Let's talk about PSI and how cams affect it...
11-04-2006, 01:40 AM
#61
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Originally Posted by engineermike
Probably because most people can reach their goals with small cams and FI. Hey, if you can get in the 9's at 140+ mph with a smooth idle and you're not interested in going any faster, then why switch to a larger cam.
I had an interesting conversation with a local turbo guru tonight. He races a car that runs in the 8's with twin turbo's and a blow-through carb. At one point, he swapped from a 242/242-114 cam up to a 259/259-114 and, lo and behold, the car ran faster with the bigger cam at the same boost level.
Mike
I had an interesting conversation with a local turbo guru tonight. He races a car that runs in the 8's with twin turbo's and a blow-through carb. At one point, he swapped from a 242/242-114 cam up to a 259/259-114 and, lo and behold, the car ran faster with the bigger cam at the same boost level.
Mike
11-04-2006, 09:40 AM
#62
Originally Posted by Got Me SOM
how much faster? Were the weather conditions the same? 60 foot the same?
Mike
11-04-2006, 10:04 AM
#63
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makes sense if he has those high flowing heads that a bigger solid roller cam would work better for him in the upper rpm levels. Was he a hydraulic cam before? Picking up 6 mph in the 1/8 is significant.
06-02-2007, 11:04 AM
#64
I am bringing this one back up.. I noticed in the entire post no one mentioned what would happen on the other end. We agree that a bigger cam will remove restriction inside the engine, but once it goes out the exhaust will we run into the backpressure issue?
06-02-2007, 11:34 AM
#65
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I think it's going to be different for blowers vs. turbos. With the wastegate, the turbo should spin whatever it needs to so it will put out that PSI. Big cam...small cam, you should put out the same PSI. It will affect how efficiently the car runs. Traditionally, a smaller cam with less overlap will work better with a turbo. That's all I have experience with...no blowers.
06-02-2007, 12:41 PM
#67
Originally Posted by Pro Stock John
A lot of backpressure at the turbo(s) means your turbos are the restriction, given a certain amount of exhaust gases exiting the engine.
06-02-2007, 01:05 PM
#68
FormerVendor
Originally Posted by VINCE
Well that is true. Now explain how a bigger cam would affect this?
I convinced myself at the time that the high backpressure was causing reversion so I tried a few different cams, such as reverse splits and high LSA's, etc, which killed power. Ends up that single pattern (or even standard split) cams with relatively tight LSA's have always come out on top with the stuff I deal with so that's what I continue to use.
I can only guess that even with average exhaust manifold pressure being 2x boost pressure a scavenging effect can still take place during overlap due to the high velocity and inertia of the exhaust gases
06-02-2007, 01:42 PM
#69
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Originally Posted by andereck
Stop it Mike, you're just going to screw up what everybody knows as an absolute with that stuff. You can't run overlap with forced induction. Why you'll lose all the boost out the exhaust....lol.
and this particular discussion is not sticky worthy....least not yet.
and this particular discussion is not sticky worthy....least not yet.
06-02-2007, 01:56 PM
#70
Originally Posted by INTMD8
My technical response to that is -I don't know-. What I do know is that when my LT1 was single turbo and backpressure was measured at 2x boost pressure increases in overlap still translated to gains in power.
I convinced myself at the time that the high backpressure was causing reversion so I tried a few different cams, such as reverse splits and high LSA's, etc, which killed power. Ends up that single pattern (or even standard split) cams with relatively tight LSA's have always come out on top with the stuff I deal with so that's what I continue to use.
I can only guess that even with average exhaust manifold pressure being 2x boost pressure a scavenging effect can still take place during overlap due to the high velocity and inertia of the exhaust gases
I convinced myself at the time that the high backpressure was causing reversion so I tried a few different cams, such as reverse splits and high LSA's, etc, which killed power. Ends up that single pattern (or even standard split) cams with relatively tight LSA's have always come out on top with the stuff I deal with so that's what I continue to use.
I can only guess that even with average exhaust manifold pressure being 2x boost pressure a scavenging effect can still take place during overlap due to the high velocity and inertia of the exhaust gases
06-02-2007, 09:14 PM
#71
Originally Posted by VINCE
You mentioned tight LSA's have come out on top in your experience.. How tight are we talking?
06-02-2007, 09:16 PM
#72
Originally Posted by Pro Stock John
A lot of backpressure at the turbo(s) means your turbos are the restriction. . .
Mike
