Runner Sizing
 

:cool-smiley-027:
Hi,

Anyone know of a formula to determine optimum runner size for heads for a 496ci? Anticipate 5500 max rpm, cam undecided, yet.
I bought some used 088's rectangles to replace the peanuts on the GenV454, and have learned they are probably too big for my application. I'm still gonna run them this year, and plan the top end upgrade for next fall....
Any help appreciated.

No reason the 088's can't work on that motor with those revs. They're not flow monsters by any stretch of the imagination. You might consider using a good oval-port aliminum dual-plane and port-matching it to the rectangles. That'll keep your velocities up. The cam is what will make or break you.

:cool-smiley-027:
Thanks for your response. Here's where I'm at:
10-2007 - bought two (1994+1995) GenV454-330
01-2008 - Eagle 11111 rotating assemblies
---out of money----
---back in "the money"----
10-2008 - buy hyd rollers, springs
01-2009 - valves, seats, little bit of port and polish,

I have two intake setups:
1. GM alum dual planes w QJets
2. Weiand Team Gs w Holley Dominators

I plan to run the dp-Qjets with the 088's and stock cams this year to shake down the boat, and am wondering if I should spend next fall's money on valves/seats in the 088's or look to something else?

I'm open to suggestions for the cams - 28' Checkmate, dual Bravo, and I don't want to break any speed records...

You don't have to mess with the seats unless there's a problem. manley SS valves are a sucker bet- you'll get better flow and much more peace of mind knowing you have way less chance of dropping a valve. At a bare minimum hit your current exhaust valves with a magnet. If there not stainless, don't use them. I'd be more concerned with valve springs- I would never use a spring I didn't know exactly how many hours and what kind of use they had. They don't cost any more than a top-end gasket set anyway. On the head, the 088 will definitely benefir from some port bowl work but beyond that, you're probably wasting your time on porting- at least for that 5500 rpm range. Sell the G's and the dominators. Unless you're going to spin the motors to 8-grand and want to spens 10 minutes every time pointing out of the wind and nursing it up on plane, they're not going to do you any good. The max carb with your 088's and a warm cam is going to be an 825 or 850. lastly, on cam the only sensible thing to do is call RMBUILDER and have him grind you one for your exact application. It won't cost you any more than an off-the-shelf setup and will give you every possible bit of power your setup is capable of.

One more thing- exhaust. If you're using the stock Merc manifolds, you're wasting your money. They don't flow worth a $hit and they won't support any high-performance cam very well without causing reversion.

Do you mean the Manleys are a good buy? I know the stock valves aren't up to much (Eaton 2-piece, Merc stock), but hoped I could srvive this year with the 4359 cams.

I agree 100%, IF I was building for my regular driving style as I pound the pizz outta them, BUT, I'm only building to shake her down this season. I have some relatively fresh Comp Cams Springs I could throw on - it didn't occur to me - thanks!!

I blended the exhaust bowls and was starting to look at the intakes, when I questioned using the 088s because of teh runner size.

This is what I wanted to hear - THANKYOU!! Finally a definitive answer to whether these are a good fit for my application. They came as part of a package deal, so I'm not out of pocket too much.

I'll PM him to get an idea of $$ as I'll need retro rollers, springs, guides, valves, probably exhaust seats

I was lucky and got my hands on three sets of Gils - one of older design with frost plugs, and two of new design - all pressure tested good except one of the newer ones has a small corrosion leak- I'm gonna try and plug it.

CHRIS - Thanks for your advice and help - much appreciated - you can see here the pitting and the width of the exhaust seat mating surface are pretty much done. If I grind them anymore, I'll be into the intake valve....

:cool-smiley-027: Here's as good s they're gonna get this year

Yes, the Manley's are a very good value and cheap insurance. Bob will sell you the Morel roller lifter which is as good as it gets- and he's cheaper on them than I've found online anywhere. He uses a billet blank with a press-on gear and they're pretty much bulletproof.

I don't know what tails you have with the Gils but the long ones (dry to the very end) are pretty good. You have to be careful with the short one's as far as cam overlap- these are more common on Bravo boats.

That's good, as I sent a PM earlier with all the stuff I think I need.
I checked the valves with a magnet as you suggested, and the exhaust have no attraction and have a ceramic coating. The intakes stick to a magnet like glue. Both have Eaton on the valve tip and int is 2.19 exh 1.88...stock stuff.

Thanks again for the advice and hook-up with Bob..I'll let you know where it goes.

What are the goals of the overall build TQ/HP @ ? RPM

:cool-smiley-027: Since the boat and power are new to me I have no baselines - I have expectations of 75-80mph from posts I've read from owners with similar power.
I spent some money on the bottom ends ($8K) and had them balanced and installed at the local speed shop. I'm not locked into any specific torque/hp/rpm goals, other than good performance and reliability. The shop owner claimed he could get 600+hp and tq @5000-5500rpm from roller setups with these blocks and heads.:party-smiley-004: