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Procharger Power
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I just did mine a few weeks ago with a13.2 motor and the cranking compression was in the 240-270 range.
Holy Christ that's high.:p Sounds to me like there isn't enough exhaust duration. Had plenty of 15:1 engines and have never seen more than about 225.
 

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Back when I ran a 13.5 to 1 motor it was always in the 190-195 range.
 

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RED ROCKET
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i am 170 at 15.1..big nitrous roller...advance the cam 6 degrees and it goes over 210 but eats pistons like that but its a beast on motor only.LOL
 

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Cam timing and the speed of the starter. Plenty of short track motors will tap a gauge out even with a low static comp.
 

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Discussion Starter #13
Thanks for the info. Seems like numbers can vary quite a bit....back to the drawing board.....

Anybody ever experiment with forward facing hood scoops? Would it be possible to loose power, and even 60' by removing one? I have a friend who freshened up his motor and car seemed to slow down across the board. Same rings, bearings, clearances etc.... and also removed the scoop. Motor cranks 200+psi and even on all cylinders, leaks down fine, re-did the valve job, headgaskets, re-checked where the cam was installed, even went through the trans and converter with no luck. Car is deadly consistent just off on power and starting to run out of ideas....
 

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Cyl pressure is based heavily off of cam timing, and is a good test to make sure the cam you have is right on. There are variables though, as it can be misleading. Just knowing a number means nothing as all the parts would need to be mentioned to know if you are where you need to be. Anything too high just means you have too small a camshaft for the combination and compression used. I have done alot of testing with this and have kept track over the years with each combination which tells me where my duration and lsa/ic needs to be. You can have a good number but can be due to a real small cam profile or too big and you will be down on power, so there is no way to know for sure if the number is right on without knowing the rest of the combination. Engine needs to be at operating temp, plugs out, carb wide open and cranked over untill the needle basically stops. Again, just keeping a consistent test from one to the other is important.
As for the forward scoop, sure, you can see e/t fall off if you remove it. Only if it was properly done from the start, being sealed off and things like that..Just haveing the forward scopp doesn't guarentee it will go faster but if done right it will and you will see a difference if removed.
 

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...THE above post is correct....!!!!

O.P.
I dunno WHY you think that it is a certain number that it is suppose to be.

the compression gage IS NOT MEANT to be used that way....

it is ONLY a comparator,..to compare one cylinder to another.

the only mannor to use a psi gage to COMPARE after you allready know BEFORE what it made.

I CAN change just about any given amount of pressure as seen on a compression gage by changing the valve lash or cam timing.
 

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Want more cranking compression? Set the lash at .050...dont run it like that...just try it on one hole...then put the lash back to where it is supposed to be and run it.
 

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I've got a good friend and customer who builds lots of winning SBC dirt track engines. He always uses a software program to predict the cranking pressure, then verifies it after break-in. He says the software is always within 10psi and a very good "double check" that everything is correct. I don't know what software he's using, but I will find out if anyone's interested. According to him, he has the best luck with 230-240 psi on high compression combos (over 13:1), and shoots for that number when selecting and installing a camshaft. His experience is that engines over 240 get very picky on the tune-up, and under 230 he's leaving something on the table.

I know this is not a drag race application, and a broad torque range is required to pull the car out of the corner. But hopefully you can learn something from his approach and apply it to your application.
 

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I've got a good friend and customer who builds lots of winning SBC dirt track engines. He always uses a software program to predict the cranking pressure, then verifies it after break-in. He says the software is always within 10psi and a very good "double check" that everything is correct. I don't know what software he's using, but I will find out if anyone's interested. According to him, he has the best luck with 230-240 psi on high compression combos (over 13:1), and shoots for that number when selecting and installing a camshaft. His experience is that engines over 240 get very picky on the tune-up, and under 230 he's leaving something on the table.

I know this is not a drag race application, and a broad torque range is required to pull the car out of the corner. But hopefully you can learn something from his approach and apply it to your application.
What octane fuel is he running with 230-240 psi?


For those interested, here is a cranking compression calculator http://www.rbracing-rsr.com/comprAdvHD.htm
 
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