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Discussion Starter #1
I dynoed my SBC twin GT35R and was disapointed by the results. I wonder if my valve springs match the combination. Normaly they should but I saw many times that you run a lot more pressure then I do. I will take a few springs out and mesure the pressure. New they were 160lbs closed / 420lbs open.

My combo is still 355ci SBC Dart bloc, Vic Jr heads 9.75/1 CR, 2000cc injectors, E85 fuel, 1/1 pressure ratio, 1000cfm TB, timing 24°@20 PSI

The cam is this one with 1.6 rockers. MAx RPM 7000 - 7300.

http://www.summitracing.com/parts/CCA-12-704-8/

I expected 1100 - 1200 HP but the dyno looks desperately like that. What do you think about that.




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You should be 250-260 on the seat and 600-630 open.
 

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Discussion Starter #3
Thanks Liljohn,
I have a revkit on this engine does it make some sense to keep it installed ? I thougth it would be good for a street application to prevent the lifters from impacting the cams
I will try some strongest springs.
 

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I run that cam in myProcharger combo with the 1.6 rockers.

With 160# springs I had float at 6K rpm.

Talk with Comp and they said not to exceed 500#'s open with the -8 core (-8 =last digit in cam number)

I ended up running Comp 954-16 springs. Installed @ 1.860" is about 230#'s seat and about 515#'s open.

No more float and I'm spinning it to 7300 , 17 psi max boost.

---Bill.
 

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Discussion Starter #5
Bill what was the difference in power ? Could you really feel it alot stronger at 6000 RPM?
What about the pushrods you run with those springs?

Thanks for the details
 

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Discussion Starter #6
I have Comp Cam hiTech chromoly 5/16 pushrods 0.080" wall.
I just installed the 954-16 springs now let see what happens.
 

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Bill what was the difference in power ? Could you really feel it alot stronger at 6000 RPM?
What about the pushrods you run with those springs?
Thanks for the details
It's been awhile (2004) when I first put mine together.
Looking back it the old Chassis dyno sheets the power was going flat @ 5700 rpm, 590 hp with the 160# springs.

After the spring change and I also found the rockers hitting the springs, so I did a little grinding on them, power went up to peak at 712 hp @ 6200 rpm, 14.5 psi boost.
This was done with small tube headers (1 5/8") and a full (small) 2.5" exhaust sys. See chassis dyno sheet below dated 5-11-2005.

Since then I have changed headers to 1 3/4" , and a 3" exhaust sys.
But have not been back to a dyno, been looking at ET and MPH for results.
Feels like power now peaks at about 6,800+, and using ET/MPH to weight calcs, it's making 775+ RWHP.

For push rods, after installing lash caps (Dart Pro 1 heads) 7.950" Comp http://www.summitracing.com/parts/CCA-7994-16/ got my geometry correct.



---Bill.
 

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Those GT35's would have there tongues hanging out at 1200hp. If they are not all in, or damn close to it, you will not see that kind of power no matter the valve spring, and if this is a auto car, forget about dyno numbers.
 

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Discussion Starter #9
OK, I will race it in the end of next week and play with the timing to max everything out. I feel like I can do a 145 + mph pass with 4000lbs
Maybe will be time to upgrade those little turbos. If they are all in, the boost should peak and even drop with RPM ?
 

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Once you set boost past what the airflow can maintain, it will start to drop. The higher you set the boost, the lower the RPM that it will start to drop and will become more obvious. If you're maxing out the turbo for just the last 500 rpm or whatever it can be harder to spot. Back pressure is a good indicator of how maxed out the turbo is too. As you approach the turbo's limit back pressure will start to rise exponentially for minor gains in boost, or will rise exponentially as RPM rises if you're only maxing it out on top (need to log it against rpm to see this, the mechanical gauge setup won't help here).
 
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