How important is intake valve lift w/street blown motor?

[DeltaT]

I picked a Comp solid roller lobe that, with the 1.7 ratio on the intake rocker, will yield me a net .630" lift. Duration is gross 242@.050.

With the AFR 235cc heads, should I bother pushing the lift higher with a lobe change? I could go to a Hi-torque .406" lobe that would get me up into the net .672" lift range. With boost, does the intake side lift matter that much? I hate to leave so much of the intake flow capability these heads have on the table.

Thanks,

Jim

[Ron C.]

Jim, for your blown street application I would stick with the lower lift. This will help spring life which will be more important than a possible performance increase, if any.

Blessings..........Ron .

[DeltaT]

Thanks, Ron. Even with this lift, do you think I'll have to change springs every few years? And if the springs were out of the equation, is adding lift without extra duration worth anything in terms of power?

Jim

[bigjoe1]

It depends on what you consider a street setup- You are going to leave about 200 HP on the table with that little cam


JOE SHERMAN RACING ENGINES

[raynorshine]

lets tell the whole story...won't you have to rev it up to see the potential..

[PWMAX]

I can give you an idea. 2 557 8-71 bbc marine engines, I built, they make 1100hp a piece with about 7 lbs boost, ran them for a few seasons, solid roller cams. He was sick of valve train maintenace, so I switched them over to hyd. rollers. Old cams were fairly snorty, 265 at .050, .748 gross lift. Switched to 248 at .050 .647 lift hyd. cams. Engines were down about 100hp at high rpm, but up to about 5500 or so, the averages were better with the hyd. cams, the idle quality was better. It is propped to turn about 6000, so, that extra power up top was never even seen. Boost is king. Want more power, change pulleys. That would be the best bang for your buck by FAR. The engines above make 1500hp with a simple pully change and race gas.

Frank

[Ron C.]

Thanks, Ron. Even with this lift, do you think I'll have to change springs every few years? And if the springs were out of the equation, is adding lift without extra duration worth anything in terms of power?

Jim

You've left a bunch of info about your project out of the equation. So I'm assuming .........well, I'm not sure what to assume.

More lift to a point will net a little more power, but more duration will get you there more. So it really depends on what your after in this blown street project. What do you want out of it???

Blessings..............Ron.

[CamKing]

Supercharged engines respond to more lift, but not as much as an N/A engine does.

Going from .630" lift to .672" lift would increase the top-end power a little bit, and your springs would live 1/2 as long. Just because a head flows to .800", that doesn't mean it wants .800" lift.
If you want to take advantage of that size head, you need to increase the duration and turn it more RPM. If the engine isn't built to turn more RPM, then leave the cam alone.

[DeltaT]

What do you want out of it???

If you're interested, here's an engine compartment shot:

http://home.mindspring.com/~jim_fisk/si ... de_med.jpg

In rough order:

- I need to have a reasonable idle. This is a sleeper and, other than some exhaust rumble, it can't sound like it is cammed to the moon. If a cop car is sitting next to me, I don't want them perking up their ears. The 3" duals with H-pipe are fully wrapped in ceramic batting and header wrap which really tones down the exhaust note.

- I would like decent cruising mileage. I've got it up to about 20mpg with the current 3.73 gears. I am going to take a hit when I convert to E85, but will retain the ability to run pump gas or a mix.

- 7000rpm is my target redline and the motor is built to handle it and not worry if I go over a bit.

- I am all right with a valvespring change every few years. I put about 3K miles/year on the car.

This car will see mostly street, some autocross (I have a 4L80E automatic with paddle shifting), some road race. It will probably get a gear change in 2010 from 3.73 to 3.08 or 3.23. Goals are ~800rwhp, 10.xx @ >140 in the quarter, 175mph or better in the standing mile.

Thanks for the all inputs. This is a great forum; I learn stuff all the time here.

Jim

[DeltaT]

Any more inputs with this new info?

Thanks,

Jim

[raynorshine]

street blown

what does that mean exactly.... this looks more like a turbo project..

[DeltaT]

It's got a medium-sized centrifugal supercharger on it, with a large intercooler before the motor.

Jim

[F1Fever]

I think the general consensus is to go with the lower lift, btw, with that car you'd take my money
The monday evening I raced an s10 all cammed up and 2-4's sticking out of the hood and the malodorous smell of lead fuel. When I asked him if he wanted to race he said "yea, I'll spot you a few lengths", I said no need and proceeded to get him by a couple.. all on 87 octane