Hello everybody! Quick question, my old motor was a 460bbc with a blower. Compression was 8.8 and boost was 6 psi. Wouldn’t that put my effective compression over 12? I am building a 468 now, and was thinking about running boost again, but around 4-5 psi, the new motor is 9.0 compression, think I will have trouble on pump gas?

Details... the old motor had dart 345 iron eagles and a smaller cam than the new motor.
new motor has Merlin iron head and a 731 cam

THeres some variables in there....... blower size etc.....

Thanks for the reply, I was thinking a 250 b&m for new motor, old was a Mega blower 420. From what I read, 12.1 seems to be the cut off with boost in pump gas. Does that sound about right?

Yes, 12 to 1 effective CR is about all you can go safely with 92 octane. Here is a chart from Holley.
http://documents.holley.com/techlibr..._tech_info.pdf

the 420 blower would be a much better choice imo.

Ok great, maybe I will just reuse that the . Thanks for the input!

To elaborate on that...
In simple terms boost is the amount of air packed into a confined space. the bigger the blower, the easier it packs the same volume of air. A smaller blower has to work harder to pack the same amount, the harder it works, the more it heats the air. a hot charge is more prone to detonation.

It seems so strange you hear of people running boost all over the place. I realize Static comp varies from build to build and whether or not an innercooler is used but.... for instance where is MT with both and also icdedpple. Thought he was running fairly high for no innercooler without issues. At one point I thought he was closer to 9:1 and like 8 pds of boost. Going back to when he was selling his engines. Looked like flat tops but i doc know he had a fair amount of chamber work done also that could have ultimately have knocked off 10 plus CC's or more. Then I thought I caught a thread where MT said he was at closer to 7.5:1. That may have been an old thread though.

Just bringing up conversation as it would be good to have people post what their running with their builds. Roots, whipple, prochargers, turbos, etc.

Clear out your your inbox I tried sending a message back to you. Yes I still have my blower for sale. It has been sitting in the garage as a spare.