CJ intake for road racing

[Performance nut]

I have been curious about why you dont see the CJ on more road course cars. It seems like all things there are trade offs but I'm wondering if this was a very specific application intake manifold.

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[WildHorse]

The advantages of a CJ over say, the 18 GT manifold come at over 7500 rpm. Revs = heat.

Then explain the BOSS intake, made specifically for the track.

 

[Bluemustang]

The advantages of a CJ over say, the 18 GT manifold come at over 7500 rpm. Revs = heat.

Yeah, exactly. More revs = more heat. So if your car can't finish a session because it overheats, that's a problem lol.

 

[WildHorse]

Which the 18+ manifold beats...

Both with a 7500 redline, so by your logic, the 15-17 would be a better track car. Less RPM = Less heat.

 

[EFI]

Both with a 7500 redline, so by your logic, the 15-17 would be a better track car. Less RPM = Less heat.

The 15-17 is the better track car, especially comparing manual to manual. And yes, a stock 15-17 revving to 6800 manages heat better than a 18+ revving to 7500.

 

[WildHorse]

The 15-17 is the better track car, especially comparing manual to manual. And yes, a stock 15-17 manages revving to 6800 manages heat better than a 18+ revving to 7500.

Good thing I shift a 7000 haha

 

[EFI]

I have been curious about why you dont see the CJ on more road course cars. It seems like all things there are trade offs but I'm wondering if this was a very specific application intake manifold.

Most likely because power, especially at the top of the rev range, is one of the last things any logical road racer would do. There are many many many other better ways to spend your money to go faster around a track than a CJ manifold.

It would take an experienced driver with an otherwise fully built race car to really get full benefit out of that manifold. Joe Schmoe running HPDEs a couple times a year is not going to be that guy, and a vast majority of people on this site fall in the latter category.

 

[WildHorse]

It would take an experienced driver with an otherwise fully built race car to really get full benefit out of that manifold. Joe Schmoe running HPDEs a couple times a year is not going to be that guy, and a vast majority of people on this site fall in the latter category.

Custom geared T56, 4.09 gears, custom cams, big ass headers, CJ intake, & never let it get below 6 grand.. Ima 1%er haha

 

[EFI]

Custom geared T56, 4.09 gears, custom cams, big ass headers, CJ intake, & never let it get below 6 grand.. Ima 1%er haha

Hope that's not all that you're doing to the car, because a guy on stock power with suspension and tires would run circles around you on track.

 

[AlbertD]

Heat is one of the primary concerns. I have made a custom sealed radiator box, bigger road race oil pan, opened grille up, hood venting, fender venting, 80/20 distilled water solution... All at stockist power levels and I just barely feel comfortable enough now to run the car at 10/10s for a 20 minute session... Even at that point I'll get close to 245ish Chts towards the end of the session. Adding power is no where near a thought or priority.

Its all about reliability, grip, suspension and most of all driver. I often see miatas pass corvettes. Power doesn't mean much unless it's that 1% as mentioned above and that's on a full prepped race car. At least that is my observation from doing this for a few years.

Now do I wish I could run an all out NA build, Rev it to the moon AND be reliable out on track... Heck yeah. Realistic ... Not really.

 

[v8hgt]

Technically the cj can produce more top end power than a gt350 IM or MY18 IM. However you need to be doing 7000 plus to see this area of the power curve. On a road course the driver has to spot apexes and such like for tens of minutes or hours hence revs will often dip to 4000 where the cj is less suitable, even a hindrance. On a drag strip the driver can just watch the tacho and keep it in exactly peek power band for the 11 seconds it takes. Part of the reason the corvette was so good in endurance races was because the power band is forgiving to the tired driver. The 911 driver has to work the paddles and tachometer with more concentration. Same is true when comparing small turbo to big NA. Eg the jag xjr v12’s vs 962’s. With a totally flat torque curve the driver can concentrate on their lines instead of missing shifts or being caught out with turbo spool up.
I am no Rossi, hence I am considerably faster round silverstone on my Ducati 1198 than on a 4 cylinder litre superbike despite being down on headline power as a litre bike, like the cj needs to be in a very narrow high rev power band to come alive and I find myself missing downshift too frequently and hitting the apex a couple of thousand rpm before power builds, hence getting passed out of corners by more experienced riders or people on big twins.

I have a gt350 IM on my 17 gt and I am honestly considering swapping back to stock manifold after 2 yrs of it as I think the stock torque curve is more suited to road driving and my mustang will never see any track work.

 

[K4fxd]

For all those reasons I believe the 18 truck manifold is the answer for a street bluemoon track car.

I think the 18 manifold will pull to 6500 and have the flat higher torque curve.

 

[Bluemustang]

Heat is one of the primary concerns. I have made a custom sealed radiator box, bigger road race oil pan, opened grille up, hood venting, fender venting, 80/20 distilled water solution... All at stockist power levels and I just barely feel comfortable enough now to run the car at 10/10s for a 20 minute session... Even at that point I'll get close to 245ish Chts towards the end of the session. Adding power is no where near a thought or priority.

Its all about reliability, grip, suspension and most of all driver. I often see miatas pass corvettes. Power doesn't mean much unless it's that 1% as mentioned above and that's on a full prepped race car. At least that is my observation from doing this for a few years.

Now do I wish I could run an all out NA build, Rev it to the moon AND be reliable out on track... Heck yeah. Realistic ... Not really.

I think there is a lot of truth to what you're saying. I appreciate you sharing your experience.

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