My motor, now that I have taken one of the heads off is equiped with 8.0:1 Forged pistons. I am running Merc rec. port magnum heads (totaly stock, 118 cc I believe), a Strip Dominator single plane intake, and a Holley 750 CFM carb. Crazyhorse and I did a valve to piston clearance test last night:

Intake: .195"
Exhaust" .164"

Lots of clearance (to say the least!)

It has been suggested that I take around .040" off the heads to bring compression up a bit. More? What will this do to the combustion chambers?? What change in compression will I see at .040"?? Also, I've been told that if you unshroud the valves in the cylinder walls (area under each valve) you can get some easy, dyno proven hp. Yes?? How about a dual plane intake???

Lot's of questions. Anyone got any answers??

Yeah, fill the v-berth with golf cart batteries and put a BIG electric motor in front of the Bravo. Then get a really cool stereo to play engine sounds recorded from KAAMA. Cover the deck with solar panels to keep the batteries charged and boat for free all summer.

Leave it to you Dave.....

install pro charger on your motor for 200 more hp .call jay at CAST-A-LINE MARINE INC. (954-966-0240)

LMAO!!

Waterfoul,

When I had my engines re-worked bu Tyler Crockett he did shave the heads a little to raise compression. I assume it was to increase Hp. The were stock 502 Mags I think the stock compression was like 8.75:1 by doing the milling he brought it up to 9.1:1. I am sure he would help you if you called him. Good Luck

'Foul,

I have heard it mentioned several times on this board that notching the top of the bores close to the intake valve will unshroud the valve and increase flow. Makes sense in theory. If you have ever looked at some of the early Chevy big blocks, they came from the factory with these reliefs, but I think it was more of a necessity with high-lift cams/small bores. Likewise, I have read that it is good practice to unshroud the valves in the combustion chambers, but you would want to have someone who knows what they are doing perform this operation - too easy to hit water jacket. You would also need to CC the chambers after this operation. Definitely be careful not to go too far down into the bore if you notch the block - don't want to relieve it where the top compression ring lands - thus relieving your engine of compression!

Since you have so much piston/valve clearance, I would consider a set of roller rockers with a higher-than-stock ratio - something like 1.8 if you don't already have them. This will effectively increase your gross valve lift. Be careful about coil bind when you do this.

Good luck with it. Are you doing a complete rebuild?

Foul, I had my heads milled .020 when I redid the top half of my engine on the Baja last year. The machine shop said that every .005 would reduce the combustion chamber size by about 1cc. They also said that if I took off more than .030 I would probably have to get the intake modified slightly. I remember figuring that the .020 would have moved me from 8.75 up to 9.0. I used Felpro gaskets which are a little thicker and overall gained .011. I figure this puts me at about 8.9 for a static CR. Raising you CR should help optimize your larger cam, if I remember its pretty good sized.

Mike,
I believe the standard head gasket is about .038 compressed. Did we see a post some time ago about a head gasket that was .020 compressed? It seems that if you could get a .020 gasket it would save the machine work effort. Can anyone verify the standard gasket height when compressed and shed any light on the .020 gasket? Maybe we should just go to General Discussion and post/view some pics an ferget abad et!
Tim T.

I have always just discarded the end rubber or cork gaskets and use hi temp silicone in place. Then you don't need to worry about the interference caused by milling your heads.

BT