I am having trouble deciding on what cam to choose for my 408 rear turbo set up. I am presently running the 408 NA with a Chet Herbert cam, spec'ed at advertised duration of 292/296, duration at 0.050" is 230/240 .592/.602 Lobe center is 114 IO BTDC 1, IC ABDC 49, EC ATDC 6, EO BBDC 54. The rest of the engine build is as follows:

Ported L92 heads
GMPP Single planed carb intake with injector bosses drilled (the one pictured)
Fast 92mm TB
Edelbrock elbow (the one pictured)
6.0L block (LQ9) bored to 4.030"
Ross pistons with -12 reverse dome
Cometic head gasket 4.060" bore and 0.040" compressed
Should be 10:1 compression I think.
4" eagle shaft
eagle rods
Hooker LT (I will be going back to the stock manifolds once the rear mount is finished)
presently Fast 39# injectors

I have taken this car out to the track a few times now and I am very disapointed in its power output. It is crap really. I paid for 580-600 hp at the crank and I think its only making 430 hp at the crank, and at our alltitude of 3500 feet. I have played with the tune enough to know the power loss is not in the tune, it has to be in the engine combo.

I have most of my rear mount set up gathered up. I need to get the larger injectors, twin in tank fuel kit, and choose the right cam. Then just lift the car and start working my buns of fabricating and installing. I am using a GT76 with a .91 Turbine AR, front mount A/A intercooler. I am looking for at least 800 rwhp at my alltitude out of this kit and I want the cam to be able to be street driven.

Thanks for the input.

 

Look not bad for duration and reasonable lifts. Should be fine. The lower lsa will give a bit of lope but likley still work ok . Most turbo cams seem to generally be 115 and higher for lsa. Some like duration like yours a normal split, some like no split and some reverse split. Lots of cam theories out there.

We need gm high tech performance to run some turbo cam comparisons and test out some of these theories. Would like to see a test with lots of cams.

 

hot cam i think its good

 

Bump^ Any other input?

 

Call a sponsor and get a custom grind for your setup....

 

yeah i would talk to a sponsor and get a custom grind but the 76 is going to run out of juice quick and i doubt youd see 800rwhp+ out of it. i would go with a pt88 or something along the lines of that. its a decent size turbo but itll leave you a lot of room to grow

 

I did this when I chose the turbo. Sponsor told me to go with the 76, people on here told me to go bigger. I am now stuck with this turbo. I did mention it is a rear mount, or maybe I left that out.

I was told by the turbo sponsor to "just try the cam out". I guess since it is in the car, thats what I will do.

It better make the power I want. The turbo sponsor sold me the 76 while telling me it will move enough air for 1000 chp. If it can not do this then they scamed me and I will expose this. I have all comunications in email with them.

The turbo is a sour subject with me. I realy do not want to go there. I just want to try to select the best cam for the combo, so I can make the power promised with this turbo.

 

I agree that you should just try the cam that you have. I don't buy into the theory that all turbo cams should have a certain split. I think that it is more a function of the head design. The L92 has a very well flowing intake port and a shitty exhaust flow. Hence the split towards the exhaust makes sense here.

Now as to why your combo isn't working. In NA form, your combo is going to be a pig. The carb intakes don't start making power until way up in the power band. If you are still running the 3800 stall, that's your first problem. The second problem is that the elbow that you are using is a known major restriction. Basically that intake has nothing down low and then the elbow kills the airflow up high. Add to that the fact that you are only at 10:1 compression and it's no surprise that you are disappointed.

I think that by just changing the elbow and adding the turbo (no other changes), you will be pleasantly surprised. If that doesn't turn out to be enough, then start swapping other stuff around.

EDIT- Do not change the headers for exhaust manifolds. That's only a good thing when building a front mount.

 

You make alot of good sence. What elbow would you suggest? All I know or can say about the elbow is when my head porter was porting my heads and intake, he was very stund. He claims the elbow did nothing negative when he tested it on his flow bench. That said, his bench does not flow what an engine flows (at least I would think, I could be wrong on this) above 4000 rpm. I can see how in the upper rpm it could cause an issue. So what do I do to correct it?

I am also thinking like you on the intake/exhaust split. The only way to know for sure is to try it, so I am going to do that.

I realy do not wish to change the stall to a higher one. Part of the reason for me going turbo is I am wanting to go to less stall when I finaly finish the 4L80. I am hoping I can compensate for less stall with a transbrake. I again could be very wrong in my thining here.

I am up to changne out the elbow to see if the top end comes alive. The car as is realy feals like the top end is missing. My builder is thinking the cam has too much exhaust duration. He said once he finished the porting the exhaust was alot better then most say. I know he only ported the intake side to match the intake manifold flow, then did alot of porting on the exhaust to make it the correct balance with the intake side. That said we both were expecting more out of this engine then we see. It does make good sence the elbow is the problem. Lord I realy hope it is that symple. I do have a friend who has one of those fabricated elbows. When the porter had my heads, he had both the fabricated elbow and the Edelbrock elbow. He tested both and he said the fabricated one had a negative effect on his bench. So we chose the Edelbrock for that reason and also because it would fit under the hood without modifying it.

As for the headers, of course I have yet to run a turbo car so what little I know about turbo cars is minimal (hence why I am here), but from what I have gathered here on LS1Tech, most people claim a rear mount turbo benifits with faster spool times using the stock manifold. Please explain what you mean.

Thanks and I will be looking forward to your recomendation on a good elbow, as well as correcting me were needed.

 

I made real good power with ported L92's and a turbo, never ran it N/A.
My cam is an off the shelf deal 238-242 .605-.610 on a 115 lsa. Single plane GMPP intake that was hand gasket matched to the fel pro gasket. I am not a big fan of the Edelbrock elbow. Might just be me, I just don't like it. I use Aaron's at intakeelbows.com it is pricey though, but did seem to work ok.
Keep in mind this whole setup will shine with the turbo. It is way over cammed for L92's NA, and with the GMPP intake is mismatched for a NA combo. It will come alive with the turbo.

 

Just do a search and you will find that swapping from an Edelbrock elbow to sheetmetal is a huge improvement in airflow up top. Your current converter should be good also. Like I said before, get a good elbow and setup your turbo. I think that it will really wake up.

 

Will do. Thanks for the info.