Visit The Dirt Forum for More Information

Author Topic:   sbc cam question
sledgehammer
Member
posted December 04, 2003 09:19 PM
I have been talking with a cam guy and he is suggesting that I go away from the ususal lobe seperation of about 106* seen on most circle track cams to a 108* to 109*. The duration would be in the .240's at .050 with a smallish lift pattern. The intakes would have 1.7's rockers on them with standard 1.5's on the exhaust. I am kind of new to this so any help would be welcome.

Sledge

66jj
Member
posted December 05, 2003 08:51 AM
sounds like a 350 cfm carb cam?

the smaller lobe separation makes a smaller power band opening up to 108 etc spreads the power over more rpm..

drags run 112 for power 3000-7000+for example.

Ive been told the same cam specs for IMCA stock car, but what are they going to use for the 1.7 rockers, I assumed big block, but found out they wont work.

Im limited to stamped steel, and roller tip.



istock59
Member
posted December 05, 2003 09:52 AM
The Lunati cam that I'm running that was designed for a small 2B carb has 108 degrees of separation. Duration of 249@.050


rico 08
Member
posted December 05, 2003 10:52 AM
The 108 lobe sep will tend to produce more power in the higher rpm range than the 106,the 1.7 ratio's on the intake side is sort of a crutch for the small carb.


Raz_900
Member
posted December 05, 2003 01:55 PM
wider lobe sep angles produce a lower peak power number, but makes a wider, smoother powerband.

Tight lobe sep angles produce higher peaks, but a 'narrow, choppy' powerband.

66jj
Member
posted December 05, 2003 02:10 PM
Does anyone know how were supposed to get 1.7 rockers on a small block in stamped steel???



66jj
Member
posted December 05, 2003 02:18 PM
Heres a email I saved from someone that has helped me with advice to build my motors for a long time. I have ran speed pro piston motors against my friends with the cats meow motors and won a lot of races, and championships.

This guy is affiliated with motors that start at 20 grand, he got a kick out of what I was running against some of his motors he charges 5000 to freshen.

This is the response when I asked about a 350cfm carb motor/cam combo. And about header size.

The first thing to do is find someone with intake/exhaust flow knowledge of those heads. The intake/exhaust flow relationship is important. If the exhaust flows as much as 70% of the intake, use a cam with even duration. If it flows more than 70%, use a cam with shorter duration on the exhaust than intake. If it flows less than 70%, then you can use exhaust duration a degree or two more. Use a camshaft with short duration-in the 245 degree @.050" range. Use higher ratio rockers, especially on the intake. 1.70 to 1 on the intake is good, 1.6 to 1 on the exhaust is OK. The intake runners in the heads and manifold need to be cleaned up-not enlarged, just cleaned up- no bad, rough spots. A very precise match between the intake/cylinder head is critical, critical, critical! When I say match-I mean exact especially on the top and sides. Use flatop pistons with as small a valve relief as possible, Zero deck height is good. GM heads don't like big headers, use 1 3/4" straight tubes, but the flange needs to be .060" larger than the head on top and the sides, even at the floor. Don't know what your rules are, try to use a 4 barrel intake if possible, single plane is best, large plenium with at least a 1" spacer(if legal). A multispark ignition helps(like MSD).

Don't know what kind of track you race on but if it is a high momentum paved track, I wouldn't even use a 350-I would use a 327. You will be able to turn 500-600 RPM more than with a 350. That would let you pull several car lengths past the flagstand where your 350 will flatten out at the flagstand.




tilley88
Member
posted December 05, 2003 02:37 PM
I used 1.7 rockers off older model chevy straight sixes one nite. Sounded like a late model and ran like a raped ape. Kept breakin 'em, so that experiment ended quickly.


autoshop
Member
posted December 05, 2003 03:55 PM
The folks at CAMSHAFT PERFORMANCE CAMS have the 1.7 rocker.

Does this combination sound like it would work well on a longish 1/4 mile track that has high banks and a D shape?

66jj
Member
posted December 05, 2003 08:11 PM
what combination sledge??? how much are the 1.7 rockers. do you mean camcraft that sponsors this site??

kplugnut has several cams in mind for this carb.



sledgehammer
Member
posted December 05, 2003 09:25 PM
I am refering to the cam conbo, yes it is the one that sponsors the forum. A full set of 1.7 int, and 1.5 ext are around 200.00.


Back to the Archives