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-   -   The GM/Merc Rectangle port head. Discuss. (https://www.offshoreonly.com/forums/general-q/322168-gm-merc-rectangle-port-head-discuss.html)

endeavor1 01-18-2015 01:34 PM

MT, you wanna take a desktop stab at mine with the current 800cfm and soon to be 1000cfm carbs? Curious what it will say.

555
9.3.1 CR
88 heads
Dart 6200 single plane
Stock hp500 cam

MILD THUNDER 01-18-2015 02:56 PM

I'll plug it in for ya this evening

MILD THUNDER 01-18-2015 05:43 PM


Originally Posted by endeavor1 (Post 4251799)
MT, you wanna take a desktop stab at mine with the current 800cfm and soon to be 1000cfm carbs? Curious what it will say.

555
9.3.1 CR
88 heads
Dart 6200 single plane
Stock hp500 cam

As I went back to look at what you have there, I happen to notice you said "HP500" cam??? OMG.

Dude, what in gods name is that cam doing in a 555 cubic inch engine? lol.

Anyhow, the program with your combo is coming back around 490HP. Going from an 800 Carb to a dominator, only picked up about 7hp, which im not surprised. Your just not making enough power to take advantage of a bigger carb.

Going with the crane 651 specs, bumps it up slightly over 1HP per ci, to 570HP with a 1050.

Switching to a set of AFR 305's with CNC chamber, still with the 651 crane cam, made the numbers jump to 671HP with a 1050.

endeavor1 01-18-2015 05:51 PM


Originally Posted by MILD THUNDER (Post 4251937)
As I went back to look at what you have there, I happen to notice you said "HP500" cam??? OMG.

Dude, what in gods name is that cam doing in a 555 cubic inch engine? lol.

Anyhow, the program with your combo is coming back around 490HP. Going from an 800 Carb to a dominator, only picked up about 7hp, which im not surprised. Your just not making enough power to take advantage of a bigger carb.

Going with the crane 651 specs, bumps it up slightly over 1HP per ci, to 570HP with a 1050.

Switching to a set of AFR 305's with CNC chamber, still with the 651 crane cam, made the numbers jump to 671HP with a 1050.

Bought the boat set up this way with M3s on it. Went back NA with what I had to enjoy it for the rest of the season. Now in the process of cam, carb, intake hunting. Don't really want to lay out the $$$ this year on new heads.

Thanks for spec'ing it out for me. Any other suggestions from the group are welcome on which direction I should go.

dereknkathy 01-18-2015 05:57 PM


Originally Posted by MILD THUNDER (Post 4251937)
As I went back to look at what you have there, I happen to notice you said "HP500" cam??? OMG.

Dude, what in gods name is that cam doing in a 555 cubic inch engine? lol.

Anyhow, the program with your combo is coming back around 490HP. Going from an 800 Carb to a dominator, only picked up about 7hp, which im not surprised. Your just not making enough power to take advantage of a bigger carb.

Going with the crane 651 specs, bumps it up slightly over 1HP per ci, to 570HP with a 1050.

Switching to a set of AFR 305's with CNC chamber, still with the 651 crane cam, made the numbers jump to 671HP with a 1050.

and this exactly where this thread started. with MT pointing out-with flow numbers-that it is time we stop relying on 60's technology for cylinder heads. 570 to 670 hp...

MILD THUNDER 01-18-2015 05:59 PM


Originally Posted by endeavor1 (Post 4251941)
Bought the boat set up this way with M3s on it. Went back NA with what I had to enjoy it for the rest of the season. Now in the process of cam, carb, intake hunting. Don't really want to lay out the $$$ this year on new heads.

Thanks for spec'ing it out for me. Any other suggestions from the group are welcome on which direction I should go.

If new heads aren't in the budget, I would strongly suggest doing a cam upgrade at minimum. Just my opinion

endeavor1 01-18-2015 06:10 PM


Originally Posted by dereknkathy (Post 4251944)
and this exactly where this thread started. with MT pointing out-with flow numbers-that it is time we stop relying on 60's technology for cylinder heads. 570 to 670 hp...

Point taken

endeavor1 01-18-2015 06:11 PM


Originally Posted by MILD THUNDER (Post 4251946)
If new heads aren't in the budget, I would strongly suggest doing a cam upgrade at minimum. Just my opinion

Agreed

MILD THUNDER 01-18-2015 06:14 PM

Should be noted, that this is just bench racing with flow numbers. As we know, port shape, runner size, and a whole bunch of other things factor in.

bwd 01-18-2015 06:15 PM


Originally Posted by endeavor1 (Post 4251479)
What was the build recipe if you don't mind sharing?

I don't mind at all. Its a bit old school but it works. 509 cu , 10.3 comp, 630ish on the cam (roller of course) single plane, 850 race prep carb , msd, gm crank, good rods 32 degrees timing. There is a bit more little stuff but that kinda covers it. No porting, just built tough. They run like a clock. Knock on wood.


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