383/400 stroker - 3.90, 3.91 or 3.92 crank?

Posted By: YYZ

383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/15/12 12:43 PM

For a low deck stroker running 6.700" rods and pistons with a 1.320 CH (Diamond flat tops) - what should the crank be ground to for final stroke?

I've seen both 3.91 and 3.90 used a fair bit, but if I'm doing the math right (and there's a good chance I'm not)

With 3.90 stroke:

1/2 stroke: 1.95"
plus rod: 6.70"
plus piston: 1.32"

Gives 9.97" against a 9.98" deck height, so all things being equal, the pistons will be .010 down in the hole

With 3.91 it goes to .005 down in the hole and 3.92 should be zero deck

So without going into major block work/measurement, which is the best choice to keep both compression up but also a margin of safety for stretch/expansion of the reciprocating assembly?

Heads will be open chamber - worked 346s

Thanks in advance

gives

Posted By: CompWedgeEngines

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/15/12 12:49 PM

You have no intentions of decking or correcting the block deck?

Posted By: sr4440

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/15/12 01:04 PM

Without all the info, how do you expect to make an informed decision? Get the block corrected, then you will have your answer.

Joe

Posted By: gregsdart

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/15/12 01:36 PM

Quote:

Without all the info, how do you expect to make an informed decision? Get the block corrected, then you will have your answer.

Joe

If you are expecting a good level of performance and anti knock resistance from this build, measuring and doing it right is the only way.
If you are running flt top pistons and will not have any quench, then you can figure compression with a deck of 9.98 and your compression should be close or less than calculated and if you chose you can live with what you get. If it is still a little high you can band aid it with a thicker gasket. There are large bore gaskets in .040 and .051.

Posted By: 67_Satellite

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/15/12 02:01 PM

Since you're asking "what the crank should be ground at", I'll assume you're using a factory crank. When I had mine done,due to the indexing of the factory crank I started with, 3.908 was all the machinist could get without going to a .010" U.S. B.B.C. bearing. Could have gotten more stroke with an undersize bearing,but I thought material left for future machining/freshening was more important than a few thou, extra stroke.Your particular crank may allow more or less depending on what it was originally ground at. Whatever stroke you end up with, machine the block to set the deck height to the desired level after a mock-up and measure session. The factory didn't always hold the decks equal side to side or end to end back in the day.

Posted By: MR_P_BODY

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/15/12 02:56 PM

Have a shop check the deck first... that will give
you a idea what you have and the decision will be
alot easier... you would be suprized how bad some
of the decks are

Posted By: YYZ

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/15/12 04:22 PM

Thanks everyone for the input

The goal was to tread the line between budget stroker vs full-on build and see what's involved

Crank is a new MP 3.75" stroke for B engines

Scenario 1 would be to low-budget - keep the 3.75 stroke, use a reconditioned set of LY rods bushed for the .990 pins and just screw it all together and hope for the best

Scenario 2 is to maximize stroke with the same crank, turn down to 2.200 rod journals and go through the rest with a fine toothed comb. Which appears to be at least a few K more

Posted By: Thumperdart

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/15/12 04:45 PM

I must be the only guy running a 3.900 stroke w/a 413 crank and 6.385 rods. Can`t tell ya any more as far as pin height etc. but almost 13 years later and all`s good.

Posted By: jafr

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/15/12 05:19 PM

More than lkely you will end up with a deck less than 9.98 I have seen blocks that need .020 or more cut to square things up. You need to square deck the block. The deck heights from the factory are all over the place. Decking it will get rid of alot of the chamfer on top of the deck, give you a nice flat surface for the gasket to seal and equalize the height of all your pistons for quench. I have a 470 on the stand for a backup and it runs very well for for it's size.
My opinion is to run the quench as tight as you safely can, this will make more power and reduce the chance of detonation. On a big bore like a 4.375 I think .040 is safe and on a small block I think you can tighten it up to .035 without seeing witness marks on the pistons or heads.

Posted By: JohnRR

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/15/12 05:28 PM

Quote:

You have no intentions of decking or correcting the block deck?

DING DING DING ... WINNER .

Vlad, my crank is 3.895 stroke with that rod and piston CH combo, but that was for other reasons .

Get the block squared first , find out what the deck is and cut the crank to put the piston somewhere between 0 and .005 in the hole .

Posted By: Cab_Burge

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/16/12 04:42 AM

With iron heads and pump gas I would shoot for 9.5 to 1 or less compression ratio

With aluminum heads I'll settle for 10.5 or less on pump gas with 10 to 15 % Ethanol

The 3.90, 3.910 strokers like to rev, in a B or RB motor, the last one I built had a set of B1-BS heads with CNC porting to M.W. sizes, it made 720 HP at 7000 RPM and was still climbing in HP at 7000

the ciustomer siad to stop the pulls at 7000 RPM because he is a bracket racer and wanted to keep the revs. under 7000 RPM

Check your cylinder heads CC and go from there

I have another stock Mopar 440 crank offset ground to 3.90 stroke for another 440 mild pump gas street build with a set of large valve ported 452 heads, I'm shooting for 9.5 to 1 on it

I'm going to use a 7.100 long BB Chevy type rod with Icon # IC-838 pistons, looking for 9.5 to 1 comp. ratio with decent quench

Posted By: Belvedere1

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/16/12 04:52 AM

Be prepared to spend some extra $$ on getting that crank to balance and cutting the counterweights for clearance. I hope yours works out better than mine did.

Posted By: 440Jim

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/16/12 03:30 PM

Quote:

Be prepared to spend some extra $$ on getting that crank to balance and cutting the counterweights for clearance. I hope yours works out better than mine did.

To get clearance of the counterweights in the low deck block, there are several ways.
1) lathe turn (round) the counterweights to about 7.25" dia, keep bobweight ~2350g
2) put large bevels on the edges of the counterweights
3) grind the clearance in the block and leave the crank about 7.50" dia

The larger the bevels, the larger dia you can leave the counterweights. The front and rear (large) counterweights will fit at a larger dia than the inner (smaller) ones.

Attached picture 7381275-Counterweight_bevel800.jpg

Attached picture 7381275-Counterweight_bevel800.jpg

Posted By: YYZ

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/16/12 03:57 PM

At this stage it's a bit of a 'what if' exercise but the point on the block is well taken.

The crank in question should not require further machining to fit the B-block as it was made with smaller counterweights and B-sized main journals for exactly that purpose. Plus an 8-bolt flange.

For turning it down if/when the time comes, being friends with a crank shop does occasionally have its benefits....

Thanks all for the great advice!

Posted By: Evil Spirit

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/16/12 08:45 PM

I'm sure this will rattle a few cages - oh well. Setting the block deck height to set your quench/combustion chamber/piston clearance is important, as eliminating mechanical interference and checking compression is again, important. Decking a block solely to square it up? More important to help make the intake seal than anything else - don't waste your time or money if you think there's "magic" power there. There probably isn't 5 HP gained by decking the block just to square it up, since most blocks aren't that far off, usually in the .010 range, and cutting only .010 off a block won't change compression enough for a big power gain. You will get the same power increase by a thinner head gasket. So if you are cutting the block to set piston to deck height - whack away. Otherwise there isn't the gain there by trueing the deck to the mains that lot of people seem to believe. I've heard of a lot of people decking blocks, but not equalizing combustion chamber volumes - HUH - whats the difference? Ones just promoted better I guess.

Posted By: Brian Hafliger

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/16/12 09:04 PM

Quote:

I'm sure this will rattle a few cages - oh well. Setting the block deck height to set your quench/combustion chamber/piston clearance is important, as eliminating mechanical interference and checking compression is again, important. Decking a block solely to square it up? More important to help make the intake seal than anything else - don't waste your time or money if you think there's "magic" power there. There probably isn't 5 HP gained by decking the block just to square it up, since most blocks aren't that far off, usually in the .010 range, and cutting only .010 off a block won't change compression enough for a big power gain. You will get the same power increase by a thinner head gasket. So if you are cutting the block to set piston to deck height - whack away. Otherwise there isn't the gain there by trueing the deck to the mains that lot of people seem to believe. I've heard of a lot of people decking blocks, but not equalizing combustion chamber volumes - HUH - whats the difference? Ones just promoted better I guess.

Piston to cylinder head quench is main reason to zero deck... .010 tolerance is unacceptable.

Posted By: JohnRR

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/16/12 09:21 PM

Quote:

The crank in question should not require further machining to fit the B-block as it was made with smaller counterweights and B-sized main journals for exactly that purpose. Plus an 8-bolt flange.

Is the crank in question a crank sold by Mopar performance in/around 2003 ? If it is have you actually tried putting it in the block ?

Posted By: RUNCHARGER

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/16/12 09:42 PM

Maybe I reverse engineer stuff. I would set it up with as much stroke as you can get with that particular crank. I would then mock it up before decking and see where it was at. Then I would decide how much to deck it.

Sheldon

Posted By: 23T Hemmee

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/16/12 09:49 PM

Quote:

Maybe I reverse engineer stuff. I would set it up with as much stroke as you can get with that particular crank. I would then mock it up before decking and see where it was at. Then I would decide how much to deck it.

Sheldon

BINGO!!! We have a winner.....

Posted By: BSB67

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/16/12 10:28 PM

Quote:

Maybe I reverse engineer stuff. I would set it up with as much stroke as you can get with that particular crank. I would then mock it up before decking and see where it was at. Then I would decide how much to deck it.

Sheldon

Me too. You'll be able to figure out if the shelving piston height will work and either move the CD around, cut the deck, or gasket it to what you want.

Posted By: Belvedere1

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/16/12 10:31 PM

That is the time frame (2002 IIRC) of when I bought mine. It was a great deal $$wise initially, but......

Posted By: YYZ

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/16/12 10:53 PM

But what?...

(and yes it is one of those cranks)

Posted By: Belvedere1

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/17/12 03:14 AM

After having to do all the extras I ended up with several hundred $$ in a brand new crank that was "supposed" to work in a B block. I think there is 5 pieces of mallory metal which is not cheap and then having the counterweights turned to clear the block, but hey, the mains were the right size at least. Like John RR, said, check it before you get too far along in the process.

Posted By: Evil Spirit

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/17/12 03:48 AM

Quote:

Quote:

I'm sure this will rattle a few cages - oh well. Setting the block deck height to set your quench/combustion chamber/piston clearance is important, as eliminating mechanical interference and checking compression is again, important. Decking a block solely to square it up? More important to help make the intake seal than anything else - don't waste your time or money if you think there's "magic" power there. There probably isn't 5 HP gained by decking the block just to square it up, since most blocks aren't that far off, usually in the .010 range, and cutting only .010 off a block won't change compression enough for a big power gain. You will get the same power increase by a thinner head gasket. So if you are cutting the block to set piston to deck height - whack away. Otherwise there isn't the gain there by trueing the deck to the mains that lot of people seem to believe. I've heard of a lot of people decking blocks, but not equalizing combustion chamber volumes - HUH - whats the difference? Ones just promoted better I guess.

Piston to cylinder head quench is main reason to zero deck... .010 tolerance is unacceptable.

Yeah, I covered THAT. But spending $100 to deck a block just because it is .010 off "square" is probably the worst $100 you will spend in a short block, because it does nothing to improve reliability, nothing to improve repeatibility (bracket racing) and is marginal at best on power increase. You would be better off putting that money towards coated bearings, piston coatings, better springs or pushrods, etc., than decking a block just to square it .010.

Posted By: JohnRR

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/17/12 02:59 PM

Quote:

But what?...

(and yes it is one of those cranks)

Have you actually tried fitting it in the block ? The best I could tell the crank was a 1053 material, Hemi 3.75 stroke replacement crank with the mains cut to fit a low deck block, the counterweights are HUGE, close to 7.5 if I remember right. I had my crank cut down to 7.200, balanced nicely after that with no metal added, 3.75 stroke in a 383 using Diamond 1.320 and I can't remember what rod, but it wasn't stock.

Posted By: YYZ

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/17/12 03:06 PM

Test fitting soon. And yes, the counterweights look huge relative to a stock 383 crank.

Given that budgets can escalate pretty quickly, staying with a 3.75" stroke and possibly the stock rod journal sizes may be the way to go.

Or does one dump the crank and start with a 3.915 stroker crank from 440source and put the money into checking/trueing it?

Posted By: YYZ

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/17/12 03:07 PM

John, on that build did you stay with the stock BB journal size or did you have the crank turned down to use a 2.200 journal?

Posted By: JohnRR

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/17/12 03:47 PM

Quote:

John, on that build did you stay with the stock BB journal size or did you have the crank turned down to use a 2.200 journal?

I ended up selling the crank before that project got finished, but it did stay with the stock rod journal size while I owned it.

It may be a wash by the time you are done if the CCJ crank needs to have the rods and mains cut undersize to fix it . the plus is it's 4340 instead of 1053 .

But also make sure the CCJ crank fits the block properly also , watch out for the crank hitting the block before the thrust bearing .

Posted By: Thumperdart

Re: 383/400 stroker - 3.90, 3.91 or 3.92 crank? - 09/17/12 04:05 PM

Quote:

Be prepared to spend some extra $$ on getting that crank to balance and cutting the counterweights for clearance. I hope yours works out better than mine did.

IIRC my 413 dropped right in my 400 block but had to be lightened for the lighter Chevy rods and pistons but don`t rmember how much and my bob weight was around 2243...........