I'm beginning to put together my performance minded 331 Caddy now. There has been a lot of discussion about interchanges between the 331, 365 and early 390. I don't know everything about this, but I have participated in some of the technical discussions and learned a lot here on the HAMB. Thanks guys! My goal is to extract some power, yet have a stock appearing 331. I don't know how much this will cost, but it probably won't be too much more than a nice 383 Chevy build. We'll see! I have no particular power goal other than as much as I can get without getting ridiculous. This means primarily off the shelf parts or modifications thereof. The work is being done at a local engine shop to my specifications. If it turns out as good as I think it will, I'm sure they will be willing to do more (once we get the recipe down). This oddball stuff is a PITA for them (my opinion- they never said so!), so I expect it to take a while. I don't want this to take priority over their normal business, and there is a lot of craftsmanship going into this which takes time. We've already waited about 6 weeks for the rods because even though they are off-the-shelf items that everyone advertises, nobody had stock. Here is the basic plan: Modified 390 crank Looooooong H-Beam rods Forged pistons, 10-11:1 range (premium unleaded pump gas) Ported early 390 heads with seat inserts Vintage aluminum flywheel (it is going into a 2600# car) The 331 will feed into a '37 LaSalle top shift trans It should yield about 398 CID when it is done. Induction will be 4 side draft single throat carbs (which I expect will choke it), but I may eventually go to 4 Weber dual throat side draft carbs. Is this of interest to anyone here?
Huh? ..of course it is. One question is why side drafts? Just wondering that's all. Do you have pics of the carbs? 2nd question is, what intake?
Side drafts are for the low hood line. The carbs are the Carter YH, the ones used on the early Vettes. BTW, everything I will be doing will work that much more easily on an early 390 block! Q1: Will a 390 crank fit in a 331 block? A1: Yes, if you leave the bearing shells out! 390 crank main bearing journals will need to be ground down to 331 specifications. Q2: Will a common aftermarket H-Beam forged rod fit on a 390 crank? A2: Sort of. I'm using BBC rods which require a slightly smaller diameter crankpin (2.200 vs. 2.250), a problem which is easily solved when the mains are ground undersize. The BBC rod is too wide, so it will need to be narrowed at the crankpin and narrow bearings will need to be used. Widening the crankpin would interfere with the crank counterweights, so that isn't a good solution. The rod bolts look close to the block, but the block will be overbored and then notched if required (and the crank is loose in the photo because there are no bearing shells installed). There appears to be plenty of clearance between the rods and the cam lobes, but this will be a watch area. The next step (while the crank is getting ground) is to get the pistons and bore the block. I will be using 4.030 SBC pistons. From there we can set the deck height we need to get good quench. We will also rebush the BBC rods to the SBC piston pin size. This explains most of the hard work that needs to be done on the short block. I'll take more photos as things progress. Can anyone recommend a rear main seal? It needs to be the same OD as the 331 block but I can grind the crank to nearly any diameter to accomodate.
Keep it up. Hopefully I can steal some tips for my build! Sent from my DROID device using the TJJ mobile app
Rod comparison- 331 rod is 6-5/8" between centers, BBC long rod is 7.1" between centers. 390 rod is the same length as the 331 but the width at the big end is narrower. 390 rod journal is 2.25" diameter nominal while the BBC is 2.2" nominal. Since the journal needs to be cut down a little anyhow, it will be offset ground just a bit as well. As we get a little further along we'll figure out what to do about the difference in bearing widths between the BBC and the Caddy. Might grind the rods narrower (there is a narrower BBC rod bearing commonly available), or, widen the journals a bit on the crank. Nothing that's a show stopper, just a decision that has to be made. The crank grinder has the crank now and will tell us how much wider the journals can go without major surgery.
And now the pistons... The new pistons are SBC blower pistons. They gave about the best compression height which is why I chose them. I don't want the pistons too far down in the hole. The small ends of the rods will need to be rebushed because the SBC wrist pins are smaller in diameter than the BBC pins. It may seem silly to make all these mods but the cost difference for custom pistons compared to off-the-shelf pistons is probably more than the cost of rebushing the rods. We'll see! If you have to worry too much about the cost you might as well just do a stock rebuild, besides, this is kind of fun! It may be a few weeks before I have anything more. The crank is getting ground now and the block is being bored. Then time for mockup to see how much we have to deck the block to minimize quench distance. Anyone have a recommendation for hydraulic rollers that will fit?
Man, I haven't updated this thread for nearly 3 months... Probably because not much has happened. The crank has been at the grinder for over 2 months now. I guess my priority is low! In any case, the engine shop has bored my block to fit the pistons. Once we get the crank we'll do a trial fit and verify how much the block needs to be squared & decked to get the proper quench height. That reminds me, we have to re-bush the rods yet to adapt the SBC pistons to the BBC rods. The engine shop sent the stock heads to the flow guy to see what they do. I especially want to know the flow difference between the siamesed exhaust port and the end exhaust ports. I'll publish that info for the greater good of humanity when I get it. Once the porting is done we can check to see how much improvement it made. Sorry this is moving so slowly, but I've got so much going on I haven't had time to harass the vendors working on this, or myself for that matter!
x2 on that count! I know its not "traditional" but thats one thing the HAMB needs a LOT more of, is flow bench numbers on these sort of builds!
Looking for recommendation! I was thinking that maybe I could adapt some hydraulic rollers from another platform (SBC?) and have a custom cam ground. Posted using the Semi-Custom double throw-down H.A.M.B. App, now 20% shinier than before.
OK, it has been a while I know! Crank is due back from the grinder shortly to begin mockup at the engine shop. Nobody seems to want to do an oddball custom grind for some reason... In the mean time, here are the flow numbers for the 390 head: .100 Intake 43 CFM Exhaust 37 CFM W/Pipe 33 CFM .200 Intake 93 CFM Exhaust 86 CFM W/Pipe 81 CFM .300 Intake 115 CFM Exhaust 115 CFM W/Pipe 110 CFM .400 Intake 157 CFM Exhaust 127 CFM W/Pipe 124 CFM .500 Intake 171 CFM Exhaust 141 CFM W/Pipe 137 CFM .600 Intake 171 CFM Exhaust 146 CFM W/Pipe 141 CFM Maybe someone more experienced than I can tell me if that is good, bad or horrible? "With pipe" must be with an exhaust pipe since the numbers seem close to the exhaust numbers. I'll have to look up some SBC numbers to see how that compares.
Subscribed to this thread. Thanks for the link. I have been told that sbc lifters should work but require custom push rods and maybe adjustable rockers off of a Stude or a custom set. I'd like to make my 365 a roller as well.. that'd just be damn cool. Any thoughts on oiling? I've read that the 390 block is suppose to be be better for some reason or another compared to the 331 and 365. Alex
Well, they had Caddy roller cams back in the day, but I would like to go hydraulic roller. With custom length pushrods (no big deal/not very expensive) and hydraulic roller lifters you shouldn't need to adjust the rockers any more than the stock setup I would think. On my setup, to adjust my valves I would have to remove multiple carburetors so that would be very inconvenient to do on a regular basis. I also want to use the stock 331 Cadillac script valve covers which won't fit (without serious modification) with adjustable rockers. The oiling issue may be as simple as having the full flow oil filter on the later models rather than the can (so-called toilet paper roll filter) that only ports off some of the oil for filtration that the earlier models had. Posted using the Semi-Custom double throw-down H.A.M.B. App, now 20% shinier than before.
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