Hi all,

I'm gonna be swapping the cam in my '77 (again) soon and I'm wondering what experiences you all may have with different options. I had a Comp XE268H in it for a short time and liked it, but after a series of events over the last 10 years it had a Sealed Power "350hp" cam for a while and now it has the stock L48 cam back in it.

I'm looking for something with noticeably loppy idle but not so extreme that it's not driveable. CamQuest recommends the XE268 (like I used to have, and liked) or the 270H, but I have no loyalties to Comp and am wondering if anyone has any suggestions of other cams/brands.

My current setup is:
Speed Demon 650 vac. carb
Performer intake
Perforer RPM heads (64cc chamber, 195/65cc I/E ports)
1.5x rockers
TCI Breakaway 22-2400 stall convertor
3.08 rear gear.

Any ideas?

 

What is going to be your final CR?

 

I'm not 100% sure of the deck clearance or piston dome size (I think they're flat top), but it should be somewhere around 10.5, possibly a little higher.

 

Look into the lunati voodo cams.

 

I like the specs on the voodoo cams.Are you going to stay with the 3.08 gears or is changing then an option?

 

A rumpety-rump cam combined with 3.08 gears would be a disaster. It would be okay for the Bonneville salt flats but not for street driving.

 

Are you sure its not 3.55 or 3.70 rear gears?

 

With 3:08 gears I would not go real radical, you need torque.

I went with Howards roller on my last build.

By the sound you know it's not stock -but makes great torque as I have a 5 speed with 3:36 rear.

 

In order to get 10.5CR with 64cc heads you need a 3 cc piston with a .040" quench. That would be a piston with a small dome. A flat top runs on average 7cc's or so with the valve cutouts which would net you a 10.03CR.
If you want to get the most out of your cam selection it is important to know the final CR. To do this you would need to cc the combustion chamber on the heads to insure they are in fact 64 cc's. Also cc the pistons in the bore to figure their volume. Short of this and you are guessing a bit.
The difference between 10.5 and 10.0 could be the difference between detonation and not on your available pump fuel.
To get volumes of your heads and pistons look here;
https://www.corvetteforum.com/forums...mber-size.html

"rumpety-rump" is not a cam spec, so I would ignore that statement.

I have been runing a 270/270 roller cam with a 108 LSA which gives a nice lopey idle and hits hard in the midrange and delivers 14" of vacuum at a 800 rpm idle. It's a nice cam even at my 9.9 CR.

Use this CR/DCR calculator to figure your compressions with various cams.
http://www.jeepstrokers.com/calculator/

If I put in my cam with your CR@ 10.03 I get a 8.35 DCR. Given that you could step it up to a higher duration cam but it would work well with the 3.08.

My 77 also has the 3.08. It's definitely a limitation for cam selection. Keep it on the shorter duration side and you'll be happier.

I was running a 2600 stall and could use more stall for mine. This next season it will be a 10" 3000 stall converter. The 12" converters are doggy vs the 10". Your stall is a bit low IMO but it's far better than stock.
Another detriment to your combo is the 195 cc intake runners. That size of runner is going to slow down the intake charge. It's workable though, I have been running a 197cc intake runner for three years now and with a sutably short cam duration and lot's of valve lift, the 108 LSA and a highish stall converter it is still lots of fun. So with the 195 cc runners if you want that bottom end torque keep the duration short, ie no more that about 220*-224*@.050 on the intake.
I think the Isky cams with their 108 LSA's would be fun and give a lopey idle.
Your performer intake is going to be a RPM limiter for performance so no use getting a long duration cam with that intake. Build the power lower down no later than 5000-5500 RPM, again shorter duration cam.

What exhaust system are your running? That is also important to get a cam spec. More restriction and you'll need a reasonable split in the duration to get exhaust out.

I think you are in the ballpark on your current choices. I also like the Lunati voodoo line of cams a 262/268 looks pretty good for your combo assuming a 10.03 CR. No 108's so a smoother idle, similar to the xe line.

 

Thanks for all of the input! It's a big help. Here is some more info:

This car is still a work in progress, so there are still a few mods that I intend to do. I plan to swap the intake with a Performer RPM when I change the cam. I'm also strongly considering swapping in a higher rear gear.

I recently installed the 2400 TCI convertor assuming that I'd have a XE268 cam in afterwards. TCI recommends 265-280 duration with 3.0-3.70 gears with this convertor.

The Performer RPM power band (1500-6500) should match up with the XE268's (or similar) band (1600-5800), which would also match the convertor's specs. Seems like it should make a nice little setup.

So, if I make those adjustments, a 268-type cam profile should be pretty appropriate, right? Won't a shorter duration cam drop the power band and mismatch the rest of the engine? The Voodoo (268-type) that some are suggesting has faster opening/closing, longer duration at .050 and greater lift. Wouldn't this make it an even more radical profile and a worse option if I don't swap the intake and gear? And maybe a better option if I do? The increase in RPM range scares me a little as the car will be a street machine primarily. I'll take a look at Isky, too.

AV8R, I'm running 1 5/8" headers, H-pipe, Super 40's out the back. I'll dig through some old papers and see if I can verify what pistons were used in the initial rebuild (someone else did that work) so I can get a better guess on my CR/DCR. With the best info I have right now, your link is showing my CR 10.02, DCR 8.29 and 8.16 @ altitude. A little lower than I expected.

 

Harold Brookshire designed the voodo line of camshafts nobody better then him.

 

If you stay with the 3.08's go with the smaller cam.The rpm intake won't hurt you with a smaller cam as much as the performer would with a larger cam.For a astreet car we are talking about splitting hairs here that the butt dyno probably wouldn't feel with a 2400 rpm converter.
If you pick the smaller of two cam choices you will usually be happier with the results.Most folks tend to over cam a mild street car.

 

With the 195 cc heads I would go with a 2101 performer or similar. The RPM intake is going to cost you torque down low and bring on your power band later in the RPM range. The 195's have to be crutched a little bit. In other words you need to try and get some intake velocity into the head to get back some of the bottom end torque.

Better to build it according to where you are going to spend most of your time. Probably below 5000 RPM I would guess.
My performer still gets me up to 6000 easily if I want it.
Here is a shoot out on dual plane intake manifolds, it might help in your choice.

http://www.hotrod.com/how-to/engine/...d-comparisons/

Your 1 5/8" headers are geared to low end power. They could become a restriction above 5000 to 5500. Kind of depends on how much flow and VE% you get from this engine. Not that they need changing just that 1 5/8" is going to be more restrictive than something bigger, where that restriction occurs would be a guess on my part.

TCI is a great converter. I'd keep that for sure. Your previous 2200-2400 stall may get higher afterwards if your torque is higher at those RPMs.

 

That's exactly why I've kept the performer intake on it...thought it might offset the effect of the big runners a little bit. You mentioned keeping the duration limited to 220-224 at most. The XE268 is 224, but it seems that a lot of folks (including you) are suggesting that the XE268 is still too much cam. Which Isky cam were you suggesting? I would agree that the Lunati 60103 will be too much. Lunati has #60102, a 262/268 that has 219/227 @.050, 112 LSA. Am I right in assuming this would be a good middle ground? Appropriate duration, noticeable idle...

Also, considering the rear gear is such an issue and that it's fairly expensive to replace, would it be better to just get different heads instead to bring the RPM range down (with an appropriate cam, too)?

At this point it seems there are just too many ways to skin this cat. Ultimately, I rarely drive this car (a few thousand miles over the last 10 years), and when I do I'd like it to be a fairly aggressive street machine, not much highway time but not much time at the strip if any either. I can adjust everything to support a RPM range of 1500-6K or I can adjust it to off idle-4500...

So, between cam, heads, gears, etc...what are everyone's thoughts on best setup combinations to pursue at this point (w/ specific part numbers, gear ratios, etc.)?

 

I have experience with Comp Cams 270H and it is a great cam, my 355ci L48 made near 300RWHP with it with a Holley 750 DP Mechanical Secondaries, an RPM Air Gap intake, 10:1 cr with 200cc Sportsman II heads.

Vette ran perfect from tooling around town to WOT with a 3.08 rear gears

 

FYI, at this point I'm considering a lunati 60102 vs going back to the comp xe268, and putting in a 3.55 gear with either.

 

Maybe, that cam has 45*(lol, public math, had to chang this twice now) of cam overlap. The XE 268 has 54* of overlap. Overlap is key in many ways. It can build power and it can kill power.
This is a statment from David Vizard.
Read this article on cam overlap. It is enlightening.

http://www.hotrod.com/how-to/engine/...mshaft-basics/

Remember this:
On my cam I chose 54* of overlap. That puts me in the lower end of the third zone on his overlap chart. I chose this because I wanted a "hot street machine" and I had the lower displacement per cylinder vs a larger engine.
To figure overlap use this formula.
(Advertised duration + advertised duration/4) -LSA = answer x 2
Ie 270+270=540
540/4= 135
135-108=27
27 x 2 = 54
It was largely because of this article and his book that I chose the 108 LSA cam. I knew a 350 was under-cubed for significant torque so I wanted to maximize that if I could with the 108. I also chose an early closing intake to minimize reversion back into the intake tract.

With the 197 cc heads this became more important as the velocity of the intake charge was lower and would therefor allow more reversion vs a higher velocity charge.

I chose the roller cam because I could give the cam greater lift at a higher rate for better breathing both during intake and exhaust strokes.

The 108 gives that lopey cam sound at idle and has some special tuning requirements to get a good idle at a lowish RPM, 600 in my case.
A 110 will also given the overlap is similar to a comprable 108 lsa cam. The 110 will make lower peak torque but will be a flatter torque curve.

So the Lunati 262/268 cam is a little low on overlap for me, but many have used it with great success.
This is the Isky 270 mega cam
http://www.summitracing.com/parts/isk-201271

It is close to the same cam I run in a flat tappet version. Mine is 219@.050 with .549" lift.
With a split duration you increase the overlap. It's important to no allow the overlap get out of control or it effects the entire RPM range.
In my case I have side pipe exhaust with little restriction. So I figured the main restriction for me was the exhaust port on the head. I ported the exhaust ports in an effort to help with this.
For a full exhaust system some consideration has to be given to the restriction in that system as well as the head. This is often the reason for the split in the intake vs exhaust duration. Additional lift on the exhaust side can also help in a restrictive exhaust situation. Maybe 1.5 rockers on the intake and 1.6 rockers on the exhaust. Adding lift to the valve is very similar to adding duration to the cam.

 

This was my last dyno with current set up. I stopped making RPM @ 5700 due to a bad secondary adjustment. The HP was still climbing when the RPM stopped.
I would like to have all my power by 6000 RPM. With these heads the power comes on late.
Previous run (lower line) was with the valve springs loosing control. You can see it significantly impacted power.
If you figure a 30% loss due to accessories (I have A/C as well) and power train losses it comes out to 406 peak HP at the crank and 426 peak torque.

This is on a Mustang dyno with my 2600 stall torque converter.
With better heads of a more appropriate size I believe that the torque would come up faster giving me a better average torque and better low RPM torque. Like I said though it is still impressive and a blast to drive. My being up at 4000 feet makes the big intake tract issue more pronounced vs a lower altitude operation might.

 

No interest in hyd. roller cam?

 

I happen to agree on the suggestion of a roller cam. It depends on how far down the rabbit hole you want to go. All told the roller conversion cost about $800 additional.
It also came with some headaches in my case. I experienced cam walk despite using a cam button. The cam was walking forward flexing the timing chain cover out. When it did this it also dragged the HEI drive forward with it. That caused some bushing wear issues in the HEI drive that fortunately I caught early enough to prevent replacement.

The fix was for me to reinforce the timing chain cover with 1/8" sheet metal that butted up against the back of the water pump.
You can also buy a more expensive timing chain cover that is much stiffer.
Forwarned if you decide to do it.