Max Dynamic Compression Ratio on 91 pump gas
#21
Registered
Platinum Member
Join Date: Mar 2008
Location: Vancouver BC
Posts: 1,181
Likes: 0
Received 0 Likes
on
0 Posts
I can't give you an exact number for the dynamic comp. ratio, but I can tell you this. I have found that I as long as I stay under 190 psi on the dynamic cranking compression I'm OK on 93 octane with a good tune. For 91 octane, I would assume that number would be around 175-180 psi. Good luck.
Eddie
Eddie
#23
Registered
Join Date: Nov 2001
Location: Pennsylvania
Posts: 3,385
Likes: 0
Received 0 Likes
on
0 Posts
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
#24
Registered
Platinum Member
Join Date: Mar 2008
Location: Vancouver BC
Posts: 1,181
Likes: 0
Received 0 Likes
on
0 Posts
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!
#25
Registered
Platinum Member
Join Date: Mar 2008
Location: Vancouver BC
Posts: 1,181
Likes: 0
Received 0 Likes
on
0 Posts
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.
#26
Registered
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!
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
Last edited by Young Performance; 11-17-2011 at 11:32 AM.
#27
Registered
iTrader: (3)
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.
#28
VIP Member
VIP Member
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
#29
Registered
iTrader: (3)
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
#30
Registered
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.
Eddie