Odd-Fire V6s

[Inu-Hanyou1776]

A couple months ago the mother got a used car, Buick Park Avenue Ultra with the Supercharged 231 V6. I've done some research on these engines and the Buick 231/3.8L/3800 is the decendant of the 225 V6 that used to be used in the Jeeps in the 60's.

What's intrigued me is how those engines back then were odd-fire motors, and the odd-fire arrangement made them very hard to stall at low engine speeds due to the heavy flywheels needed to smooth them out.

So now I'm wondering, if I get an S10 4x4, I might just also save up afterwards and try to swap a pre-85 90-degree Chevy V6 in it, since it's an odd-fire motor too. Who in here has driven vehicles with these odd-fire engines in them? How were they? I've heard they have a pretty good rumble to them with free-flowing exhausts.

 

[mikey_d05]

Just get a heavy ass flexplate or flywheel. That way you won't have to deal with the odd-fire crap.

I know people make ridiculously heavy flywheels for 'Yota 4 bangers. My friend wants to swap one into his wheeling rig.

 

[GREENPANE]

www.earlycj5.com has allot of good info on this engine. I had a 52 chevy pickup with a jeep chassis under it. That odd fire would not stall for anything! Good little motor. I put a clutch in it and the flywheel was like 2'' thick. If I recall it weighed 75 lbs and I think there are 100 pound ones as well.

 

[Inu-Hanyou1776]

Hmm, Buick motor into an S-10. Not a bad idea I think. If I wind up with an S-10, hopefully a '75 to early '77 odd-fire 231 won't be that hard to come by. If not, I may check in over there at earlycj5.com and ask them if its possible to convert the later even-fire engines to odd-fire. GREENPANE, what about the sound of the exhaust note? How rumbly did it sound? I'm thinking the thing would have a nice, built in rumpity-rump note to it.

 

[mikey_d05]

You're missing the point, if you have a late model even-fire engine, put a heavy flexplate or flywheel on it, and you have a motor that's really difficult to stall. Why go through the hassle of trying to convert an even fire motor to odd fire? The exhaust sound?

 

[Inu-Hanyou1776]

The exhaust sound?

You hit the nail on the head. I read some too about some guys trying to make the even-fire motors run like the odd-fire ones by playing with the firing order and the camshaft (swapping in an odd-fire cam and playing with the plug-wires) and they couldn't get 'em to run. No, you have to swap in the odd-fire, common-pin crank, cam and distributor, so I'd ask on that other forum then if new odd-fire cranks can be had anywhere and whether they could be put in the even-fire blocks.

 

[GREENPANE]

They do have a deeper sound to them. I knew a guy who cammed up a 4.3V6 in a S10 and it souned quite a bit like a heathy V8. One of the best sounding V6's I've ever heard! It must have been over cammed though, it was slow! Oh, those on those odd fires you can't swap the wires on the cap if you stab the distributor in the wrong, the cam that the points ride on the distributor shaft are spaced differently. Weird stuff!
.

 

[MaxPF]

There was never any such thing as an odd-fire 90 degree Chevy V-6. The 200 and 229 Chevy V-6's were "semi-even-fire" motors. They had a crankshaft with an 18 degree split, and it gave a resulting firing sequence of 132-108 degrees (common pin odd-fire motors have a 150-90 degree firing sequence). Limiting the split to 18 degrees allowed them to keep the rod journal size at 2.10" (which is the same as a small block) without seriously weakening the crankshaft, while at the same time making the engine smooth enough that it wasn't constantly cracking accessory brackets (a common problem with the odd-fire Buick). Later, GM realized a true even-fire motor is better, and they increased the split to 30 degrees (not to mention increasing the bore to 4.00", which gave us the tried-and-true 4.3: V-6). In order to keep the crank strong with the reduced pin overlap they increased the rod journal size to 2.25". Anyways, there is no compelling reason to use an older odd or semi-even fire motor if all you want is a heavy flywheel. FWIW, the late Vortec 4.3's (98-up) are probably the best as far as their powerband goes. It's peak torque is 235 lb-ft at only 2800RPM, which is good for a 4x4. By comparison, the Heep 4.0 liter straight six made the same torque number, but it did so at 4000RPM. So much for the old "straight sixes produce more torque down low" BS

 

[resurrected_jimmy]

For what its worth I had a 64 cj-5 with a 225 and outside the frame headers to glasspacks and it would put a lot of V8's to shame. It was almost impossible to stall that engine. Mine had an 85 lb flywheel on it. In low range you could let off the the clutch and if it wouldn't move the tires would just spin with no throttle, not too hard to do with 7.00 x 16 tires I guess. You can find complete odd-fire motors for sale fairly regularly. I would go that route if I were going to attempt the swap you are considering. I have one sitting in the garage. It needs rebuilt, has a couple of burned valves. I've been saving it for a flat fender swap if I get another one.

 

[3 on the tree]

In high school (70s), my best friend had a 65 Skylark with the 225 and 3 speed. We put duals and glasspacks on it. It did sound much like a small V8. Be aware that the bellhousing pattern changed somewhere in the transition from odd to even fire. Also, Buick made a 252 cubic version, with turbo and Q Jet 4 barrel that they put in Rivieras.

 

[marv_springer]

hopefully a '75 to early '77 odd-fire 231 won't be that hard to come by.

Yes it is....

There's another problem. The better flowing heads come on 79 and later 231/252's. They work waaayyyyy better than the older ones. I believe the 79 heads could only be put on 77 & 78 blocks, and not 75 & 76's.

I was real heavy into the odd fire thing years ago. I thought the common pin crank was stronger, and so I mixed a 77 block & bottom end w/ ported 80's heads, hot hyd cam, 350 pistons, and shafted rockers. It was a durable sand dune motor for my 67 CJ5 that ran to 7k rpm more times than I can recall.....

Still..... I can think of no reason that an odd-fire engine would be more resistant to stalling @ low rpm.

Marv

 

[mikey_d05]

Still..... I can think of no reason that an odd-fire engine would be more resistant to stalling @ low rpm.

Marv

The 75 lb. flywheel.

 

[marv_springer]

agreed...... I guess I was saying I think it's the flywheel not firing order.

Marv

 

[mikey_d05]

Yeah, that's why people offer heavy ass flywheels for Toyota's. It gives the motor a ton of rotating mass which sucks for accelleration, but does wonders to keep it moving.

 

[MaxPF]

The Chevy V6 is still a better motor than the Buick V6. Not to mention the fact that it has a regular Chevy bellhousing pattern, so any smallblock bellhousing will bolt up.

Like others have mentioned, there is nothing stopping you from putting a heavy flywheel on a 4.3 V6. Not that you need it, since the 4.3 makes more torque than any Buick 231. Now, if you really want an odd fire motor, here's what you do: Call up Lunati, Callies, or any of the other crank manufactirers and order yourself an odd fire crank for the Chevy V-6. Get one with a 3.75" stroke (they will make it in whatever stroke length you want). Then call up Pace performance and order yourself the siamesed V6 Bowtie block. Have it punched to 4.125", get an appropriate set of pistons and rods, and get an odd fire cam from Comp Cams (196 intake, 206 exhause duration at .050" lift). Get yourself a pair of late Vortec V6 heads, have steam holes drilled in em (like 400SB heads) and slap em on. Viola: now you have a 300 cubic inch odd fire V6 that makes around 300+lb-ft of torque Add a heavy-ass flywheel, and your good to go.
Yeah, it wouldn't be cheap, but hey, it's only money

 

[oldtoyboyd]

GM Performance use to sell a cam, crank and a distributor in a odd fore setup for the 4.3 . It was used in racing setups if I remember correctly.
Daniel