7.4 BBC Build
 

Hi Guys,
I read through the JanH 454-build thread.
Pretty interesting and I have a similar situation.
I just spun a rod bearing in my Mark V 7.4. After removing the engine and tear-down, it's clear the motor is a "target motor" rebuild. The cast crank was already turned 20-20, so after spinning the bearing it's junk. Since I have to replace the crank, might as well stroke that *****! My current plan is a 4.310 bore x 4.25 stroke aka a 496. My plan is an Eagle forged crank, Eagle 6.385 rods, and some -5cc forged pistons.

For the top end, I have the "peanut" heads and after reading the 454-build thread I can guess how the group feels about them. However, I'm not married to them and I may try to find some good oval port heads. My issue is the compression ratio. If I run the -5cc pistons, I should have around 9:1 compression. Acceptable on 91 pump gas. However, if I upgraded to aluminum heads, I could run the more standard -18cc pistons for around 10:1 with no problems. If I get good CI oval port heads, it doesn't change that math, but they flow better. Problem is changing the top end to alum is at least another $4-5K and I'm not sure I want to spend the cash right now.

The boat is a 1994 Formula 232LS 23' with a B3. It can push around 55 mph WOT right now and I'd like to get 65/70, cruise at 50-55. I've heard B3's really drop off over 60 mph, but I'm more interested in the fast cruise.

So, my plan is to build a solid 496 bottom end and run the peanut heads for now. Then maybe replace the top end later. Of course, that'll mean I'll have 9:1 on alum heads. Sounds like a good blower combo?

If I did the whole NA setup now with the alum top end, I think it will cost me $10k. or roughly double my current cost. The motor would have -18cc pistons with 10:1 compression. Totally fine with alum heads. HP estimates? With a mild cam, I think this motor could easily make 450hp maybe more? Put my top end around 61mph?

Ideas? Suggestions?

Thanks,
Rob

If it has 2 bolt mains, then I'd scrap the stroker idea.
https://www.michiganmotorz.com/7-4l-...p-1991-current
https://www.michiganmotorz.com/8-2l-...5-hp-1991-2001

No, it’s a four bolt main. I’m having it line bored just to ensure it’s straight as well.

I would never stroke a two bolt main; however you can retro fit angle bolt caps on a two bolt block. I would do that.

Which heads are you calling peanut ports? If they're 297 those are good 99cc heads.

If you're going to invest in increasing the stroke, it makes no sense whatsoever to fall short on the heads "if" you're plan involves doing better heads later. Do it all now, or don't do it at all.

I agree. Nothing worse than bad head.

I see you're in rare form this morning SB...........personally Id find a gen 6 502 block as the platform to build a 540

HawkX66 I wish I had the 297’s, but I have the 156’s. Everything I’ve read says they’re pretty bad.

Just did a pair of 496cu motors and ran on the dyno, made 535hp/560 @4800 rpms putting in a 28 Eliminator Gen 4 4 bolt main blocks , eagle kits, 4.25 cranks 10.1 ,crane cam 132561 , 088 steel heads with Ferrera valves 2.25/1.88 Heads where new from Aerohead of Indy . merlin intakes and 850 carb.

Inrecovery that sounds like a nice combo. Are you concerned about detonation? Did you have to do much clearancing on the block?