Stock Buick 350 10.25:1 Pistons?

[joesregalproject]

For those of you who haven't seen my posts lately, I'm doing a 'quick and dirty' rebuild on my '76 Buick 350. I'm doing a flex hone on the cylinders, re-ring, new crank and Rod bearings, timing set, and gaskets and seals. I want to hop the motor up a little, and do it on the cheap. I've already found a used comp cam with it's original lifters to use.

The stock compression ratio of my engine is 8.5:1. However, the 1970 and earlier 4 BBL Buick 350s had different pistons and were 10.25:1 compression. Now, obviously I probably won't get to 10.25:1 because my heads are different, but I can probably get in the 9.5-9.75:1 range by using stock 1970-earlier 4 bbl pistons.

So I'm trying to find stock, standard bore pistons from a 1970-earlier Buick 350 4BBL. TA Performance sells forged ones, but they are in the $400 range. I see that RockAuto carries several sets of pistons, but they don't list the compression ratios. Can anyone who maybe knows a bit more than me help me out?

 

[Bonnewagon]

When I had my Buick 350 I read that all Buick 350 heads used the same size combustion chamber. That meant that each motor's compression ratio was determined by the piston. By using that logic I would assume that to get the ratio you want you would need the pistons for whatever motor came that way from the factory. I had a '68 LeSabre with the 350 and, yes, the 10.25 high compression ratio was not working with the garbage gas available. So I swapped in a two barrel '74 350 block and used the big valve '68 4 barrel heads on it. The '74 was 8.5 compression and worked very well. I could buy whatever-was-cheapest gas but the 4 barrel big valve top end breathed great. I would be hesitant to change pistons. I would instead look for better heads. I am no Buick expert so research this thoroughly before spending money.

 

[64nailhead]

For those of you who haven't seen my posts lately, I'm doing a 'quick and dirty' rebuild on my '76 Buick 350. I'm doing a flex hone on the cylinders, re-ring, new crank and Rod bearings, timing set, and gaskets and seals. I want to hop the motor up a little, and do it on the cheap. I've already found a used comp cam with it's original lifters to use.

The stock compression ratio of my engine is 8.5:1. However, the 1970 and earlier 4 BBL Buick 350s had different pistons and were 10.25:1 compression. Now, obviously I probably won't get to 10.25:1 because my heads are different, but I can probably get in the 9.5-9.75:1 range by using stock 1970-earlier 4 bbl pistons.

So I'm trying to find stock, standard bore pistons from a 1970-earlier Buick 350 4BBL. TA Performance sells forged ones, but they are in the $400 range. I see that RockAuto carries several sets of pistons, but they don't list the compression ratios. Can anyone who maybe knows a bit more than me help me out?

 

[joesregalproject]

When I had my Buick 350 I read that all Buick 350 heads used the same size combustion chamber. That meant that each motor's compression ratio was determined by the piston. By using that logic I would assume that to get the ratio you want you would need the pistons for whatever motor came that way from the factory. I had a '68 LeSabre with the 350 and, yes, the 10.25 high compression ratio was not working with the garbage gas available. So I swapped in a two barrel '74 350 block and used the big valve '68 4 barrel heads on it. The '74 was 8.5 compression and worked very well. I could buy whatever-was-cheapest gas but the 4 barrel big valve top end breathed great. I would be hesitant to change pistons. I would instead look for better heads. I am no Buick expert so research this thoroughly before spending money.

Yeah, I'm still not sure I want to swap them. I'm trying to do this on the cheap, just a fun and easy build to keep me occupied this winter. I'm not so concerned about what gas I'll have to use, I can get VP leaded 110 octane relatively cheap. For as much as I'll be driving the car, it shouldn't matter a whole lot.

 

[64nailhead]

My wireless keeps dropping out so bear with me.

First off - I've never looked into 350 Buick specs -HOLY Shcow - 10.187 deck height, 6.385" rods, 3.85 stroke, 3.8" bore (smallish) - all equate into a small block that makes big block torque!!!!!! WOW!

The 1st concern to every build is keeping the quench distance under control - .040-.045" is most desirable but nothing over .050" (for sure.) If it isn't disassembled yet, then you can measure the quench distance. I jst did a quick search on Summit's site and found crappy low piston ht piston's that will kill you quench distance. How bad are your pistons? If the motor is in good condition and doesn't need a re-bore, then you have an excellent chance of being able to re-use your pistons. This requires some measuring tools (or a machine shop). I know you mentioned you wanted to do a dingleberry hone job and slap it back together, but sometimes you can't get away with it - you really need to get it measured to know what needs to be done.

On another note - these motor specs define tire burning torque! I've never heard of the SBO's plus's or minus's but these specs define 'build it' to me. Compression ratio - if you can keep it in the 9.5:1 ratio with an appropriate cam, then you should be able to keep the detonation under control with careful tuning. You can always have your pistons cut to drop the ratio by .5-.75:1 - it's not difficult. The most important issue is the quench distance.

Hit me with some part numbers of what you've found and I'll figure the SCR and DCR to make sure it will work with pump gas.

 

[joesregalproject]

My wireless keeps dropping out so bear with me.

First off - I've never looked into 350 Buick specs -HOLY Shcow - 10.187 deck height, 6.385" rods, 3.85 stroke, 3.8" bore (smallish) - all equate into a small block that makes big block torque!!!!!! WOW!

The 1st concern to every build is keeping the quench distance under control - .040-.045" is most desirable but nothing over .050" (for sure.) If it isn't disassembled yet, then you can measure the quench distance. I jst did a quick search on Summit's site and found crappy low piston ht piston's that will kill you quench distance. How bad are your pistons? If the motor is in good condition and doesn't need a re-bore, then you have an excellent chance of being able to re-use your pistons. This requires some measuring tools (or a machine shop). I know you mentioned you wanted to do a dingleberry hone job and slap it back together, but sometimes you can't get away with it - you really need to get it measured to know what needs to be done.

On another note - these motor specs define tire burning torque! I've never heard of the SBO's plus's or minus's but these specs define 'build it' to me. Compression ratio - if you can keep it in the 9.5:1 ratio with an appropriate cam, then you should be able to keep the detonation under control with careful tuning. You can always have your pistons cut to drop the ratio by .5-.75:1 - it's not difficult. The most important issue is the quench distance.

Hit me with some part numbers of what you've found and I'll figure the SCR and DCR to make sure it will work with pump gas.

I'm no engine expert, but I do know Buicks more than any other engine. They are definitely torque motors, they have an almost square cylinder bore x stroke. Their biggest faults are the oiling systems are mildly inadequate and the heads don't flow very well.

Here's the part #s I've found-

Mahle/Clevite 2241801- Listed for both a 1976 Lesabre with 350 4BBL, and 1969 GS with 350 4BBL

EngineTech P15048- Listed for 1969 GS 350 4BBL
EngineTech P15318- Listed for 1976 Lesabre with 350 4BBL

 

[joesregalproject]

The engine is fully disassembled but I have yet to mic the cylinder bores to see if there is any excessive taper/wear. Just by looking, they don't seem too bad.

 

[online170]

Here you go;

https://egge.com/part/egg-1000-l2343-8/

 

[MrSony]

My bores were mirror smooth when I took my 350 apart. Ridge was a thick as a coin. If you have any significant ridge at all, you will need to get a ridge reamer or risk wasting the honing stones on getting that ridge gone. I got some hypereutectic pistons from summit (https://www.summitracing.com/parts/uem-1749h-030/overview/make/buick) These ones, and they've stood up to my abuse. These ones are .030 over though. My local shop only charges 18 bucks a hole to bore an engine so yours should be around there. It should be the same price for .010 to .060 over. I think I had them sonic check it to be safe can't remember how much it was. You gotta check the taper of the bore, if I remember right anymore than .010 difference from TDC to BTD is asking for a rebore. You could hone it out, but you'd never be sure exactly how much you took off. Also With Buicks, or the 350 at least, you don't have to pay extra for the torque plate to simulate the cylinder head being on when they bore it because all the 350 Buick bolt holes in the deck are blind, they have a bottom and don't go into a water jacket.


Hey 64nailhead, if you would be so kind, could you do some of your math wizardry on these pistons I suggested? I really don't know the compression ratio of them and they are in my motor right now so knowing would be cool.

 

[olds307 and 403]

I guess it depends if you actually have 8.5 to 1. Did Buick use shim head gaskets from the factory? How far do the pistons sit in the hole? Do the heads CC what the factory says? For example the 73-76 Olds 350 is rated at 8 to 1 with shim head gaskets. If you put Felpro head gaskets on, you get around 7.8 to 1. The #8 heads off my two 76 350's cc'd at 77-78 vs the factory spec 79. Most big block Olds heads CC considerably more than the 80cc spec. My 403 heads cc'd at 86 vs the 84 spec. If you can mill your heads enough to get 9 to 1, go for it. While you are at it, add the big factory valves, bowl work and the matching springs for your cam.