SBC road race cam selection

Hey! I thought I’d ask the collective for a cam recommendation. My 3rd Gen camaro has a T56 and 3.45 gears behind a GMPP SP350 crate motor (never had the valve covers off!). It’s got 385 HP and 405 lb/ft. “Fast burn” heads are actually rather impressive, out flowing Brodix Track 1’s up to .600” lift. The hydraulic roller cam is mild with .474”/.510” lift and 210 deg at .050”. I run 1 5/8” hooker shorties and Y pipe to a single 3” side exit, I never rev past 5800... BUT I’m switching to 1 7/8” full length headers so I want a cam to work with them.

This is a track only car, I got a couple ideas like the comp cams 307 and Crowers “high lift” series of hydraulic roller cams. Problem is most cams are made for EFI combos’s as I think my base motor is an LT1 style motor but not reverse coolant flow. I run a Holley HP series 750dp carb and MSD 7. I’d like to hear from somebody who has road raced a small block in a 3000lb car, if possible lol!! But I’ll listen to any educated opinion...

thanks!!

matt

In reply to Matt : camshaft selection is too track dependent.  Tracks like Elkhart Lake depend on a really broad power range since you come out of the corner at relatively low RPM and pull all the way through the gears to top speed three times per lap.  

Mid Ohio on the other hand can allow more peak power since the corners tend more towards the higher exit speed. 

Then tracks like Blackhawk are all about bottom end grunt, pure low RPM  torque. 

Then too, what sort of driver are you?  Would you rather out pull someone out of a corner or squeeze past diving inside on the brakes?  

One approach calls for torque and traction, the other approach demands aerodynamics and braking power.  

Or to translate it into car speak, are you a Cobra racer or an XKE RACER?  Both may turn identical lap times but how they get there is directly opposite. 

just a good 3/4 cam, Lol,

  as frenchy say's...............   but like me you ain't gonna change cams between shows. That cam really is mild with a large exhaust over lap. with the right springs a 525 lift intake and what is in vouge for exhaust nowdays could put you in the 425hp range. 50 hp from where you are now isn't too hard , for me I would enjoy the engine you have and build a race engine over the winter.

easier to build from scratch than try to modify that nice engine, and you could sell it if needed to get the new engine out of Machine shop Hell

http://www.flowtechinduction.com/fti-custom-hydraulic-roller-camshaft-sb-chevy-austemper/

Great replies - thanks! Ya Frenchy your right, track and style are paramount. i'm only on 1 track and that's a 1.3 mile 9 turn course (see very old pic lol). . i'm only using 3rd and 4th for the whole track, there is a low speed (turns 3-4-5, 40-45mph) left-right-left section and i'm at 3300 in 3rd and it blows the tires off if i squeeze the throttle too much, so i was hoping to move the torque peak up a little bit. one of my buddies says i should be in 2nd in 3-4-5 to get out of the torque but I don’t like revving it that much. There's a 911 that beats me up and watching a video of us both nose to tail through that section was an eye opener - all you hear is the 911 because hes flat and i'm off the gas.

GTXvette id love to build another motor, in fact i want to build a pump gas 18 degree motor. This crate motor i have now is really nice, i got a crush on these fast burn heads lol! ironically I've been hesitant to crack it open and mess with anything because its really a gem and i don’t want to make it worse. This winters project is big tires, a cage and safety stuff because i want to hill climb the car. the headers and cam are a weekend project. maybe i’ll just put 4.11 gears instead of the 3.45?

Strong suggestion.  The 2.66/0.50 gearset in the T56 needs a lot of rear axle ratio.  3.45s are a tough one to match up with a T56.  Works on the street with a mild cam, but not so good with a big cam and race.  I realize that road race is less about getting moving and more about staying fast, but a swap to more cam duration will make those 3.45s a big mismatch.  4.10s minimum.

When I planned to swap from my 4L60E and 3.08s to a T56, I had to go to 4.10s just to keep the same basic final drive ratio spread.  Some guys to all the way to 4.56s or 4.27s. 

4L60E has a 3.06/0.70 first and OD, so final drive spread with 3.08s is basically 9:1 up to 2.1:1
T56 with 2.66/.050 with 4.10s gives a final drive spread of about 11:1 up to 2.05:1
T56 with your 3.45s will give 9:1 up to 1.7:1.  Higher gears will be useless unless you're hitting 180mph, and not enough torque multiplier for the lower gears, particularly because you're giving up low end torque with the bigger cam.

The one caveat to this is if you have an early T56 with the different (lower) ratios.

Oddly enough, I did the 4.10 swap in the Impala, but then never did the T56.  Now my final drive spread is 12.5:1 up to  2.9:1.  I'm spinning 3000 rpms on the highway and first gear is pretty useless, but its lots of fun getting chirps on the 1-2 and 2-3 shift.

Edit:  One other caveat to this is that I'm not a road racer, I'm a bench racer with a lot of hotrodding experience.

The only comment I have regarding the with t-56 in the 95 LT1 3.42 rear gear Camaro Chumpcar that I rent a seat in. He's recently been having issues with the 5th 6th and reverse shift keys/springs. It gets shifted at 5-5500rpm. 

Apparently it's a common issue with road races t56s even though 6th and reverse basically never get used. 6th failed and ate up the 6th and reverse. He deleted 6th gear completely and and in the last 24 hour race the 5th gear shift key or spring failed. 

It might get to a point where 5th gets deleted and a drop the rear down to a 3.08 or similar. 

That being said we've found that ringing the car out using 3-4-5 seems to yield similar laps times as 4-5 with 3rd only used when really needed. Granted endurance vs sprint style racing are two different things as well as driver style. Going for the last possible tenth is a bit different than running quick consistent laps and saving the equipment.

great information - thank you!

In reply to Greg Voth :

Guys I know racing a 5.3/T56 3rd gen dropped back to using only 4th on track. They don't lose enough time to make up for the added reliability. The clutch never wears out, the gearbox never wears out and they get decent fuel economy. And it's still bloody fast.

Matt said:

Great replies - thanks! Ya Frenchy your right, track and style are paramount. i'm only on 1 track and that's a 1.3 mile 9 turn course (see very old pic lol). . i'm only using 3rd and 4th for the whole track, there is a low speed (turns 3-4-5, 40-45mph) left-right-left section and i'm at 3300 in 3rd and it blows the tires off if i squeeze the throttle too much, so i was hoping to move the torque peak up a little bit. one of my buddies says i should be in 2nd in 3-4-5 to get out of the torque but I don’t like revving it that much. There's a 911 that beats me up and watching a video of us both nose to tail through that section was an eye opener - all you hear is the 911 because hes flat and i'm off the gas.

GTXvette id love to build another motor, in fact i want to build a pump gas 18 degree motor. This crate motor i have now is really nice, i got a crush on these fast burn heads lol! ironically I've been hesitant to crack it open and mess with anything because its really a gem and i don’t want to make it worse. This winters project is big tires, a cage and safety stuff because i want to hill climb the car. the headers and cam are a weekend project. maybe i’ll just put 4.11 gears instead of the 3.45?

 

The best solution is to do the calculation yourself.  Do you have any on board shots of the tach, hopefully showing where you are on track?  

Start breaking it down, X% at 3500-4000 RPM.  Y%@ 4000-5000  Z% @ 5000-6000. 

Now predict passing opportunities and give the RPM that happens bonus according to your past history.  Don’t bother with those you don’t race with.  ( different class or massively superior car/ preparation/equipment ) 

Now buy, borrow,  or rent one of those engine analyzer programs.  

Set it up by your specs as they exist.  If you don’t know flow numbers for example guess and adjust until the power predicted duplicates your power.  

Once you have that entered try the various camshafts  ( on computer ) based on published specs 

then compare each camshafts performance against where you need power on the track.  

Dont be afraid to try a whole variety of camshafts. Including off brands and ones you don’t think suitable.  It only takes a few minutes to look them up and enter the specs.  

In an hour or two you should have your answer. While you’re at it try all sorts of things.  Different length headers, different size intake, rocker arm ratios, compression ratio, fuels,  anything and everything.  

I actually did some reverse engineering playing video games on different tracks and comparing lap times of similar cars to mine against my lap times.  Then punched in the added power to see the gain in reality.  

It took me months to do because I’m a computer Luddite.  Someone who really knows computers could do it in minutes but I’m not that person so I did it the slow way.  

I learned that a lot of the expensive stuff made either minor or no real lap time improvements. I bought that program a long time ago and still use it to decide where to spend my money.  

You must be new to the forum, because you have this all wrong.

What you're supposed to do is go to your favourite cam grinders site and find the cam you like best. Then post on here asking for cam advice while also emailing the manufacturer of said cams.

When the recommendation from knowledgeable engine builders and the cam manufacturers is almost exactly the same but disagrees with yours, you do the obvious thing and order the cam you originally thought you wanted anyway.

That's how the internet works.

You have a combination that works for a reason. A motor that is very easy to drive in a car that's geared for exactly that. Much more cam and it's going to be lazy and slow.

These motors work so well because the cylinder heads work so well. You're making almost 400 hp with low compression and less than 210 degrees duration. What the longer exhaust duration does is allow you to still rev higher than you normally would, hence why you're almost at 6k with so little intake duration (which also makes it really easy to drive). GM really knows what they're doing here. 

You don't change the cam to match the headers. It's done the other way around. You can try the headers as is, and it may work fine, especially with that 2 into 1, but If you really want to try something, see if it's possible to run 1.6 rockers. You'll pick up some lift and a little duration at the same time, but not enough to cause a drivability problem.

I have a fair bit of experience with this stuff. And I'm a cam grinder.

In reply to Suprf1y :

I have s project that involves re grinding the OE cams on a Mazda motor. Can I PM you? 

By all means.

If I can't help you I can probably direct you to somebody who can

In reply to Suprf1y :

Ya new is what I am. I posted an introduction in the appropriate section. It appears I put the cart before the horse!

there are so many choices, And having put many cams into many vehicles, I had a ball park idea what I want but would like other experienced ideas prior to opening the motor. that’s why I mentioned the comp cams grind and the Crower series, they seemed like a good start but there is always value in exploring experienced opinions, like yours. as frenchy and GTXvette, Curtis (and you!) et al mentioned, I could be barking up the wrong tree. So More research is required. 

Im not opening this motor if I don’t have to. I’m going to put the headers on and see how it is. But prior to that I’m stepping up the wheels and tires as I’ve only got 245/45/16’s on this car and by all accounts i should be running 275-40-17’s....and that will have an effect on everything. 

Thanks!!

Sorry, I'm not a road racer, but decreasing power (at a certain RPM) because you don't have the traction/suspension/chassis to put down the power seems like a really backwards way of solving the problem...

I think it sounds like you have a real sweetheart of a motor.  I'd be very hesitant to gimp it up trying to address chassis/tire issues.

Oddly enough I have had better laps in a car with a misfire.

In reply to doc_speeder :

It may seem that way but as GTXvette mentioned it’s not backwards at all. In fact at Targa Newfoundland a couple years ago guys were de-tuning their cars quite a bit to go faster. For me to change the power curve doesn’t imply I am de-tuning, but trying to keep the same power levels just at a different RPM. I’ve got 400 lb/ft at 3300, I’m at 3300 +\- 200 rpm at 5 corners and it blows the tires off too easily for my driving style (thank you Frenchy!) - If I can move that to 3800 then I can get on the gas earlier with less consequence. 

But as I mentioned i am stepping up the wheel/tire combo before anything else, and this will change the dynamic completely as all research indicates this is a 2 second/lap decrease in times. So I do need more research before I change the cam, I might just put the pipes on and run it, like it was mentioned. In the name of scientific process, making 1 change at a time is the way to go and that’s what I’ve been doing for a couple years with the car.

im just quite glad there are some real knowledgeable people on here that take time to answer my terribly vague and poorly placed question!!

Suprf1y said:

By all means.

If I can't help you I can probably direct you to somebody who can

I will P.M. You my idea.  The short of it is taking a miller cycle motor and re grinding the cams to make it an auto cycle motor.

In reply to frenchyd :

Frenchy this is GOLD! i would have replied earlier but i had to read this a few times - i am such a Luddite and nobody uses that term anymore awesome LOL!! I haven't looked at any analytic programs for, well ever! I used to drag race a lot and I had a program called Quarter Jr on my 286 back in 92 or something so i'm probably not up to speed LOL!!! i will have a look around to see what is being used now...its a long winter ahead.

Fast forward to today where my 5 year old can use my iPhone better than i can: i use an app called Track Addict and i duct tape my phone to the rear view mirror and use the GPS data with track map and speed overlays to compare laps, its pretty good. One of the instructors in our club told me to just look at the tach when i hit my track out mark and use that RPM to compare to the previous lap to see how im doing. it was sound advice and i will try to get the tach in the frame next time so i have a video record of the RPM at each corner and not rely on my old but "convenient" memory. then i can use your formulas - i cant wait!

thanks again!!