Retrofitting a pre-computer engine in a G=Body

[MrSony]

For comparison, my 9.5:1 350 Buick runs perfectly fine on 91 corn water with 12* initial, 22* of advance all in at 2500, and too much vac advance. Too lazy to install the limiter plate. Crane makes a good kit, 99600-1, that lets you tailor exactly the amount of vacuum advance you want, and the rate at which it comes in via the adjustment screw in the nipple. But I also have a pretty tame cam, on a 112 LSA with 276/281adv. duration and mid 4s on lift.

 

[Oldscarnut]

The photo is from Supercars Unlimited $600/set, specific for 68-70 350 for stock bore, +.030 or +.060
http://www.supercarsunlimited.com/350-Piston-d984.aspx

350 1968-1970 10.25:1 comp. ratio. Standard bore. Set of 8.

350 1968-1970 10.25:1 comp. ratio. .030 oversize. Set of 8.

350 1968-1970 10.25:1 comp. ratio. .060 oversize. Set of 8.

 

[Oldscarnut]

I love the idea. I used a Pontiac 400 in my '81 Malibu wagon because that's what I had lying around. It was great. But why are you afraid of low compression? High compression demands high octane gas or various tricks to prevent detonation. Low compression lets you use the cheapest gas available. Even better, low compression allows you to use all the old-timey hot rodding stuff we all love. Stuff like big cams, big carbs, lots of timing advance. All with no detonation. I don't know how Olds did it but Pontiacs used different heads to adjust compression. And Buicks used different pistons for the same thing. So I used '75 4X heads on a '70 GTO 400 that was almost too much for the A body wagon. I used a Pontiac 350 before that and your Olds 350 would be perfect.

I will stay in touch as you are the first I have come across who has been through this. There are soooo many ifs at this point, but once the engine is in one piece, the 3.8 comes out and it will be a long time before I finish, mostly due to lack of funds. I'm working alone mostly and I'm 66 so some days become short. I also live 20 miles from the nearest parts, so I get detoured sometimes because I need to make a run. I am actually wanting around 9.5:1 so pump gas will work. The reason I am avoiding lower is because I have a cam that needs a bit more than 8:1, the stock pistons. The idea is to end up in the middle between 8 and 10.25, and so if I am correct with Olds, staying stock with the heads and not milling will get me there. I have the larger valves that will make it breathe better. I have always wanted torque more than HP. It I wanted a 7 grand capable engine I would go with SBC but I will not be racing this ,,,well much except with the rice burners than need an education

 

[Oldscarnut]

For comparison, my 9.5:1 350 Buick runs perfectly fine on 91 corn water with 12* initial, 22* of advance all in at 2500, and too much vac advance. Too lazy to install the limiter plate. Crane makes a good kit, 99600-1, that lets you tailor exactly the amount of vacuum advance you want, and the rate at which it comes in via the adjustment screw in the nipple. But I also have a pretty tame cam, on a 112 LSA with 276/281adv. duration and mid 4s on lift.

That is what I am shooting for. Thanks for not poking holes in my plan 😊

 

[Oldscarnut]

For comparison, my 9.5:1 350 Buick runs perfectly fine on 91 corn water with 12* initial, 22* of advance all in at 2500, and too much vac advance. Too lazy to install the limiter plate. Crane makes a good kit, 99600-1, that lets you tailor exactly the amount of vacuum advance you want, and the rate at which it comes in via the adjustment screw in the nipple. But I also have a pretty tame cam, on a 112 LSA with 276/281adv. duration and mid 4s on lift.

I am installing a W30 Automatic Cam and I already have the W-31 valves and springs. I am going to need some pro help on distributor advance but the carb is being jetted according to my build so it should not take too much tweaking. I'm stealing from 68 442 technology with a capactive discharge ignition, kind of a pre HEI method of spark control.

 

[fleming442]

I think you have a solid plan.
Your main concern seems to be with wiring. Luckily, the starter is on the same side, so you can keep everything ORIGINATING from the drivers side. The ECM harness on the passenger side can go, though. Pull the inner fender, and undo the 2 screws on the grommet retention plate. Then, pull the grommet and wiring.

 

[MrSony]

I am installing a W30 Automatic Cam and I already have the W-31 valves and springs. I am going to need some pro help on distributor advance but the carb is being jetted according to my build so it should not take too much tweaking. I'm stealing from 68 442 technology with a capactive discharge ignition, kind of a pre HEI method of spark control.

http://everyday-performance.com/distributors.htm
the dudes over at everyday performance have a distributor service. I've bought two of their carbs and both were awesome. I bet their distributor services are just as good. I'd imagine they'd be able to set you up with a distributor, maybe even a numbers matching or at least era correct one if you don't have one, plus answer a lot of your questions. my knowledge mainly stems from HEI's, don't really know sh*t about pre hei stuff. some of the other members on here most likely do.

 

[olds307 and 403]

I ran a 204/214 cam with .065" quench on a 9.6 to 1 Olds 350. It pinged and just wasn't fun to drive around town and the filled crossovers also made it run shitty in cool weather. It ran horrible till Everyday Performance did the Qjet. Use this calculator https://uempistons.com/p-27-compression-ratio-calculator.html and seriously plug in the pistons at .040" below deck, it will give close to the actual compression. There is a member on ClassicOlds, Fun71 who used those pistons thinking he would have 9.5 to 1. He actually ended up with 8.8 to 1 compression, not terrible but not what he wanted. The .011" shim gaskets will help a lot but they cost almost as much as Cometic gaskets. The W30 auto cam has 216/217 duration at .050", someone posted a Supercars cam card on Classic Olds, if this the 285/287 duration cam. It is very close to my custom 214/214 .472/.472 on a 110 LSA, the Supercar cam is on a 113 LSA. Don't forget to throw in a 2000+ stall converter as well. The stock 1600 TH350 stall blows. My 70 went from 1/4 block burnouts with a 2300 flash stall 2004R that died to barely eeking the tires with a factory 1600 flash stall TH350C converter. The orginal 70 trans stalled the same. Chevy, Pontiac and Buick are not the same as an Olds V8, they like completely different timing curves. I run nearly 60 degrees part throttle on 8 to 1 motors and it really helps part throttle, that is another reason why my 9.6 to 1 Olds 350 sucked, I had the timing dialed back so much. It ran mid 14's with more in it but the 7.9 to 1 Olds 350 that ran mid 15's felt more lively around town. Even this 9 to 1 350 liked low 50's timing for response but it was a hair much causing the bucking. I dropped it to mid 40's and noticed much less part throttle response. I currently have the Mallory distributor and CDI box and have a similar curve, I may add 5 more degrees on the vacuum advance, it should help.

 

[Bonnewagon]

Way back when they first took the lead out of the gas we had lots of problems with detonation. My 9.5 compression 400 eventually suffered broken ring lands. Everything to defeat it was just a band-aid. Low compression was the answer. I had a Pontiac 350 in my '68 Firebird and I used a set of '72 455 heads on it. The calculated compression was around 6.5 to 1. That should have been un-usable but I put a Crane cam in with 262/270 advertised at .427/.454" lift. I ran 52° total timing and it came in fast, and a fat jetted Q-jet. That motor ran like a raped rat and it never pinged even on the worst gas. I know that is an extreme example but my point is that instead of trying to use as much compression as one can and living on the edge of detonation, it is better to go a bit conservative and have a nice cushion. Early detonation is inaudible and the damage is occurring without you even realizing it. That is why they put detonation sensors on the block because If you hear pinging it is too late. Also on a purely street car driving around in traffic carbon can build up and raise the compression over the safe zone. Sitting in bumper-to-bumper traffic can over heat the engine and cause detonation. Even driving up a large hill with a full car can do it. It sounds to me Chuck wants to do this only once and use what he has so my advice would be to take all of the posted information and come to a conclusion- then drop the CR a bit just as a margin for safety.

 

[Texas82GP]

Thanks for not poking holes in my plan 😊

You're in the right place. This forum is loaded with knowledgeable guys that don't mind helping.

It isn't uncommon in my opinion to swap an Olds 350 in a G-body. With the TH-350 a non-CCC carb and distributor, you don't need the ECM or its harness. Should be a fun car. Consider starting a build thread on here. We love them, and we love pictures!

Welcome to the site from Houston.

Best,

Jared