The 340 is closely related to both the 300 and 350 but the lack of aftermarket performance parts make it an oddball.
parts for the 340 Hi there, I am rebuilding a 1966 Le Sabre with a 340 and ST300. The engine is not a nailhead, as for performance, if you can find a 340 4 barrel intake and the pistons from a 4 barrel 340 engine that would help, (the pistons in the 4 barrel carb version are a different shape and give 10:1 compression ratio instead of the 8:1 in the 2 barrel carb engine) the intakes for the 215, 300 and 340 are three different widths! ( I could'nt believe that when I heard it, but unfortunately it's true) so you have to find a 340 intake for a 4 barrel, there are no aftermarket intakes available, that's the only down side. The same camshaft, followers,all valve gear, except the pushrods (different length) can be used, water and oil pumps are also the same( but watch for long nose and short nose water pumps or the fan belt pulley wheel won't line up with the crank wheel). you can get roller rockers, adjustable pushrods and performance cams from Poston enterprises, Poston also do headers for the 340, BUT when I spoke to them to order a set they said that they would not fit the Le sabre as they were designed for the GS Skylark which is an "A" body car ( the 66 LeSabre is a "B" body). I am too far away to get a set on trial but I am sure they might be able to be adapted to fit!, saying that most people I have spoken to say that the factory manifolds flow really well and it is not worth replacing them. You can also have the block bored out to accept the 350 pistons bringing the C.I. up to 350ci, look through some of the old postings in the small block tech section for lots of info on the 340, and check out the power some people get from them. It's good to have a 401 waiting in the wings, it just depends on what you want the car to do for you, good luck, let me know how you get on, cheers Louis :3gears:
The pistons on a 4 barrel 340 are different from the 2 barrel huh? I found a 4 barrel intake for my 340 and will be switching, should I also get some new pistons, I just saw some from postons. Thanks in advance. Joe
Also Ive been told to go to a 750 cfm carb, Id like a few more opinions on this too. Stock was a 550 cfm, and Im putting headers/flowmaster x-pipes exhaust, 4 bbl and cam in. Thanks again. Joe
Theres been some new pistons on Ebay for awhile...some company is selling them all the time, I think around 100 bucks or so and they have been 10 over, 30 over, so on and so on..do a search and you'll find them.
Yea I saw some on ebay when I was searching around, 30 over is $154 and 40 over is $98. Wonder if they are actually good, Im always a little nervous buying off ebay, unless its a $7 keychain like the one I just bought (penguin with buick in the middle). With the 4 barrel conversion do I need new pistons like that? Suppose it couldnt hurt anything. Joe
I guess email the seller and ask him if they're for a 4 or 2....theres also a regound crank on there for 340.
compression ratio info Hi there, Yes the pistons are different, the pistons in the 4barrel 340 give a compression ratio of 10.25:1, where as the ones in the 2barrel 340 give 9.0:1, again it depends what you plan to use the car for etc. here are the compression figures for 340 engines from 1966, from my 1966 service manual. engine code MB, is a 4barrel 340, compression ratio is 10.25 : 1. engine code MC is a 2 barrel 340, compression ratio is 7.6 : 1.(this was an export only engine). engine code MA, is a 2barrel 340, compression ratio is 9.0 : 1. If you can get a 4barrel intake and carb and a set of pistons for a 4barrel I would go for it. Another option to consider is that the standard pistons for a 350 will fit on the 340 rods in the 340 block, all you do is bore the block as if you were fitting oversize pistons. Its an odd size bore!. ie. you get standard pistons and you get 30 thou over and 60 thou over(for most engines), but if you get a set of 350 pistons they are 40 thou over the size of the standard 340 pistons so you bore 40 thou over and use the standard 350 pistons. This also puts your engine size (displacement, cubic inches) up to 350ci. There is a thread on the board somewhere giving all the details of this, cheers Louis
Thanks for your input Louis, I guess I'll just have to see about my financial situation in the spring, Im starting a new job making commission so I hope Im going to be making more. I did send money for an intake today and should be getting it soon. Thanks again for your input. Joe
Be aware that the MB engine uses gasoline requiring an octane rating that would be over 96 in terms of today's rating system. Accordingly, you would find it difficult to keep the engine from pinging on pump gas if you were to install the original 10.25:1 MB pistons. I have had to run a 3:1 premium gas/racing fuel mixture for many years.
96 Octane huh? I dont know if I can get that around here, highest Ive seen is 93 and I use that. I dont think Im going to go for the pistons, maybe in the future but not this year. Joe
Hi, I have a 340 4bbl with 10:25 to 1 comp. It has 172,000 miles on it and runs on 93 or less octane with no pings or knocks. The motor is stock, and has plenty of HP for me. I do use 100 octane once in a while because it seems to run even better and the exhaust doesn't smell so nasty! Good luck in your endevor. Mark
Had the intake off mine yesterday..WOW the carbon build up!!..had to take a screw driver to the cross over ports...totaly blocked off! ou:
