Let's talk about cams...

[SoundGuyDave]

I decided to post this here, rather than in the main forum, since the drag guys don't seem to have any concept what "part throttle" is...

I honestly know JUST enough about camshaft specs to be dangerous, so I'm hoping that somebody(s) that really understands how a cam will react based on the specs would be willing to chime in and share the tech.

As you folks know, I'm running TT with NASA, and am thus spending "points," so dollar cost is not the overriding concern, but fitting into a class restriction is. Basically, what that boils down to, is that I have to run bone-stock heads, stock valve sizes, but the cams and valvetrain hardware are both essentially open for discussion. ECU tuning is obviously wide open, as well. PLEASE do not recommend turbos or blowers, the points cost is INSANE. The car weighs in at 3600lbs, with a stock 3550 trans, and a 3.73 gear set in the rear.

I came up with a few contenders, including one specifically recommended by a cam manufacturer, but I would love some informed opinions. What I don't want to do is start playing musical camshafts through the season.


............................adv.......adv..........0.050.......0.050.......lift........lift.....
CAM....rpm.range....intake....exhaust.....intake......exhaust....intake...exhaust....LSA
Stg1....900-6700.....256.......267...........221.........228.......0.523......0.538......112
Stg2....950-6900.....264.......275...........229.........236.......0.535......0.550......112
FRPP.................................................221.........240.......0.472......0.433......110
BBR1..1500-6000.....270.......276...........227.........233.......0.480......0.480......114
BBR2..2000-6500.....284.......294...........241.........251.......0.492......0.492......114

Three manufacturers are represented, each with an obviously different philosophy in cam design. The comp cams tend to be conservative with duration, but very aggressive with lift, where the BBR cams are the exact opposite. FRPP seems to land in the middle, but has the narrowest LSA of the three.

FWIW, comp recommended the Stage I cam. Obviously, I'm least concerned with peak HP/TQ numbers, but want the largest possible area under the curve, and the powerband can't be peakey, as you folks are well aware.

I'm absolutely NOT concerned with idle quality, "lope" characteristics, sound, etc. This is all about power. I don't know if I will get it, but I would like to see power in the 350-360HP range (power-to-weight ratio limit is 357.5HP at class minimum weight of 3450, which I want to get down to eventually). I'm also hoping to pick up some more revs at the top end, since with the shorter tires, I'm finding that I have to make one more shift on some of the medium-length straights than I really want to. Each upshift=time wasted...

Supporting mods include a C&L Racer CAI, Steeda billet deletes, ARH 1-3/4" longtubes, offroad-H pipe (no cats), EH2O pump, and Roush UDP setup.

 

[Vapour Trails]

Is your car your DD and is streetability a concern? I think comp pointed you in the right direction. Duration does seem to erode drivability.

You may bb able to find dyno plots in the tech section, but the results may be confounding as each car will have different mods and tunes.

 

[SoundGuyDave]

Thanks, I did scroll through as many dyno plots as I could find, but most of them seem to be either built engines or FI of some sort, and yes, you're right, it IS highly dependent on the supporting mods and the tune... I've got Eric Brooks doing my tuning, so THAT end, I'm not worried about.

While the car is technically street-driven, it's not a DD by any stretch. It comes out of the garage, to the track, runs around in circles, and then goes back in the garage. With the suspension under it (almost all rod-end bushed) and a pretty stiff clutch, I avoid rush-hour like the plague. I'm not really worried about off-idle manners at all. 95-98% of the street miles on it are on the highway heading to and from the various tracks that I run; anywhere from 60min to 5 hours away.

If I didn't get divorced and wind up living in a townhome instead of a house, I'd have a trailer. Such is life.

 

[ArizonaGT]

Subscribing...

 

[Cookiemonster]

why not stick to the meat and potatoes setup (I know you cant do head work) comp spr stage 2s

 

[SoundGuyDave]

why not stick to the meat and potatoes setup (I know you cant do head work) comp spr stage 2s

That one is the second line on my list, and is under serious consideration... I just don't know how the part-throttle response will be, nor do I know where the powerband really lies. With all the cams, I'm planning on doing valvesprings, and I don't have a problem doing lockouts or limiters for the phasers, either. I just don't want to go through the install, tuning, break-in, and testing over and over again. If I can find a good, solid cam the first time out, I'll be happy. Do you have the Stage II cams?

 

[irishpwr46]

is a stroker out of the question as well?

 

[Cookiemonster]

That one is the second line on my list, and is under serious consideration... I just don't know how the part-throttle response will be, nor do I know where the powerband really lies. With all the cams, I'm planning on doing valvesprings, and I don't have a problem doing lockouts or limiters for the phasers, either. I just don't want to go through the install, tuning, break-in, and testing over and over again. If I can find a good, solid cam the first time out, I'll be happy. Do you have the Stage II cams?

no, however thats the cam I will be getting and the cam every one has been recommending to me. I believe you can maintain VVT and keep the low end, though I wouldn't quote me on that. I also am curious on part throttle response and if the power delivery is smooth through out the power band.

keep us updated on your finds.

 

[SoundGuyDave]

Unfortunately, yes, it is... I have six "points" to play with here, and a 6% displacement increase (281 to 298 CID) would burn all six. I will stipulate that I will make power with the increased displacement, but my gut is telling me that a good set of cams will make more than just the raw extra 18 cubes, particularly since I would be restricted to the stock compression ratio. I may be wrong, and if so, that would be worth considering. How well do the strokers handle the revs with standard kit components? I can't afford to go "unobtanium" here...

Right now, with the tires, suspension, and engine bolt-ons, I'm pretty close to maxed. I don't see being able to do a "clean sheet build" this season, but I'm anticipating having to refresh the motor for next year (2011), so that could be under consideration then.

 

[trill gear head]

Im pretty sure you'd gain more with cams and LT's than with just increasing cubs and assuming your not gonna do anything to the heads.

 

[marksti]

IMHO...coming from a guy that did do cams on a road racer s197:

Skip the cams at this point...you'll lose too much under the curve..and you won't pickup enough if you go mild like a stage one.

The factory cams rock for road racin..and you can rev them out to 6400 amd still make power with a good tune anyways...cams will give you more hp ..but they won't give you anymore MAX rpm.

Focus on losin weight or better suspension or aero: I know you still have room in those departments

A few local hardcore racers the that run TT/Restricted classes went that route and seem to have made the right call

Thats just me tho...I do like the way they sound a WOT

 

[SoundGuyDave]

Marksti:

I think I need to chat with you... I'll PM you my phone number, or you can PM me yours, if you want to save the dime...

I'm about maxed out in suspension, short of an SLA, and I know that's not going to give me the gains I'm looking for. My main competition in class are a couple of hair-dried AWD imports, and they're killing me on the straights! Think 350HP Evo IX on Hoosiers, and you'll be sync'd to my nightmare.

Most of the tracks that I run are the typical "club" type tracks, a shade under 2 miles long, with limited high-speed straights and corners, so I don't know how much aero is really going to help me. An air dam and splitter are six points, and I'd be a little afraid that I would be unbalanced without a wing, which is another 4 points.

As for weight, with full fuel and driver, I'm sitting at 3690 with a competition minimum of 3450, so I know I have room to go. If I were to figure out how to drop all the weight, I could spend the 6 points on additional weight removal, down to a minimum of 3370, where my adjusted power/weight would allow me to make a max of 349HP. For me to drop any significant weight (the car, really, I'm 5'11" and 150lbs, so no real help there) I would have to start seriously carving up the car. My race weight is with the Steeda radiator support, Steeda competition cowl hood, rear seat delete, aluminum racing seats, and with the normal deletes: axle weights, brake dust shields, trunk-junk, etc. For me to drop further, would be less than simple: AC and heater delete, interior delete (!), evap tray, cut out the parcel shelf, and start hole-sawing the chassis where I could, and slap in a full cage. I honestly don't know if I am all that interested in doing that. If I did, the car would NOT be streetable, even remotely. If I did, the letters "TTB" would be changed to "AI" in a heartbeat.

 

[US-1]

Dave,

You should look into the Comp 127400 cams. Since most of your tracks are mid-range throttle runs I think you need something with good lift and short duration with a narrow centerline. These cams work out like this.........

Lift: I=.523/E=.538
Dur @ .050": I=221/E=228
LCA = 112
Intake Centerline = 102

The cylinder charging these cams should give would be great for part-throttle response...in effect they would act like a higher compression shortblock. The narrow lca should make for some great area under the curve too.

 

[pacettr]

Subscribing...

 

[SoundGuyDave]

Dave,

You should look into the Comp 127400 cams. Since most of your tracks are mid-range throttle runs I think you need something with good lift and short duration with a narrow centerline. These cams work out like this.........

Lift: I=.523/E=.538
Dur @ .050": I=221/E=228
LCA = 112
Intake Centerline = 102

The cylinder charging these cams should give would be great for part-throttle response...in effect they would act like a higher compression shortblock. The narrow lca should make for some great area under the curve too.

Thanks, SD! That's actually the part number that Comp recommended, and is also the top line on my list in the first post... It's not really so much part-throttle runs, as it is balancing the car through the corner with the throttle, and having a huge, peaky cam is a little crazy under those circumstances. More than likely, that's the direction I'm going to go. I know the -400 cams are new, so I'm not expecting to get reams of data from owners, but your description of the cams behavior puts my mind at ease a bit. I appreciate your comments!

 

[US-1]

Damned if it isn't on the top line of your list. Didn't even notice. I guess the "Stg 1" thing threw me off. I believe my "part throttle runs" terminology is exactly what you mean by "balancing the car through the corner with the throttle."

These are the types of specs I used when building street engines (even pushrod stuff). You get excellent cylinder filling which helps torque and the tighter LCA keeps the torque curve lower in the rpm range which helps with throttle response.

 

[pacettr]

SD - what would you recommend for my setup?

 

[US-1]

PJ cars should have come with the 127300 cams. What are you looking to do with the car?

 

[pacettr]

PJ cars should have come with the 127300 cams. What are you looking to do with the car?

Primarily a street car that sees the drag strip and the road course occaisionally. I just want it to be faster I just wonder if/how much a better cam (for my combination) helps me.

 

[Cookiemonster]

How much faster could you possibly want? Is the PJ engine forged?