I'd need to measure that. Part #212137
Looks like there is quite a bit of stock.
http://www.jepistons.com/Catalogs/SR...dome_open.aspx

Open up the chamber on your heads some to drop the CR more.

+1
Yup, having JimV do a chamber port was in the plans. I still haven't deducted the volume for my bore notch, pistons -0.014" in the hole, head gaskets and stuff. I don't think I will have much trouble getting to 9.0 or below. The last resort was to cut the pistons, but I really don't want to take the engines down any further.

Anyone have any opinions on the polished witness on the bearing? There was some Right Stuff in the bottom of the oil pan and in the screen of the oil pump.

Roller cam buttons?
http://www.jegs.com/i/Comp+Cams/249/...Fe5FMgodGjAAlw

rookie,it looks like a small amount of dirt went through the bearing,those are the cam button,s i like to use.i think i would have the piston,s flycut before i changed the cc on heads.be careful with your tune,keep it fat,im not sure how much heat that piston will tolerate with a blower .what length rods do you have? im guessing 6.135.

Intercoolers????

Yes 6.135" Just going to have some material removed around the ex valves. Then get a total head volume.
No, I don't plan on spinning them that hard. And I see innercoolers as a catch 22. Put on a restriction to cool a charge then have to spin them harder to make up for the restriction that was just added and then add more heat to the charge you just tried to cool.
I have a dual probe handheld pyrometer and I will measure charge temp delta above and below blower.

Please post the results of the pyro temps when you get it set up, interested to set the differencial, I ran a similar roots blower back in 1989 at 5lbs boost, really started heating up at 5200 rpms for a 3 min blast, added water/alcohol injection to help. I know they have made many advancements in blower technology since then, but I hate the thought of backing off the timing due to a heated air charge. but as most modifications go it becomes a trade off. Keep us posted, sounds like a sweet project!

No, I don't plan on spinning them that hard. And I see innercoolers as a catch 22. Put on a restriction to cool a charge then have to spin them harder to make up for the restriction that was just added and then add more heat to the charge you just tried to cool.
I have a dual probe handheld pyrometer and I will measure charge temp delta above and below blower.[/QUOTE]

I think if you do your home work you will fined that intercoolers are anything but a catch 22. It's the easiest HP gain you can make. :whistle:

.[/QUOTE]

I think if you do your home work you will fined that intercoolers are anything but a catch 22. It's the easiest HP gain you can make. :whistle:[/QUOTE]

I would like to see the results of his test, only thing better would be to bolt a intercooler on and then do a pull, making note of hp and temp changes.

I think a intercooler might be worth some power on a small blower overdriven a lot. But with a big blower under driven , there just isn't much heat made at marine roots boost levels 5-7lbs. I'd rather not make the heat nor have the restriction, vs make the heat, add a cooler, turn blower faster, etc.

Many guys used to bolt chillers on the baby blower merc motors. Nothing gained until pulleys changed to spin blower harder, then maybe 2-3mph, with an extra 2lbs of boost.

I swapped from a single carb non intercooled 250 blower to a dual carb non intercooled 420 blower. Boat gained 4-5mph running 1lb less boost than I was with the 250. You can see where 7% under will run cooler than 80% overdriven.

I think if you do your home work you will fined that intercoolers are anything but a catch 22. It's the easiest HP gain you can make. :whistle:[/QUOTE]

I would like to see the results of his test, only thing better would be to bolt a intercooler on and then do a pull, making note of hp and temp changes.

I think a intercooler might be worth some power on a small blower overdriven a lot. But with a big blower under driven , there just isn't much heat made at marine roots boost levels 5-7lbs. I'd rather not make the heat nor have the restriction, vs make the heat, add a cooler, turn blower faster, etc.

Many guys used to bolt chillers on the baby blower merc motors. Nothing gained until pulleys changed to spin blower harder, then maybe 2-3mph, with an extra 2lbs of boost.

I swapped from a single carb non intercooled 250 blower to a dual carb non intercooled 420 blower. Boat gained 4-5mph running 1lb less boost than I was with the 250. You can see where 7% under will run cooler than 80% overdriven.[/QUOTE]

Good points and perspective. I also would like to see some hard data for the results. I am still a little leary of bolting a intercooler on top of the engine with the potential for cooler leakage via wear or damage. At some point though you have to factor the inefficiency (rotor leakage) of a large blower at low boost to make the HP you are looking for.