I am slowly building a 408 sb for my '90. I am looking to use AFR 210 competition port heads for a road racing application. I have talked to companies such as Crane and Comp cams, as well as Tony from AFR, and they all came up with about the same recommendations. I am looking into getting a custom ground cam to have power from 3000 to around 6500 RPM and shifting between 6800 and 7000. Tony told me to look for cams that are 242/248 and have .600 or more lift for these heads. I know JAKE just had a thread going where he stated if the exhaust flows 70% or more of the intake then a single pattern cam will benefit. According to the AFR website they advertise these heads to flow 308cfm int and 235cfm exh at .600 lift. This is about 76% exhaust. So why would Tony have such a big split on the cam? 248 would be too much for that high of RPM, I would think, so I was looking at something in the 242/246 or 242/244 range. I like the lobes from Bullet cams, and I am going to give them a call soon, but I was wondering what you guys' thoughts would be? The Bullet cam I had in mind is:

Int: HR299, 242 at .050, .625 lift with 1.6 RR
Exh: HR303, 246 at .050, 630 lift with 1.6 RR
LSA of 110-112?? I want around 400-450 RWHP and some streetability. A little lope on the idle would be nice too. I understand the wider LSA makes for a flatter torque curve, which would be nice for road racing, but what becomes too tight ot too ?

Yes? No? Close? on my suggestion...

 

The way the heads flow I agree with your assumption. However how is the rest of the exhaust from the headers on back to the mufflers? Do you have catalytic converters and are they high flow? Do you have a high flow muffler? IMHO the more restrictive the exhaust the more exhaust duration you will need. If you feel you have a good flowing exhaust system than you can cut back on the exhuast duration. I would favor a 112LSA for the street.

 

I have TPiS long tube headers and duel 3" pipes with two high flow cats and an x-pipe and LT1 mufflers. However when I am at the track I bypass the mufflers and just use the cats as race mufflers.

 

You think this place will know more than those pros?
Mamo knows his stuff.

 

I know Mamo knows his stuff which is why I was confused by the big split even though the exhaust flows more than 70%.

 

Any other input on the lobes or LSA?

 

I asked about this after purchasing AFR heads. I believe the ideal of a single-patter cam to be geared for an ideal situation of either: heads/headers only, situations where even higher exh/int percentage exists, or for low-rpm power production.

One reason for eliminating a split duration [and using a single pattern cam] is to keep from bleeding off TQ -- especially at low-rpms. (Removing some of the exhaust duration reduces the overall/combined duration). With your higher rpm application (and the 76%), some split has to be beneficial -- otherwise it wouldn't have been recommended.

After purchasing AFR's myself, every person/company I've asked [about using a single pattern cam] has said at least 4-degrees is necessary/useful when choosing a cam.

If a couple of degrees is critical to your application, why don't you let a designer flow the parts and design a cam for you?

 

Sounds like a pretty free flowing exhaust. I don't think you need much of a split. 2 to 4 degrees should do it. On my car the cam designer recommended a single pattern camshaft. It has worked out very well. I have read many of Tony's camshaft replies and have talked to him myself. I bet he would agree.

 

Thanks for the info. I dont have money for the heads but I am trying to build around using them. This build has been going on for a couple years as I acquire money.

 

FYI: Talked to Bullet Cams today. I asked to make sure I guessed correctly.... They did confirm that more split becomes necessary as rpms climb. As rpms climb and the valve-open time shrinks, it gets harder and harder for exhaust to escape

So, for higher rpm applications, they do recommend some split. Basically, Bullet guys said if over 6k rpms, build in some split.

 

Yes I too called Bullet cams the other day and this is what they recommended:

Intake: HR297/382, 242 @.050, .611 lift
Exhaust: UHR300/3823, 245 @.050, .611 lift
LSA: 110 degrees

I too was told even though the heads are very good flowing that the higher RPM would benefit from a split. These guys really know what they are talking about. When I talk to Comp or Crane they have a little different opinions on what I should get but cant really explain why. Bullet cams told me everything I wanted to know and why.

I think I will be ordering this cam.