SBC rod stroker trick on a NA stock crank

[CTX-SLPR]

Howdy,

First, no this is not a turbo motor question. Thinking about a new motor for my Engineering mule car. Was thinking the SBC rod and 4.000in bore piston trick on a 4.1 for more cubes. Any reason this would be reserved for the forged cranks only?

Thanks,

 

[novaderrik]

what is the "SBC rod and 4.000in piston trick" you speak of?
are you talking about using cheap and readily available Chevy pistons and rods in a 4.1?
if so, please, tell me more, since i've got a good pile of SBC parts laying around...

 

[Nasty Wendy]

Because we have split journal cranks the power made by the first 5 cylinders has to be tranmitted through that relatively small segment that connects the no5 and no6 journal. Because our Buicks have 2.25" rod journals this adds significant strength to that journal. When you grind them down to increase stroke and use the Chevy rods you take away meat in the area that can least afford it. Forged cranks being stronger handle this much better than stock cast cranks ever will. And I'm sure you aren't stroking it to make less power.

 

[CTX-SLPR]

First off... I think you mistake my purpose, both of you. Nova, this is definately not for the turbo motor crowd with the stock crank. I believe Bill Anderson was marketing a stroker kit based around an offset ground Eagle forging and some sort of piston combination. I had just bought my custom Diamond Racing forgings for my 4.1 so I had no interest since it would have mean selling them and loosing on the investment.
Wendy, I don't plan on throwing much power at this, 200hp probably tops. I'm more after more low end torque than I am total power. Even a full stripper with aluminum hood, decklid, coresupport, bumper braces, and drums is still not the lightest of cars. I'm just interested in getting more usable power for daily driving, this thing will be a commuter, not a racer. I can see your point which is why I asked. Grind them down to the large journal 2.1 and use long rods and some cheap dished pistons for around 9.0 compression for running on cheap gas.

 

[Nasty Wendy]

I have never done this so I can't give you any experienced based advice. I feel that you are asking for trouble though. Making more torque equates to putting more stress on the crank. A 9.0:1 NA engine maynot have enough umph to hurt it but again I've never done it.

 

[fuzzyGN]

If all you are doing is a simple low power N/A engine I can't imagine all that work and expense would pay off. Here is another idea though. Find a set of 3.0L rods. They are 6.33 in length vs. the stock 5.96 in length. Then with a 4.0" bore and small end busing to match the smaller pin, an off the shelf 383 stroker piston with work. Even a flat top piston will give somewhere around 9.5 to 10:1 CR. Of course it all depends on what deck height and CC of the heads come out to. This will take the piston weight from stock at about 800 grams to somewhere near 450 grams. Then there is the smaller pin. The Buick pins are REALLY heavy compared to a SBC. You can take a few pounds off the reciprocating assembly by doing this. This will make for a much easier and less expensive build.

 

[novaderrik]

If all you are doing is a simple low power N/A engine I can't imagine all that work and expense would pay off. Here is another idea though. Find a set of 3.0L rods. They are 6.33 in length vs. the stock 5.96 in length. Then with a 4.0" bore and small end busing to match the smaller pin, an off the shelf 383 stroker piston with work. Even a flat top piston will give somewhere around 9.5 to 10:1 CR. Of course it all depends on what deck height and CC of the heads come out to. This will take the piston weight from stock at about 800 grams to somewhere near 450 grams. Then there is the smaller pin. The Buick pins are REALLY heavy compared to a SBC. You can take a few pounds off the reciprocating assembly by doing this. This will make for a much easier and less expensive build.

this is the kind of stuff i love reading.. hot rodding at it's finest.
has this combo ever actually been built, and if so, how hard was it to balance?
what cars would i find the rods in?
i'm thinking an off the shelf reverse dome piston would get the static compression down (while keeping the quench nice and tight) to where E85 could be used with 15psi of boost for one hell of a potent street/strip combo.

 

[fuzzyGN]

I have gathered all the parts but have yet to actually build it. That could prove to be the real trick; the balancing. With that much weight taken off the rotating assembly, it could make the crank swiss cheese. Although if you were to leave it external balance, then one could attack the weights on the flexplate and balancer first and then go after the crank for final fine tuning. I don't really know how hard it would be to make it internal balance. The biggest problem with the 4.1 block is the deck height. Even the stock piston is somewhere around .080" in the hole. With this trick, it would lower the DH some but it would still be down a ways. Also from experience with 2 different block, the decks don't tend to be very straight. One block I had to deck .025 to make it right. That one was probably/hopefully the worst. Anyway, that will decrease the deck some but we are still talking about .050". For my application, I am shooting for about 13 to 1 so I will probably have a custom piston made in a flat top and close to zero deck to take advantage of the quench. For a turbo app, you would almost have to run a reverse dome to keep the compression reasonable. With E85 though, I wouldn't be sceered to run the compression at 9 or 9.5 to 1. It would have tons of torque.

The 3.0L engines were usually in the smaller FWD cars. From what I recall, the were made in the late 80's. I don't know for sure if that engine was built into the 90's or not. I actually bought mine at a machine shop for cheap.

 

[novaderrik]

what kind of a "small fwd car" has a 3.0 in them? off the top of my head, i can't think of a GM 3.0 motor unless you are talking about the 3.1. i think Ford had a 3.0, as did Dodge.
as for the piston being down in the hole too far- why not just offset grind the crank to give it more stroke, which would push the piston up toward the deck just that much more. and for the balancing problem, look for heavier pistons that make the final bob weight more closely match the stock Buick numbers.

 

[asloan5]

as far as i can remember 85-87 small to mid gm cars ie grand am lesabre calais olds88 regal fwd could come with 3.0 buick motors

 

[CTX-SLPR]

The Buick derivative low buck 3.0 and the later 3300. The deckheight on a 4.1 is the same as on a 3.8. I just got back in town so I'm going to mess around with my engine assembly calculator as to what commonly available parts would generate on an engine setup like this.

 

[CTX-SLPR]

Better combo.
Stock Buick 3.400in stroke crank
Buick 3.0 3.633in rods
4.1L block at 9.530in deck height
KB 141 pistons (4.00in bore, 1.490in compression height,28cc D-dish, 0.9272in pin, and 555 / 145 gram piston/pin weight)
With a 0.040 gasket and 45cc heads you get 9.18:1 compression. Sounds like I found my combo. There is also KB385 which has a stepped dish and a 561 gram weight with the same elsewise.

 

[novaderrik]

Better combo.
Stock Buick 3.400in stroke crank
Buick 3.0 3.633in rods
4.1L block at 9.530in deck height
KB 141 pistons (4.00in bore, 1.490in compression height,28cc D-dish, 0.9272in pin, and 555 / 145 gram piston/pin weight)
With a 0.040 gasket and 45cc heads you get 9.18:1 compression. Sounds like I found my combo. There is also KB385 which has a stepped dish and a 561 gram weight with the same elsewise.

sounds like you found MY combo, too. now, i just need to find some donor cars....

 

[fuzzyGN]

Ah yes, the 366 piston. My biggest problem will be finding one with enough compression for my needs. A big stupid solid roller cam and aluminum heads need a lot of compression to make up for the inefficiencies. Remember, mine will be a N/A and mostly a race car. I can't remember though if I really did pursue that fully, I may have to check again. All of this really boils down to what the machined and final deck height comes out to. I originally started off with the longer rod idea to intentionally reduce the weight of the piston because they were SOOO heavy. Any weight you can remove (to a point obviously) will reduce wear and make the throttle respone crisper. I guess I figure at this point I am so deep in I may as well just do custom pistons and that way I get exactly what I need/want. One could drive themselves nuts working all the combos.

 

[unboostedV6]

......I still have those forged flattops in my basement...3.830 and 4.005...just in case ! GB

 

[CTX-SLPR]

k141, ATV Parts & Accessories, All matching items for sale.
But they are both 0.030 over.

 

[charlief1]

This thread is getting very interesting. I like the idea of using a 3.0 rod and the extra legnth will give you a better torque curve for sure. The biggest question is whether or not you can find the pistons inexpensively.
Charlie

 

[fuzzyGN]

The pistons are inexpensive but to use them, the small end of the rod would need to be bushed down. I still haven't got a solid answer from several different shops (even Scat) about if they would/could make a bushing for the Buick rod dia of .9398 to use a SBC pin of .927. If that can be done for a good price then the pistons are any SBC piston with the compression height appropriate for your CR. For a turbo app, it may yield too high. For a high compression it may prove difficult to find. But for modest compression N/A motor, about right. I was looking at the 383 pistons with a 1.425 CH which would leave the top of the piston about the same place it was to begin with. It would end up somewhere near the 9:1 range depending on parts used. Of course this was all on a 4" bore 4.1L.

 

[FJM568]

Best way probably to do that would be to open the pin bore in the rod bigger and then bush it back down so that the bushing walls would be thicker...Just don't know how big you can go on the rod safely...

Otherwise, doing it without opening up the holes bigger, you would only have approx. .006 wall thickness on the bushing, which wouldn't give it enough tension to stay installed properly...

IMO...

 

[BlownV6]

For those of you looking for most bang for the buck especially for the higher compression. I probably have around 4 or 5 Carrillo rod and JE or Wiesco piston packages I would sell for $500.00 if anyone is intrested. Mike