I bought a p600b 9 psi setup and i need advice on head selection.
I have a set of pocket ported gasket matched LT4's, and a set of ported LT's...LT1's flow 252 cfm and 191cfm at .600 with 1.94-1.50 Manley's...
Which heads should i use? I'm putting in a set of forged pistons for 9:1 compression and i also need a cam recommendation.
I called ATI, they weren't much help.....I figured you experienced blower guy's would know. Thanks for any help.

 

I'd get some flow number on the LT4's to see which is better. Absent that, I'd make a guess that the fully ported LT1 heads will be better.

Either of the following two cams works for 90%+ of centrifugal LT1 cars. Which to pick depends on how high you want to rev. The bigger cam requires very stiff valve springs and definitely upgraded pushrods and good quality rockers. The smaller cam can get away with quite a bit less spring and probably stock pushrods.

CC XE lobes #3190/3192 on a 114 LSA and a 114 intake center line. 214/224 @ 0.050" .530/.567"

CC XE lobes #3192/3196 on a 114 or 116 LSA with an intake center line of 112 degrees. 224/236 @ 0.050" .567/.585"

Rich Krause

 

Rich,

What are the RPM differences between the two cams that you listed?

 

Smaller cam peaks at ~5,800rpm, the bigger cam ~6,400. They are the most aggressive of the XE lobes and even with a lot of spring are prone to valve float. I am using the 224/236 cam and even with CC #977 springs, which are ~130 on the seat and have a ~440lb/in rate it, will float the valves at ~6,700rpm with my setup. So, these lobes may not be the best thing for an NA setup, but are wonderful for a blower car. You just set up your blower to produce the desired max boost at the above rpm's and you are good to go. The large "area under the (lift) curve" combined with positive manifold pressure is an awesome combo.

Rich Krause

 

Great, thanks for the information Rich. I will plan on building my combo around the larger cam.

BTW, how does the different LSA affect the performance/drivability/enjoyment/sound of the car?

 

the 114 lsa will give you better driveability, easier to tune, and it is much better for a blower setup. It will not lope as much because the overlap will be less. the 224/236 is a great cam lots of people use it.

 

Sorry to intrude with a question for Rich but it goes along with the topic. I am running AFR 190s and just bought the smaller cam you were talking about. You mentioned using 977 springs. My AFRs are cut for a 1.530" diameter spring and looking at the Comp catalog saw the 929 spring which has a little more pressure and a recommended max lift of 0.650". Would these work well if I used 1.6 rockers?

Thanks guys

 

Thanks for the help Rich, I would like to run peak power at 6000 or so. I will be using stock rods and a Scat 9000 series crank and forged pistons. ARP main studs (a little insurance) and rod bolts...It will be fully balanced and should live on 9 psi....
Just wasn't sure which head to run, the larger runners and valves,or the ported LT1's with flow #'s...I would expect the LT4's intake flow is the same, but the LT1's are bettor on the exhaust. This is an M6 car that is mostly street driven by the way.
Thanks for the cam recommendation's.

 

Yes, but if you want this cam be careful what you order. What most people have is the low lift version. What you want are the lobe # I listed. And a 116LSA is better for the bigger cam, most of these are made on a 114.

Rich Krause

 

That spring looks good.

Rich Krause