A stock 305 with an 8:71 at 1:1 on pump gas? An 8-71 with 1:1 pulleys on a 305 makes 20-21 pounds of boost! I don't know what will give first.....your cast pistons......your stock rods.......or your stock crank. None of that can stand up to that kind of boost. Thats not even considering the fact that it will detonate like mad on pump gas unless you run some type of ignition retard that references off boost and some $12 a gallon race gas. Unless you plan on throwing 8k at your motor, take the blower off. Or.......put it underdriven on a mild big block.
Wow, lots of responses. I can't begin to respond to them all, but I'll just say I under-drive the blower now by a bunch, I finally got the timing sorted out and it runs much better. Unfortunately, it ran a little too well, and it decided to take a literal "spin", which ended up messing up a few little things on the chassis and one side of the headers... I got the boost down to 15.5psi @ 6,000 rpm (but I'm never going to run past 5,000 for obvious reasons). Heck, the way it pulls, it only needs 2,500rpm; anything more and the rear-end breaks loose like crazy. If anyone is building a lightweight blown car, let me just say, please respect the power! I just got the belt today and took it for a "drive" after messing with timing and carb tweaking for an hour. It finally decided to clear itself up after a while and it's very hard to control to say the least. I never thought I'd say this, but I think I have too much power for street use. Which is sad, because I really wanted to run the blower. P.S. The carbs have no power valves. P.S.S. My alternator wiring is 20" away from any ignition wiring. P.S.S.S. It will only run up to about 3,000 rpm with the blower belt removed, since it chokes out (too rich). And my pop-off plate never opens unless it backfires; which is quite rare now. I'm running premium 91 octane with a little alcohol mixed in. Man alive though, gotta respect the power... Twice the power to weight ratio of the newest Corvette... sheesh.
Also, I limited the timing with no vac advance and much softer advance springs to come on early, and it only goes to about 28-29 BTDC degrees now.
sounds like your getting there "If everything seems under control you're not going fast enough" lol Mick
And boy does it go fast too. One mistake on that throttle pedal and an instant 50mph becomes reality. So does a 360 spin and taking out a fence or two, haha... which also involves a flat tire, dirt everywhere, and a bent steering column.
Look for the possibility of a worn or broken intake valve spring or warped or burned intakle valve. My broher just bought a T-bucket with a Chevy 400. It was also backfiring and it turned out to be a bent rocker arm. Bill
Soooo, the car runs good now as I geared the boost down. I drive it like a grandma but still, it's fun. Anyone ever mix E85 with normal gas to make a (roughly) half and half mix of gas and alcohol? I can get E85 here from a few places so it wouldn't be too much of a pain and I think it would (I think) run cooler and not detonate/ping when I step on it.
The Jalopy Journal
