Right now I have MK-IV 454, '70 LS-6 rect port heads, will likely go with RPM Air-Gap intake, and Holley 850 w/mech secondaries. Still have to get the rest of the parts. Now I know that many would recommend large oval port heads for street use, which this will be. My uncle is doing this restoration and building the engine, and he thinks the rect heads are the way to go (partly because I already have them). At any rate, I'd like some input on the current config, and suggestions on a cam to go with it. It's a '70 Chevelle with 3.73 gears and will have a TKO-600 (haven't fully decided on that one yet, may go with M22). The car will be driven daily for a while, but will spend some time at the strip. So this is where I am right now. Is the 850 too much? Better off to ditch the rect port heads for large ovals? Cam? Thanks for your help. I'm trying to learn these things before the engine is built. graemlins/beers.gif

Wyatt,

This is very similiar to the motor I am putting together now. You didn't mention compression, mine is coming together at 9.5/1 with Merlin 310CC rec ports. For my set up, 3.73 gears and T400 trans, I an dropping back to a 2200 - 2400 stall converter and going with a small hyd. roller. [ZZ502 cam : 224/234 @ .050, .521/.540 on 110LSA, 108ICL]. Although I could go a lot bigger, I decided to stay conservative this time and try the big heads/small cam combo. The 454HO works the same way and has a very smooth power band, not huge, but still a nice driver quality. It has less compression at 8.75/1 but uses 10 degrees less int. duration also. From what I can gather, even the mild cam motor I am going with should still make about 475HP at a reasonable 5500RPM.

I think you will have to define what type of performance quality you want first.

While ovals may be optimal, you can tweak certain parameters to gain some mechanical advantage with the rect ports ( other than using a 3500-7500 rpm power band!).

1>) As Joe alludes to above, don't overcam it! With two small solid cams I've run in the 427, the big port heads give the cams more range.

2>) If its an occasional use vehicle you don;t mind running good gas in, keep the calculated DCR quite high to bolster low speed torque, 8-8.25:1 is about right.

3>) May want to ask your uncle about laying the valve angles back a bit to enhance low- and mid-lift flow 20-30 degrees.

4>) Most importantly, select a camshaft that not only works in your specified power band, but is done on a tight lobe separation, keeps the dynamic compression high ( intake closing at around 62-68 ABDC assuming 10-10.25:1 ) and uses asymetrical profiles to enhance inlet charge ram effect. The cam should also be installed advanced, again to aid those effects.

If its supposed to be an LS6 car, I'd set the static compression to 10:1 and use Harold Brookshire's 403A3 Lunati cam set out on a 112 LSA, or the next smaller profile ( which is not a race profile) in the A2 on a 110 lsa, for example. It's like $15 extra to set a custom lsa.

Either cam will out power the stock LS6 cam. These are solid cams, hence the question about whether its supposed to be an LS6 car. If not, something along the lines of the 302A8 hyd cam would seem to be a good fit. These are general recommendation tht fit the aforementioned cam selection criteria. There are likely other cam's that will too. Use the mentioned cams as a guideline.

You have to decide how much of that 'rumpity-rump" idle quality you want. Be careful what you wish for!

Thanks for the advice guys. It's nice to have suggestions, since I'm a novice at this.

The car will be driven daily for a bit after I get it, so it'll need to run on 91 pump. Although it will look like an LS6, it doesn't have to be identical internally. Like many, I want the best performance I can get in a street ride. If I can't make this combo work, I'll just have to buy some large ovals and send them to my uncle. Is the 302A8 a Lunati? I'll look it up. As for compression, I'd like 10:1 or lower for pump gas. How high CR do you think I can get away with using one of the above cams and 91 octane?

Thanks again for the insight. TC is such a resource, and you guys are great, helping the novices here. If you have any more advice for this setup, fire away. I have a few months to plan.

One more thing. If the description of a cam says it's a good cam for street performance/strip car with auto trans, is it not as suited for a manual trans? I'm not sure why this would be. Thanks.

Actually,

Depending on the manual trans, rear ratio and tire size the opposite is true. Many BBC Chevy stick cars have either the M21 or M22 close ratio trans with the 2.20 1st gear and could benefit from an increase in low end torque.

I agree with everything stated above. Dynamic compression must stay relatively high to make good low end power with the Rec port heads. Are you using the LS-6 original 291 head or the crate engine 990 head?

Reguardless, cc the head because the advertised chamber volumes are more than advertised. Try to get them cc'd because you'll loose more compression than you think by going with the advertised compression. An L-72 head with a stock piston has been as low as 10.2 to 1. That is a full piont down than where it should be. Good luck and it should run well.

JIM

PS......The LS-6 cam is a good cam. You do need to run some compession with it.

The Crane I ran was very similar to the stock LS6 cam, albeit on a dual pattern.

If you go wioth the TKO tranny, trust me, low speed torque will NOT be an issue with that gearing. It'll be moreso with the M22 which has crappy gears ratios IMHO, unless it 4.10, 4.33, 4.56, etc.

My opinion, keep the rect heads, use the gearing advantage of the TKO to get the motor up to 3500-4000 fast, and select a cam that will let it run to 6200-6500 rpms.

The LS6 cam will want all of 10.25-10.5:1 to run on 91 octane. I'd do some careful DCR calcualtions once you know your comnbustion chamber size, piston dome cc, etc. You'll wnat DCR numbers a bit lower than I mentioned before to be 91 octane friendly. Likely a 1/4 pt lower, so the target DCR is around 8, not 8.25. I;d shoot for anywhere from 7.7 to 8.0.

With a modern cam ( shorter seat durations and much better .200 durations), you'll want to keep STATIC compression at under 10:1 to be 91 octane friendly. IMHO.

Additionally, a modern cam should give you a better pull in the mid range at a lower DCR than the LS6 grind, which , as stated by Jim who races Pure Stock with one, is a decent cam if you give if > 10.5:1 static. However, the best power with that grind will occur at a higher DCR than a modern , toghter lobe separation , grind.

In short, if you are running the TKO with a first gear of, what 3.05 X 3.73 rear gear = 1st gear ratio of 11.3:1.

Buddy, with that kind of first gear, it'll be at 6000 + rpm after you say "one one thousand", so oval ports will only be better for the first 100-200 millisenconds of the pull!

Moreover, it's still a debate in my minds eye, but if you want a quick stick car that doesn't break things or sit there and roast the tires, you build the engine the old fashioned way, for HP, and you gear the heck out of it. ( although I will try a 496 later on which will be designed to run through an M20 and 3.31s. That will be ovals, already ahve the 049s in the garage for it.)

The TKO allows you to do that and still keep cruise RPMs down. Build the motor to match the power band of the tranny/rear in gears 1-4. That's what I did. Built a 427 that makes it's best power from 4500-6800, where the shift point is. All the wrong stuff, rect heads, 2" headers etc etc.

Not a 10 second ride mind you. But so far VERY competitive with the street cars running ovals and still able to miserly go 16 miles on a gallon of fuel. Not bad, imho, high 11/low 12 ET and 16 mpg.

All with " the wrong" heads. Clearly, they're not wrong for this ride at all. And my L88 074 heads SUCK as compared to most aftermarket castings.

Use the TKO and rects. The M22 will defintely prefer ovals, as you'll be counting 2-3 seconds before the first shift. It'll need all the mid range torque it can to pull 3700 lbs through a weak, imho, 8.2:1 1st gear ratio.

Oh yeah, you beter practice the 1/2 shift. It's kinda cool pulling the stick just as you clear the Christmas tree before the 60' mark!

Good luck. These are simply my opinions and are only based on building ONE 1967 stick car with a HP-built 427 which needed to stay "retro", i.e. 1971 vintage ( Doug Nash 5 speed, GM tripower, GM alum heads - pretty much stock L88 internals with a modern cam). Needless to say, I'm pleased with an easy 12.20 run the first time out. Sticks are harder though. Given the 67's trap speed of anywhere from 116.8 to 118.5 mph, it should be running 11.60s with a decent 60'.

No design flaws there, I beleive.

Hey, check out Pat Kelly's DCR calculator page if you havent already. While there are limtis to any mathematical estimate, it will help you design a system to work with 91 octane fuel.

Good luck Wyatt, I best get back to my real job!

I thought this was your job? tongue.gif

Wow, some great info here. Thanks for the help guys.

Jim, the heads are orig LS6 291 heads. But I'll need to run 91 octane in it, so CR can't be too high. I need to spend more time with Pat's DCR calculator I guess. Is your LS-6 still 11.25 to 1? What fuel do you run? A few years ago, there was a VP station here that had VP at the pump! But at over $4/gallon, that would get expensive.

427L88, you have a great point re: the TKO. However, it will be the 600, with 1st of 2.87. That's still a lot better than 2.20 1st though. Wow, you're getting 16mpg? If I can get anywhere close to that, it'll be a big bonus. How is it on the street at low RPMs?

Hey, what do you guys think of the Comp XE 274H, with 230/236 @.050 110LSA? Advertised RPM range is from 1800 to 6000, which seems about right.

Thanks again.

GRN69CHV, when will you have yours running? I'm curious to see how it's going to work out. Seems like an effective setup! Keep us posted!

Car won't be back on the road until about March or April. I am pulling the car apart to repaint it and plan to drop the new motor in while the front sheetmetal is off getting media blasted. Right now the car is tucked away in the garage. I did drop the new GenVI block and the rotating assembly off at the shop today so they could get started with it - should have it back in a couple of weeks.

Just to give you some background - my planned combo is based on the Frankenrat 454HO article that Chevy Hiperformance ran. Basically just taking the aproach of a 454HO/425HP motor and making a few subtle changes in the build (a little larger cam, little higher CR 8.75 up to 9.5/1, and a little better cylinder head). Nothing fancy.

Resurrecting this old thread...

Well after a 4 year break from the resto, the '70 Chevelle is now on the rotisserie. Since I've been out of the loop for a few years, I thought I'd bring this thread back and see if you guys had any suggestions for a cam to work with the LS6 heads I'm going to be using in the BB. I'm still going with the TKO600 and 3.73 gears. Still shooting for <= 10/1 cr for use with 93 octane.

Also, opinions on intakes? Is the airgap still a viable option (I haven't bought the intake yet)? Thanks guys...it's good to be back on the restoration road.

I was at the machine shop a while back to dyno my motor and had to wait on them to take an LS- off the dyno. It was 11-1 compression, sq. ports and all, the only difference was it had a Comp. tight lash solid LS-6 repop cam in it. It made 450 h.p. and 502 ft. lbs. of torque at I believe somewhere around 52-5500 rpm. Also you can't compare those 074 aluminum heads to the 990 sq. port heads. That is the smallest square port ever made and would have to be a great street head. I think the iron sq. ports are all way to big for anything sane to drive on the street unless it's over 500 cubes. Just an observation, not being critical, hope it runs great. L.T.

Good grief!!!!!
Four year hibernation!
Didya grow a beard too?

RAMBO has the 454HO with the rect port heads and small cam. No shortage of torque there... runs high 12s at 106+. Though listed as 8.75:1, they have less actually.

If you have the gearing with the TKO, just keep the rect port heads. Since you have them, keep them. The oval port heads really shine with modest 'sport gearing'

I use the regular RPM intake, save a few bucks. Same power....
The 850DP will be fine!

Good grief!!!!!
Four year hibernation!
Didya grow a beard too?

RAMBO has the 454HO with the rect port heads and small cam. No shortage of torque there... runs high 12s at 106+. Though listed as 8.75:1, they have less actually.

If you have the gearing with the TKO, just keep the rect port heads. Since you have them, keep them. The oval port heads really shine with modest 'sport gearing'

I use the regular RPM intake, save a few bucks. Same power....
The 850DP will be fine!

Haha. Grew a beard and lost my hair. Fair tradeoff I suppose.

Thanks for the advice guys.

The Voodoo 60204 from Lunati should work well with 10:1 c.r. although daily driving might not be tough. http://store.summitracing.com/partdetail.asp?part=LUN%2D60204&autoview=sku