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#1544593 - 12/07/13 09:30 AM another 3.79 vs 4.00 vs 4.125 sb stroke comparisons
mopar dave Offline
master

Registered: 01/04/07
Posts: 2726
Loc: flint michigan
just getting some ideas on paper for next rebuild for the 408 and would like some opinions from the guys in the know on this topic.
current 408 uses 230cc port indy head with 11.4 comp and an indy intake for induction.
3.790
1.895stroke
1.250ch
6.400rod
1.688rod ratio

4.000
2.000
1.250ch
6.300rod
1.575rod ratio

4.125
2.062
1.250ch
6.250rod
1.515rod ratio

pistons will be mahle and most likely a custom piston. flat tops for the 4 and 4.125 stroke but a 4cc dome for the 3.79 to make about 13:1 comp on all 3 combos and using a 927 pin. i'd like to have my forged eagle crank offset machined to make to stroke I need. my whole objective here is to build something that will get to the other end of the track the quickest. which would best and why? or would it be best to just rebuild the 408 with 13-13.5 comp and be done? all opinions welcomed. thanks

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#1544594 - 12/07/13 09:39 AM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: mopar dave]
b1dartsport Offline
super stock

Registered: 02/14/05
Posts: 858
Loc: western pennsylvania

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#1544595 - 12/07/13 09:40 AM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: mopar dave]
MR_P_BODY Online   content
Master

Registered: 06/13/03
Posts: 44361
Loc: Romeo MI
Dave... my W-9 heads are about 275 cc runners so I
have to turn up the revs to make them efficient but
I like the revs... depending on the bore I think I
would go with more stroke to make the torque and then
you could cut down on the revs... JMO
_________________________

W-9 9.08 @ 149.6 NOW ON E-85
Mike "Raff"...(180)Watching over us
CAR IS FOR SALE

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#1544596 - 12/07/13 09:40 AM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: mopar dave]
mopar dave Offline
master

Registered: 01/04/07
Posts: 2726
Loc: flint michigan
also, pistons will be about 450g and will use a roller cam in the .700 lift range. i'm thinking the shorter stroke will eliminate some side loading and with a longer rod for better rod/stroke ratio may produce better power and help the block last longer than a 4.000" stroke.
the 4.125 stroke should make better torque which I need as my best 60' with 408 has been a 1.45. but with a 6.250 rod would give close to same r/s ratio as my current 408 with a 6.123 rod.

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#1544597 - 12/07/13 09:44 AM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: MR_P_BODY]
mopar dave Offline
master

Registered: 01/04/07
Posts: 2726
Loc: flint michigan
mike, that's entered mi mind also. another thought was maybe my heads cannot keep up with my 4" stroke because of the faster piston speed and the 3.79 would slow it down and get a better cylinder fill.

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#1544598 - 12/07/13 09:48 AM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: mopar dave]
MR_P_BODY Online   content
Master

Registered: 06/13/03
Posts: 44361
Loc: Romeo MI
Quote:

mike, that's entered mi mind also. another thought was maybe my heads cannot keep up with my 4" stroke because of the faster piston speed and the 3.79 would slow it down and get a better cylinder fill.




Thats what I dont know... what runner can handle what
piston speed... being that mine are a fair bit bigger
and I have the short stroke my peak torque is at
6200 rpm
_________________________

W-9 9.08 @ 149.6 NOW ON E-85
Mike "Raff"...(180)Watching over us
CAR IS FOR SALE

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#1544599 - 12/07/13 09:52 AM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: mopar dave]
Dunnuck Racing Offline
mopar addict

Registered: 03/18/07
Posts: 3292
Loc: Northern Indiana
Don't get too caught up worrying about side loading. Here is a piston from my 4.125 stroke with 6.250 rods. 5 seasons and almost200 dyno pulls later.

Keith


Attachments
7950217-IMG_20131022_174715-1.jpg (112 downloads)

_________________________
www.dunnuckracing.com

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#1544600 - 12/07/13 10:09 AM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: Dunnuck Racing]
mopar dave Offline
master

Registered: 01/04/07
Posts: 2726
Loc: flint michigan
wow those look good with that stroke. just seems like a 3.79 and with a 1 688 r/s ratio would eliminate friction and binding to possibly make more power with a small head than a 408 and make the stock block last longer. the factorys use the 3 3/4 stroke in a lot of different engines for a reason and there's a lot of fast motors out there using that stroke. almost like a magic stroke, that's why i'v been stuck on that stroke, but i'm open to all opinions or info here. currently my peak hp is at 6600rpm using a 260/269@50 .700 lift roller.


Edited by mopar dave (12/07/13 10:11 AM)

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#1544601 - 12/07/13 01:18 PM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: mopar dave]
FastmOp Offline
master

Registered: 01/20/03
Posts: 3543
Loc: Hot Rod Ridge
Bottom line




There's no replacement for displacement

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#1544602 - 12/07/13 01:21 PM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: mopar dave]
Darryls-Demon Offline
super stock

Registered: 01/13/08
Posts: 776
Loc: Glendale Az
This is an interesting thread. I am kind of in the same boat I have an X-block and a pair of 59 degree W9 heads. Thinking of going with a 4.125 stroke and hoping the block will go 4.100, but my car is a street-strip deal and I like to run 3.73s in the car.


Attachments
7950503-DragWeekandvaction2013041.JPG (61 downloads)


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#1544603 - 12/07/13 02:19 PM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: Darryls-Demon]
MR_P_BODY Online   content
Master

Registered: 06/13/03
Posts: 44361
Loc: Romeo MI
Quote:

This is an interesting thread. I am kind of in the same boat I have an X-block and a pair of 59 degree W9 heads. Thinking of going with a 4.125 stroke and hoping the block will go 4.100, but my car is a street-strip deal and I like to run 3.73s in the car.




Put a gear in it with OD.. best of both worlds
_________________________

W-9 9.08 @ 149.6 NOW ON E-85
Mike "Raff"...(180)Watching over us
CAR IS FOR SALE

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#1544604 - 12/07/13 02:51 PM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: MR_P_BODY]
Darryls-Demon Offline
super stock

Registered: 01/13/08
Posts: 776
Loc: Glendale Az
Quote:

Quote:

This is an interesting thread. I am kind of in the same boat I have an X-block and a pair of 59 degree W9 heads. Thinking of going with a 4.125 stroke and hoping the block will go 4.100, but my car is a street-strip deal and I like to run 3.73s in the car.




Put a gear in it with OD.. best of both worlds





I have looked into doing a OD unit. Looks like one would cost around 3000 dollars and add weight to my already too heavy car.

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#1544605 - 12/07/13 02:57 PM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: Darryls-Demon]
MR_P_BODY Online   content
Master

Registered: 06/13/03
Posts: 44361
Loc: Romeo MI
Quote:

Quote:

Quote:

This is an interesting thread. I am kind of in the same boat I have an X-block and a pair of 59 degree W9 heads. Thinking of going with a 4.125 stroke and hoping the block will go 4.100, but my car is a street-strip deal and I like to run 3.73s in the car.




Put a gear in it with OD.. best of both worlds





I have looked into doing a OD unit. Looks like one would cost around 3000 dollars and add weight to my already too heavy car.




I went with the 518 which is MUCH less but does add
weight... the GV is lighter with a 727 than the 518
but it is $3000 plus the drive shaft... I'm sure you
can find a few places to loose the weight
_________________________

W-9 9.08 @ 149.6 NOW ON E-85
Mike "Raff"...(180)Watching over us
CAR IS FOR SALE

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#1544606 - 12/07/13 03:10 PM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: MR_P_BODY]
1967dartgt Offline
master

Registered: 10/23/07
Posts: 2920
Loc: Hilltown Pa
How long is the GV unit? Would you get in to driveshaft angle problems on a A body .

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#1544607 - 12/07/13 03:17 PM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: 1967dartgt]
MR_P_BODY Online   content
Master

Registered: 06/13/03
Posts: 44361
Loc: Romeo MI
Quote:

How long is the GV unit? Would you get in to driveshaft angle problems on a A body .




Its only like 6" long and the angle hasnt been a issue...
plenty of the DW guys run the GV... my 518 is probably
a bit longer than the 727 and GV... but when I set
up the engine and trans in the Rampage I set it so
it was pointed straight at the pinion then rolled
in the pinion angle
_________________________

W-9 9.08 @ 149.6 NOW ON E-85
Mike "Raff"...(180)Watching over us
CAR IS FOR SALE

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#1544608 - 12/07/13 03:58 PM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: Darryls-Demon]
mopar dave Offline
master

Registered: 01/04/07
Posts: 2726
Loc: flint michigan
4.100 might be pushing it on the bore with that stroke. I was thinking 4.040 bore for strength and .060 over would be max. i'd like to get some input on this topic from someone who has tried these different crank combos on a dyno or at the track to get some more real world info. don't want to spend a bunch of money on extra machine work to only find out it runs no better than my currnet 408. Andy, you out there? any other engine builders that can add to this?

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#1544609 - 12/07/13 05:54 PM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: mopar dave]
B3422W5 Offline
master

Registered: 01/20/03
Posts: 8669
Loc: Portage,michigan
Personally, with the heads you have, or W5 heads like I ran, I think the 4 inch crank is plenty, and well suited to both making power, torque, and longetivity, and reliability.
Bigger the bore the better. I also like the longer rod, ran a 6.300 rod.
At 4.100 bore the CP domes were only a hair over 400 grams.
Bumping your compression up like you are talking about with a 4 inch stroke and correct matching components will make more than plenty of torque to make your car 60 foot plenty good.
I know it can be done. I would strongly suggest a better block than you are using so you can reliably run a bigger bore, sticking with your current stroke,and calling Dwayne Porter and having him spec you out the proper roller cam once you get a good shortblock put together.


Edited by B3422W5 (12/07/13 05:56 PM)
_________________________
71 Duster with 323" magnum. Pumpgas, iron heads [Email]231@50[/Email] hydraulic cam, 3415 race weight. 11.79@ 113.37 so far . More to come.

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#1544610 - 12/07/13 10:49 PM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: B3422W5]
1967dartgt Offline
master

Registered: 10/23/07
Posts: 2920
Loc: Hilltown Pa
I used to run a 4.09 bore and a 4 in crank in a stock block with a .620 roller and 12 to 1 compression with Indy 245 heads. It went 9.90s on motor and lived many years.

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#1544611 - 12/08/13 01:59 AM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: mopar dave]
mopster Offline
member

Registered: 12/09/04
Posts: 125
Loc: Finland
With 3.79" stroke your rpm range will be about 350 higher, and with 4.125" stroke 200 lower. What is best for you depends what rpm range works best with the rest of the combination. Your chassis and the track you race has also a great meaning to this. If you can handle more torque without hooking issues you will most likely be faster with more sroke, assuming the rest of the combination is optimized for that stroke. However, the difference might not be much, and your money could be better invested in somewhere else.

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#1544612 - 12/08/13 07:07 AM Re: another 3.79 vs 4.00 vs 4.125 sb stroke comparisons [Re: mopar dave]
Raymond Offline
member

Registered: 09/14/09
Posts: 49
Loc: Maryland, USA
I have the 3.79 with the 6.4 rods in a w5
motor. N/A the motor made about 700 h.p.
Now with a single turbo it dynoed at 1027 rwhp.
If you are interested i have two sets of mahle
power pack flat top piston for this combo.

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