Guys,

I was looking at building a 383 and using the cola 3.8" Stroke Crank. I have heard that it is a nice crank to use for a stroker. What are the advantages/disadvantages of using this crank for a stroker motor?

Brandon

 

Well with a .030 overbore it will actually be a 388.

I don't think you will find much in the way of pistons meant for that stroke so you will likely be left using regular "383" pistons and have to cut as little as possible off the block square decking it, actually be best if you could find a block with a very deep deck height some guys have found stockers where the piston is down .030+ in the hole where most I have seen were more like .025 and with this crank and a standar .030 piston that would but you at a zero deck without getting to machine the block square and true.
Have to watch head gasket selection too, where most of us use thin ones I think you will endup at zero deck or maybe slightly above and using a Felpro .039 gasket.

This crank is a nice one but the stroke is odd because GM used it to sell new "383s" actually a 382 with a standard 4.00 bore, not the overbored used engine .030 usually used.

 

Look in the GM performance parts catalog, they have about 6 pistons to choose from for it (different bores etc)

The cola crank is a top notch piece.

 

So if i use this crank, i wont be able to machine the block square and true. I will already be at zero deck height?

Brandon

 

No, what he is saying is to use standard 3.75 stroke pistons you'll have to get the block decked to "zero" so that they are not so far in the hole at top dead center. you figure the 3.80 stroke is .050 longer thn a regular 3.75 stroke. The stock deck height is 9.025 "zero" decking makes it a square 9.00 inches, with a zero deck you'll still have .025 in the hole at top dead center with a standard 3.75 stroke piston.

Now a real thin head gasket will make it workable , say a .030 or .028.

 

I don't have the GMPP catalogue handy and the PDF wont load page 244 like I want, are the choices actually good ones?

.026-.029 gaskets are very commonly used on the LT1, I would call the Felpro .039 thick. Probably going to want to aim for .035 or better quench so a zero deck with the Felpro piston or even .005 out of the hole should be OK. But zero deck and use a .029 gasket and you are taking chances.

 

WS Sick, NO he's actually on the right track here. I know this can all be a bit confusing but, since the 3.80" stroke crank is +.050" longer stroke, (and, hence, +.025" longer "throw"), than the 3.75" crank ....... using pistons with a "compression height" designed for a 3.75" crank ..... will put the piston +.025" higher in the bore. Using the 3.80" stroker crank with pistons designed for a 3.75" stroke crank .... will put the piston at zero deck height at 9.025" from the crank centerline. Got it?

 

I did a search and i found this post. I read through the whole thing but i am not sure i fully understand.

https://www.camaroz28.com/forums/sho...light=cola+3.8

Right now i have an unmolested factory 2 bolt main LT1 block and i am about to purchase a Cola 3.8" Stroke crank. What do i need to do to get this thing to work?

 

I think I sounded a little more discouraging than I intended.

Is there a rotating assembly in the block you plan to use?? If so bring a few pistons to TDC and try using straight edge and feeler gauges to guestimate how far down in the bore the pistons are, near the center of the piston to minimize the impact of rocking on the measurement.

Hopefully it is at least .025 down. You would just need to talk to the shop about taking off as little material as possible to square deck it and the pistons may well endup slightly above deck and that will have to be figured in when choosing a gasket.

If the shop just blindly took it down to the usual 9.00 to get a zero deck than that could be a potential problem as I am not sure how much it is safe to have the piston out of the hole.

 

You're right, my mind was working backwards today.....lol

The pistons I've seen in the GMPP catalog were all flattops and were a hyper material. Good for street, but not all out.

 

Have you purchased the 3.800" Cola crank yet? Nothing wrong with that crank but you should know that it will need 3 or 4 slugs of heavy metal for the balance if you want to use the LT1 style neutral crank damper. That crank from GM is designed for use with a weighted damper.

That 3.800" stroke is kinda neat. Already mentioned but that will put your piston top right at 9.025" if you use a rod/piston combo designed for a 383 stroker (3.800"/2 = 1.90 + 6" rod + 1.125" piston = 9.025"). So minimize the amount of block decking. If your block ends up at say 9.010" deck height then your pistons might be 0.015" out of the hole. The you'll need a mighty thick head gasket and Cometic makes them any size you want.

Karl Ellwein

 

I looked at the same build myself, but the cost of balancing it for a lighter bobweight ultimately led me to a 396 with a bit more displacement.

The cola units seem to get good reviews and go for a sweat price compared to other forged units.

If I recall correctly, my calculations were for a thin 0.029" gasket, block decked to 8.980", and 396 pistons (0.010" in the hole). Alternatively, you could shave the block more and get a thicker gasket I suppose.

The other plan was a stock block (9.020"-9.025"), 383 pistons (flush to 0.005" out of the hole) and a normal 0.039" Felpro gasket. If you can get a straight and level stock block this is defintely the better solution IMO. I actually had a very low mile "warranty" block from a local who pulled it at 200 miles to swap in a stronger engine. Just got rid of it however when putting in the 396.

Nice part about the longer stroke of course is the ability to go with less bore and still get the displacement boost for low rpm grunt... nitrous guys and high-rpm guys both like that idea.

 

The block is bare right now. I disassembled everything a few months ago. I work in a machine shop so i have access to all kinds of inspection tools but since there is nothing in it, i cant really use your method of seeing how far in the hole the piston is.

The block hasnt had any machine work done to it yet. I think i have almost made up my mind to go ahead and purchase the crank. I think its a very nice piece and there are ways to make it work even if im not at the theoretical 9.025".

I am planing on using this with 6" rods, "383" pistons and ported factory casting heads. A custom grind .600" lift cam and all the other necessary parts. Want to have a pretty strong NA motor that will probably see some spray in the future.

Am i going in the right direction to a good build?

 

With access to tools like that I think you should be able to measure deck height without a rotating assembly in it, but yeah I think this will work well. Just like I said the shop has to be aware and not wack the block down to 9.00 like they do with most other builds.

 

so is deck height the measure from the centerline of the crank to the top of the block?

once i get this measurement...where do i go from there?

I still need rods, pistons, rings, bearings, splayed caps, etc.

If you need more info about what my goals are just ask as i dont know where to start or what exactly what you need to know.

Thanks for all the help so far!

Brandon