are the 340 and 300 different blocks? and what can you tell me about the 340's. I know nothing about them.
No, the 300 and 340 use the same block. Both engines use a 3.750" bore. The 300 has a 3.4" stroke, the 340, a 3.850" stroke. In 1968, Buick debuted the 350 which used a different block with a 3.800" bore and 3.85" stroke. more info on the 300, https://www.v8buick.com/index.php?threads/a-guide-to-building-the-lil-guy-the-mighty-300.191151/
Larry, Nope, 340 has higher deck height, longer rods and larger main bearings. Chris and Jim Blackwood have turned down the mains and put a 340 or 350 crank in the 300 block. Also Hot Rod magazine and BritishV8 had 300 stroker motors.
No. The lifter bores are different spacing . Since exhaust is ever other valve vs the Siamese center exhaust of the 350. Valve pattern Ieieieie Eiieeiie I believe cam bearing size is different also
That's what I was wondering. I knew the valve arrangement was different but didn't know if you could bolt the heads and use the cam from a 340. People have bored the 340 to a 350 though, right?
Should be okay but good idea to sonic check. They used to sell .060 over pistons for the 300, 340 and 225 V6.
good question but no it’s not possible without a custom cam although it’s been talked about there isn’t really enough reason to warrant the effort and $. depending on core shift and sonic testing yes it’s likely a 340 could be bored to get 350 cubes but it’s an expensive way to attempt to make more power.
Which is why I was wondering if you could put the 340 heads and use a 340 cam to make what looks like a 340 but was actually a 350.
I have a 350 cid 340 sitting on an engine stand in the shop that I will consider selling later in the year, the bores are .050" over. Do a sonic check first and don't go under .100 on the wall thickness if you can avoid it. Try for .150" or better on the thrust side. .030" overbore is generally considered safe without checking. The deck is 9/16" taller than the 300 so the intakes are not interchangeable and I don't think there are any aftermarket intakes for the 340, although it's possible to use spacer plates with the 300 intakes. I have a pair of those that I had waterjet cut for an intake I'll be building later this year. But 300 aluminum heads will fit. This engine has those, 7" long Scat rods, Venolia pistons, and 10.5 CR. Runs very well but needs the rear main seal journal ground down to remove the hash marks, a new cam, and head gaskets. (I used copper gaskets and they ooze coolant. The deck is 0-ringed btw.) Got maybe 2K miles on it. I'm going to a stroker 300 because it fits better in the car. In fact I've got an iron head 300 almost installed now to run while I'm building the stroker. Once the stroker goes in I'll probably do the work on the 340, swap the iron heads onto it, and sell it as a complete engine minus the intake and cam. Should be a pretty sweet deal for someone who'd like to have a good 340. The cam journals are stepped on the earlier SBB and straight on the 350 so no interchange. Also the positions of the lifters are staggered by up to 3/8". Besides which the port layout of the SBB is better, at least on the TA heads. Note though, the TA/Rover heads have a 32cc chamber so although they should work on a 2bbl engine, on a 4bbl engine they will require alcohol. The 300 makes a good stroker motor and has more aftermarket parts available for it. Bore is the same as the 340. The crank mains have to be cut down 1/2" and the oil slinger thinned out. With custom pistons up to about a 6.3 or possibly a 6.4" rod can be used depending on the ring package and pin size. I'm using 6.2" ex-nascar Carillo rods with Honda/Toyota inserts, and no, I did not have the journals offset ground, but it's been done. Rod to cam clearance is close enough without that. Currently waiting on the machine work to be finished on the block and balancing on the rotating assembly then two of them will go together. BTW, TA also built one of these. Not sure what rods and pistons they used though. Jim
So, what you are saying is it there's a chance. Nobody has done it for a low-benefit, high-cost upgrade. LOL. I'm curious but not motivated to attempt it. I'd assumed if it were easy someone would have tried it by now. Do the heads bolt up between blocks? If the cranks are dimensionally compatible, I'd assume the bore spacing is the same. If someone were to grind a 350 cam with EIEIEIEI instead of EIIEEIIE and the 340 heads bolted up, would a 340 intake work?
No, I'm saying use this: No, I'm saying use a 350 short block, 340 heads, 350 cam ground to EIEIEIEI, flipping the 3rd and 7th cylinders on the driver side and 2nd and 6th on the passenger side. Perhaps you could build it the other way, a 340 short block with 350 heads with a 340 cam ground EIIEEIIE. All just a bench exercise.
I love this site! The answers to all the questions are here! Thanks for all the input. I really appreciate it!
You'd run into problems with pushrod clearance going past the intake runners. That's the thing that sets the cam lobe position front-to-back and as you approach the center of the engine you have a 3/8" difference which is more than the thickness of the intake runners, so it'd be a real problem at the center pushrods. We looked at this really closely about a half dozen years back and decided it just really wasn't practical. Jim
