about getting some good HP without adding the supercharger?

Thanks,
David Morrison

1997 Mustang Cobra
1987 Porsche 944 (NA)
2004 Ford F-350 Dually
1988 Mustang AV8SS Unlimited race car (sold) :(

[nckissfan]

replacing the MAF will not gain you much, unless you are supercharged. I say keep the money for something else. Get some pullies, they help squeeze out some horses. As for CAI, I am running the upper and lower pipes from Western Motorsports. They fit under the stock stb. I didn't know that the JLT would fit under the Maximum stb. That is cool. Adding longtubes helps in the hp department, but steals a little from the tq department. The 4.10's are awesome in these cars. I have them in mine, and love them, really opens the car up. You could replace the drive shaft with an aluminum one. That will free up a lot of weight, and strain on the drive train.


shedding weight is a good way of gaining on the competition. You could rear seat delete(if you don't need it).

[Tnmustcobra]

I don't know if I want to go with underdrive pulleys since that will slow down the water pump and run into possible heating issues. I like to open track this car and I currently do not have any overheating problems. I already have the rear seat out of the car. I have all the MM stuff (coil overs, control arms, CC Plates, panard bar, etc...). I have thought maybe the 4:10 gears would help and also am considering the Aluminum driveshaft and also an aluminum flywheel. I will probably wait till I need a new clutch before I get the flywheel though. I don't know if 4:10 gears would reduce my top end enough to max out on straights like at VIR or Road Atlanta. I was hoping to get more HP or TQ and still keep the 3:73 gears. I just don't want to spend $4000 right now for a supercharger...but may have to start budgeting for one. Anyway, I pretty much have the handling and the brakes where I like them and now am trying to look at the motor next.

David Morrison
1997 Mustang Cobra
1987 Porsche 944 (NA)
2004 Ford F-350 Dually
1988 Mustang AV8SS Unlimited race car (sold) :(

[cvalois1]

David, is your car primarily daily driven with ocassional track use (road course and/or dragway)? The 4:10s would be good for the street and dragstrip (0 - 100mph) but probably not as good on road courses, as you'd loose some top end in the straights and depending upon the gearing in your tranny is stock.

I have 3:73s and think they're decent for the road courses, but I started to notice I'm topping out at 130 - 135mph in 4th gear at 6250 - 6500 rpms and shifting into 5th at the point doesn't add much. I've actually been thinking of going down to 3:55s to gain a little more on the top end. Like you, I've made suspension and chassis upgrades to keep up with the stock 385 - 405hp Z06s and similar type cars.;)

The big advantage those cars have are they are well balanced and weigh less. Like NicK said above, try reducing weight, starting with the aluminum DS and a rear seat delete and maybe going with a lighter weight battery and/or relocating it to the trunk. Anything to reduce rotational mass in the drivetrain, wheels and brakes helps considerably. From there the weight reduction can get even more expensive, such as stripping your interior and going with lightweight race seats, tubular k-member, a-arms and coilover suspension.

By the time you do all that, you could probably buy a decent supercharger kit. It just depends on what you want to do and how much you're willing to spend. Good luck:thumbsup:

[Tnmustcobra]

The car is garaged for the most part and primarily is used for open track and also am contemplating some TT with NASA in 2009. I bought the car new and it has 33,000 miles on it. The first 3 to 5 years had some driving to work and around town or an occassional trip out of state. I ran NASA HPDE 1,2 and 3 for about 3 to 4 years before I built the race car (1988 coupe) and raced in NASA American Iron Extreme and AV8SS Unlimited. I will still take the Cobra out on the street for some playtime or to check suspension adjustments. I tow the car to the track. I know a stock 96 thru 98 Cobra with the 305 HP will not top out in 5th and I would always just run it up to 4th gear on the track. After installing the offroad H-Pipe, 3:73 gears, K&N filter and the chip, the car would pull a little in 5th, but I still was able to keep it in 4th at tracks like VIR and Road Atlanta, which have some pretty long straights. I also was running in the 130-140 MPH range on those tracks. My thinking was that if I could get to around 400hp (at the flywheel ) then maybe I could pull 5th on some of the straights without having to go to the 4:10 gears. Now that I have all the MM suspension installed (coil overs, tubular control arms front and rear, CC plates, panard bar, Koni DA, etc...) I expect to be able to go into the corners a little faster and come off a little faster as well. I already have the rear seats and trunk panels and carpets removed and since I have the MM suspension parts, my weight has dropped a little. I could probably take out the AC stuff and get some lightweight race seats (would like to have a seat for passengers). Some of the weight saved would be offset by adding a roll cage. I am running CCW wheels and run a competition tire like the Hoosier or the new Goodrich R1, so wheel and tire weights are lower. I still know those Vettes will be fast down the straights. I am aggressive on the brakes and can go deep into the corners and roll into the the throttle coming out of the corners as best as the car can grip. I try to find the line around the track and drive my line. I can keep pace with these Z06's under braking and in the corners. I just need a little more out of the motor to at least maintain speed with them down the straights. Then, maybe I will be able to get past them and pull away with late braking and rolling thru the corners faster. I am only talking about stock C5 Z06 Vettes..not the C6 Z06 Vettes.

I will do what I can do to reduce weight, but still am trying to figure out how to get more HP/TQ out of the car. I was hoping that by posting on this forum, that I might get some advice on getting more out of the motor. These mod motors are not easy or cheap to get more out of them and sometimes I wish I had an earlier model like a 95 with the 5.0L that is so easy to put in cams and stroker kits. Looks like not much I can do to get a lot out of the motor without spending a fortune. I had to sell the race car because the budget to run that car was more than my wallet could handle, but it was fun and worth going broke! Guess I'll go with the aluminum driveshaft and a throttle body for now and try to lose some weight off the car. My main obsession is to get the Vettes.

Thanks,
David Morrison

1997 Mustang Cobra
1987 Porsche 944 (NA)
2004 Ford F-350 Dually
1088 Mustang AV8SS Unlimited race car (sold) :(

[cvalois1]

The addition of LT headers to your current set-up will probably show the most gains. Forget shorties. With the LTs, you'll need a new mid-pipe too. You might see 320 rwhp. Maybe consider an aluminum flywheel next time you have the tranny out or are replacing the clutch.

If your goal is 350 - 400 rwhp NA, you'll need to spend more than just adding a supercharger, unless you have experience or know someone to help you pull your motor and do machine work. It sounds like you already know this.;)

On the cheaper, not so evasive side you could pull off your upper and lower intake and sent it out for porting and polishing, which will probably run anywhere from $500 - $1,500. From there, it gets more evasive, dropping/pulling the motor, pulling your heads off and porting them from $1,000 - $2,000+ and you might as well factor in a valve job while your at it. While the motor is out, that's the time to the cams too ($750 - $1,500).

Then while everything is off the block a big bore and/or stroker kit could be done ($1,500 - $2,500). If you go the ported and cams route, you'll also probably want/need a set of larger 30lb injectors, better fuel pump & new tune ($500 - $1,000). It gets real expensive really quick. Ball park figures to do all this yourself is $5,000 - $7,500, $10,000+ if you buy all the parts and pay someone to do the work.:eek:

For me, keeping up with the general maintenance open tracking the car (tires, pads and rotors) and the cost of HPDEs is considerable enough on an annual basis, nevermind owning and maintaining an actual race car. Seat time at the track (not mods) is the best money spent IMHO:thumbsup:

[cobrabitn]

You can get 375- 400 rwhp if you change the heads on your Cobra along with a couple of other mods. You will need the FR500 heads to make this happen. If you want a naturally aspirated engine for the track, this is the way to go and I recommend this for what you are wanting to do with your Cobra.

P.S. I also recommend not going any lower than (numerically higher) 3.55 gears for the track especially at VIR.

[Lumpydogs]

Tony,

You always give good advice :thumbsup: but what about the no lower than 3.55 for VIR? My 4.10 was fine at VIR last year. Just curious.

[puzzle13]

You need to talk with Burke concerning all of your questions!! His car is going through a huge process concerning the engine, FR500 heads that have been completely ported, the motor is built, he has 3.73's in the back and is topping out at 130 - 135 at 7000 rpms, and he wants more. The long tube headers are a problem with the 97's due to transmission conflicts. If I understand correctly you can't remove the tranny without removing the headers, and to remove the headers you have to take the engine loose. As I said ... contact Burke at bdbadcobra@hotmail.com ! He is tracking the car a lot and it is one fast Cobra!!! The throttlebody issue ... you will have to grind with both throttle bodies to get full performance, which is not a bunch without a supercharger. With the BBK you have to grind away at the plenum so the openings match the BBK openings. It will work without this, but won't work to its full potential. Again ... contact Burke for first hand info as there are complications with the FR500 heads also, but his car is in my garage being put back together and we can send you pictures. Yes, he also had fun getting a brace to fit with his JLT cold air. First hand knowledge is always best.

[cobrabitn]

You have to see where you max out in 4th gear when you are running at VIR. My 5.0L is maxing out at 120 mph and when I hit 5th, it just dies. Having 4.10's is good for the street but if you are maxing out at VIR and still have asphalt left then you should go to a higher or even stock 3.27's. You don't want to waste the power you have by holding steady. JMHO

I was going to say that Mike about Burke but I didn't want to put his e-mail addy out there with all of the spam bots we have visiting our forums every day.

[Tnmustcobra]

Lots of good information here and I appreciate everyone's input. I will look into some of these mods and even though the performance heads and cams seems the way I would like to go, I'll have to see how the budget works out before I can make those purchases. I will probably wait till after the 2009 season ends before diving into the motor. I am also thinking hard about what I can do to lighten the car and some of those things are take out the AC, replace the leather power seats with some good lightweight race seats (will add harnesses and roll cage) and possibly change the windshield to Lexan. Another thought is to purchase some dummy doors with the roll up handles from the Mustang salvage yard and gut them out and replace that glass with lexan or equal. I am definitely getting the aluminum driveshaft in the next week. I see some NASA events at VIR and Road Atlanta coming up this spring and will definitely see how the car has improved since all the MM suspension goodies are installed. I will watch 4th gear down the straights and see what RPM I am running to see if a gear swap might be considered. I will talk to Burke and see what he can tell me about all the work he has done to his Cobra and get some good feedback from him before I start anything inside the motor. In the meantime, if anyone is going to be at VIR or RA around March, let me know and we can meet at the track!

Thanks,
David Morrison

1997 Mustang Cobra
1987 Porsche 944 (NA)
2004 Ford F-350 Dually
1988 Mustang AV8SS Unlimited race car (sold) :(

[puzzle13]

Who are you running with in March at VIR? Or did you mean CMP? Burke will be at CMP and his car should be quite quick! He pulled the A/C, cruise control, fiberglass hood, etc. I told him you would email him and he said he would help as his modification list is quite long!:D

Tony ... I was worried about that too, but Burke has nothing to do these days except hang around in my garage, so I figured a few extra email might keep him busy!!

[Tnmustcobra]

I was looking at the NASA mid-Atlantic schedule and they have dates with VIR full course on 2-21/22-09 weekend and then again on 3-28/29-09 weekend. I was thinking the March weekend would be a little warmer weather and the last time I went to VIR in February it rained. The NASA Southeast schedule shows CMP on 2-6/7-09 weekend, then Road Atlanta on 3-14/15-09 weekend and then back to CMP on 5-2/3-09 weekend. I really like VIR and RA as they are my favorite tracks. I have not been to CMP since it was reconfigured and I bet it is really fast now. I guess the "Kink" is gone....I really liked that feature! I just looked up the CMP schedule with the Cobra Club March 14/15 weekend and that is tempting, too! I also noticed Burke was running Tech and Scott Whitehead was classroom instructor. Would be good to see what Burke has done to his Cobra and maybe run in the same group. I also could say hi to Scott....we "bumped" into each other at Nashville Superspeedway a few years ago. Scott is really a cool dude and he helped me with my set up on the race car. Last time I came to CMP and ran with the Cobra Club...back in 2006 or 2007...I think... I helped instruct and might try that again if there are any openings for instructors. All these dates are so close together it will be hard to make a decision.

David Morrison

1997 Mustang Cobra
1987 Porsche 944 (NA)
2004 Ford F-350 Dually
1988 Mustang AV8SS race car (sold) :(

[brkntrxn]

The "kink" (ie T10) is still there in the new configuration at CMP (full course). Only T12, T13, and T14 have been changed, along with repaving in some of the other key turns around the track.

Here are some of my thoughts (some are echoes of those above):

- As for your 97 and any modular 4.6 car with low torque, weight reduction is the key. Consider swapping the k-member, deleting AC, lightweight wheels and body parts, etc.

- An aftermarket throttle body on a naturally aspirated 4.6 does not provide any gains. Unlike the 302s, the stock 4.6 TB is good for over 600hp in most applications, so I wouldn't bother with that upgrade.

- Cold air intake such as JLT

- Ported and polished heads and intake are good proven ways to get gains.

- Headers. Longtubes are better, but you may have issues with dropping the trans later. If someone makes them, look into mid-lengths for your car. I have JBA shorties on my car and I like them, but they are leftover from the blower setup where longtubes are not as important.

- A set of aftermarket (properly degreed) cams, but that can get expensive because you are tearing into the motor

- A bump in compression and a .020 overbore are also good if you happen to go that far (so is stroking it but that is another can of worms)

- Don't forget suspension. More ground is made up in turns and in braking zones that on the straights.


Kevin


(edit: added longtubes comment)

[puzzle13]

I was looking at the NASA mid-Atlantic schedule and they have dates with VIR full course on 2-21/22-09 weekend and then again on 3-28/29-09 weekend. I was thinking the March weekend would be a little warmer weather and the last time I went to VIR in February it rained. The NASA Southeast schedule shows CMP on 2-6/7-09 weekend, then Road Atlanta on 3-14/15-09 weekend and then back to CMP on 5-2/3-09 weekend. I really like VIR and RA as they are my favorite tracks. I have not been to CMP since it was reconfigured and I bet it is really fast now. I guess the "Kink" is gone....I really liked that feature! I just looked up the CMP schedule with the Cobra Club March 14/15 weekend and that is tempting, too! I also noticed Burke was running Tech and Scott Whitehead was classroom instructor. Would be good to see what Burke has done to his Cobra and maybe run in the same group. I also could say hi to Scott....we "bumped" into each other at Nashville Superspeedway a few years ago. Scott is really a cool dude and he helped me with my set up on the race car. Last time I came to CMP and ran with the Cobra Club...back in 2006 or 2007...I think... I helped instruct and might try that again if there are any openings for instructors. All these dates are so close together it will be hard to make a decision.

David Morrison

1997 Mustang Cobra
1987 Porsche 944 (NA)
2004 Ford F-350 Dually
1988 Mustang AV8SS race car (sold) :(You should run VIR on Feb. 7 & 8 with Vernon and myself at the Tarheel event. We always seem to get good weather at that event ... knock on wood! The kink is still there at CMP and imho it really isn't any faster or better, just different. I think Vernon, Burke & I are going to run RA with MVP Track Time in November. I have heard too many negative things about HPDE's with NASA. We are trying to maximize track time per event now. We will be looking at the schedule during our bowling event in G'boro on January 10th. Burke got his engine running tonight and now we will be putting the finishing touches on reassembly & bodywork over the next few days. I should be getting my 03 back from paint on the 5th. Burke is waiting for an email if you want to discuss mods!

[Tnmustcobra]

I just looked at the track map for CMP and notice the changes made and that the kink is still there. I just thought I had heard mention that the "kink" had been modified. I think the changes are good and will make a nice continuos turn going thru 12 and 13. Turn 14 looks to be wider and I am sure the racing series will appreciate the wider track and greater radius to get around 14 and have a little more room to make the pass. As far as NASA....What I like about this asssociation is having the HPDE, TT and race groups on the same weekend. If someone wants to eventually race in a series, they provide a variety of classes to choose from and you can talk to the racers and get their input on cost and effort. Track time may be less...I think they usually had 4 sessions per day at 25 minute sessions...but the classroom instructors and in car instructors were usually very informative and thorough on the physics and techniques for driving fast on a track. I learned a lot from Dan Unkefer and when I had advanced beyond the HPDE classes, I would still ask him questions on certain areas of the tracks that I was driving and where I felt I needed to pick up speed and he was always willing to share his time to help when asked. You could also ask different drivers what they were doing as there are different driving styles and cars handle differently, so you may find the answer that best fit your style and car's handling characteristics. I know that if you want to race Mustangs, then NASA has 3 classes to choose from; CMC, AI , and AIX. Each of these classes have different levels of cost to go racing and the classes are pretty competitive. I also raced in the AV8SS series and that was similar to the AI/AIX series, but covered a greater geographical area of tracks verses the closer track selection of the NASA regional groups. I never raced in the SCCA (just autocrossed in the local region here in East Tennessee). I attended open track at Road Atlanta with the Panoz group a couple of years ago and I enjoyed the fact that I could let a passenger ride with me....my brother would ride with me and we had a blast! They just required the same waivers and equipment as the driver in order to ride. I don't think they do that anymore as I have seen some accidents on track with passengers and I think the risk was too great to let drivers with limited experience take out passengers as they had a tendency to over drive the track ...probably trying to show-off. I was running in a TT at a Hyper-fest at Beaver Run in 2003 and they were letting spectators ride with us during a special session and the spectators were able to experience what it was like to be in a car on track at speed.

Back to the original topic. I have e-mailed Burke and gave him some info and will await for his response. I think the heads and cams ....possibly a stroker kit would be what I would want to do, but will probably prepare some planning before going into the engine and will wait until after the 2009 season ends to allow proper time to possibly go in this direction. For now....just try to set up the MM suspension for the track and improve my skills with the car as is...maybe try to shed some weight here and there throughout the next few months.

Thanks to all. Sorry for being so long winded! I can't help it ...I like fast cars and driving fast and that is my passion! :D

David Morrison

1997 Mustang Cobra
1987 Porsche 944 NA
2004 Ford F-350 Dually
1988 Mustang AV8SS Unlimited race car(sold) :(

[brkntrxn]

You should run VIR on Feb. 7 & 8 with Vernon and myself at the Tarheel event. We always seem to get good weather at that event ... knock on wood! The kink is still there at CMP and imho it really isn't any faster or better, just different. I think Vernon, Burke & I are going to run RA with MVP Track Time in November. I have heard too many negative things about HPDE's with NASA. We are trying to maximize track time per event now. We will be looking at the schedule during our bowling event in G'boro on January 10th. Burke got his engine running tonight and now we will be putting the finishing touches on reassembly & bodywork over the next few days. I should be getting my 03 back from paint on the 5th. Burke is waiting for an email if you want to discuss mods!
I think someone has been looking at my spreadsheet.....


Kevin

[tcrews]

You have to see where you max out in 4th gear when you are running at VIR. My 5.0L is maxing out at 120 mph and when I hit 5th, it just dies. Having 4.10's is good for the street but if you are maxing out at VIR and still have asphalt left then you should go to a higher or even stock 3.27's. You don't want to waste the power you have by holding steady. JMHO

I was going to say that Mike about Burke but I didn't want to put his e-mail addy out there with all of the spam bots we have visiting our forums every day.Tony, a stock 4.6 Cobra (96-98) can pull 160 mph in 4th gear with 4.10s.....at 7,000rpm. With stock gears your top speed is going to be in the low 150's. Some of the cross country racers have shown videos of their cars pulling 160 mph in 4th (something they said they couldn't do with 3.27).

Now Tnmustcobra, throttle bodys on these cars do nothing except remove money from your wallet. Unless you add major major supercharged boost...you should stick with the stock one.

Your "basic" power adders that work will be:

Underdrive pulleys
Headers (longtubes will make more usable torque in the powerband)
Offroad X or H (specific to going longtube or stock/shorties)
Cold Air Induction (not much...but will help)

Your "advanced" power adders that work will be:

Ported/Polished heads
Cams (specific to your needs and modified/stock heads)
FR500 Heads/Cams and Intake
Big Bore or Stroker engine...though if you plan on long term high rpm, the Big Bore is a much better choice for you. The 4.6 has a relatively long stroke for such a small engine....making it longer and having such a high revving nature is not something I'm fond of.
Higher compression (if staying naturally aspirated).

If you've got the desire and money I'd suggest the following:

Ported/polished stock heads and intake
Big Bore 5.0(money) or a .030 overbore (cheaper) with Forged pistons/rods with a bump in compression to at least 10.5:1, probably even 11.5:1
BBK Longtube headers, offroad X/H pipe
CAI of your choice
4.10 gears

Have the build discussed with your "builder" to maximize the air flow/velocity for your intended use, primarily in head/intake porting and cam choices. These engines love to stay in the upper rpms and having good flowing engine will really move the car, but too much "early" air flow (low air velocity) can kill your torque coming out of a turn unless you can hit a good RPM to keep the air moving (this is where the 4.10s, bump in compression help...4.10s for rpm, compression for torque).

of course reducing weight is like adding free horsepower so anything you can do there will help.

[brkntrxn]

Tony, a stock 4.6 Cobra (96-98) can pull 160 mph in 4th gear with 4.10s.....at 7,000rpm. With stock gears your top speed is going to be in the low 150's. Some of the cross country racers have shown videos of their cars pulling 160 mph in 4th (something they said they couldn't do with 3.27).



Tom,

I disagree with that statement. From running the calculators and from real life experience, a Cobra in 4th gear (1:1) with 4.10s and 25-26" tires, it will max out in the mid 120-130 (depending on rpm). My 99 Cobra was setup in that exact manner (26" tire, 275/40/17), 4.10 and at 6600 rpm redline going through the traps (or at the straights on VIR) it was hitting 124 in 4th gear.

Specifically, in 4th gear (1:1 ratio), 26" tire, 7000 rpms, 4.10 gear = 132.06 mph. 5th gear in that setup will take you to 197mph if you can get past aero issues.

4th gear, 26" tire, 7000 rpms, 3.55 gear = 152.52. 5th gear will take you to 227mph if you can get past aero issues.


Kevin

[tcrews]

The biggest problem, beside aero-dynamics, with calculating out is that those calculations are based on unlimited horsepower.

I may be off on what I was remembering....I just recall some of the cross-country racers discussing the merits of gear changes, etc... It might have been that a stock Cobra will stop pulling in 4th gear before redline and will not pull at all in 5th while a 4.10 geared Cobra will pull 4th to redline and still pull some in 5th.

So I must have been wrong on the gear (4th vs. 5th) but I distinctly remember the discussion and the associated pictures they posted of their Cobra's speedometer. I have the picture "somewhere" and I'll see if I can find it (3 computers, 1 laptop, 4 TB of storage....it might be a while).

I just remember the discussion involving weight, aero, resistance and the engines ability to pull/push the car beyond certain rpms (.....as torque and horsepower deminished the rpms would hold before maxing out)

Basic calc show:

160 mph - 3.27 - 4th gear - 6,848 rpm
160 mph - 4.10 - 5th gear - 5,752 rpm

I doubt any would use 5th in road-racing.....but these cars do prefer rpm (to a point of decreasing HP/TQ) and 3.27's sure don't help them.

[brkntrxn]

The biggest problem, beside aero-dynamics, with calculating out is that those calculations are based on unlimited horsepower.

I may be off on what I was remembering....I just recall some of the cross-country racers discussing the merits of gear changes, etc... It might have been that a stock Cobra will stop pulling in 4th gear before redline and will not pull at all in 5th while a 4.10 geared Cobra will pull 4th to redline and still pull some in 5th.

So I must have been wrong on the gear (4th vs. 5th) but I distinctly remember the discussion and the associated pictures they posted of their Cobra's speedometer. I have the picture "somewhere" and I'll see if I can find it (3 computers, 1 laptop, 4 TB of storage....it might be a while).

I just remember the discussion involving weight, aero, resistance and the engines ability to pull/push the car beyond certain rpms (.....as torque and horsepower deminished the rpms would hold before maxing out)

Basic calc show:

160 mph - 3.27 - 4th gear - 6,848 rpm
160 mph - 4.10 - 5th gear - 5,752 rpm

I doubt any would use 5th in road-racing.....but these cars do prefer rpm (to a point of decreasing HP/TQ) and 3.27's sure don't help them.
I agree. And the upper 5th gear potential is only a theoretical based on unlimited horsepower and no regard to aero issues.

People do use 5th in road racing. Anyone with a 4.10 gear or lower (numerically higher) will need 5th on long straights such as VIR full course back stretch (and maybe the front stretch), Roebling Road front, Road Atlanta back stretch, etc. to continue accelerating... rather than running it up to redline and holding it there while getting passed by someone willing to upshift to 5th.


Kevin

[Tnmustcobra]

I have ran my 97' Cobra at VIR in stock trim with the 3:27 gears and then later made about 40 rwhp gain and swapped to a 3:73 gear. Had R compounds later as well. With that set up I still had no need to shift to 5th since I only ran 4th up to about 6800 rpm on the back straight. I do know that when I was running a conservative lap and short shifted into 5th, the car still pulled a little....but that was at about 125 mph or so. Not sure what speed I was running because my speedo has not been corrected since the 3:73 gears were installed. Now that I have all new MM suspension parts and some more experience from the AIX and AV8SS Unlimited racing series, I feel I will be coming off the corners with a little more speed. I had wondered what the math was for going to 4th gear with 4:10 gears...which looks to be about
130mph-135mph maximum. I know all the Road and Track articles for the 97' Cobra also stated top end was about 156 as tested and was in 4th...the car slowed down when they shifted to 5th. The aero issues are the big problem for 5th gear. That was part of the reason for the original question for HP gains as I thought if I could get above 400 rwhp, then I could stay in 4th most of the time except on really long straights and then I could pull 5th better if needed with the 3:73 gears. I know that by swapping to 4:10 gears, I would accelerate off the corners better and should be able to shift in 5th if needed and still pull decent until I reach the latest braking zone. Of course, now that I see how difficult and costly it is to get 400rwhp from the 97' Cobra, I still don't have a clear picture what I want to do. I would have preferred to keep 3:73 and not have to use 5th, but 4:10's would be cost effective for better acceleration. I have made some weight savings as that is one direction to go in lieu of spending money to make more hp. 20 pounds here...20 pounds there...not much, but every little bit of weight loss helps. Let's see...how about if I lose about 20 pounds as well!

David Morrison

1997 Mustang Cobra
1987 Porsche 944 NA
2004 Ford F-350 Dually
1988 Mustang AV8SS Unlimited race car (sold) :(

[brkntrxn]

On my 99, when I had the supercharged 554rwhp and 4.10s setup, I absolutely had to shift to 5th because I was hitting 140+ on the back stretch of VIR. With 4th winding out at 124 with my 6600 shift pill in the shift light, I had to go to 5th to continue accelerating up to 140-145 by the time I got to the beginning of the braking zone.

Fast forward to late last year, I now have naturally aspirated 324rwhp (mustang dyno, more on a dynojet) and 3.55s, I stay in 4th since I don't have the power nor the gear to wind out 4th to 6800rpms before hitting the same braking zone on the back stretch of VIR.

Just my .02 on my experiences.....

I say go with the 4.10 if you want and go for weight reduction.

[snakbitn]

I have a 98 cobra with 310 rwh 302 tq with 373 gears and I hit 135mph @ 6800 redline in forth gear. And at all the long tracks I go to 5th it still pulls alittle up to around 145mph at like vir or road atlanta but that is all it will do which is pretty damn quick but the car weight is 3100 lbs plus my big a--.

[cobrabitn]

I basically have problems pulling in 5th gear with 302 rwhp and 333 ft lbs of torque in my 5.0 Cobra.

Thanks for clearing that up brkntrxn as I thought the number Tom gave was a tad high. Personally, you have other options like gear changing in the transmission like going to .85 instead of the .68 to one. That will allow you to run fifth gear on the front stretch at VIR and still be pulling all the way to turn one. Remember, I run a 5.0 so 4.10 gears would be out for me as I couldn't take it but I probably would be able to use 5th more if I did go to that gear. I might be going there too much though... :rotf:

Oh, to stay on topic, the throttle body would be a waste of money just like Tom said! :thumbsup:

[Cobra99.kr]

A good source guide for high performance Mustang is a book authored by Sean Hyland, High-Performance Mustang Builder's Guide 1994-2004 put out by CarTech (www.cartechbooks.com).
They also put out How to Build Max Performance 4.6 Liter Ford Engines.