OK, here is what you get when you set a 300 4bbl intake on a 340 block with 300 aluminum heads, photos below. As you can see the intake sits about 3/4" above where it would on the 300 relative to the decks, which are about 5/8" taller. Figuring the sine of a 45* angle that means the intake actually sits about 1-5/8" above where it would be relative to the crank centerline. But even so this swap is feasible if building a light weight 340. It won't breath as well as an iron head motor but will still run just fine, and would be a good candidate for forced induction. To make the intake work requires spacers. At least .750" on the ends and .810 on the sides. A bit more would be better. One way is to use 1/4" aluminum to make a lifter valley pan, creating a 1/2" air gap under the intake, and with 3 sets of port gaskets about a 3/8-1/2" side spacer is needed which can be fabricated without too much difficulty. The pan will require the use of a hydraulic press brake to form the 45* angles. (Note it isn't easy or even particularly safe, but I hear it is nonetheless possible to saw aluminum plate on a table saw with a carbide blade. I'm just passing that rumor along, not suggesting you try it. In fact I officially recommend that you not try it.) Now bear in mind, the heads used could just as well be TA Rover heads. In which case the intake might be somewhat limiting but there are single plane intakes available such as the Willpower, Harcourt, and even Huffaker. So a strong NA build is definitely possible. A few Hilborn type IR injector stacks are still floating around too, which is another bolt-on option. The 340 crank has 3" mains. I believe the 300 has 2.5" mains but I should be confirming that within days, as well as weighing the iron and aluminum heads. If someone would like to weigh and post 300 and 340 iron intake weights I'll be able to tell you how much weight reduction the alloy heads and intake gives. I should also be able to give a complete engine weight for the aluminum head 2bbl 300. I'll be removing the flywheel, starter, alternator, exhaust manifolds, fan and PS pump as the weight of those can vary a good bit. Jim
I've got a 2bbl iron intake and 2bbl aluminum I could weigh if I find a big enough scale. I can tell you the 300 crank definitly has 2.5 inch mains, and I decided to just buy a 350 crank I saw for sale rather than go through all the headache of pulling the motor in the junkyard and risk having a trash crank. I can measure that when it gets here if there is any question, though it doesn't seem like there is at this point.
Duffy, for the present purposes a bathroom scale is an acceptable option. Thanks for confirming the mains, I'll take my time removing the crank. Got the 340 crank sitting by the lathe. I'll make an extra effort to get the head weights tomorrow. I did weigh them once already and the aluminum ones are 18lbs with the rockers but not the head bolts or valve covers. Can't remember exactly what the iron ones were but it was between 50 and 55lbs.
You will want the 300 crank to compare with the 340/350 crank. the seal area is different too. Duffey, How are you doing on your project?
The iron heads weigh 47.5lbs with the rocker shafts and bolts but without the spark plugs or oil shield. So that is a 60 lb reduction with the aluminum heads. The intake will add to that, maybe another 25lbs. Cranks for the 215, 300 and 340 are all within a pound or two of 60 based on my past measurements and the 340 block is 2lbs heavier than the 300 at 142lbs. I will confirm those numbers as I am able. It is true that the smaller mains should mean less weight but you might pick it back up in the main webs. Anyway the big difference is the aluminum as we already knew. But here's a shocker for you. I weighted the 300 on my Fairbanks balance beam platform grain scale and it came in at 320 lbs on the nose! That was without: Exhaust Flywheel Starter Alternator PS pump Carb (2bbl) Fuel pump Pulleys Hoses, wires or spark plugs Just the basic engine, just as it appears in the photos below. But if you can't complete that engine under 400 lbs you just aren't trying. Jim
Well I got the oils mods done on the block and have it at the machinist for hot tank/magnaflux. Unless the 350 crank is cracked (pretty unlikely right?) I will be going with the aluminum topped 300 stroker option. I will keep one of the 300 cranks I have until I have the 350 crank turned, then hopefully sell them to some Rover or 215 guys.
Once I have the 300 torn down I will set that crank by the lathe and begin turning down the mains on the 340 crank. There is also a specific diameter for the rear main seal journal to use with the neoprene seal, I will need to find out what size that is for the 300. I'll try to get some photos as I go. I have another job on the lathe that I need to finish up first though so it'll be a few days at least.
Jim, I think the oil slinger is different and the main journal bearing feed holes move over and need to be chamfered back also.
Maybe a question to expand--as I've been looking for bearings, etc. I can see some price difference between 300, 340, 350 and Rover engines. It seems like rod bearings should swap between all the Buicks right? Don't Rovers share the same cam bearings? I'm just thinking this info might be helpful from a price standpoint.
Yeah, that would be expected. I'll take it down to .020-.030 over and have it ground. But I have to finish a power steering unit first. 2 piece column with EPS. I'm finishing up the slip joint and firewall stub. Jim
Duffey, Stick with the 300,340 bearings. The Rover cam bearings are same ID and spacing as they use the same cams, but don't know if OD and 2 front oil holes are in same position. I would also get the T/A grooved front cam bearing and booster plate. Did you weigh the 300 rods? Balance and lighten the 350 rods? Larger valves? What pistons did you settle on? Probably should answer on your old thread to not hijack Jim's. For you and Jim, Best Gasket 300 rear neoprene seal (also fits Nailhead).
It's OK, we can both use this thread I think. Thanks for the info on the rear main seal. Still need to get the journal diameter for it. The 300 rods are about .4" shorter than the 340 rods. Just shy of 6" for the 300 (5.960-5.963) and 6.387 (6.385 actual) for the 340. The 340 pistons have about 1/2" between the wrist pin and the oil ring, I haven't looked at the 300 pistons yet to see if they have more or less. I used 7" rods in my 340 with 3/4" wrist pins and had maybe 3/16" between the wrist pin and the oil ring. Next look at the deck height. The 300 deck height is: 9.543 and the 340/350 deck height is: 10.187, a difference of about 5/8" (.644") so a 6.4" rod could be a good choice, depending on the ring package and wrist pin used, and a 6.2" rod should work with no issues. The practical range then would be 6" to about 6.4" and the longer rods give a rod ratio that will cause less stress on the cylinder walls which tend to be thin. I have begun looking at rod sets on ebay in that range with a 2" big end. Most will have SBC width and small end diameter but both of those issues can be dealt with. I used the 7" rods in the 340 because they already used the SBB big end bearings and I was able to buy them for around $120/set (Scat brand). They were FHF aftermarket rods. As far as I know a shorter version is not available. BUT, if an inexpensive set of decent aftermarket rods can be found (such as NASCAR take-outs) that makes it much easier to justify custom forged pistons. Jim
My 350 crank got in today and it looks to be in great shape, it would probably only need polishing but I'm obviously taking the mains down and I will have the rod journals ground 10 thousandths to get proper bearing clearance. Keep us posted on what exactly you have to do to your crank Jim, as well as how long it takes.
Pulled the crank today and sat it beside the 300 crank. Other than the main size the obvious difference is at the flywheel flange where the 340 crank has an offset balance weight sort of like what you might see on a SBC crank. Makes a good external identifier, the 300 flange is just a simple round. I'll do some clean up and measuring, I want to compare the seal journal and slinger area, so that will be next. Then soon as the lathe is freed up I'll start getting set up to cut the mains down. Jim
Jim, A while back I found Lunati had conversion bearings that allow the 2.1 Chevy rods on 2.0 journals Opens up a lot more rod possibilities. Unfortunately they are standard size only. Not a problem when cutting down the 340/350 crank. If they had undersize they would really have something. Buick 3300 V6 pistons compression height of 1.31 is pretty close for 6.25 rods. Pins are different though. There are some 6.25 SBC rods on Ebay with the large journal for $198. https://www.ebay.com/itm/For-SBC-Ch...118030?hash=item25dbc8294e:g:OK0AAOSwjRpZXZvk
The problem with using the 2.100" vs the 2.00" rod is the bolt to bolt dimension being farther apart in an already cam clearance challenged environment. Even the factory sbb 350 rods were designed with extra clearance in them, with the bolt head on the earlier rods and the shorter threaded side for the cap screw later rods. That being said, they are .135" shorter than the factory sbb 350 rods so they may work because they will actuate further away from the cam than the longer factory ones will. Kind of how the sbc 400 rods that are coincidently .135" shorter than all other sbc rods(5.7") that were ever used in production for cam clearance with the extra stroke. Plus they can be clearanced all the way into almost the center of the bolt if need be(need to maintain the drilled center to be able to measure bolt stretch), Eagle even sells them that way for the 4.00" stroke small block high lift cam stuff. You even have to run a small base circle cam when running a 6.00" rod and I haven't seen an aftermarket sbc 4.00" stroke crank that you can run a shorter rod without machining the crank throws down to clear the piston skirt when using a shorter rod. So for the cheap set of rods you need to buy the special bearings, have the big end machined down and possibly have to buy a small/reduced base circle cam.
Derek, Thanks. The wider rod would move closer to the cam, but shorter length does help. The 3300 piston I mention above has a deep dish and would probably yield around 8 to 1 compression. The 95-97 Ford Mazda 2.3 Sohc flat top and 1.335 compression height, would be about .040 down from deck. Would probably be around 10.5 with 6.25" rods.
