Camshaft split

[jeff swisher]

Dont beleive this: "every four degrees you retard a cam it moves rpm up 200,and for every four degrees you advance a cam it moves rpm down 200."
Everytime i have retarded a cam i lost topend and midrange and gained nothing down low..but that may depend on aplication.
all my aplications like advanced cams i guess.
When you run the big split profiles you will be able to pull more R's before the power falls off the cliff,,not much more HP but when you need to over rev it the big split helps,,,as long as the valvetrain is up to parr.

[blackflag]

So on a 327ci if you move intake seat duratio from 272 to 332 it moves the rpm up only120?

[CamKing]

So on a 327ci if you move intake seat duratio from 272 to 332 it moves the rpm up only120?

No.
Re-read the post.

In a 327ci, a 272 duration will move the power up 520 RPM over the 260 duration, but a 332 seat duration will move the power up 640 RPM over the 320 duration. Both are 12 degree increases, but they don't gain the same amount of RPM.

On a 327ci, going from a 272 to a 332 will raise peak power 3,160 RPM.

[novadude]

Mike.... question about your 260-to-272 seat duration 327 ci example...

I assume this applies when the engine has adequate intake port flow, and we are retaining the same port when we change duration. How much does intake flow alter this equation when you go from "enough" to "more than enough". Will the basic rpm / intake duration relationship hold true, or does a large, high flow port change things?

Also... just curious... 260 deg seat duration peak hp is at what rpm in a 327 ci, according the method you are using to calculate numbers above?

[blackflag]

Ok,so on a 400ci if you increase 12 degrees 260 to272 you raise rpm about 449,and with the same change on a 350ci it moves the rpm 497.

[jeff swisher]

I assume these are for Mikes cams that he sells..and not all engines will respond the same...You guys will need to do a lot of your own trial and error.
I have played with the comp high energy and magnums,,in the same engine it works for me like this.
350 chevy ported factory iron heads, This is my own trial and error...The 292H was retarded 4 degrees and that made the shift point go down to 7200rpm, it did not have any guts above that at 4 retarded
another note i used the 280H with some lo po 1.72 intake valve heads and that made max rpm lower,,it was 6700rpm with the tiny valve
I also tried stock 441 heads with 1.94 intakes and the 268H ,,the shift rpm on that was 5500 then replaced with ported 1.84 valve heads and RPM increased to 6500...Like was stated head flow has a bunch to do with it,,as does a good chamber and an excellent tune.
I have also used the 305H 253@ .050 and these all being Hydraulic cams the rpm was held to 7500rpm.

268H 6500rpm shift point .218@.050
270H 6900rpm shift point .224@ .050
280H 7200rpm shift point .230@ .050
292H 7500rpm shift point .244@ .050

[novadude]

Jeff... I don't know how you are still making power with a Comp 268H in a 350 at 6500 rpm? I'm sure it might rev that high, but from what I've seen (and experienced with similar cams), power starts dropping off above 5500 rpm. Interesting that you are twisting it that high and it is still pulling. I realize it will shut off earlier if the heads don't flow, and maybe you had killer heads on your car, but 6500 rpm still sounds high with 268 deg seat duration and 350 ci.

[panic]

All simple answers are wrong.

[CGT]

268H 6500rpm shift point .218@.050
270H 6900rpm shift point .224@ .050
280H 7200rpm shift point .230@ .050
292H 7500rpm shift point .244@ .050

These are shift points and not peaks, two different things.

[jeff swisher]

That is correct,,shift points not peak,,,It is interesting though when i try different heads, The heads are not killer heads by any means just very effecient.
You get the jetting off a few jet sizes or the timing pulled back even 2 degrees from optimum and you will see a 500rpm loss pretty quick.
The carb size makes a big difference,,when i run a 600cfm on my 47dodge (350 powered) or others with this combo i will be down 800rpm on the top,, no matter how i jet it,,,and i see soooo many people saying 600cfm is all a 350 needs, what works for them sure dont work for me.
Fact our 292H is in a 78 nova 350 with a tunnelram and 2 600's and runnin 11.94 at 116mph and some change on 91 octane no aditives this is a daily driver. I am a little low on seat pressure and running stock pushrods and he keeps it at 7400rpm to keep the guts in the lifters..a tick or 2 past 7500 resulted in some comming apart
That is due for a valvetrain revamp..actually going with a 292H on a 106LS

I have a current 268H in my 47dodge truck i had it ground on a 106LS 1.84 intake valves and 6500 on that one is the norm.
currently with all the 108 degree days i had to pull some timing out and now it is 6200..It was cool the other day and i was getting on the highway (with the good tune and timing) blowing the tires off around the clover leaf, I said to myself about time to shift, felt like it was starting to nose over, looked at the tach and she is swinging 7000 rpm...not optimum shift point,,,but nice to take note of....Before you call BS i will say i was quite surprised myself.

This 268H i have used in a couple builds and with non ported heads 5500 is it ,, and the ported just have better velosity and filling capabilities....I have also seen 7400rpm with the 270H and still pullin' another 1 time deal early morning and i was playing with an agressive tune and some T.E.L. and other chemicals and set it up lean....Those R's worried me and i fattened her up..Daily driver you know,,,got to make it to work..I am not over agressive on springs either with these grinds. 110 seat and in the low to mid 300's open. although the larger 292 and 305 like more seat pressure.

Something about the lobe profile on the comp grinds is, they will rev
Hope that above info helps.
Another rpm killer is a tight engine...I set up my 350's with cast pistons and .0035" piston to wall these are old big skirt deals the 345np piston...I found at .0015" i was down 1000,, darn thing would not pull at all. I have ran that slug at .0045" and no different than .0035"..The pistons get a deburr and smooth treatment,,to keep detonation down also

[blackflag]

My experience with comp cams are great for revs, but short on power. Thats in all out race motors. I have comp in brand new engine,gona give them another try.

[CamKing]

All simple answers are wrong.

Really?
a^2 x b^2 = c^2

e=mc^2


The simplest answers, are normally the purest, and most correct.

[ou812]

My experience with comp cams are great for revs, but short on power. Thats in all out race motors. I have comp in brand new engine,gona give them another try.

Are you letting Comp pick the cam for you or ??? Can you give us some examples?
I'm just curious, not doubting at this point.
Brian

[CamKing]

a^2 x b^2 = c^2

should be a "+", not "x"

[blackflag]

Used to let them pick the cams,they were always wrong for my motors. Now picking own profiles,setting fast times and winning races (not comp). The only reason try a comp in new motor is I did not build the motor,cam was alread in motor from a very respected builder,if I dont like the power curve I will recam with something that works for me.