Blown Alcohol BBC Suggestions

What kind of rods are you BBC guys running? BME, GRP, Brooks, Manley? What about rod length in a 540" standard deck (9.8) with a 4.25 crank? Just getting ideas for a possible future build on the back burner.

 

4.610" Bore
5.25" Stroke
6.385" Oliver Rod

1.5:1 Rod/Stroke ratio.

568 CID

 

540 short deck

that rod ratio seems a bit steep. can you build a tall deck motor? how about a 10.2 or 10.7 block? Im no expert, we run a 477 chev 4.5 bore 3.75 stroke 7.00 rod length. that long rod seems to be easy on parts

 

Short deck 548, 4.530 x 4.250, 6.525 rod. JE piston with 1.120 compression height. Either Childs & Albert or Manley Super 70 Nitrous rods.

 

I'm assuming you mean 4.25" stroke? I was wanting to put together a 4.5" bore x 4.25" stroke with a +.250 rod. Is this too long of a rod? How about a standard 6.135"?

 

What's the weight difference between a short deck and tall deck block? That's a big factor with boats. My blower intake is for a standard deck, but I guess I could use spacers.

 

My bad typo... Yes, 4.25, NOT 5.25.

I should have also noted it's a 10.2 deck.

 

Here are the rules I play by.

You make the bore as big as you physically can for the situation.
Then back figure for the stroke length and you have it.

I put little emphasise on rod ratio.

With the canted valve head you need the bore size to get the head to flow.

Things that come into play with bore size selection;
-whats the cid limit
-can the block be filled
-what size blower, limitations?
-alky or ?

If you answer these questions I can help focus in on an answer.

We've successfully used Howards for 20+ years.

We've done 4.5 stroke in a 10.2 deck with 6.650 rods, so 4.25 in a 9.8 would call for 6.375 long rod.

 

10.2 deck KB Olds
6.700" Brooks B2 rod
4.500" bore
3.75" stroke
Jerry @ Brooks was very helpful to me since day one.

Keith

 

BBC Blown Alcohol Compression

Not to change the subject but how much compression is good/ bad ? how much timing?

 

I'm going to say 11.7:1 on the compression. That's what I've heard to be perfect. Timing I'm not sure, but I'd guess around 33 or 34 degrees?

 

Rules

What are your rules?
Can you run Big Chief style heads?
Any blower size and overdrive?
CID limit?

 

I sent you a PM. I don't need the power you guys are making. It's just an 8.0 second bracket boat. Nothing fancy, just a nice BBC that will make 1200hp and last.

 

Well heck, you can do that with standard GM 990 heads.

I ran a 4.350" bore for the past 10 years without an issue with a standard truck block.

 

I know of guys running similar setups with standard blocks, but I guess my philosophy is do it once, do it right. I'd rather invest $2k in a Dart block and a strong rotating assembly than shortcut it and have to rebuild after something lets go. I hear the GM blocks don't last long up around the 25lb. boost range. I also like the idea of increased thickness between cylinder walls.

 

adam are you still interested in the blower i called and left a message but havent heard from you give me a call

 

Hey Jim, I was on campus late last night and have been at work all day. I still have my 8-71. I'll be in touch.

 

4.25 crank & 9.8 block

Something else to keep in mind is that when a 4.25 or larger crank is used in a standard deck height block, the pistons are drawn a long way out of the bottom of the bore at BDC. When the piston rocks at BDC it is not very well supported. While there are lots of motors out there doing this and lasting Ok, if you had the choice at the beginning to use more deck height and rodlength it would be worth considering.
Jim