3.785 stroke verus 4 inch stroke

[fishman]

I have been hearing mixed opinions on a sbc build i want to do...some people tell me not to do the 4 inch stroke only go to 3.785 stroke as the 4 inch stroke causes issues like a diffrent oil pan and pistons sticking out to far..............can i get everybodys opinion before i decide to make a 421ci pump gas motor or a 434ci pump gas motor and making around 700hp..........thanks

[rustbucket79]

Lots of companys building both versions with great success. Make no mistake, the shorter the compression height (and skirt length) the more piston rock you'll have.

If you set the 3 different pistons beside one another, 406/421/434 all using 6" rods, the 406 uses a 1.125 compression height, 421 uses a 1.062, and 434 uses 1.00. Pretty minimal difference between the three isn't it? 1/16" per change.

[Rizzle]

If my math is right (good chance its not) you'd have to spin the 421 just over 200rpm more for the same hp numbers, with the same parts.
Or, with the same hp/torque peak rpm numbers, 97% of the power. But very simple math, so I'd like to see what others say if its correct or not.

Yeroon

[raynorshine]

If my math is right (good chance its not) you'd have to spin the 421 just over 200rpm more for the same hp numbers, with the same parts.
Or, with the same hp/torque peak rpm numbers, 97% of the power. But very simple math, so I'd like to see what others say if its correct or not.

Yeroon

agree with Rizzle....i need a really good reason to not grab the extra cubic inch....rule book..etc..

[CNC BLOCKS]

4 inch is geat with a tall deck but but in a 9.000 deck I prefer the 421 which seems to be very populat now a days as the 421 has a better rod ratio not as much piston sticking out of the bore at BDC can use a bigger base circle cam and seems to be a happier engine.

[T-flow]

Like what was said above in all post's.
But depending on head choice, you may never see any difference in power what so ever with more cubic inch. 421 VS. 434 with a standard style head might even make more power with 421ci's. Plus cam to rod clearance is Nuts with a 4.0" stroke. 410-415ci would be my choice unless you go Tall Deck.

T-flow

[bigjoe1]

I have made both the 421 and the 434 , and I would never build a 421 again unless the customer just has to have it.. The 434 is better EVERYWHERE, even with heads that are too small ( whatever ) This is another one of those deals where if you dont get enough cam duration, the performance will not be as good as it should be.


JOE SHERMAN RACING ENGINES

[PackardV8]

only go to 3.785 stroke

Is that a typo and you meant 3.875" stroke?

Also, you haven't told us the budget, the intended use or the time you're planning between freshening the rings.

Agree with Joe; if it's mostly strip and if budget isn't constrained and if shorter ring life is accepted, then go 434".

jack vines

[DaveMcLain]

If I was spending my money I would put in a 4 inch stroke even though it's not without some drawbacks. Sealing the pan might be a little tougher, rod selection becomes very important for cam clearance but other than that a 4 inch stroke with a 6 inch rod poses no special problems otherwise.

[Hanzeng]

I'll throw something else in to the mix- What block?

I wouldn't build a motor with the hp you have as a goal with a stock GM block- not worth the money invested into a known weak block. Therefore in my opinion-

GM block- 3.750
Aftermarket block- 4.000

[fishman]

yes it is typo should read 3.875 stroke

motor right now is a dart little m with billet steel main caps and is zerod nine inch block
cams is a solid roller 264-272 duration with 634 lift
heads are AFR cnc 210s
headers are equal length 1 3/4 ceramic coated
intake is a ported 2925 super victor with a adapter 2 inch with a AED 1050 dominator on top
piston are mahle just over 12 to 1 cr
rods are i beam scat with the 7/16 rod bolts
crank is a eagle 4340
pan is a moroso rear sump 7 quart side kick pan with scaper and windage tray
dynod at 637 hp @ 6700 rpm and 562 torque @ 5200 rpm

new motor
will have AFR 235 they flow 340 cfm
camking recommends this cam 273/276 duration and 448/436 lift and 110 lsa and use 1.6 rockers so lift will be 717/698 and 7500 rpm......i dont really want to rev it more then 7000 rpm.......also he recommends 1 7/8 headers.....the headers on the car are hand built 1 3/4 ceramic coated equal length tubes.....if i got new ones it would cost a wack of coin not going to spend that kinda money for a few extra horse....

car has been on a diet just putting on fiberglass front clip,hood,scoop and doors........car is down to #2200 lbs
running a ultra bell glide with a 5800 rpm stall 8 inch torque.. ford 9 inch with 4.56 gears..tires are 32x14x15.......fastest car ran with old motor was 9.64@ ...........139.76 mph.........figure 700 hp car will run 8.90s

[levisnteeshirt]

just saw a 434 took apart after 3 seasons of hard super late racing , sb2 heads , it looked really good inside except the thrust bearing had a problem , compstar chinese crank , howards rods , mahle pistons , coating on the skirt was all but gone ,, i'd say if it would have had new bearings put in every year , the thrust bearing might not have looked so bad , but thats me

[fishman]

The car is strip only...I started buying coated bearings ....cam..rod..mains and coated pistons been getting 3 years but the rings seem to go first maybe need to go to a diffrent ring been using the ones that come with mahle pack

[Eric68]

You can build a 3.875 stroke 427 with a 4.185 bore. The larger bore is no problem with your block. You can also use a shorter rod to get a taller (better) piston. With your heads I don't expect that you would be rev'ing it to the moon anyways.

[CNC BLOCKS]

You can build a 3.875 stroke 427 with a 4.185 bore. The larger bore is no problem with your block. You can also use a shorter rod to get a taller (better) piston. With your heads I don't expect that you would be rev'ing it to the moon anyways.

The 427 would be nice build with 6 inch rods is not a problem 1.062 is not a really that short. A shorter rod you would have a lot of piston hanging out of the bore at BDC. Shorter rod means shorter counter weight which you may have to put heavy metal in the crank.

On that big of bore is best to use a .950 reach head stud and bottom tap the holes and drop a ball bearing to bottom the stud out on VS using a stud that bottom out on the deck as it to hard to keep the cylinders round and get go ring seal. Those blocks will go 4.200 no problem with the correct studs.