I have seen several posts on here about not running a balancer on a blown motor, street or race - the blower belt absorbs a lot of vibration and you don't need the balancer and the hub is stronger to withstand turning the blower.
I don't have time to read all the responses. But, the idle mix screws will do very little above the 1/4 throttle you claim is where you're having the problems. You'll have to change JETS if your problem is due to a lean mixture. This may sound stupid....but either close the choke a little at a time or duct tape a little at a time where the choke should be if it's been removed and see if it runs better. That'll make it run richer long enough to see if that's actually the problem
Just an FYI I run 32 degrees advance at all times on my avatar motor. It starts every time no backfires. When I originally put it together I was using 12 degrees initial with 30 all in by 2000 rpm. It was too retarded at idle. Headers glowing at idle, hard to start with backfire etc. I thought at the time a lean condition but only changed the timing to fix it so assumed I was burning a lot of fuel in the exhaust. I would doubt that this would be a solution for your motor. Mine is 355 SBC running a 671 with 7.5:1 static compression and 19% under driven making it pretty tame. Cam is .488 lift 282 Duration @ I and .511 lift 292 duration @ E with 1.5:1 roller rockers.
I seem to recall that the BDS (blower drive services) website states that too. The added mass of the lower pulley and belt acts just like a damper.
Yes, I know about a crank-hub being less rotating mass and better for it, but I might run another motor without the blower so I figured I'd get a damper instead. Wish I could afford all the trick parts to do it how I want; then I would go with a hub AND a damper to swap for either/or. =) Groucho: My carbs are set-up for racing so they don't have chokes or even choke holes for a choke-plate-shaft. It seems to be running better now that I changed a few things. Turns out there was some aluminum-oxide built up in the carbs from sitting too; so that could have been part of the lean problem and backfiring. As soon as funds allow, I'm ordering a set of the most under-driven pulleys I can fit without scraping anything. I guess I'll be getting rid of a set of vintage Wieand blower pulleys then... 33t on both. I could try giving it no advance at all if I keep having problems. Good tip as that would eliminate timing issues in the upper rpms. I'm running a Mallory 45,000V coil.
just buy a 38 or 39 tooth top pulley and drive it.your building this engine all wrong anyway and if you want it to live just do the swap on the upper pulley and have fun till it blows.you do under stand you have a very powerfull bomb under the hood if you abuse it right?just dont do burnouts in front of my house.
I just ordered a 41t top pulley. I'm not planning on abusing it. It's just (for now) to go out on weekends and such. Oh don't worry about that, I won't. =P
Seems pretty simple to me. 1:1 8-71 on a stock 305 SBC? Your stock valve springs aren't going to hold the valves shut with that much cylinder pressure. With all that backfiring, now you likely have ruined an intake seat or valve. After a valve job, you are going to have to lower the compression OR underdrive the blower OR raise the seat pressure on the valve springs... ...but what do I know, right?
I'm lowering the drive ratio and going to run a low rev-limit to keep max pressure down for now. Turns out a previous owner messed up a few little things on this motor, so I'll be building a better one soon, with both under-drive and a lower compression ratio.
What he said^^^ Get a hotter coil and drop the gap on the plugs down to ~ .025 Spark blowout is pretty common on boosted applications, Even with Modern Coil on plug ignition systems you need to decrease the gap, not to mention a drop in electronic conversion kit or points.
Oh oops! That's what I meant, "plug" gap. I don't even have points anymore, haha. I must've been tired. Currently waiting on the blower belt, everything else is ready to go... mostly. Yesterday afternoon I had the radiator water inlet and filler neck relocated because the new blower pulley was touching it. So now it fits better than it ever did and I'm happy with how it looks for the most part.
I'm no expert on blowers, but I built a slant six with a 471 blower and from my experience, timing is everything on a blower motor. Keep backing the timing down until it does not backfire and run it there. Where my timiing is set on the six is way retarded than anyone ever said. I've been running it for 10 years and not had a problem. Robert
you need a lot of initial like 18-20 and you need to cut the amount of mechanical advance in half of what a regular curve has, limit the advance to 12-14 degrees mechanical at the crank for a total of 32 -34, I then use a BTM to take out total advance when it sees boost pressure to prevent knocking If you just use the distributor as it is and set the initial where it likes it, you'll have 20 + 24 = 42 = way too much total advance
When I bought the motor, probably about 3 months ago. Another good point. I can't wait until the belt shows up so I can test it out. Speaking of backfiring, I had a pita of a time with the 69 (yes, I know, not technically allowed in the Hamb) Camaro 388 stroker tonight. It had been sitting for winter and I went to start it up and it was backfiring like crazy and would hardly idle. When it shut down it would stop rotating very quickly too, which had me wondering if something internal was wrong (even though oil pressure was excellent). I checked lots of things, put new plugs, timed it again, checked for open valves, flattened cam, etc... About 2-3 hours worth of checking things... turned out someone (not me) switched plug wires 5 and 7 with each other?? Runs better than ever now after I fixed that, but how the heck that happened, I may never know. Ha, I love easy fixes though, man do I... Gave me a bit of a scare though, as this was the most powerful thing I've owned (until I began this hot rod build).
post a picture of this engine your having trouble with.why do you need a different belt when your only adding a couple extra teeth on the pulley,you should have enough adjustment with the tensioner pulley.pic of the front of the assembled engine would be great.
I think I posted a pic earlier, it's not the best pic though; it's of the front of the motor. I went from 33 top and bottom to 32 bottom and 41 top. The old belt was literally one tooth too short, I was sad, haha. Also, when everyone says "locked out" timing" does that mean it stops advancing at say 32 degrees, or does that mean it is literally @ 32 degrees all the time? Even when starting and idling? It's acting a bit funny, and I want to see if I can eliminate the timing issue since I don't have a 6AL MSD box...
Are your Holley carbs manifold referanced for the power valve? If you don't know what I'm talking about there is a good chance they are not and the power valves are not coming in causing a lean condition. I've attached a quick cheap way to do it. Make sure you fully understand before attempting this mod. This has to be done when running blowers with Holleys. It could also be that the power valves are blocked off. If that's the case it has to be jetted heavy to compensate. Do research on Blower manifold referanced power valves.
Another thought. Check your alternator charge wire and make sure that it is no where near your MSD or electonic distributor leads. This will cause misfires because of the electrical noise. Ask me how I know.
I'm no blower expert, but I did stay at a Holiday Inn last night... I think there are problems with this motor configuration that can't be fixed... it's like running a Dominator on a stock flathead-- no matter what you do, it will never be right... an 8-71 at 1:1 is just producing too much boost, especially on such a small motor... the pop-off plate should NOT open under running conditions, it's not like a turbo waste gate, it's not meant to be a boost control device, it is only a safety device for when something goes wrong... (and as someone already mentioned) if it is opening, that is very possibly the cause of the back-firing... also the boost pushing open valves is also likely... I hope this saves you some needless tuning. (And by the way, the blower spinning without a belt is normal and correct... you can easily drive the car without the belt.)
i think you should pull the rotors out of the blower and drive it.you will never get the engine to run right the way it is now.and your pics dont show up on the site. you are building an engine right? cause motors run on electricity.
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