What stroke for your Buick V6?

[KrisW]

Hey all.

I know the stock stroke is 3.400. I am asking how far you guys are going before doing some sort of block clearancing.

I know from my Jeopardy knowledge of old Buick engines that our V6 engines use nearly the same layout as the first generation Buick small block V8. The 215/300/340 engines... They are similar in block dimension, bore spacing and deck height/width. The 350 is higher/wider by a little.

The 300 uses a 3.75 bore and 3.40 stroke. The 340 uses the 3.75 bore of the 300 and the 3.85 stroke like the Buick 350. The 350 uses a wider deck than the 340 (or our V6 engines) but if the 340 can accommodate this stroke I'm wondering why our V6 blocks can't.

Or, can they?

 

[KrisW]

Anyone?

I see some 3.6xx-ish strokes out there. Can you get there by offset grinding the crank to 2 inch rod journals? and then use aftermarket connecting rods?

Help?

 

[S2V6RACER]

There is a lot of different stroke cranks out there. 3.625 stroke is very common and they were originally made that way. You can offset grind to pick up stroke, but that will result in a smaller rod journal and it is said that it weakens the crank. With the availability of off the shelf cranks for less than $400 it would be dumb to even bother offset grinding a crank now.

 

[KrisW]

Well, there you go!

Who do you recommend for the crank? Can I get one with a 3.85 stroke like a Buick 340/350 V8?

How much stroke before the block needs work?

Thanks!

 

[John Wilde]

Ken Duttweiler was talking about a 3.7 inch with me but I never finished that project.

 

[CTX-SLPR]

The 3.8 and 4.1 share with the 3rd generation SBB, the 350, not the 2nd Gen 300/340. That is the 225 Dauntless used 64-67 by GM and 67 to like 74 by Kaiser Jeep. When Buick bought the V6 design back they retooled it to share stuff with the 350 just like they retooled the 198 Fireball to the 225 Dauntless when the 1st Gen aluminum 215 was sold to Rover and Buick went with the aluminum top end 300 in '64.

 

[KrisW]

The problem with that argument is, well, just about everything.

The only thing that got re-tooled when GM bought back the Buick V6 from AMC was the bore size. They changed the block casting to give a 3.8 bore instead of the old 3.75 bore so that they could use 350 pistons on the assembly line. If you take one of the 75-77 odd fire 3.8 engines and set the long block next to the older 3.7, it's VERY HARD to see any difference. They even kept the old nailhead looking valve covers until they converted the crank to even fire! They also continued to run the smaller valves and nearly identical cylinder head castings from the 80's as well.

The odd fire crank was still retained and still kept the 3.4 stroke that had been in use since 1964. Also, the intake manifold will swap between the newer V6 engines and the old 225 from the 60's. I've done it. You can also use the odd fire HEI on the old 225 if you clearance the LF intake manifold bolt and a little of the casting.

My point of all of this is that the deck width and height is the same as a 300/340 Buick engine, not the 350. I don't know why Buick increased the deck specs on the 350 instead of just casting a larger bore on the 340 Block. The world may never know (or care.) I am only worried because I don't know if there is some sort of bad mojo in the 3.8 block if you use a 3.85 stroke. And, the point of all of this is that I want a larger Buick V6. I don't want to (and won't) run a 4.3 chevy.

If I can run a 3.85 stroke (like the 350 Buick) then that will immediately give me a 4.3 liter Buick engine. If I use it in a 4.1 block then it starts to become a monster. In my firebird that gives me a decent sized engine up front with seriously awesome handling all around.

I mean, imagine a Turbo Trans Am with a 4.6 liter Buick Turbo!!

 

[bison]

The cam location is the limiting factor in the block. Rods get too close to the cam on big stroke applications. 3.625 is the most readily available of the bigger stroke cranks for the 90 degree 6. You can play around and squeeze every last bit out of it if you want to spend a ton of $ and get around 290 ci. Ive heard of it being done but never saw it myself. What do you plan on using for a block?

 

[bison]

I don't want to (and won't) run a 4.3 chevy.

I mean, imagine a Turbo Trans Am with a 4.6 liter Buick Turbo!!

You can get 4.5 liters fairly easy with a 4.02 bore. I think you would be limited by ohter things in the f-body before you could maximize the output of a 3.8 in a TTA. Intercooler limitation, differential upgrade (a lot of extra $ on top of the cost of the engine), and a fuel system and aftermarket ecm. Id look into building a strong stock block if your goals are 10.50 or less. Beyond that you are asking for a lot and probably dont want to cut up a TTA for a fuel system and put a different rear in it.

 

[turbodave231]

You are much better off increasing displacement by going with a larger bore than a larger stroke. Longer strokes cause more rod angularity and stress. The piston will also rock in the bore more with larger strokes.

Larger bores promote airflow by unshrouding the valves.



I am convinced that 3.625 is the practical limit for stroke these engines. At his stroke we need to clearance the connecting rods to clear the camshaft lobes. Could you go bigger? Yes, but you would need to do some redesign work on the con rod or go with a very small base circle cam, but why?

Dave

 

[KrisW]

What do you plan on using for a block?

That question will be answered when I get my stroke problem solved.

I'm not running (or ruining) a TTA, so don't worry about that. I'm big on engine swaps, that's all. I've run Buick and Olds V8s in my third gen firebirds before and I want to do a Buick V6 this time. I pretty much have the peripherals ironed out; I know what fuel system, heads, exhaust, wiring, ECM (programmed by me, thanks to thirdgen.org) and such that I will be using.

I am not trying to get 10.50 or less. I like to be deep into the 12's and still drive to work or just drive 1000 miles to meet a friend and not worry. Like I said, I've done this with a Buick 350 and an Olds 350 in firebirds with no issues. Even the rear end is not much of an issue now that you can buy 12 bolt and Dana 60 housings for third gens from Strange.

I'll refer to my Buick Power Source manual about the bore vs. stroke issue. They do show a 4.5 liter by using a 4.1 block with the 3.625 stroke.

 

[KrisW]

I am convinced that 3.625 is the practical limit for stroke these engines. At his stroke we need to clearance the connecting rods to clear the camshaft lobes. Dave

Thanks, Dave!

This was the type of info I was looking for, all along! It also explains why I busted a camshaft all to hell in my 340 Buick small block once when I over revved it after blowing first gear in my first firebird! That has never happenned to one of my 350 engines and now I know why.

The 340 uses the 3.85 stroke, the 300 uses the 3.40. I never broke my 300 engines, either.

Okay, 3.625 stroke it is. I think I saw one of those crank forgings on ebay for 400 bucks.

I may very well use a 4.1 block but I have some 3.8's to work with as well.

Hmmm.....

Thanks for everything, guys. You're the best and so is this site!

 

[CTX-SLPR]

2nd Gen and 3rd Gen SBB heads and cams are radically different. They changed the pattern and everything. You can physically bolt a set of 350 heads onto a 300 or 340 block but nothing lines up on the top side. You can swap the oil pans between all of them and even the V6's if you cut the nose down 2 cylinders. The 1st Gen 215 block is different so the oilpans and intakes don't cross but the heads do if you want, in fact a very popular swap is to use the '64 300 heads on the 215 block with a 300 crank. What I'm saying is that the 2nd and 3rd Gen SBB's and thier decendent V6's are pretty simular. But the fact that the 350 and the 3.8/4.1 share pistons means its been redesigned to fit. in much the same way the 350 came out of the 300/340. I can't comment on deck height. The head valve pattern is tough to say since the 300 is EI EI IE IE, the 350 is EI IE EI IE. If you pull a cylinder from anywhere on either pattern you can get the V6 EI IE IE.

 

[KrisW]

Well, to put one issue to rest, the 70's/80's model blocks are not re-engineered radically from the 60's models. The ONLY difference is the fact that they were cast to use 350 pistons and oil passages were changed to oil through the pushrods instead of the rocker shafts. When Buick changed to even fire they started modifying the block further but the deck height did not change. The last of the rear drive Buick V6 engines still share geometry with the 300 Buick, not the 350, only difference being .050 bore difference and some slight oil passage mods.

I know the Buick Small blocks pretty well. I have been inside and out of them more than a few times. That's how I got into Buick V6's. I first started pulling them out to put Buick V8's in and then I got interested!

Anyway, the reason I was interested in this was because the V6 and the 340 and 350 use the same timing set, meaning they have the same cam to crank centerline distance. If one engine can run a 3.85 stroke with NO interference problems why can't the other?

If there are clearance issues and the V6 engines need their rods clearanced after 3.625 stroke is delivered, then I don't see a 3.85 stroke as doable.

I just can't wrap my head around the REASON that one can and one can't. The ONLY difference between the 350 and the V6 is the deck height/width. The 340 shares those specs with the V6 exactly and I HAVE had the clearance problem once and I didn't understand why. Buick must have known something was up, for two reasons.

1. They only ran the 340 for two years and then re-tooled the block for the 350. They wouldn't do that for no reason. No manufacturer will spend money for no good reason. They could have easily re-cast the 340 block for the 3.8 bore and made their 350 with much less expense.

2. When Buick wanted a larger V6, they re-tooled the block instead of using their already proven setup of 3.8 bore x 3.85 stroke of the 350. They made a one off block with a one-off bore size instead of re-using the 3.85 stroke stuff that they had around for the 350, which they discontinued. They didn't use different heads or anything, so why?

I suspect both questions have the same answer. Something about the block specs of the 300/340/V6 engines will not support the larger 3.85 stroke. The re-done 350 block will.

I may never know the real reason Buick did this. What I do know is that I can run a 3.625 crank in my engines, and I will!!

Thanks again for the help!

 

[CTX-SLPR]

GM said that all divisions will have a 350, only reason for the 350. I guess Buick decided to change the valve pattern for some reason at the same time, that's probably the answer to why they didn't redo the 340.

Theory on why the 350 will support the larger stroke, counterweights. They tried stuffing a 350 crank into a 300 and there was rather serious counterweight clearance issues and it put the rod bolts very near the cam. If you are a member on Database Error do a search for 350 crank in a 300 and there is some of the documention from D&D linked there. KendallF (secondhand six racing) had a 3.675 crank I think that he had dug up somewhere but he had to do a ton of oilpan rail and other cylinder case grinding to fit it in. I also believe that there is no way it would clear a stock oilpan rail oilpick up gallery and required an external pickup.

Edit: Looks like V8Buick has been hacked or something.... its down right now

 

[KrisW]

That is great info, thanks.

I am sure the re-arranging of the valve pattern had to do with keeping in line with the new big block engine and leaving behind the pattern of the old nailhead for good.

I am definitely going to use a 3.625 crank. Nothing bigger. I don't want to go nuts. I just want the largest displacement to start with before I get to the boost.

Thanks for everyone's help.

 

[bison]

That is great info, thanks.

I am sure the re-arranging of the valve pattern had to do with keeping in line with the new big block engine and leaving behind the pattern of the old nailhead for good.

I am definitely going to use a 3.625 crank. Nothing bigger. I don't want to go nuts. I just want the largest displacement to start with before I get to the boost.

Thanks for everyone's help.

For you desired performance level you dont need anything but a good running stock engine. 12's are so easy they could be had in a few hours with a fuel pump, chip, tires, and a little driving experience. Good heads, proper cam selection, the right turbo, and proper tune will do a lot more than just increasing displacement. Unless you want to do both but if your considering a stock block (especially an un-girdled one) then i dont see any reason to use anything other than the stock stroke OEM crank. Do some more research on here. There are several stock crank cars that have run over 135mph at 3600 lbs.

 

[KrisW]

Thanks for the advice.

I am doing this engine in stages as I strengthen the car. The first stage will be an N/A engine while I get the transmission/rear/frame/suspension ready. Next will come the forced induction.

Besides, if 12's are so easy with a stock 3.8 in a 3rd gen, then maybe I'll do 11's with a 4.5!!

It's certainly okay to be faster!

I also want the extra cubes to help compensate for my lack of racing experience. Add to that the fact that I'm running a frowned upon standard shift transmission (I hear turbo guys stick out their tongues at those) and a little extra displacement will go a long way.

Thanks again; I will certainly be soaking up as much as I can as I put this thing together!

 

[PHILBUILT65]

the odd fire 75 motor was a direct coppy of the 225.with the exception of the 3.8 bore rod journal size of 2.0 in but people complained about the un even exhaust note so the simple solutoin is to split the crank pin 30 degrees.this allowes a 120 split for even fireing.the idea came from the 305cid v6 engine of the mid 60s that came in the gmc pickups.also v6 detroit diesels of 1942 to present era. due to the split pin design cross section was reduced to an unsafe level ergo the 225 crank pin diameter more overlap.now the rod big end diameter interfers with cam lobes.3.625 is about the practical limit of stroke without special cam lobe sizeing. more stroke reduces the overlap and weakens the crank. buick says 2.99 is practical for 11k rpm limited by piston speed 3.625 is limited to 8800 according to my buick book.

 

[PHILBUILT65]

btw the 350 uses 2.00 crank pin diameter and the piston speed is a bit high at 6200