70F85

Hey Guys I have a 1972 455 pulled from a Custom Cruiser 400 turbo trans with a fresh rebuild that has 150 miles on it. Its in a 70 F85 with stock rear end. I only put in a mild cam with new springs and lifters, stock pistons, turned crank. I put a Air Gap intake with a 750 Demon duel line carb. My issue is that its really really weak the thing don't want to smoke the tire. I have a guy rebuilding the stock Qjet that came on this motor and I was wondering if the Intake is alot of my problem. I cant afford the nice factory looking alum intake but I do have the factory cast intake. My timing is set around 12 deg with a hei distributor. I would try about anything right now. Thanks

joe_padavano

Well, your biggest problem is likely the 2-something rear axle in that car.

70F85

Thanks for the post Joe. If the gear is the problem and its only getting 4 mpg, I don't understand why it ran so much better with the 350 than with the 455. I don't have that many miles on the fresh motor so i'm still working out a few bugs. I have spent my whole savings on my car and it embarrassing at a stop light.

joe_padavano

OK, so let's back up. What was the configuration before, and what did you do when you swapped in the 455? The problem may be the basic engine or it may be something else that you changed and we don't know about. We'd like to help, but we need all the info.

oldcutlass

IMHO your timing needs to be advanced, 12 will not cut it. Needs to be closer to 18 deg btdc. When you do this you may need to limit your vacuum advance depending on which Hei you've got. What your looking for is around 36 deg mechanical total timing all in @ 28-3000 Rpm. Then set your total with vacuum advance to 45 - 50 deg BTDC. Just watch for pinging.

This will perk it up.

olds 307 and 403

First off try around 20 at idle for timing. Most HEI distributors have less mechanical advance. You are probably only at 8 to 1 but any 455 should destroy the tires. Oldscutlass beat me to it.

svnt442

Are both the motor and trans fresh, just the motor, or just the trans?

Stock pistons can mean a couple of different things. Did you re-use your old pistons or buy "stock" replacements? What was the advertised compression ratio on the pistons if you bought replacements?

I agree with what was said above...set the initial at 20deg @ 1100 RPM with the vacuum disconnected.....not at idle....and go from there. You can also get a weight kit so you can back down the initial if need be, but that will be determined with starting issues if any arise.
Don't mess with the carb until you get the timing ironed out....one thing at a time. If you go changing multiple things at once you won't know if what you did actually fixed the issue because you may have made it better with one change, but totally messed it up with the subsequent changes.

cutlassefi

If you're not sure what piston is in it then do a compression check first. That'll go a long way in telling you what piston may be in it.
Then before you take everyones' word to just crank in more timing (I hate when you guys tell people to do that), check the current total first. It may have a long slow advance curve. Then modify the curve accordingly.

Let us know what you come up with. And that RPM is absolutely the wrong intake for that. Hope this helps.

svnt442

Well if it's an HEI that hasn't been modified it will have a small amount of mechanical advance built into it. So unless someone states that it has an advance kit in it I guess we all assume (yeah...I know...you and me ) that is has a factory mechanical curve in it so it would need more initial.

cutlassefi

I hear you Randy. But don't you think it would be prudent to check and see exactly what he's working with first? I do.

Jmo

svnt442

Oh absolutely. I just seem to gravitate towards the worst case scenario and work backwards from there for some reason...lol.

Yes...check the intake for leaks first and if that checks out then tear into the engine.

cutlassefi

Now you're talking!!

oldcutlass

I too was making the assumption that the engine has no vacuum leaks. I also made the assumption of 12v at the distributor. However, we all know that 12 deg is not allowing the engine to run properly period with a stock or aftermarket HEI.

70F85

You guys are great lol Ok here is maybe the best info I have. The 70 F85 came factory with the gold 350 rocket/ 350 turbo. It has been without a heart beat for 18 years. I had a donor 72 455 custom cruiser / 400 turbo with the original rear end . I had it torn down and freshened up with a mild cam. I used the same dish pistons. Air Gap intake with a 750 demon carb. I have done nothing to the tranny but changed the filter. I have one of those 50.00 red top HEI dist from the swap meet. The car sounds bad *** with a smooth idle but when you stand on it at the stop light the kids laugh at me from the school bus. I have a 20 year old timing light i'm working with so tell me which one that i need. I'm just a cop so I'm not as smart as most of you guys so please talk slow southern Any advise would be appreciated. Also headers with a mini starter

svnt442

OK so you most likely have the old timing tab on there from the points dist that stoppes at about 16 deg. You're either going to want to pick up a dial back light, a newer plastic tab that has 24 deg on it or you can even mark your balance at 10 deg retarded (put the mark on 10 advanced and mark the balancer) and then work from there to get to the 20 degree advanced to start with. Remember to unplug the vacuum from the distributor and set the idle at 1100 rpm when checking the initial timing. Then after you have it set you can back it back down to about 750 in park (warm).

oldcutlass

I'll make it simpler, disconnect your vacuum advance line and plug it. Set your timing to 18 deg BTDC. Leave the vacuum advance disconnected tighten the distributor bolt and close the hood. Take the car to a decent hill and drive up part throttle and listen for pinging. If it pings decline the timing 1-2 degrees, if does not ping then repeat this time floor it and see if it pings. If it pings decline timing 1-2 degrees and repeat.

Next thing we will set your vacuum advance.

cutlassefi

DO NOT DO IT THIS WAY!!!!!!!!!!!!!!!!!!!

Do it the right way. Check your total after bumping up the initial.
I've been standing right next to a 455 on the dyno when it lost 14hp from the previous pull because of detonation after advancing the timing. I nor the dyno operator ever heard a ping or a knock.

QUIT TELLING PEOPLE TO DO IT THIS WAY! Are you going to buy him new pistons when he grenades' it?

Octania

Read post #12:
https://classicoldsmobile.com/forums...-pressure.html

Perhaps your intake is designed for higher rpm use, and the stock intake would be better, but do what you can timing-wise before carb and intake work.

A wise man here once put forth the proposition that "90% of all carb problems are electrical problems" - if you consider timing an electrical issue, the shoe fits.


13000

oldcutlass

He is not going to destroy his engine. I included the settings he should use with a dial back timing light in a previous post above the down and dirty way. I also stated not to reconnect his vacuum advance until later.

So your saying that everyone should use a dyno to tune their cars?

cutlassefi

No you totally missed my point.
My point was it was clearly detonating yet I never heard a thing. Have you ever heard that detonation is the silent killer? Well I'm here to tell you it is, period.
Whatever, it's your *** when he punches holes in his pistons or beats the rod bearings out of it.

oldcutlass

Yes Mark, I agree detonation is the silent killer of engines, however the settings suggested have been used for years and are widely acceptable on the conservative side. The method I suggested has worked long before dyno's became widely available.

There is always the chance that power tuning an engine will always enhance wear and tear. If the OP wants to be safe then he can leave it at 12 and not exercise the fun peddle.