After 1 summer of running this "throwed together" setup i'm thinking about making it a little more "sophisticated"...

right now as it sit
engine(010 1976) 357cu.in cast piston, x rod, gm crank...balanced, was in a circle track car
edel perf. Rpm 170cc(int) heads(64cc)...never worked
edel perf Rpm air gap
holley 650DP....basic tune
xe274
hedman LT headers 1 5/8" dual 2.5" with one magnaflow(xpipe muffler)
stock gm rocker/fuelpump/hei dist mecanical

trans built 700r4 manual shift
3500 10"conv
4.11 gear and 28" hoosier slick(need 16" wheel because of ls1 brake)

car have subframe and Rod end lca/panhard bar

car was going great all summer....running mid 12 at 110mph on hot day....best of 12.29 at 110mph on a cold day high7-8 1/8 about 1.65-1.70 (60') depend on track prep

downside....car stopped pulling hard before 6krpm....and i'm sure theres more power hiding somewhere.

The new thing i will had this summer...whant to know if im going the right way

fuel system
Aero S/S pump with bypas reg set at 5.5-6psi...3/8 line
ignition
mallory 685 ignition box
rocker
1.6 comp cam magnum roller tip

this should help my top end power???take in consideration that i will be using a sniper kit running 100shot....maybe 150 if wallet allows

thanks for your help....
Seb

 

Before you throw a bunch of money/parts at it check the valve spring pressures. The engine won't RPM like it should if they are getting weak. It will act like a fuel starvation problem.
Sounds like you have a velocity type setup going on with the dual plane and 170cc heads, smallish cam, and smallish carb. I wouldn't expect gobs of RPM's, but paying attention to the springs and other low cost details like checking fuel pressure with a guage through the traps couldn't hurt.
Those relatively smallish heads could still use more duration and carb to help compliment the top end trap RPM. The intake should be fine.

 

What is your compression ratio and race weight?

I wouldnt expect the XE274 to perform much further past 6000RPM. My car would run best shifting around 5700RPM. You say you had the stock fuel pump in the car? That is most likely why it's losing power up top.

I'd think a combo like that could run in the 11.70's without too much trouble assuming your car isn't a tank.

 

weak spring....my heads have about 4k km in it how can they be weak

comp should be around 9.3-1 I know its low...cast0.04 over dished piston and about 3600lbs with me and gaz

Thanks for your help
Seb

 

wowie... at only 9.3:1 and 3600lbs your car actually looks to be running unbelievably good. Either way a new fuel system might be the ticket to quicker times.

 

Soon as you said "stopped pulling hard at 6000" all I could think of was valve spring pressure. Second guess would be a lack of fuel at high rpm.

The XE274H cam is rated at 0.490 lift which is just within the limits of stock springs. The 1.6 rockers will increase that to 0.522 lift but are the heads set up for that much lift? It's possible you've already had coil bind and some valve springs could be broken. That cam only has an operating range of 1800-6000 rpm.

Pull the rocker covers and visually check all the valve springs.
Borrow or rent an on car valve spring pressure tester and check spring pressures. How much pressure does it take to start opening the valve?
Do a compression test.
Do a leak down test.
Change the fuel filter.
Pull the plugs and check for any damage and plug gap.

 

good to know...ill work on tuning the carb a little better, removing some weight...putting new parts above and I should be looking at high11 time slip...Ill try shifting 5500-5700rpm and shifting in 4th in the end of the 1/4....I may be switching to 3.73 or 3.42 this summer...i think my 4.11 are to much with a 700r4 and will start to break near 1.5x 60'

Seb

 

forgot to had heads are rpm performer rated at .560 lift.....stop pulling hard before 6000rpm....forgot to had at the end of the strip....1 and 2 its pulling good...thats why there is some confusion....sorry my bad

Seb

 

Did it pull hard over 6000 rpm before? If so then it sounds like it might be a fuel problem. Lack of fuel at high rpm isn't as noticeable in the lower gears.