[bulletpruf]

Fellas -

I'm building a road race engine and it's time to pick the camshaft. I'm new to road racing, so could use a bit of advice here.

Car is a 1971 Javelin AMX (sorry for the non-Chevrolet content!). The plan is to keep the car street legal (barely) and race it in the NASA American Iron series. Should weigh about 3,200 pounds with driver. Trans is a T-10 close ratio (2.23 first), 9" rear with a 3.50 gear. Engine is a .030 401 that's been balanced. Forged crank, rods, and pistons. Aluminum flywheel. 9.8:1 compression (a little lower than I would like, but can live with it). Stock Edelbrock aluminum heads. Single plane intake (Torker) with a Holley (have a few to choose from; thinking 750 DP or something like that). Max rpm is going to be 6,500 or so. Headers and 3" exhaust. Plan to run a solid flat tappet cam. Edelbrock says no higher than .580 lift with their springs. Manual brakes, so no need to worry about vacuum. Not worried about idle quality, either.

Guess my first question is what do folks look for in a road race cam? I'm thinking that a nice flat torque curve would be nice, with hp up to 6,500 or so. Problem I see is that a wide LC (112?) will give me a flat torque curve and a tight LC (106?) will give me more max torque and increase my cylinder pressure, which I think will help with my somewhat low compression. Think a larger cam with a wide LC will be lazy with 9.8:1. Figure I will be making around 450 hp with the right cam.

Here are a few grinds that I think are in the ballpark:

Comp has a solid flat tappet cam that may be a bit too big - it's the 290B6 or 10-601-5 Hi Tech. 255/266 @ .050, .576/.570, 106 LC. RPM range of 3800-6800 sounds about right. I'm right at the limit with the stock springs here, too.

Crane has a solid that's a bit smaller - #861201, 238/248 @ .050, .512/.533, 112 LC.

Crane PowerMax #861241 sounds good except for the wide LC - 248/258 @ .050, .533/.555, 112 LC.

I like the Comp Hi Tech with the 106 LC, but it may be a bit too big. I can also get something custom ground for not too much $.

Your thoughts?

Thanks,

Scott

 

[Steve439]

I'd contact one of the good cam guys for a custom cam.
I know UDHarold has posted about cams designed to take advantage of your large lifter size.

 

[cstraub]

Is it a 304 or a 401? If you have room you need to put a 1" spacer on that torquer intake.

I would not let valve springs limit my cam lift.

 

[bulletpruf]

Is it a 304 or a 401? If you have room you need to put a 1" spacer on that torquer intake.

I would not let valve springs limit my cam lift.

It's a 401.

Thanks

Scott

 

[bulletpruf]

I'd contact one of the good cam guys for a custom cam.
I know UDHarold has posted about cams designed to take advantage of your large lifter size.

Ok, I'll track him down.

Thanks,

Scott

 

[66360horse]

If the power max was on a 110 ls I would say that, but what I will say is why the single plane? Wouldn't you want a dual plane wit you predicted max rpm of 6500? Also a dual plane would capitalize on your touque you are wanting, I don't think a road raing engine would stay in single plane territory very long.

 

[cstraub]

Based on the Ebrock and 401 CID and power to around 6500 you are looking at something in the following:

630/590
245/253
106

Couple of things. Ebrocks have "untapped pontential". A good 3 angle valve job with some bowl blending will yield you about 10 to 15 more CFM and equats to about 30 more HP. Also will make the cam smaller.

 

[bikeron]

You have to work backwards from the tires once you know the RPM band where your engine makes max power ...you take the diameter of the tire then look at the available rear end ratios, then tranny ratios so that no matter what gear your in your always in the power band of the engine..

In my case, 3:70 rear end 255 40 17s, 2.87 1st, 1.89 2nd, 1.28 3rd, 1.00 4th, .64 5th

I use 2nd, 3rd, and 4th for most tracks. My RPM never goes below 4K.

Performance trends makes a great tool for this analysis:

http://performancetrends.com/tg.htm

Once you have this figured out and you know you are going to use the engine in the 4K to 6.2K region then you have the cam designed to make a power band in that range. This also has to take into account the head design, valve size and intake manifold.

If you can't get the power band up at the levels I talked about then go and redesign the whole drive line with a different RPM range that is appropriate for the engine..

Ron

 

[Steve439]

Ok, I'll track him down.

Thanks,

Scott

"Cstraub" posting in this thread is one of the good cam guys too.

 

[bulletpruf]

Based on the Ebrock and 401 CID and power to around 6500 you are looking at something in the following:

630/590
245/253
106

Couple of things. Ebrocks have "untapped pontential". A good 3 angle valve job with some bowl blending will yield you about 10 to 15 more CFM and equats to about 30 more HP. Also will make the cam smaller.

Ok, the Comp Hi Tech cam sounds somewhat similar to that - 106 LC, but with less lift and more duration.

Good point on the heads. I realize I'm going to be leaving power on the table by installing them unported, but that's the plan at this point.

Probably should have mentioned in the first post that this doesn't have to be a max hp build. I figure I need it to get me through at least one (likely 2) seasons of track events - - need some "seat time" and need to get my competition license before I build the ideal engine. Car will also see some street time.

When I do start the wheel to wheel racing (again, this is 1-2 years away) NASA American Iron has a 9.5:1 weight/hp and 9:1 weight/torque max. At that point, I'll need to build a 304 or 360 that I won't have to radically detune to be legal.

Thanks

Scott

 

[bulletpruf]

You have to work backwards from the tires once you know the RPM band where your engine makes max power ...you take the diameter of the tire then look at the available rear end ratios, then tranny ratios so that no matter what gear your in your always in the power band of the engine..

In my case, 3:70 rear end 255 40 17s, 2.87 1st, 1.89 2nd, 1.28 3rd, 1.00 4th, .64 5th

I use 2nd, 3rd, and 4th for most tracks. My RPM never goes below 4K.

Performance trends makes a great tool for this analysis:

http://performancetrends.com/tg.htm

Once you have this figured out and you know you are going to use the engine in the 4K to 6.2K region then you have the cam designed to make a power band in that range. This also has to take into account the head design, valve size and intake manifold.

If you can't get the power band up at the levels I talked about then go and redesign the whole drive line with a different RPM range that is appropriate for the engine..

Ron

Performance Trends software looks like a pretty good resource. Should be helpful in deciding on a rearend ratio.

I'm running an AMC close ratio T-10 with 2.23, 1.77, 1.35, 1.00 gears. I should be able to get some use out of first gear on the track, depending on what ratio I run out back.

Thanks

Scott

 

[UDHarold]

The AMC/Chrysler profiles would use your .904" lifters very good, but give much higher net valve lifts than you current springs can handle.
But cam durations can mean different things. Crane has a .904" lifter cam that is 294 at .020, 258 at .050, 166 at .200, and .3733" lobe lift--their name for it is F-258/3733.
I make a .842" lifter that is better---TF71, 284 at .020, 255 at .050, 166 at .200, and .3667" lobe lift. Ten degrees shorter at .020, same size at .200, and the lifter runs .049" away for the edge, for exceptional wear and reliabilty.
Using CStraub's cam specs, a TF62/TF73 gives 270/279 at .020 243/251 at .050, 162/162 at .200,.365"/.360" lobe lift, .584"/.576" gross valve lift, .568"/.560" NET valve lift.
The TF71 was runner-up in either the 2002 or 2003 Winston Amatuer Championship, in a low-compression engine.

Hope this is of interest.....

UDHarold

 

[bulletpruf]

The AMC/Chrysler profiles would use your .904" lifters very good, but give much higher net valve lifts than you current springs can handle.
But cam durations can mean different things. Crane has a .904" lifter cam that is 294 at .020, 258 at .050, 166 at .200, and .3733" lobe lift--their name for it is F-258/3733.
I make a .842" lifter that is better---TF71, 284 at .020, 255 at .050, 166 at .200, and .3667" lobe lift. Ten degrees shorter at .020, same size at .200, and the lifter runs .049" away for the edge, for exceptional wear and reliabilty.
Using CStraub's cam specs, a TF62/TF73 gives 270/279 at .020 243/251 at .050, 162/162 at .200,.365"/.360" lobe lift, .584"/.576" gross valve lift, .568"/.560" NET valve lift.
The TF71 was runner-up in either the 2002 or 2003 Winston Amatuer Championship, in a low-compression engine.

Hope this is of interest.....

UDHarold

Thanks, Harold. Enjoyed speaking with you today.

Scott