Cam overlap? (no guesses please)

[Squirtcha?]

Cam specs and reversion have been done to death here on the forums, and I've searched and researched for an answer to this question to no avail. What is the maximum degree of overlap you can get away with when using logs or wet headers?
It's been talked around, but never directly answered. I've got a buddy that's looking into cams for a mild BBC 454 build up (log exhaust on a V-drive) and he could use the information to aid him in the selection.
I'm running a Clay Smith hydraulic flat tappet 108 centerline, 244 duration and .570 lift with 28 degrees of overlap and don't seem to have any problems. With my combination,the cam produces a very flat torque curve on DD (in the 400 ft. lbs range all the way from 2500 rpm to 6500 rpm and peaking at 502 ft. lbs. at 5000 rpm). The horsepower curve is also very flat and peaks at 525 hp at 6000 rpm. This is similar to what he's looking for.
Thanks
Dan

[Cas]

DAn,
I can't answer your question about the maximum overlap but here's a suggestion on a cam. I've got this one in my engine and I'm pretty happy with it. It's kind of going against some people's ideas about cams but I was able to see dyno sheet comparisons of a couple of different cams installed in the same engine. The peak HP and TQ was virtually the same so I chose the cam that wouldn't put as much stress on the valve train.
I installed it at 0º, ran good but I'm leaving some ponies on the table since I'm only getting to 5100 rpms. This winter I'll be taking a couple things apart so I can reinstall the cam at +4º. That'll lower the peak by about 300 rpms.
ISKY CAMS
Grind No./Type
296 HYDRAULIC High performance use/bracket racing. Good idle. 2800 Stall. . Up to 800 CFM Carb. RPM-Range
2500-6500 Valve Lift - INT .510
EXT .510
Valve Lash Hot - INT .000
EXT .000 ADV Duration -
INT 296°
EXT 296°
.050 Duration -
INT 234°
EXT 234°
Lobe Center 114°

[Cas]

if you're going to run it on DD, the other numbers you need are
ivo- 3
ivc- 51
evo- 51
evc- 3

[Squirtin Thunder]

Dan,
I ave been told by many people that .250 Dur.@.050 is max for wet headers.
Logs you shouldn't have any problem but being the flow is down I wouldn't go over .240@.050.
That is just me
Jim

[Taylorman]

I cant answer your question but this picture is interesting study material. I have been reading about cams all morning. I have finally seen the light. I have finally figured out with certainty why everyone is saying to adjust valves using the EO/IC method. This picture says it all.
http://carcraft.com/techarticles/116...basic_10_z.jpg

[ttmott]

Dan,
The answer is as tough as the question; each cam behaves differently depending upon the total engine combination. Combination meaning:
1. induction - carb and carb size (1 or 2) or EFI and EFI calibration.
2. Intake manifold - ram, dual plane, open plenum, or for EFI ram size and length
3. Heads - chamber vol and type, runner length and vol., valve sizes.
4. Desired maximum operating torque range (RPM)
5. Exhaust - tubular headers (diameter, length, collector size and length) or in your case log manifolds.
6. Ignition specifics.
7. Cam degree (straight up or advanced or retarded).
The answer is: get what you think your engine combination and load criteria and call Comp Cams, Crane, Clay Smith etc. and talk with them. The bottom line is, and this is what they will tell you, keep the overlap to a minimum (read that gross lift) when using non scavanging exhaust systems otherwise the reversion will kill your bottom end power and idle qualities. Overlap, especially when dealing with flat tappet cams, is a result of the gross lift; the higher the lift the greater the overlap. This is why roller cams are the king for dual use boats.
I am sure this only messed you up.....
Tom

[ttmott]

Oh Yea and most importantly -
8. Piston and C.R.

[Fogged Gullwing]

Dan,
Dont log manifolds inject the water just after the risers? I know they dont do it at the ports because they basicly water jacketed. I would not think that they would be affected by water.
Just a thought BK

[BobS]

Dan,
Most of the engine builders hang out in the gear heads forum, you may want to go fish over there.