300HP from a 340 4bbl? with a 8.4:1 CR ?

**ScottLESABRE400(66)** · 09-20-2015, 12:00 PM

Hi,
I was told by the machine shop that with a 1 up cam and stock valves I can get close to 300 HP from my rebuilt 340 4bbl. with a 8.4:1 Compression ratio . Is this possible ? I don't like the idea of giving up the 365 FT. Lbs. of torque that came stock with the 10.25:1 CR. . Could someone let me know how much Horsepower I can get with this engine if the new build only produces a 8.4:1 compression ratio.

Thanks,
Scott

**Dr. Frankenbuick** · 09-20-2015, 02:14 PM

I think you can still get Buick 300 high compression Pistons that will yield 10:1 or so static compression in your engine. Those and a slightly larger cam with a later closing intake valve should run on 93 or 91 octane without any issues.

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**ScottLESABRE400(66)** · 09-20-2015, 05:45 PM

Thanks a lot.

**Dr. Frankenbuick** · 09-20-2015, 06:18 PM

You might also be able to use the high compression Buick 350 Pistons if sonic testing indicates there is not too much core shift in your block.

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**ScottLESABRE400(66)** · 09-21-2015, 01:48 AM

Originally Posted by ScottLESABRE400(66)

Thanks a lot.

I'll get with the machine shop guy today. I'm still not sure what he meant when he said I could get close to 300 Hp with the new 8.4:1 CR.
I need him to clarify the info. . Thanks for the input, I'll use yours suggestions. If it is only a matter of a few more bucks I'd like to do it now while the motor is out of the car. It's a 66 Lesabre and I'd like to get a little more power out of the 340.

**telriv** · 09-21-2015, 06:36 AM

Go to V8Buick.com & do a search. Joe did his 340 with great results. His screen name is : GSGTX

Tom T.

**Bob** · 09-21-2015, 09:36 AM

Personally, I would build it with the stock pistons which were rated at 10.25-1.

http://www.teambuick.com/reference/specs_300_340.php

Perhaps they have a set of low compression pistons on the shelf.

**bob k. mando** · 09-21-2015, 11:38 AM

You might also be able to use the high compression Buick 350 Pistons

don't waste time looking for Buick 350 pistons, it ended production in 1981 and has little aftermarket support. look for Buick 231 / 3.8L v6 pistons, same bore size.

I don't like the idea of giving up the 365 FT. Lbs. of torque that came stock with the 10.25:1 CR.

why is he discarding the 10.25 : 1 pistons?

also, HP is a function of Torque and RPM.

http://www.teambuick.com/forums/show...sepower+torque

IF you're going to lower the absolute torque peak
THEN you must raise the rpm range of the engine, simply to maintain your HP number, much less gain HP.

he says he's keeping the stock valves ... is he planning on doing any porting work at all? the restrictive ports and valves are well known as the primary HP / rpm bottleneck on any Buick.

sure, you can kludge around it with more cam ... but why the **** would you do that?

why wouldn't you keep the high comp stock pistons and put your bigger cam in AND GET EVEN MORE POWER?

frankly, any decent 'power' gasoline engine build should be able to approach 1hp / ci without too much trouble. the 1970 Bu 350 ( pretty much an overbore 340 ) was factory rated at 315hp Gross HP. if he can't beat that, he's talking pretty weak sauce.

where are you? perhaps we can recommend a reputable Buick builder?

unless you're racing, you don't really care about big HP numbers ( which you're only going to see north of 5000rpm ) anyways. you want a fat torque curve from ~1500-4000rpm for getting around town.

a Buick v6 or Land Rover v8 builder should be able to help if no other options are around.

**Dr. Frankenbuick** · 09-23-2015, 04:11 AM

Originally Posted by Bob

Personally, I would build it with the stock pistons which were rated at 10.25-1.

Last time I built a 340, sealed power didn't have a number in the book for a high compression 340 piston. They did have a high compression piston for the 300 that was the same as the high compression 340 piston though. Those two engines have the same bore and compression height. It is the stroke that is different.

**ScottLESABRE400(66)** · 09-23-2015, 03:36 PM

Yeah, I'm trying to give the machine shop guy a break. I plan on giving him more input on friday( I'm busy as hell at work). I would like to know what he thinks of the condition of my stock pistons. I had the oil pan dropped and had a good look before I had it towed to my mechanic , they may be fragged. At least two had spun bearings. A lot of metal in the pan bottom. It was a mess. Dose anyone know how hard it is to recondition these pistons? I already know the crank and cam are toasted.
I would like to have the heads ported. Im not sure what would be an optimal porting procedure for the 340. Could one of you guys give me some directive?
Thanks,
Scott