You are approaching this motor much the same as I did my AMC 360 motor. I used 400 SBC Chevy pistons in it also.... KB claimers are cheap ! This little motor was making just over 500 hp in my OT Spirit. Some times it just takes a little imagination and creativity to build some of these old motors, but it can be done. I have another formula for the AMC motor that I would like to try some day..... that one won't be cheap though. Those flow numbers aren't terribly bad for stock heads. To get an idead of how other heads flow check this. Here are some comparison numbers for sbc and sbd Lift / AMC 502 / Chev 370 / Dodge 'J' Intake .100 70 60 55 .200 143 122 112 .300 192 167 161 .400 213 190 198 .500 220 199 210 .600 228 203 205 .700 236 203 Exhaust .100 59 40 49 .200 113 80 106 .300 146 114 125 .400 150 128 132 .500 152 135 134 .600 153 143 136 .700 153 Your motor will gain a lot if the heads are done right. You will be building more towards torque I assume so the head flow should work well once ported.
Thanks for the info! My car will weigh about 2600# (fiberglass bodied sports car), so I doubt I can do anything to kill enough torque to be harmful in my application. In fact, with my skinny tires and an open rear end killing torque may be a benefit! The stock 331 runs out of wind at a pretty low RPM (about 4,000?), so I'm looking to greatly expand the RPM band. Current plan is for six Carter YH side-draft Corvette carbs on a fabricated manifold to maintain a low hoodline.
Am I right in assuming that these rods (for a Pontiac) would also work in a 365 Cad? Then maybe contact J&E for some pistons that might resemble something close to Pontiac to be cheaper? Or am I really off and this has been thought about already? Alex Eagle H-Beam Connecting Rods 6625PP3D http://www.summitracing.com/parts/esp-6625pp3d/overview/
They might work. You'll have to check the bearing width and the pin diameter and width. I think the length and the bearing diameters are the same. If they use the same bearing shells you can be assured the big end will be similar. The rod width was different between the 331 and 390, not sure where the 365 falls. I wanted to go to a longer rod so I chose a Scat BBC 7.10 length rod. The rods still need to be modified for my application because the pin diameters are different between the BBC rod and the SBC piston. Custom pistons were more expensive than rebushing the rods though.
Any idea on the route you'll take with the crank or the rods? You were talking about widening the crank for the BB Chevy rods or narrowing the rods to fit the crank. I just totally dissembled my motor over the past couple days so now it's research time before part buying. I thought I remembered reading somewhere that a 427 Chevy oil pump can be retrofitted to an old Cad motor.. but now, of course I can't find anything on it. Do you know anything about that? I'm posting in the thread instead of a PM so maybe someone can search for this later. Alex
There is a "narrow bearing" available for the BBC rod. We are planning to use that and narrow the rod. To widen the crank journal much would mean cutting into the cheeks of the counterweights which might be much harder than just narrowing the rods. Never heard anything about using a BBC oil pump. Please post if you find out anything on that. Hopefully my motor will be in the mock-up stage soon so we can finalize all this stuff. Turns out the head flows between the middle and end cylinders were within a few CFM of each other. That tells me that the exhaust port, at least in the stock head, isn't really a big factor in the flow- the valve and seat area is probably where the most restriction lies. It also appears, and I'm no porting guru, that the intake is severely restricted (compared to the exhaust) at lower lift numbers. The shop is going to unshroud the intake valves as best they can and back-cut them to improve flow at low lift. We'll get the result flow tested again and see how much it helped. Maybe I should start a kick-starter campaign to pay the flow bench guy? The graph in the first attachment shows the flow result. In the second attachment I have added boundaries for where the intake valve should be compared to the exhaust. From what I have read, you want the exhaust to flow from 75% - 85% of what the intake flows. By these charts you can see how I developed my conclusion that the intake flow is the problem at the lower lifts. The intake flow is in the proper range above .400 lift. Below that it is deficient. The range where the intake flow should be is shown by the green and red curves in the second attachment. Once this is balanced (intake flow inside the green and red boundaries), it definitely doesn't mean that the flows are acceptable for the application, only that the relationship between the intake and exhaust is correct. The engine should at least be breathing efficiently. From there, both the intake and exhaust may need to be opened up further. And I'm not sure you can ever get there from here. We'll see what happens after they work on the intake a little. Could make things worse for all I know! Hopefully someone here that knows more than I do can chime in.
Found the link on where I saw the 427 Big Block Chevy oil pump. http://www.allardregister.org/home/2013/5/23/19-cadillac-engine-tuning-tips.html (#15 ) Problem is they don't say anything on what needs to be done or how easy it is. They also recommend a "modern" harmonic balancer, but again, don't recommend one or note one that would work well. So I guess more research. Just thought 'd post the link to show I wasn't totally crazy Alex
I wonder how old that article is. I've seen it before, some years ago. How long ago was anyone running stock cast iron pistons I wonder? To bad they don't mention hydraulic roller cams! ;-) Posted using the Semi-Custom double throw-down H.A.M.B. App, now 20% shinier than before.
Just called the engine shop, please stand by. They should have the flow numbers after porting available shortly. Hopefully a status on the crank grinding as well. I've had so much going on that I haven't been following up like I should. If the car was ready for the motor I would be more concerned!
We have progress to report! Crank is back from the grinder with the rod journals offset ground to BBC spec. The main bearing journals have also been ground to the 331 block spec. Remaining crank work is to grind the rear main seal area to fit a rubber seal, perhaps Mopar, instead of the rope seal and bore the hole in the end for the manual trans bushing. All the rods need to be re-bushed to adapt the BBC piston pin bores to the SBC pin diameter in the pistons. For the time being one rod was double bushed (bushing within a bushing) for mockup only. The rods are now out getting custom bushings made and installed. The end result is we are down about .042 from the deck. We want to install a head and valvetrain to make sure we have good piston to valve clearance before we deck the block. The pistons are SBC blower pistons, so the tops of the pistons are very thick so we'll have room for any valve notching we have to do. Right now we have no idea how closely the valve reliefs will match up to the Caddy heads. On the other end, the rod bolts clear the bore OK, but the rod needs to be ground thinner so both will fit on the journal at once, so the bolt heads will move closer to the bore. If anything needs to be ground, it likely won't need much and there should be plenty of meat. The rod is pretty massive, but it still clears well internally. By the time we get a cam bearing installed, there should be plenty of room. We will verify during later mock-ups. Still waiting for the post-porting flow numbers... Sorry updates have been so slow, but lots of other projects are in work and the car is a ways off until it needs the motor.
Nice! And thanks for the pics. I'm working with a machinist right now and we are kind of learning while doing. Your thread here is making certain parts a little quicker as it's been done already. Thanks for following up. Alex
Did a piston to valve clearance check today using the stock valvetrain with a stock 331 cam. Here's the engine setup with some light valve springs just for mock up: IMG_8911a by c322348 posted Nov 7, 2014 at 3:46 PM We did not use a head gasket because the block cut of .042 to get zero deck on the pistons is roughly equal to the thickness of a head gasket. We turned the engine through one revolution with some clay in the combustion chamber: IMG_8914a by c322348 posted Nov 7, 2014 at 3:45 PM We sectioned the clay with an X-Acto knife and you can see the piston to valve clearance: IMG_8931a by c322348 posted Nov 7, 2014 at 3:44 PM The exhaust had about .125 clearance while the intake had about .140 clearance. IMG_8919a by c322348 posted Nov 7, 2014 at 3:45 PM Not sure what the cam lift is on a stock 331 but it doesn't look like there is too much room for a lot more lift without working on the valve pockets in the pistons. Being blower pistons this shouldn't be a problem if it is necessary, there is plenty of material to work with on the head of the piston. Just as a refresher, this is a 331 block with a 390 crank offset ground to maximize stroke with with BBC long rods and SBC blower pistons. Read the thread to better understand why I did it this way.
For the small end of the connecting rods, do you have any info on what size the bushing is or more like is there a bushing from ford ,chevy, olds etc that you are modding for the correct fitment / size. We are looking at trying to get rods possibly pre-bushed correctly for the combo but are trying to save a bit of time if we can't buy them that way and ordering the close one and then machining. Thought it was worth a shot asking. Alex
Interesting read. Are you sure you need to bore the end of the crank for the manual spigot bearing,on my 365 I seem to remember there was a thick washer/spacer that just pulls out to leave a deep enough bore to press in a bush for the spigot.I think I drilled into the end of the crank and got a fright when the drill punched through and I thought I had drilled into an oil passage.As I was running the tap though the washer/spacer just pulled out.I think thats how it went,I could be wrong.
I still have the 331 crank. As soon as the other machining is done (still have to decide on a rear main seal and machine the crank in that area to suit) we'll drill the end of the 390 crank to match the 331. I'm not sure they ever had a manual trans behind a 390 from the factory, did they? Maybe in a Hearse or Ghostbusters ambulance?
Not sure if this will help you c322348 or anyone else. We found out that Manley will custom make bushings for their rods for less than $20.00 a bushing. We were not sure if Eagle rods and Manley rods had the same bore for their small rod end where the bushing fits. But that might be a way to save some cash if someone needs help with that and the custom bushings.
Dude.....kickass ! Definitely something not seen every day....and for that particular reason, I like it ! Manual transmission wise....other then the adapter stuff......the Allard guys....I believe had the J2X Lemans cars with a Borg Warner T-10 four speed (57era) behind the 58-59 Cadillac 390's....but hell....who knows what the input shaft differences would be....nor what the bellhousing references would be ?? Awesome play time you're doing with this build. Keep up the good stuff !
Thanks for passing that along! Good to know. Mine are already done. I think the engine builder used a local connecting rod shop.
any way to get the early pics inthe thread to work? I have a '51 331 that is about to go under the knife. it already has a cam, big heads, aluminum adj rockers, factory dual carbs and Duo-coil distributor. Not sure how far ill take it but really needs a bore to be perfect, so wondering about stroking as doesnt seem like much is out there for stock pistons that are decent.
Hi Han - In the process of rebuilding my 365 Cad. I've been scrounging all over the net for info to do this right. I got some info from Chris at Cad 500 out of Albuquerque. He said over-boring these blocks to 3/8" is pretty safe and also stated some racers back in the day used to go 1/2" over (crazy). That still sounds huge to me but maybe with measurements this info might be able to help you make a decision on a setup. Give him a call, he seems to know a lot about these motors as they've built a few. I'm not endorsing Cad 500 in anyway, just passing along the info. Hope this helps. Alex
I have subcribed to this thread to learn more about the early Cad 331. I can understand the stroker aspects of this thread the costs may be prohibitive for most. It really is to bad that there isn't just one thread that covers more of the standard build and interchanges between all of them
The gyrations I'm performing are basically because I wanted a 390 in a 331 block with forged pistons and better than stock rods. It is a couple years in the making because of this. A stock 331 would have been a no-brainer using Egge Machine stock replacement parts, but what fun is that? I've always wanted to do a build like this...
Progress! Crank is done, including drilling the end of the crank for the bushing used with the manual transmission. Short block is ready to be assembled. In the mean time we have finally had the head flowed after one of the ports was modified. The result is below. You'll note that at .300 valve lift, the intake really doesn't flow much more than the exhaust which is a problem (115 vs. 115 stock, 123 vs. 118 ported). With the stock ports the intake and exhaust flowed the same at .300. The head porter will continue to work on whatever the restriction is in the intake at .300. If he can fix that the intake flow will probably go up across the board. The rule of thumb is that the exhaust should be between 75-85% of the intake. That is what the red and green curves depict. If the blue line can stay between the red and green lines, this aspect should be optimized. At .600 a SBC 462 casting is at about 218 on the intake and 137 on the exhaust. The stock exhaust was about equivalent to the SBC, but the intake is where the work is really needed. I'll post again as soon as the results of the additional work on the intake port has been completed and flowed.
It would be great to see some pics of the port work. I recently tidied up the ports on my 390, and although the head guy told me I had done a great job, it would be good to see what a pro does. You can see pics of my amateur headwork if you click on the 1959 link in my signature
Dimadee, looks like you are doing some great work! I will certainly post photos once the portwork has been completed. In case you can't tell, I have a great interest in data, that's why I bothered to get the stock ports flowed for comparison purposes and make all these graphs. The porter told me that cutting the back of the valve might help and I figure that reducing the diameter of the valve stem might help too, but not sure if the valves have enough meat to do that. If they can solve the intake restriction at .300 lift the flow bench testing will have been very worthwhile I think.
Final Porting Flow Numbers 390 Head by c322348 posted May 10, 2016 at 1:06 PM The head porting is finally done! You can see the numbers in the illustration above. The biggest concern was that at .300 lift the intake and exhaust flows were nearly identical. The exhaust flow should be between 75% and 85% of the intake flow according to the "experts." The porting was able to get it to 87.5%. The blue line is the actual intake flow, the purple line is the actual exhaust flow. The red and green lines may be confusing, but they show the upper and lower limits of the 75% - 85% range; that's where you want to be. As long as the blue line is in-between the red and green, flow rate is optimal. To recap, the engine is a 331 block with an offset ground 390 crank using SBC blower pistons (to get a piston pin height in a useful range). The block was decked .060 to achieve a -.010 deck clearance which will yield a .030 quench height with a .040 thick gasket. Displacement will end up at 399 cubic inches with a 3.910 stroke, 4.030 bore and 7.100 BBC rods (bushed to SBC piston pin diameter with the big-end narrowed to fit the crankshaft journal). All this will result in a 10.7:1 compression ratio. The application is a 2600 pound sports car. The power will go through a 3-speed '37 LaSalle top-shift trans and back to a 1950 Ford rear. It would have been a lot easier to use a 390 block, but I wanted to use a 1953 331 block like the car was originally built with. We've already got a Steve Long custom cam and we're picking out some better than stock valve springs. Final assembly should begin soon! I'd like to run the engine on a dyno, but I might need to borrow a better intake manifold. The fabricated manifold I plan to eventually use may be a bit restrictive for this engine.
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