454/420hp REBUILD Compression
 

I'm embarking on re-building my 454/420hp motors. I will be using the 990 iron GM heads having the bowls and ports re-worked and using Gold Crane Rollers. ALSO, Bore notching the cylinders!

Before I finalize on a Cam, I want to have the heads flowed to match the cam selected. I intend on using a Hyd Roller set-up . Probably around 575 - 590 lift and mid 230 duration with @ 112-114* lobe separation. I believe this cam would be similar to the hp500 roller cam.

Other components include:
Dart HP500 intake
CMI e-Top Headers
800cfm Holley Marine Carbs (mechanical secondaries)
Crane or MSD ignition systems.
Forged Pistons w/ Balanced Crank assembly

Is 9.5 : 1 too high?.

My engine builder suggested going as high as 10:1 knowing I will be filling up the boat on the trailer using 93 octane!
However, that scares me unless I carry 5 pints of 104plus when 89 octane marina gas is used.

Re: 454/420hp REBUILD Compression
 

Mtgbiker,
It has been my experience that one of the biggest mistakes a marine engine builder can make is “chasing” compression ratio. In your application, the difference in round figures for a full point of compression will net you approx. 3-4% power. That’s 20 HP on 500 and 10 Hp per .5 point. Arguments are made regarding SCR vs. DCR, IVC angles, etc. but until you pull it at max VE/peak torque you wont know the threshold of detonation. Point is, there’s lots more HP to be made elsewhere without the consequences.
Bob

Re: 454/420hp REBUILD Compression
 

Bob, I emailed you about 60 days ago and you suggested intake wedges, port and bowl work for these heads.

I am in complete agreement with you about creating safer hp. The bottom line is that my builder will honor me as the customer when I tell him what I want and I would appreciate everyone's input. It's better to do my "due Diligence" then be left with the consequences after the build. :D

Re: 454/420hp REBUILD Compression
 

Has anyone used a merc (Dart) HP500 carb intake on a warmed 454 with re-worked GM 990, 188 or 088 iron heads ?

Re: 454/420hp REBUILD Compression
 

MTGBIKER. I upgraded my HP500s last year and have a few spare parts to sell.
2 of each:

CAM

LIFTERS TRAYS DOG BONES

THERMOSTATS AND HOUSINGS

Let me know if you are interested in any of these?

Thanks
Shawn

Re: 454/420hp REBUILD Compression
 

[QUOTE=shawn]MTGBIKER. I upgraded my HP500s last year and have a few spare parts to sell.

Shawn ,

What cam did you install in your motors?
Carbed or fuel injected?
Are you running Gil Exhaust or headers?

Thanks, Dan

Re: 454/420hp REBUILD Compression
 

Dan, the cam is 238 @ 620 and 248 @ 629, thay are carb motors with Gil exhaust. They made 599HP at 5600 on the dyno.

Shawn

Re: 454/420hp REBUILD Compression
 

Excellent Hp. Its nice to back it up with Dyno numbers too :D

Are you using the factory heads and intake? If so, any mods? Or did you change them to a aftermarket set-up?

Dan

Re: 454/420hp REBUILD Compression
 

9.5:1 is on the edge with iron heads. it could live with enough
cam but i would back it down a touch.

Re: 454/420hp REBUILD Compression
 

I used the stock heads and had them ported and polished. I also had the intakes matched to the heads and installed a V6 module in my TB ignition. I have spooled them up to 5800 - 6000 once in a while.
My CR is 9.3 and I just use 93 octane.