Boost

[Animal Magnatism]

Does increasing boost lower the RPM where peak power is made, given everything else stays constant?

[EXTREMEBOATS]

:argue: Well I'll take the shot and say "YES". My 85 Chevy dually has a 174 B&M Pro Charger on a STOCK .040 over cast piston big block. No real changes for a blower and I put the most overdrive I could on it. I get 8 pounds boast by 4400 rpm and she pulls a 12,000 pound trailer like its not there. When I orderd the kit I requested the smallest pulley they made for the blower and ofcoarse I was asked why... When I explained my needs they more then agreed I was on the right path. By turning up the blower I would move the power band lower to pull the load without cranking up the rpms. And on every thing i've put a blower on its worked the same. Now remember blowers like turbos they are load sensetive. The more resistance they feel the more they will responed. Again this my opinion and I have proven it on several different combonations. YOURS MAY NOT BE THE SAME. Good luck and if you need more input call one of the many blower companies. They will be more then helpfull.
Mike

[Animal Magnatism]

Thanks for the reply Mike, I was starting to think no-one had any knowledge of, or experience with this. My next step was to e-mail a couple of the blower companies (which I'll still do). The reason I'm asking is the cam I've currently got is a little big for the rpms I want to be doing, I'm about to increase my boost by about 10-12 lbs and am pondering whether to go down in cam size (by about 10deg @.050) or not.
Thanks again.
Paul.

[Robbie Racer]

Does increasing boost lower the RPM where peak power is made, given everything else stays constant?
I pulled 3 different dyno sheets that Larry Peto dynoed for me for two different motors so you can compare. All RPM numbers are at peak power.
Dyno sheet 1: 580" BBC
2% OD = 867 ft. lbs @ 4600 RPM and 933 hp @ 6500 RPM
18% OD = 975 ft. lbs @ 4500 RPM and 1054 hp @ 6700 RPM
Dyno sheet 2: Same 580" motor but with some minor modifications.
1% OD = 905 ft. lbs @ 4600 RPM and 993 hp @ 6600 RPM
20% OD = 1078 ft. lbs @ 4600 RPM and 1163 hp @ 6600 RPM
Dyno sheet 3: 621" BBC
12% OD = 1058 ft. lbs @ 4600 RPM and 1191 hp at 6600 RPM
33% OD = 1190 ft. lbs @ 4400 RPM and 1279 hp at 6500 RPM (note: dyno stopped recording at 6500. May have reached peak hp at 6600 if not stopped run early).
Based upon these dyno sheets it seems to me that changing boost could lower the RPM slightly where peak torque is made. Hope this helps answer your question.

[Animal Magnatism]

Thanks RR.
What was the increase in boost you got, going from 1%OD to 20%OD?
Paul

[Robbie Racer]

The boost was 5.5 at 1% over and 11 psi at 20% over.
I made an error in the torque number (in the above post) at the 1% OD and have now corrected it.