Is that for a NA or blower motor?

:evilb::evilb: Um, Yeah. I thought we were discussing BLOWER motors :evilb::evilb:
FOR SALE: (8) nice 4.630 dia ashtrays, only used ONCE!!

That's interesting because mine with 3.25" pulleys (2.15:1) I get 6psi. Must be my dome pistons reducing volume in the chamber vs your 8.4:1 pistons. Why you didn't have to slow the b&m down as much I'd say the 177 rpm was at peak efficiency and now the b&m rpm is under its most efficient speed. Just a guess though.

My cranking pressure is 175lbs so that might explain why I stay out of detonation so well with the 9.5:1 and forced induction on 93 oct.

This is one of the best threads I've seen in a long while.

BT

Have you verified that psi with another gauge? It seems high for a blower motor, that's why I was asking Eddie if his numbers were for a blower deal too. I could be way on the conservative side but mine are usually around 150ish or a little lower depending on the application. Clearly yours is working well which is awesome and you can't argue with real world results!

Another cool thing is how underated the mini blowers are. Everyone discounts them right away but they work great for what they are. We built a 557 out of spare parts last year with bb2x's, a crane 651 cam, and a 250 blower with a pair of 750's. Before I ran it I called the blower shop to ask if there was anything I could do to get some boost out of it bcause I was sure the blower was too small. They told me it probably wouldn't make any boost on that size engine but we tried it anyway. It made 6lbs and almost 800hp on 89 octane! I thought it was pretty cool for a spare parts motor with a mini blower.

It doesn't actually translate into pressure on a gauge. Just because it's 180 or 190 with using the formula doesn't mean it does it on a gauge.
I just did a comp test on a particular engine before we pulled it down to be freshened. It's a 598 with a 5 liter. The formula says it's almost 180 psi. Actually, it shows 160 on a comp gauge.
I use that number for both NA and sc. I don't neccessarily get all the way up to it for either engine. I just make sure that it's under that. It depends on the what I'm building and what it's going in as to how close to that number I want to get. However, I have been right there with an SC engine. It has to have a very good tune and there isn't much room for error. I generally try to stay in the 175 area or lower. The 190 number is an absolute max for me.
Eddie

Same deal with a buddy of mine. He has some 598's, dart heads, weiand 256 blower, no chiller, 3psi of boost. Engines made over 800hp. For 3psi, he is driving his blower the same ratio as I am, but I get 6.5-7 with my little motors. His 598s with that setup have been extremely reliable with that setup for 4 seasons.

I have a similar set up, 540 CID, alum heads, 250 SC (2) 750's, No intercooler, 4 lbs boost @ 5,000 rpm. I have jetted for 12.0 - 13.0 A/F . Timing is 30 degrees. Dyo sheets says 650 Hp, I have Aluminum Gil type manifolds with EGT probes just above the aluminum in the SS pipe. @ 3,000 rpm EGT is 1250 degrees, 5,000 rpm 1,380 degrees. Boat is V bottom 12,000 lbs . Is this too hot or any ideas how to lower EGT

Maybe a little more timing and fuel?

That's awesome, whether it's a spare parts engine or not. Have you done any of the 250/256 blowers with a single Dom.? Do you like the 2-4150's better than the single Dom? I have always done a single Dom on that blower with good results. Never tried 2 smaller carbs.
Eddie