smcurro

Some situations have recently changed for me and I am now going to be able to start rebuilding my 350 right away! Of course that means I have a bunch of questions...

For my 350 I am looking for a mild rebuild. I want to run the car on 87 gasoline with zero engine knock/pinging. I wanted to build a compression ratio of about 9:1 but my engine builder thinks I shouldn't go higher than 8.5:1 on 87 or I may have some pinging. I definitely do not want to deal with engine knock/ping again. (It blew the rings out before, causing the need for this rebuild) What do you guys think? (see my cam selections below)

I will be using my stock rocker arms and my rebuilt #6 heads which cc'd out to 64.5 . I will also be using exhaust manifolds and dual exhaust (I think its 2 1/4 inch). I have an Edelbrock Performer Manifold #3711 which I will be using. I will also be using the original q-jet. For a cam I would like to use Comp Cam's #42-227-4 or #42-228-4 High Energy cam. Edelbrock's #3712 Performer Plus cam is another choice I would consider. Which of these cams do you guys feel would be best? Any other good cams for this engine worth considering? (manufacturer and part number please)

I will be using either a th400 switch pitch or the original th350 when I install this engine. At the moment I have 3.55 gears (open diff) but I would like to change them to 3.08 or 3.23. I really like the switch pitch feature of the th400 and I'd rather use that transmission. What do you guys think?

For head gaskets I have pairs of both Felpro 8171PT-1 and 8506PT. I have been unable to find the compressed thickness of either of these head gaskets, however. I called summit racing and the guy said they might be 0.041" each but he was just guessing. Anybody know the compressed thickness of these particular gaskets? What other head gaskets do you guys think would be good for me?

Now as for pistons I have no idea what to use. This is really where I need the most help. Like I said I am looking a compression ratio somewhere between 8.5 and 9:1. I can go either 0.010", 0.020", or 0.030" over. I do not want to go 0.040" over unless I absolutely have to. Please please please make some piston suggestions!! (manufacturer, part number, and if possible dish cc please). I do not mind paying extra for a forged piston so long as it gives me the correct compression ratio. (I do not want a 0cc/flat top piston.)

Piston to deck clearance/distance is another area where I am unsure of which way to go. I read somewhere that the piston to deck clearance and head gasket thickness should add up to somewhere between 0.040" and 0.047" to provide a optimal "quench" area. My engine builder recommended a piston to deck clearance of 0.05" but says he can cut it to any amount I want under the existing number. What do you guys think? I understand in order to build the compression ratio I want this number may need to be changed a bit. I will be checking all numbers in the compression ratio calculator before making my decision.
( http://www.csgnetwork.com/compcalc.html )

Well, that's all...As always, thanks for any help you guys can offer!!

f-85

I think you need another engine builder. My buddy runs a 72 468, iron heads alittle port work, balanced, mild cam, delco HEI, street car, 9.7:1. He only runs 87! ONLY! 3900lb car ran 12.40 on 87.

Like you said you will be fine 9:1. Maybe you should look into a local Olds engine builder. Where are you located maybe someone can recommend a shop.


Keep the 3.55 and get a built 700. JMHO

smcurro

My engine builder does know Oldsmobiles, he just finished building a 468 with edelbrock heads and the works. I think he has funny ideas about compression ratios, however, because he was telling me he was sure the 468 with alum heads and 10.2:1 comp ratio he just built was going to knock on 93, if only a little.

I think his reasoning for telling me 8.5:1 max was that he figured I wanted to keep the engine running for a long time and based on the fact that pump gas has gotten worse and worse historically in the future it is going to be even worse than it is now.

What does your friend run for initial timing? Max timing? What rpm does it come in at?

Any more info you can give would be a great help! Thanks!

mp71conv

Take your time and get all the information that you can find.
I just finished rebuilding my 350 and spent ten times the amount of time
looking at information than actually rebuilding.
My advice is to talk to a good machine shop that knows olds.
As for comp.ratio. you should be ok with 9.5-1, but make sure
you check the cam specs out also. The time that your intake valve closes
on the comp stoke will help determin your dynamic comp ratio, which is very
important>

good luck

mp71conv

Read this
http://www.empirenet.com/pkelley2/DynamicCR.html

f-85

From what i understand the aluminum heads can run a comp >. higher then a iron head on the same oct. I think its odd that he thinks that way being an engine builder. Ive just seen otherwise.

My buddys timing i think is set 18 initial, and for sure 36 total. hits the traps at about 5800 or so. I ran the car myself at byron this last year. my best time was 12.40, but from the ticket i can find

rt .015
60' 1.751
330 5.099
1/8 7.916
mph 87.35
1k 10.364
1/4 12.448
mph 107.79

BTW this is his street car. His drag car does 9.45 482 olds (all motor)

f-85

Good info!

f-85

LOL ok now i get it. LOL Im not for sure, around 3500 i think. I can ask to be sure.

captjim

Unfortunately, piston choices are very limited for us Oldsmobile guys. If you run .030 bore of 4.085, stock stroke of 3.385 and a piston to head of .045, you will need a 16 cc dish. Unfortunately, that is not an option. The "stock replacement" pistons are the 22 dish units, which are also destroked. Since you have already rebuilt the heads, your best option, IMO, is to get the flat top Speed Pros and spend the extra $100 or so to have the dish cut into it. That, matched with a cam in the 210 @ .050 on the intake and .470 lift should work well for you.

A word on quench. It is tossed around a lot, but most guys don't really understand it. Oldsmobile heads are old technology, slow burning chambers. There is very little quench area. The quench area is the flat part of the head inside the bore of the cylinder that matches up with the flat top of the piston. On modern heads,, quench is very important. So, if your pistons sit down .020 and you run a .045 gasket, the 6 cc dish Speed Pros give you a 9.4 to 1 Cr. Piston to head will be .065, but again, that is not that important on our heads. In my opinion.

smcurro

That is excellent info and an excellent program. I just have one question. Halfway down the page it says:

"Staying below 8.25 DCR is probably best for trouble free motoring."

But this statement applies to 91 or better, as specified previously. At the end of the page it says:

"I have received several request regarding what is the best DCR for lower octane fuels. At this time, I don't know."

Any ideas what the maximum dynamic compression ratio would be for 87? I have a cam/piston/clearance combination that yields me 8.03:1 DCR and 9.25:1 SCR but it would require a custom 14cc piston. captjim, 100ish for all eight right? I would have guessed a bit more to have pistons custom dished. 100 wouldn't be too bad for a fine tuned DCR and SCR. I would need to find a shop that does that kind of work however, my machinist isn't set up for it.

Thanks for the info everyone!

captjim

We charge $12 per piston. If you want to be trick, have a "D" shaped dish to match the chamber shape. Any engine builder that does custom work should be able to handle it. Piston to valve issues are common place and cutting reliefs into pistons on the mill is a daily procedure at our shop.

cutlassefi

I agree with most everyone here, 9.0 to 1 should be no problem on 87. One thing everyone didn't mention was cleaning up the flashing and any and all rough edges in the combustion chamber. That helps, no question.

IMO though I believe optimizing the squish area helps too. From my own experience I run 42-44 degrees of timing on mine with 9.7 to 1, cast iron heads on 89 octane in Florida.