stezhead54

So i have a chevy 307 block (yes i know most people think it's a boat anchor) some tbi 305 heads (which i know everyone hates), and i'm looking at a cam to open up the intake side a little more than the exhaust. All of the cams that i've seen have either more exhaust timing or an even amount of timing for both exhaust and intake. What i am curious about is if someone makes a cam with slightly more intake timing vs exhaust timing. Could i also just use 1.6 rockers on the intake and leave the exhaust at 1.5? I've read that the 187 heads have poor intake flow, but not too bad exhaust flow. Which is why i'm looking at something like this. Also i plan on putting a tpi system on it and i know they aren't known for their flow characteristics either. I guess what i'm trying to figure out is if i would have to get a custom ground cam for this build or if there's something already out there.

Fast355

iTrader: (2)

I would put something along the lines of a Comp 252 or 260 in that setup. The 307 actually has a more oversquare bore/stroke combination than a 305. You can think of debored 327 or stroked 283. The 307 is basically a large journal 283 block with a large journal 327 crank.

stezhead54

Checked those cam specs and they're both opposite what i was asking about. What about the comp 12-400-4 cam. I'm wondering about the intake and exhaust duration on the tpi intake manifold mostly. i understand that the tpi manifold doesn't flow very well at higher rpm's, so i was thinking that a longer intake duration might help that.

gwarren007

iTrader: (1)

Since the 305 uses "swirl ports" with a swirl in the runner, that is why the heads flow less. The "swirl" helps promote torque as well the TPI is designed for torque. Going for a longer duration on a 307 could really hurt any power that could /would be made.

IMO any cam over 210* (@.050) will hurt the 307/Tpi combination. A Comp
Cam 4x4 cam 12-235-4 IMO would be a great cam for this combo.

http://www.compcams.com/Company/CC/c...x?csid=95&sb=2

rusty vango

you need to work on the exhaust side of things. as this is where the flow problem is. more flow=more useable power

Fast355

iTrader: (2)

On the cylinder head itself this is simply not the case. Both sides need to be worked equally. The I/E ratio is already pretty good on the Swirl Ports, but both ports could flow better. On most TBI head builds the engine would do well with a SINGLE pattern grind. With the better I/E ratio the engine would not benifit from a dual pattern grind with more exhaust duration. The intake valve is also bigger and the port stalls out under .450" lift.

Adding intake duration will not do anything except make the low-end soggy as it is the runner cross sectional area and resonant frequency from the long length that keep the torque curve where it is. I would recomeend tightening the LSA to 110* and keeping the duration under 215* @ .050 and the lift near the .450" mark. The older 252H10 and 260H10 grinds do very well on a swirl port head engine, especially with TPI.

Fast355

iTrader: (2)

If it were my engine this is what I would use and I have done quite a few TBI and TPI builds using swirl ports.

The 252 will make a little more off-idle torque and be a little better suited for stock exhaust manifolds and exhaust system. The 260 would do well with a slight boost in compression ratio, headers and a free flowing exhaust setup. The 260 would also benifit from a slight increase in stall speed if you are running an automatic.

http://www.jegs.com/i/COMP-Cams/249/...d=#moreDetails

http://www.jegs.com/i/COMP-Cams/249/...rentProductId=

The biggest cam I would consider would be the 268, but it would just about require ECM chip tuning and some other mechanical considerations. Like 3.42 or 3.73 gears and a ~2,800 rpm converter to run best.

http://www.jegs.com/i/COMP-Cams/249/...d=#moreDetails

Fast355

iTrader: (2)

I had a Crane 272H10 (Equivalent to the Comp 268H) in a .040" over 305 with a pair of 350 swirl ports on it (1.94/1.50" valves, 64cc chambers, 9:1 compression) and a dualjet carb on top with shorty headers, dual exhaust and a TH350 with a 3,000 rpm converter and 2.73 gears. This is how it ran in a Heavy old C10 truck.