Bret, Kurt, others: thanks for your thoughtful input!

Bret: any comments on what Kurt said? Looking forward to your email.

Rich Krause

 

Great point, Bret. I hadn't even thought about that, but of course it makes perfect sense.

 

We ran into the same issue on my motor, we were going to try and use a 1.5 rocker to achieve ~.700 gross lift, but couldn't as you can't get enough lobe lift given the OEM journal diameter. I believe the maximum lobe lift even achievable for a factory SBC Cam journal is ~.460". This is of course decreasing the Base Circle down as far as is reasonably possible w/o risking any problems w/ the cam breaking/bending etc.

This is just 2nd hand info given to me by my cam guy.

 

Kurtis, we went with 0.43" lift to achieve 0.688" at the valves with a 1.6:1 ratio. Pretty much the same theory; big lift at the cam, good geometry up top.

 

I have to say that I never thought about the relationship between base circle and lobe lift. Obvious when you think about it, but I never thought about it! Bret: Thanks for bringing this up.

Rich Krause

 

On top of that a small base circle will take stiffness out of the cam. When you are running aggressive lobes and mucho spring pressure that's something to worry about. Billet cams help all of this but my custom solid flat tappet stuff always uses the stiffer cores because the cast cams are not as rigid.

Rich in your combo it's more of a tug for and against than most guys.

You want big boost (17psi) so the small overbore is a good idea.

The long stroke does cause the problems with the bottom end because of the extra clearance, but on the other hand the extra cubes help out low speed and will take more cam, which is all good. I'm about the biggest advocate against the 3.875" stroke setup, but you have to go high end forged crank for one, and 2 it actually has some really good advantages for you.

What are the rear end gears in your car?
What's the max engine RPM?

Bret

 

Bret: 3.42's. I shift at ~6,500 with the current setup and don't really want to go much higher. With the 27" tire I am currently using it goes through the traps at a shade over 140mph and ~6,300rpm. If it goes much faster I could go to a taller tire, or even a 3.08 ring and pinion.

What do you think, 3.75 or 3.875?

Rich Krause

 

I can only add that a 396 stroker crank with 5.85 Eagle H beam rods and L19 rod bolts is a BAD combo for clearancing....

I'm thinking about building a 2nd block and swapping all of my parts over by next summer except the rods....

Also the H beam rods are only good for 750HP according to my builder at the crank and I want a bit more than that...



Mike

 

Is that with the pistons upside down or right side up?

 

My builder was doing mockup and just didn't pay attention.
However he was when he got to this point:
http://www.azsupersport.com/images/n...motorpics5.jpg

http://www.azsupersport.com/images/n...motorpics9.jpg

Mike

 

I suppose that's as good an excuse as any other.

 

You do have a pretty big converter, and it all depends on how much that slips around town too. If it never gets low in the RPM range then the 3.75" will do because you have the blower to make up for that.

On the other hand you keep the max revs down, as long as the rod choice doesn't compromise the block strength by excess clearancing then you will be o.k. The lower the gear the more the added cubes are needed. So if you plan on going faster then the 3.23 and 3.08 gears will like the 3.875" stroke. If it was a M6 I would defineately say go with the longer stroke. Right now I think that you would not be to far off on going with the longer stroke.

Again, Rich has a different combination and his needs are much wider than most. Having a car with that much power and the ability to drive it around town like it's stock are very hard things too pull off. The only way is with a pretty good budget. For any normal budget a 3.75" crank is the way to go because you get more for your money then.

Bret

 

Had good onversations today with Callies and JE. Bottom line is that with the piston I want to use (-31cc inverted dome) it looks like it may be best to stick with a 3.75" crank. Even with a 5.7" rod, the compression height for a 3.875" stroke just isn't enough. As I m typing, an alternative occurs to me: I suppose I could use 400 rod, but that would create a really extreme rod ratio.

Any thoughts on the extremly short rod setup? If not, I will likely go with the 3.75" crank.

BTW: it's a long story as to why I even pulled to motor this year. Just did a leakdown and it was only 3%, so if I had any sense I would just put it back in. But I got the bug to do a 4.010" setup and really crank up the boost. I wish I knew why, I guess it's that old horsepower addiction kickng in again.

FWIW, I am using straight 4-bolt caps again, not splayed. Gonna try a new cam with Brets professional (vs. casual) help and finally get the intake side of the heads ported.

Rich Krause.

 

All rods really do is connect the crank to the pistons.

Going with that little of a rod will cause premature bore wear so yeah it's probably a bit too short.

On the other hand Rich, why not custom pistons? In the next day I could give you the minimum deck thickness of those pistons you want to run and ring land depth. You could copy that, have a little more weight taken off the non-important areas and then run whatever rod you want too with the 3.875" crank.

Custom pistons is the main reason I recomend against a 3.875" stroke. 3.75" strokes have a piston for about every combination you can think of.

Bret

 

It's been said that nitrous, boost and cocaine are about equally addictive. Probably a cost parallel there, too.

Using nitrous on a boosted engine: is that cross-addiction?