Camshaft and reversion?
 

Would this camshaft create reversion in a 454 w/ EMI and stainless risers?

Comp Cam 11-420-8 Hydraulic roller
215/215 @.050, .566/.566, 110* LSA

The cam is already installed in a recently purchased boat

Thanks for the input.

Paul

You should be just fine. Stock 454 May is 224/224 at 0.050 with 114 LS degrees if my memory serves me.

Mine are 232/234 with 114 LS. Stainless Marine with Captain's call.

Your cam seem pretty mild.

I'm not so sure...now I don't know my cam specs really well, but 110* lsa should give it a really good lope. I'm thinking that the cam will revert.

I'm with bajalion, he doesn't overlap at 0.050 (-5*) with that little duration. Shouldn't be a problem.

I asked this same question a couple of weeks back.

Lots of people responded, and I got quite an education on cam duration, lobe separation angle, and overlap.
I also spoke with two camshaft manufactures on the subject...

bajalion is correct on two counts:
A 454mag or 502mag Cam is 224°/224°, 114°

With a duration of 215°/215° even with 110° lobe separation, you should not have any problems.

Overlap Calculation
 

Just to set the record straight:

Overlap is proportional to Reversion

Overlap is the time that both intake and exhaust valves are open at the same time.

LC = Lobe center
TDC = Top dead center
CL = Centerline (from TDC)
IND = Intake duration @ 0.050 tappet height
EXD = Exhaust duration @ 0.050 tappet height

LC = (Exhaust CL + Intake CL)/2

Overlap (at 0.50) = ((IND + EXD)/2) - (2 x LC)

So at 224/224 with 114 LC = negative 4 degrees overlap

215/215 with 110 LC = negative 5 degrees

228/232 with 114 LC = 2 degrees

Please correct me if I'm wrong.

No problem!!!:)

Re: Overlap Calculation
 

You are quite categorically WRONG!:D

(That was fun.:D :D :D )

Reversion is a function of overlap AND the distance from the cylinder that the exhaust mixes with the water. In cars and marine dry exhaust setups, there is never an issue with reversion. Some wet exhaust systems will mix the hot gases further down the line than others. You can also modify some exhaust setups to mix further from the engine.

For instance, EMI suggests for their Thunder system you keep duration under 230 with a 114 LSA. They get a little more liberal with the stainless riser setup. BTW -- this sounds like you would be fine, but I wouldn't trust my memory and you shouldn't either. Give them a call, and their tech support people will help you out.

If you end up with negative 5°, is there any overlap?
Without both valves open, how you going to suck water in?

May I join in? I think you most certainly can have intake/exhaust reversion in any dry system....it's just not water reversion. I read this in Chevy HiPerf Mag about 45years ago.-non-member smilie-