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Stock Chevy 350 cam suggestions please

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Stock Chevy 350 cam suggestions please

Postby metriccar » Sat Aug 27, 2011 1:14 am

I am running a "pure stock" circle track car on a 3/8 mile oval dirt track. I recently built my first engine, a 355, and I have about 15 nights on it.
Here were the specs: 10.2:1 compression ratio, flat top pistons and camel hump heads. 355 chevy. stock intake, heads, and exhaust manifolds, quadrajet carb. No porting whatsoever. 3.73:1 rear gear with a 1.82 powerglide. 3100 lb car with me in it.

I had a howards cam 110812 in it.

Specs are:
Duration at 050 inch Lift 248 int./252 exh.
Advertised Duration 286 int./294 exh.
Valve Lift with Factory Rocker Arm Ratio 0.534 int./0.542 exh.
Lobe Separation (degrees) 106


This cam was installed at 104 degree intake centerline.

The engine has about 165 cranking pressure and 9 inches of vacuum at 1000 RPM.

I've been watching some videos and what's happening is I'm getting absolutely killed on the starts, I start keeping up at the end of the straight (I'm at 6000 RPM at this point) then go into the corner where they're pulling away from me again coming out of the corner.

I talked to some other circle track guys on another board and they all tell me the same thing; my cam is too big. Apparently cam manufacturers have the habbit of giving me too big of a cam, probably because they're listening to the RPM I want to run (3500 or more coming out of the corner, the theory being to come out of the corner at a decent RPM where you make good power to accelerate quickly) out of a stock engine, I don't know.

But they're telling me to run something with about 235 degree duration. All I can say at this point is the cam company techs are giving me different suggestions than the guys who race.

So I ordered this cam:

Comp Cams 12-648-5
Duration at 050 inch Lift 240 int./246 exh.
Advertised Duration 270 int./280 exh.
Valve Lift with Factory Rocker Arm Ratio 0.510 int./0.519 exh.
Lobe Separation (degrees) 108

What throws me off is Comp's description is this is good for a 9:1 compression motor. Meanwhile I milled my heads down and will now get 10.7:1 compression. But I also notice there's a wider LSA so I'm thinking I may not be making any improvement??? These are all solid lifter cams by the way, flat tapet.

Someone else suggested this cam:

Comp Cams 12-646-5
Duration at 050 inch Lift 236 int./242 exh.
Advertised Duration 266 int./276 exh.
Valve Lift with Factory Rocker Arm Ratio 0.501 int./0.51 exh.
Lobe Separation (degrees) 108

I'm starting to think this may actually be better, given the wider LSA may offset the shorter duration some.

These are both Comp Cam's "XT" ramp cams, where theyre supposed to have a lot of "area under the curve" and have a good amount of lift for a short amount of duration. Anyone have any input between these two?

My other thought was to get an old Duntov 30-30 cam or the old LT-1 cam. Now I know everyone says these are old and outdated but they seem to be within the same horsepower range, 320-350 HP or so, as what I would expect my car to make. It sounds like-the old cams are longer duration and low lift. Everything I read about these cams on message boards from people who had these cams in their car back then (I wasn't around back then and I'm just learning about cams now) say these cams were poor performers under 4000 RPM but ZOOMED to the moon!!! All the way to 7000 RPM!!! BTW my engine seems to be making less power after 6000 RPM but that may be the stock camel hump heads, I have plenty of valve spring pressure. And besides, these guys back then may have just been joyriding, not running right beside someone else with another small block chevy doing everything he can to get in front of you. But I know if I get one of these old cams I may be in the ballpark, and that long duration/low lift may be a good tradeoff and work decent at high RPM's.

What if I installed the 12-608-5 at a 104 degree intake centerline?

I'm just trying to get the most power out of this engine and on other boards, other people going back and forth with similar specs as mine unfortunately seem to worry about power brakes, what it does at 2000 RPM, and how they can get that lumpy sound or whatever, me I just want to win races!
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Re: Stock Chevy 350 cam suggestions please

Postby crazyman » Sat Aug 27, 2011 1:54 am

Stock.. I know I'll be hated.. What about 305 heads like the 601 casting? Velocity is key as well as flow.
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Re: Stock Chevy 350 cam suggestions please

Postby F-BIRD'88 » Sat Aug 27, 2011 6:25 am

I would move the cam to a 99-100 intake C/L.
I would try opening up the valve lash a bit.
I would replace the head gaskets with .015" shim style to raise the cr.
I would get to work on that Qjet carb. A AFR meter will be a big help.
I would lock out the advance curve and try 34 to 38deg timing
I would look at the accessable areas of the intake and exhaust manifold
looking for areas that need sweetening.
The motor will show you what it likes.
Put more gear in the car.
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Re: Stock Chevy 350 cam suggestions please

Postby jonsjunque » Sat Aug 27, 2011 9:38 am

I was going to suggest it, F'bird mentioned it.....

Try a differential gear ratio change?? Just enough to get over that hump?

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Re: Stock Chevy 350 cam suggestions please

Postby Keith Morganstein » Sat Aug 27, 2011 9:41 am

metriccar wrote: All I can say at this point is the cam company techs are giving me different suggestions than the guys who race.



The best advice I can give you is to contact Mike Jones of Jones cam designs. Nobody is better (IMHO) with circle track stuff. Mike will work with you and grind a custom cam for your application. The cam can be made for your combination, track and driving style. It will cost $100 more than a comp cam, but it's well worth it to get it right.

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Re: Stock Chevy 350 cam suggestions please

Postby donc » Sat Aug 27, 2011 9:48 am

106 lsa in at 102 cl try advancing what you have to 102 in cl first se how it comes off corner If corners are real tight maybe 101
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Re: Stock Chevy 350 cam suggestions please

Postby swatson454 » Sat Aug 27, 2011 10:22 am

Assuming you have 1.94/1.5 valves, I'm kind of liking something along the lines of the first Comp grind, 270/280 but on a 106. I'm curious to see what Mike has to say.
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Re: Stock Chevy 350 cam suggestions please

Postby Cedarmachine » Sat Aug 27, 2011 10:36 am

Many many years ago we had sponsored a hobby stock car. In playing with different cams, we actually found that running a wider lobe sep. widened up the power band and the car pulled out of the corners harder and then higher on the straights. We were running cams as wide as 112 degrees and our driver loved them. He pretty much won almost every race that year and the track championship. He was pretty good at setting up a car, so it wasn't all the cams doing, but we ran a lot of stuff and that is what we stuck with.

510/510 lift, 234/242 at .050, 112 sep, 106-112 Intake lobe center comes to mind..We could run the 461 heads and such back then too. Usually on flat top 355s.


Look at the rpm range..you wouldn't run a 106 degree cam in a performance marine motor, yet it has the same operating range for the most part.

Just a thought..oh, I might add, this was back in the 90's when Bill Berry was still alive. They used to grind us new cams for like $55.00 so it was fun to experiment. There are some weird cams out there thanks to us.
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Re: Stock Chevy 350 cam suggestions please

Postby CamKing » Sat Aug 27, 2011 11:22 am

Part# M72352-74337-106
288/296 @ .012"
244/243 @ .050"
.352"/.337" Lobe Lift
106 LSA
102 ICL

This should come off the corner so much harder, that your RPM at the end of the straight will be higher then it is now. You'll want to gear it for around 6,400-6,600 at the end of the straight.
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Re: Stock Chevy 350 cam suggestions please

Postby RCJ » Sat Aug 27, 2011 6:29 pm

If you have already ordered a comp cam it makes it simple, put it in at 102 and run it.In my experience you are on the right track and the new cam will be better.
3.73 x 1.82 =6.78 not knowing your track that sounds like plenty of gear for a 3/8 track.With stock manifolds I never turned over 6000.I've tried putting in too much cam to kill bottom end for a dry slick track.It worked in the race but hurt us so bad on restarts we when back to the correct cam.
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Re: Stock Chevy 350 cam suggestions please

Postby vintageracer » Sat Aug 27, 2011 8:19 pm

It is possible that your chassis setup is keeping your corner speed down? If you are slower in the corner than your competition and cannot put the power you have down on exit it will make for a long night. Spring rates, front end alignment, tires and sway bars have to be right even in "stock" classes.
If it was easy all of my neighbors would race too!
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Re: Stock Chevy 350 cam suggestions please

Postby bigmike » Sun Aug 28, 2011 6:16 am

But they're telling me to run something with about 235 degree duration.
someone gave you some good advice. Some of the best circle track advice I ever got years ago from a very sharp circle track racer was. "You don't drive a dyno".

Given the exhaust manifolds and stock intake rule i like the looks of this choice.

Comp Cams 12-646-5
Duration at 050 inch Lift 236 int./242 exh.
Advertised Duration 266 int./276 exh.
Valve Lift with Factory Rocker Arm Ratio 0.501 int./0.51 exh.
Lobe Separation (degrees) 108
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Re: Stock Chevy 350 cam suggestions please

Postby COhrp » Sun Aug 28, 2011 10:46 am

What are your exhaust restrictions? There is a big difference between rules that say "log manifolds, 2" pipe, no X, Y, or merge pipes" versus "2.5" Corvette manifolds allowed, any pipe configuration after the manifold".

The thing is that you don't want to run much overlap if you have restrictive exhaust.
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Re: Stock Chevy 350 cam suggestions please

Postby CamKing » Sun Aug 28, 2011 12:45 pm

Don't get caught up in .050" durations it can be very misleading.
Look at my Intake lobe I suggested. it's 244@.050", and that's 4 degrees more then the Comp 240@.050", but only 2 degrees bigger at .020", and mine's probably smaller at the actual seat duration.

If you just look at .050" duration, you would think a 236@.050" would make more low-end power then a 244, but that may not be the case.

Look at the other durations between my 244, and an off the shelf style 236@.050 cam.

Duration@: My244 / generic236
Seat : 288/292
.020" : 272/270
.050" : 244/236
.200" : 157/148

Max Lift: .352"/.340"
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Jones Cam Designs
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http://www.jonescams.com
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Re: Stock Chevy 350 cam suggestions please

Postby eric's 327 » Sun Aug 28, 2011 5:51 pm

I'd return the Comp and buy Mike's cam.
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