Help with cam timing?
 

406 sbc
Comp cam XE262 H-10

@ 106 intake centerline
@.006 lift I---open 25* BTDC close 57*ABDC
E---open 69* BBDC close 21* ATDC

If I retard cam 4*, I get slightly higher and flatter torque curve. It also changes the the intake opening to 21* BTDC and closes the exhaust 25* ATDC.

What I was worried about was the exhaust valve staying open the extra 4* to 25 * into the intake stroke and possibly getting the exhaust water sucked back into the engine.


Thanks,
Charlie


P.S.
I'm trying to change my email address but can't find the edit link.

Re: Help with cam timing?
 

Hey Charlie,
I don't know the answer to your question. There are a lot of really good engine builders here. Hopefully one of them will respond. Are using Desktop Dyno to get your torque curves?

Dave

Re: Help with cam timing?
 

Be careful retarding the cam timing. It takes away much needed low-end power that's needed in a marine application.

Re: Help with cam timing?
 

call the comp cams tech line I called them about retarding the cams in my motors also they should be pretty helpfull

Re: Help with cam timing?
 

Charlie,
I don’t believe retarding this cam XE262H (12-238-2) is necessary. Given the displacement of your engine, with overlap rated @ (46º seat), a short seat of 260º/272º, 218º/224º @ .050", reversion should not be an issue.
You also have the alternative of selecting the (12-236-3) XM262H… 262º/268º
218º/224º…. 462"/. 477" on an 112º LSA, that rates overlap (41º seat) to further reduce the possibility of reversion.

That being said, you may want to consider re-evaluating your selection dependent upon your intended usage, max WOT, C/R, cylinder heads, etc. A 406, turning in excess of 5000 RPM, with quality components, may not reach its full potential without a longer profile.

Bob

Re: Help with cam timing?
 

Hey Dave,
Yeah, I'm using the new version of DTD. Really disappointing but hopefully It's giving me a way of comparing small changes in cam profiles.

Ed, batty,
I'll give comp cams a call. Like I said above, I was making comparrisons from the DTD.

Bob,
I'm not a go fast. Just a fishing boat trying to get better mileage. CR is 9.12:1 for 87 octane. Thanks for a little more peace of mind on the reversion thing.

Would I reduce chances of reversion more with my planned 'thru transom' exhaust or should I stick with thru prop.(merc BII)


Thanks guys,
Charlie