Retrofitting a pre-computer engine in a G=Body

[Oldscarnut]

Some of you may have seen my previous posts on other threads, but if not, essentially I am putting a 1968 Olds 350 W-31 spec engine in my 1980 El Camino. I already have a BOP TH350 and the previous owner had beefed up the suspension for a SBC. The question I have now is about the computer control. The Buick engine has a computer controlled carb and ignition and the O2 sensor. If I am returning to a CD ignition using stock distributor, and a Qjet, is there any reason to keep the computer control? Are there any other functions controlled that are not evident? I think if I return to 1968, the CAT Convertor goes too and a standard exhaust system installed, not just cat back. I would like to hear thoughts. My 68 engine has all the new goodies that make it perform and yet be efficient without loosing all of the horsepower, and running smoothly. Can I just D/C the computer and have a 1968 El Camino?

 

[TURNA]

No they are 2 separate harnesses just remove it and install your "new" engine.

 

[Oldscarnut]

No they are 2 separate harnesses just remove it and install your "new" engine.

Thank you...that is a good plan!

 

[Oldscarnut]

Wow I am moving my questions here because ClassicOldsmobile cannot simply answer a question, they must tell you how much more they know about my car and engine build than i do. I am all for advice, but poking holes in every process I do is tiresome. I have built two W-31 350's and a W-30 455 before and to my knowledge they are still running strong and without hiccups. So the fact that I am retrofitting a 1968 into a 1980 car seems to unhinge them a little. Maybe it is retrofit and the 12 year gap. It all comes down to $$$ for me. There is the "old", fix what's broken, anticipate problems, and the new way, leave nothing old if there is something new that can replace it. What a waste of money! I got the engine cheap and its a good one. Because I am doing most of the building, not paying $100 an hour to have it done, I am going to have a "new" engine for about $3000. Check out the price of stock to HP crate engines. I have the time just no money to waste, so what better way to do your last ever project? I still like to read the cautions, because they have changed my parts purchases, but I also know there is more than one way to build Dr. Olds engines, but probably only one right way! The question now is CR and I have a pretty good idea. The 9:1 pistons are NLA so it is either 8:1 or 10.25:1. Since I want a bit of pep in mine, 8:1 is out of the question. The 10.25:1 pistons are still dished and are cast as ALL Olds pistons. Forged according to the Machinist are heavier and harder to balance, not to mention about double the cost. All of the equation for the CR is stock/same except bore size which I do not yet know until the machinist does his magic. At worst it is 10.25:1 but it could be lower and to my mind, that is better. Without vvt and a computer, O2 sensors and Cat Con. I will only have on way to retard the spark, the distributor, and the advance curve. We have pretty good gas in WA, I could get double thickness gaskets to lower the CR slightly...but there are not many other ways to lower compression by a single point other than pistons. My original build was going to be 9:1 as I have built two that way and they were perfect! What say you?

 

[CaliWagon83]

Familiar theme. We have a lot of refugees from other forums that aren't as welcoming or informative. GBF is a great community. We're glad to have you.

 

[Oldscarnut]

Thank you!

 

[olds307 and 403]

Who's pistons are those? The only cast pistons I know of for the Olds 350 have huge 24cc dishes, you would be lucky to have 8 to 1 compression, here is why. All the cast pistons made are way short on compression height, 040" or more. This lowers compression a lot and forget about quench. Those look like 6cc dish pistons, you will be around 9 to 1 without decking the the block. I would get a hold of Smitty from M+J Proformance to get the .011" shim head gaskets if you want to use cast pistons. Not only are forged much stronger, the Mahle 10cc dish have a ring pack worth 10 hp and along with the cheaper and less efficient Speedpro LF2321 6cc dish forged pistons have taller compression heights. The Speedpro sit .025" in the hole, the Mahle even less I believe. With a clean up mill on the deck, .040 cheap Felpro head gaskets can be used with the Forged pistons, I wouldn't with cast pistons and I wouldn't deck a block that much either. I love the Olds 350, my personal favorite V8.

 

[Bonnewagon]

I love the idea. I used a Pontiac 400 in my '81 Malibu wagon becuase 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.

 

[olds307 and 403]

Olds used basically two chamber sizes along with SBO and BBO port sizes. Both had large and small valves, depending on the application. This doesn't include 260 or 307 garabage heads and any of the later Pontiac made "A" heads which all had poor exhaust ports and small 1.5" exhaust valves. Problem is with generic replacement pistons and the common mid 70's to 80 larger chamber heads lead to about 7 to 1 compression, fine for 1950, now not so much. Modern V6's put out over 300 hp with 8 to 10 speed transmissions with better rear gears than most of our cars and nearly twice the mileage. His 9 to 1 goal is perfect. My 9 to 1 Olds 350 ran fine on 87, minor bucking with 22 base timing, a quick curve and 30 degree vacuum can with manifold vacuum, a 20 degree can fixed it. It also has decent performance and mileage for what it is.

 

[Bonnewagon]

I would be happy with 8.5 but 9 to1 is OK if everything else is spot on. HEI and a correctly tuned carb will go a long way to defeating detonation.