Comp 308R S/R in a .060 over 455?
 

Starting to build a new .060 over 455 to replace the 406 in my 81 T/A. It's a B/W T-10 4 speed car with a 3.42 geared 10 bolt.

I've had this Comp mangnum 262/262 solid roller cam on the shelf for quite awhile now. I originally picked it up with the intent to put it in my race car. I just picked up a nice used set of Comp solid roller lifters for it.

If I was to use my 94cc Greg Merrick ported 6X-4 heads, compression would be 9.59:1 using .039 4.25 diameter head gaskets with a total of 469 CI. I would use my Hooker Super Comp 4 tube headers and good flowing mufflers.

It's a street car with some occasional strip time so it needs to be reasonably drivable. Think this cam is a good fit? I do live at 5800ft elevation.

Grind Number:308R
Cam Type:Solid Roller
Camshaft Series:Magnum
Usage:Street/Strip
Advertised Intake Duration:308
Advertised Exhaust Duration:308
Intake Duration at .050 Inch Lift:262
Exhaust Duration at .050 Inch Lift:262
Intake Valve Lift:0.575
Exhaust Valve Lift:0.575
Lobe Separation:110

It’s a single patton cam, really designed for low intake to exhaust flow ratio, so its really going to depend on what your intake to exhaust flow ratio is on your heads. So it would be good for a head with 65 intake to exhaust flow ratio. If it turns out that your heads have 75 % intake to exhaust then its not going to be a good cam for those heads.

It depends how much street time,that’s a lot of came with 3.42 stick shift.Hope no power brakes,they might need a helper.What is the first gear in the ST 10?Tom

Sure, go right ahead if you don’t mind the strongest part of the motors power band starting to kicking in above
4200 rpm!
I say leave it on the shelf.

Also not to mention what that level of power will do to a T10.

?? Gach I think has his info backward to what I ussually go by, the flow ratio turned around. High flow E/I ratio is usually what shows gains with more of a single pattern cam, reverse splits, ect. I think he he is looking at the other end of the horse (I/E ratio).

Generally when you move up in elevation the single pattern cam will shine, the engine isn’t making as much power versus a lower elevation, the exhaust profile can have less curtain area versus the same RPM at a lower elevation. On the flip side of that, with the thinner air the single pattern raise’s the VE higher and gets in trouble pretty quickly if the octane is on the edge of not working.

It is a pretty slow profile, I think at your altitude the engine will be a point low on compression. I would have to figure some numbers though, I am just guessing. I have ran a 262*@.050” SR single pattern on a 112* , and I have a 252* on a 112*, and a 272* @.050” on a 110 in Pontiacs. I don’t expect you will find the 262* on a 110 to have the idle unmanageble.

For the engine parameters you described I think it would run better overall running a 10* smaller and the LSA moved into 108* from 110*, and a bit more aggressive intake profile. But you got it, it would be a decent starting point, it will have a noticable idle for sure, and I would not expect much grunt below 4000.

I looked up the cam profile, it is ground not much different than a hyd roller profile, actually it is less aggressive than many HR’s. If you decide it is worth a try, and were to use it in the engine as described at that elevation, I would install it with some extra advance. I am going to say it should be installed at 104* instead of the as ground 106*. From what I recall, it think that profile has a pretty large lash window, it can go out to .026” lash (hot) without being overly noisy. For a driver, and fairly low compression you could make that cam more manageable on the street with some extra lash. Still big on the street for most people, but manageable in a 455. The altitude with that combination though is a concern though, I think even with those small mods it will be pretty soft on the bottom end at 5800 ft.

For your altitude though I still think it would run the hardest with at least a full point more compression and less advance, more like 108 on the ICL, the intake lash then could be tighten to find the sweet spot for the fuel it needs to run on. I think you’d find the engine would be happier overall.

Thank you so much Jay for your time and effort. I'm new to the roller cam game, I had originally picked up this cam for the race car but late found a better suited solid roller for it. I'll look around a little for a more suitable cam for this engine. A cam like this would certainly be a better fit.

http://schneidercams.com/288-92Rponroller.aspx

Otherwise, I'll transfer over the Comp 270S or another Ultradyne SFT cam that I had in the race car years ago that also came from Greg Merrick. The specs on that are:
Duration @ .050 243/247
LSA 110
timing events .050 15.5 47.5 Intake, 57.5 9.5 Exh
Gross lift .510 .525
lash .026

As a comparison, my cam in my race car (in my sig) is slightly bigger than that roller and my car goes 10 flat but uses 11.2:1 static CR. It would be a little rowdy on the street.

The Ultradyne looks really good. Even at 5800 ft I don’t think the 270S isn’t enough cam in a 469.

Years ago when Chris Mays at Comp was helping me with a combo he suggested a single-pattern cam at the time, this with a higher exhaust/intake ratio on the ported Edelbrock heads which were about a 79 percent ratio.
That and he considered how it would also compliment the low compression ratio, which was a crappy 9.7:1 with the aluminum heads. Admittedly the rpm operating range was a tad bit higher than many 5000 rpm truck motor combos often touted out there and apparently that can influence the decision. The engine made peak power at 5800 RPM. Not isolated though, I believe it was Bob Cook at Bullet that also recommended a single pattern cam at the time.


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The point I was trying to make was, the intake to exhaust flow ratio of his heads plays a big part in cam choice.

This is funny my intake to exhaust flow ratio is 80% but its not a single pattern cam. Should I call Comp and tell him he got it wrong..

Yes!Tom

Yes I should ?

These are old pictures and I've never had them flowed

Nice looking ports ! If you get a chance get them flowed.

I can tell you this the 6X-4 heads are arguably one of the best D-Port heads, do know this the Super Stock guys hunt for them, or they use too..I’ve sold 2 sets.

Here is what Harold Brookshire from UltraDyne said on the subject within a post here on PY years ago:

"On most cylinder heads, whenever I have around a 75 percent exhaust-to-intake ratio, I use an 8 degree bigger exhaust cam. If the ratios under 70 percent, I use 12 degrees, and around 80 percent, only 4 degrees. Whenever the ratio gets around 85 percent, single pattern cams seem to work as good as anything."

Possibly the design of the cylinder head should be a factor. I will suggest in the above statement Harold had a Pontiac iron head in mind.
In addition the complete exhaust system flow from exhaust valve to the tail pipe should be considered. Can you can't simulate what happens in a exhaust system on a static flow bench !


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So now what your saying is comp recommending a single pat and cam for 79-80 intake to exhaust ratio, is wrong and Harold is right !

I guess I am the only one that believes that CR also is a factor?

Stan