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

S

ScottLESABRE400(66)

Member
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
 
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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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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Thanks again

ScottLESABRE400(66) said:
Thanks a lot.
Click to expand...

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.
 
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/sho...epower-and-Torque&highlight=horsepower+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? :clonk:


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.
 
Bob said:
Personally, I would build it with the stock pistons which were rated at 10.25-1.
Click to expand...

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.
 
Just want the most hp for my hard earned buck

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
 
Again Scott, do a search on V8 for the write-up Joe did. A lot of questions can/will be answered as it was ALREADY done by someone.

Just my thoughts.


Tom T.
 
practically speaking, the Bu 350 uses the same crank as the 340.

is there any special reason you're trying to keep the original block? going straight to an 'SP' code, 1970 350 with a cheap freshen up would be the simplest way to fix this.




I already know the crank and cam are toasted.


losing the rod on a 340 / 350 normally takes out the cam ... because the rod shatters the lifter valley.

the 'problem' is that the SBB ( small block Buick ) design was originally only 215ci ( 1961-63 ), with a much shorter stroke and deck height. what this means is that the cam-to-crank spacing is VERY tight for the 3.85" stroke of the 340 / 350 and leaves almost no clearance between the ends of the rods / crank throws and the bottom of the block.

once you take the intake off, there's a good chance this block is a total loss.

340s can be had, but you may have to have patience if you really want one. there are only 2 years of production ( 1966-67 ) and they were competing with Buick 300s and Nailheads / BBBs across the various Buick models.

a 1980s turbo 6 would also be a decently easy swap, although there's obviously a lot more plumbing involved in that.

most common solution would be dropping in a 455.
 
Here is a link to a Hot Rod article with a Buick 300 stroked to almost 350 CI: http://www.teambuick.com/forums/showpost.php?p=77835. It made almost 400 HP and was over 400 in TQ. Most of the things done to that engine would work in yours as they share the same heads and a similar intake manifold. You would need the right porting, pIstons, headers, cam and carb to make similar power, but be carful what you wish for as the power will be available higher in the RPM range requiring a matching torque converter stall.

I would have sent you to Greg Gessler for porting, but he no longer is porting heads. I think he did the ones Tom was talking about belonging to Joe. He might have an idea of whom to send them to now, and he is still selling carb parts on the Gessler website if you want to contact him. TA Performance might also port them or know who has experience with porting 300/340 heads.

This is a very easy engine to build as most parts stock are ready for increased power. My Dad has a 340 engine running in his Sportwagon that I built in the early 1980s as a teen with a larger cam and carb. I beat the snot out of that engine in a Skylark with a ST 400 and 3.23 rear gear. I ran it for 5 years or so and then traded it him for a 430. It still runs nice without any smokes or problems.


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I KNOW who did port Joe's heads & it wasn't Greg. This "other" person also did Joe's intake manifold. He does this on the side with a flow bench. He DOES have a job, family, etc. & really doesn't do it for a living, just as a favor when he gets time too "play". It may take 2 yrs. or longer +. But, he does enjoy it along with "playing" to see what kind of results he can get & he DOES KNOW what he's doing.


Tom T.
 
Food for thought and build info to live byi

telriv said:
I KNOW who did port Joe's heads & it wasn't Greg. This "other" person also did Joe's intake manifold. He does this on the side with a flow bench. He DOES have a job, family, etc. & really doesn't do it for a living, just as a favor when he gets time too "play". It may take 2 yrs. or longer +. But, he does enjoy it along with "playing" to see what kind of results he can get & he DOES KNOW what he's doing.


Tom T.
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Thanks for all the info. The machine shop has found a set of 340 heads. They will do what sounds like basic porting.I can add an intake and more porting as well as headers later. Don't get me wrong , I want as much HP as i can get but money is a major factor. I hope to get the bottom ( out of car engine work) done and move on to more upgrades later. I plan on using stock 10.25:1 pistons, having the heads shaved down to accommodate the new head gaskets and adding an additive called race gas to maintain high octane. If I can get 300hp w/365FLBS TQ it will do for now. I'm still open to any suggestions. I have read the recommended threads. Thanks again for the direction.
Scott
 
stock 340 pistons

ScottLESABRE400(66) said:
Thanks for all the info. The machine shop has found a set of 340 heads. They will do what sounds like basic porting.I can add an intake and more porting as well as headers later. Don't get me wrong , I want as much HP as i can get but money is a major factor. I hope to get the bottom ( out of car engine work) done and move on to more upgrades later. I plan on using stock 10.25:1 pistons, having the heads shaved down to accommodate the new head gaskets and adding an additive called race gas to maintain high octane. If I can get 300hp w/365FLBS TQ it will do for now. I'm still open to any suggestions. I have read the recommended threads. Thanks again for the direction.
Scott
Click to expand...
The shop found stock 340 pistons. Type-o
 
If you wind up with a cam with a 220* @ .050" intake duration and a wide lobe separation, you may have a dynamic compression around 8:1 with a 10.25 static compression. That would work with 93 octane without any fuel additive.

I run Torco unleaded fuel additive in my supercharged brand F vehicle. It brings the octane level to about 96 with about 16 oz in 15 gallons and 104 octane with about 48 oz per 15 gallons. Mixing gets old after a while.


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Octane boost

it makes sense that a lot of guys don't trust the 93 octane rating and would rather use an additive with regular. The reason being the 93 dose not sell nearly as well and will most likely be old. The guy dong the build on my 340 said I have a choice of 9.5:1 stock 340 pistons or 10.25 340 stock pistons???? I think i will go with the higher compression.
 
I use Torco strictly as a precaution on the street tune. It just provides protection against a bad tank of 93. This summer I installed a knock sensor and ignition retard system in that car making Torco less necessary for the street tune. It will pull 10* timing from any knocking cylinder on the next stroke and advance a few degrees a stroke until the point it is just shy of knock. Some guys have flogged this system with a tank of 87 octane and their engines are still very alive with no issues. I don't know I would trust my engine to that test!


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