to any guys out there who have built there own blown motor for the street, what drive ratio are you running on what octane fuel. some people tell me they can run 1/1 or even 10 over, i am building a 392 6/71 and from what information i can find 10% under is about all i can run on pump gas. over here we can buy 98 at the pump but i do not know if it is measured the same RON?
my 303 Olds with 4-71 blower is running 1:1 estimated compression as stock advertised 7.25:1 with aprox. 6 pounds boost all stock internals including cast pistons. works fine on pump gas for nearly 10,000 miles so far my 371 Olds with 6-71 blower; target is to start with 1:1 pullies estimated compression ratio is to be around 8.5:1 with again aprox 6 pounds of boost to start will adjust up or down from there this motor is being built to take a little more punishment forged pistons, blower grind cam etc
one of my cars, the nova (a few years to new to be hamb friendly)has a 355 small block w/a 6-71, 8.5-1 compression, 11% underdriven 7lbs of boost, very mild cam timing, big afr aluminum heads ,has over 10,000 street miles,runs easy 10.60 ets on pump gas at 3500 lbs
Hit the search ****on for lots of threads on blowers, there is a **** load of info here. Octane in the US is based on the R+M over 2 octane rating method, should be the same for you. The quick run down for a blown street car is set your compression ratio no higher than 8:1, run 10lbs or less, mind your timing and you will never have a problem. Yes, there alot of variables, but that is a nice rule of thumb for a street motor that will make big power and live forever. I have almost 50 thousand miles on my daily driven blown street car, with no issues whatsoever. Good luck, -Abone.
I'm running a 6-71 on a 355 SBC. 7.5:1 Static compression and 20% under driven, 32 degrees advance at all times. 5-6 lbs boost. Runs fine on 92 octane. It's 20% under because those were the pulleys that came with the blower set-up when I bought it. Probably would have gone 10% under otherwise.
to nanos32, Do you know this because you have a boost gauge. I have a chart from jegs which i think is from weiand and it says that a 350 with a 6/71 @ 1;1 will give 15.3psi.
Doesn't the actual boost depend on the head flow? Poor flowing heads have a lot of restriction so will show more boost,right?
hadn't seen that chart till just now, by their numbers my estimate is off too, my numbers were based on what two different reliable blower builders recomended.. but by Weiand's chart I may want to underdrive mine too.. 'was told I should see six or seven pounds, Weiand's chart just about doubles that.
Here is the formula for pulley size ratio and fianl compression with pulley ratios. Blower Boost Formula- Pulley Sizing Bottom Crank Pulley Diameter divided by Top Pulley Diameter X 25.58 X Blower Size ( actual CFM ) divided by C.I. ( of engine ) -14.7 ='s Boost Actual Compression @ " X " Boost Boost divided by 14.7 +1 X Enine compression ( static ) ='s Final compression at wide open throttle Keep in mind generally you will loose 3% of 14.7 per 1000 feet of elevation. Hope this helps. Max Sr. @ H & H
Go here http://www.blowerdriveservice.com/techcharts.php and then scroll down to the 6-71 charts. I believe that Jeg's chart is for the Weiand blowers. I'd go with the BDS Charts...to be SURE, I'd call Dyers, and ask them...
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