4.125/ 4.250" stroke stock block SB combos

Wondering who is running bigger then a 4" crank in a production block SB and what your combos are performing like? Thinking about maybe going to a larger crank then 4" if it's worth it

Cant see much use for them personally.
To me, probably about the best combo is a big bore with a 3.79ish stroke.
Dont see many if any guys running W8/9 stuff with more than a 4 inch stroke. And most of the other heads are too small to need bigger than a 4 inch arm( if that even)

Did a 427 SB a few years ago for a street driven track car. Nice engine, made a ton of torque and pushed that car to 150+ mph on the road course at PIR.

Street Combo or Race only???

The 4.125 arm from Bloomer has 2.00 journals and uses the 6.200 chevy rod with a .927 pin, so it fits in the block much better than the 4 inch kits with the stock size rods.

These guys wind the heck out of their engines to get the power out of them. I will be researching this shortly myself for my 360-1 heads or if I strike gold possibly a set of Edelbrock Victors. This is my bracket piece so I refuse to beat on it to bad.

Maybe the rainbow chasers John.... but lil ole bracket guy, that enjoys a nice 9 sec pass, like myself I don't feel like I've "beaten" on my stuff. 6800 shift point, trap at 7200. I could put the 4.3 gear back in and trap at 7K. While it bothers me that with the parts I have I could REALLY have some fun.... my bank account thanks me for our "mild" decisions. btw, 4" stroke here with 6" rod.

Really the question is what head are you running and what does it flow. I run with another small block guy. Running 4.250 crank to get to 444 CI. Because we run stock appearing we have to run production cast iron head. X heads in this case. You really are asking a lot of the x head to flow 444ci. The block is half filled. Performance wise you need a serious head to use the CI. Longevity wise jury is still out for me, with a stock block I personally don't know of one that for other reasons has stayed together for long period. Such as car was sold,something else broke,ect. Strokers hide power which is why they are popular with stock appearing. just my two cents I think I plan on 427 inch limit for the next build, but it's a couple years away and everything's subject to change.

I agree with Don. I have seen alot of fast combos using that 3.79 stroke. If i were to do another sb project some what budget build like i do, i would search out a good x block and use the 3.79 crank with w9' s or edel victors. Gm and mopar used a 3 3/4 stroke in a few motors, must be some thing good about it .

Exactly what I had. Replaced the 3.79 crank and 12.5 pistons with a 4.125 crank and dish pistons. More power, and runs on pump gas, so I'll never go back. Listed the 3.79 crank on here for 300 bucks, no takers.

I use an X block on my bloomer 4.250 w/ Indy 360-1. I shift at 6500. It’s been 5.66
My R block molnar 4.125 W-8 had been 5.53 at 3000’ DA shifting at 7200. I might be a little afraid of a stock block, if I used on I’d sure use a girdle or something to beef the bottom end

Street and strip, and I know my heads may be a limiting factor (stock indy 360-2 cnc 230 heads). I have had my engine up for sale to go BB since nitrous is out of hand in price here now, but havent had much interest so I am going to pull and freshen it... I thought about going to bigger stroke, porting the heads and running n/a. Its a stock block but half filled, and it already has a 4" crank.

Would it be worth it to go bigger? Id like to stay pump gas but raise cr from where it is now (10.4:1)

Theres a guy over on the east coast(Steve Clukey) that uses a sb n/a combo using an X block. Not sure the stroke, but spins that thing to 8000-8500rpm on shifts. Its in a duster and has been in the high 8's. Very impressive sb.

PM sent.

I have a set of w9's that would go great with that.

4.25 stroke SBs are awesome. All the crap about the heads not being big enough out there is bull pucky. An x head flows almost what a 906 BB head does and tons of guys are running them on 440 CID engines. A decent ported eddy SB head flows about what a ported 906 does and again lots of 440s run great with 906s. A good W2 flows similar to a decent eddy BB head and again tons of guys running them on 440-512 CID engines.

The real question should be how many cubes X RPM do you want to turn. I always build the biggest bottem end the budget can aford, nothing like loafing along at low RPM and still posting great time slips.

Yeah. And guess what stroke those 440's with smallish heads that run good are using..... 3.75.
Nothing wrong with those huge strokes i guess. But on a dinky bore and will all the side loading and terrible rod ratios.... why? Especially for a race only motor. Are guys running them and naking power, sure. Just to me, that 3.80 ish stroke and a big bore seems optimal.

Comparing apple to apples I’m gonna say about .20 difference between we shall say a 408 and a stock stroke 360.

Years ago when Hensley built my first stroker( 416) i asked Ken Hensley( who i have a ton of respect for) what difference there was between a 340 and a 416 all other things being the same. He said 3 tenths. Never forgot him saying that.
Real world, my 360 has run 11.20's at 10.4 compression with mild eddies at 3300 with a 727.
My little brother has a new 416 with max effort Shady Dell eddies, 12+ compression, same weight, and he has a 904. Admittedly he is having teething issues with it, but thus far he has been 10.95 at 120. 1.5 mph faster and 3 tenths quicker, and he has a 904, which is definately quicker. I am sure it will run a good bit better, but so would mine with a 904 i have on the shelf and a convertor correctly specced( one in car car now is a tight 4500 flash) devinately "off" with what i have.
So yea John, i agree. Why toss that huge crank around for not much gain. 4 inch to me is more than plenty.

I agree. when I first replaced my 12:1 ported J head 340 with my w2 headed 408 I was very disappointed. Ran the same 4 speed and 4.10 gears although the 408 was 10.5:1. took me another 6-8yrs to get it in the mid tens. That 340 was a very impressive street/strip motor. It would be fun to do a x block with the 3.79 crank roller cam and w9 or victor head. I would think it would last along time buzzing it to 7-7500.

I have a 4.100 bore 48 degree R block sitting here with a 3.79 billet crank, roller cam and lifters, two sets of pistons, a set of Arrow rods, a W7 intake, and Jessel rockers for W7 heads. The deal was to good to pass up so some day I may see what this combo will run. I think it would be an interesting project

We will get to find out real soon what a nice 3.79/ W9 deal will run. By good local buddy Scottb has exactly that combo built and ready to go for next season.
I dont want to spoil his news, but suffice to say its a mighty stout piece. Big bore, lots of cam and compression, and attention to detail. CNC W9's by Modern

Since you already have the 4" stuff, are the pistons reusable? I don't know if it would be worth it, but I love driving mine on the street with the 4.125 assembly. I have 3.89 gears with a 29.5 tire so it's a pretty mild gear, and I can stab it in any gear at any speed and the response is instant. It made 500+ torque from 4200 to 6400 (540 peak), so it's a fantastic pump gas street motor.

I love it when guys talk budget then mention a roller cam and heads that take special rocker gear, headers and intake manifolds. My engine has a set of twenty year old Crane Gold 1.5 rockers and a 600 lift solid flat tappet cam with stock port windows and geometry. Pretty boring stuff for an engine that's shoved me to 10.39-128 NA and 9.43-139 on a small plate. I know, the numbers aren't very impressive compared to the race cars around here, but it has over 6000 street miles on it so far, drinking 89 pump swill.

Here's a combo off the top of my head based on what I just did with a 4 inch crank, only this one would cost less, using stock valvetrain parts.
Magnum block at 4.030, 4.25 stroke, 6.2 Hbeam sbc rods, 1.350 (?) Co pistons, 12.5 compression with a flat top piston. All this for 434 cubes. Big mutha thumper hydraulic roller, EQ heads with 2.02 intakes, bowl ported , use stock valve train, 850 and an Airgap intake . Should make 540 hp, 560 torque.
Shift at 5800, change plugs and oil for seasonal maintenance.
That is what I see as a good, stock block 4.25 stroke combo. The stock block should live fine, sure, you can say the piston side loading would be higher, but that is balanced by a lower shift point. I can see a lightened A body going 10.00 all day long and the driver is comfortable,

I'd do the 4.125 and not look back for your combo.

That sounds like a bad ass package.

Cool! Can't wait.

By some what budget, I mean no 2000-3000 dollar block. molnar crank and rods ect. sure the heads will cost a bunch, but that's where most of the power is at. Heck, I built my 511 on some what of a budget at about 8000-$8500. Ya just have to shop around. What would a 650-700hp pump gas crate 511 cost? $15000 or more?

The whole bottom end is reusable I am just toying with going bigger since it will be apart for freshening....sorry my top end isn't budget enough for ya, not my fault I got it for quite a good deal. Your combo sounds impressive, but I would be curious to know what your car weighs too 👍

You can offset grind your 4" mopar journal crank to a 4.125" by using the 2.00" '327' chevy journal rod. Bobweight will be lighter too since you also go to a lighter .927 pin.

I like the 4.00 inch stroke SB combo. At 4.125 and 4.250 you start to run into things. Oil pump, windage tray, etc. start to get in the way so the assembly just takes longer and you have to be willing to modify parts and/or buy different parts until you find a combo that works. Using the smaller Chevy rod journals sure helps. For a race engine it might be worth going with the Honda journals or something like that. I think the Hughes Engine kit uses a 4cyl rod bearing to get the size down.

mshred,
I think the 360-2s are perfect for your budget since you already have them!
My heads are 220cc intake runner, and even with the mild flat tappet cam it made peak HP at 6600, so I think your heads could handle more stroke and still be effective.

My car is a real deal street car with big radiator, alternator, two seats, two batteries, 8.50 cert cage, all factory glass and bumpers, 15 gallon cell, then you add in a 300+ driver and it's certainly no lightweight! OK, ok it's 3150 with me and the nitrous bottle on board, those Chrysler engineers really outdid themselves in 1962...

mopar dave,

This is not a personal attack against you, as my own brothers think similarly, I'm just trying to advance the conversation. I'm not trying to invalidate anyone's opinion, just asking that you spell it out in hard numbers.



The typical 4" stroker kits with stock style rods run around 1700$ to 2000$. The 4.125 and 4.25 high quality kits from Bloomer and Molnar are about 500$ more.

W-9's, in another thread it was discussed are 6K by the time they are ready to make serious power.

Any head that requires offset rockers just added another 500 to 1000 over the budget of a standard head.

Then we have to have the conversation about the cost difference between a roller cam and all the associated parts versus a flat tappet. Is it really wise to have a .700 lift roller, with a short valve and a 1.88 installed height?

I've also never understood the love affair with big bores. Granted, I know they make a little more power, but in the conversation of small block mopars, we are dealing with a finite amount of available blocks. My X block was standard bore 4.04 after 15 years of racing, when I ordered the 4.125 stroker kit, I only punched it to 4.070. Why go right to max bore immediately?

For guys more versed in big blocks, remember when 4.15 was the go to stroker kit? Then the 4.25 stuff with the 2.20 journal came out and it was lighter and easier to assemble. Same way with the 4.125 stuff with 2.00 journal over the 4.00 kit.

I have offset ground 4 in cranks to 4.23 (using honda journal rods) and used SBC large journal rods with callies 4.25 dragon slayer cranks (no longer available) and have never had to do any real significant mods that I wasnt already doing for most 4.000 in. builds. I do tend to use lighter rods than many of the beefiest H-beam rods that are on the market.

Windage trays vary but I have used simple spacers and also trimmed some of the tray.

I'm running a 4.125" crank with a 2.00" rod journal and didn't have any Clarence issues.

MoparBilly, please check your pm’s.

What kind of rpm’s is suggested with these big arms ?

What block does the 3.79 crank fit that you have?

Mine peaked at 6750 on the dyno and at the track I usually shift around 7000.

If I remember right the 3.79" stroke was purposely derived to allow a 6.123" rod combo to fit relatively easily within the "new" (at the time) Race blocks shorter 9.2" deck. The 3.79 gives you a 1.18" compression distance with a standard 6.123" rod.

But I think it also can give you pretty close to a near zero deck height when replacing a 3.58" stroke in a 360 while using an off the shelf low compression Smog piston....pretty clever.

This was similar to the reason the 4.15" was settled-on for the big block stroker crank, with only an .022" overbore it allowed you to use an off the shelf 400 piston in a 440 and make a 493.

We've got a 1977 360 block running on the street with the Bloomer 4.125 kit. I like it.

Running a Super Victor single plane, 950 cfm 4150 and using some modified Indy LAX heads and running on 91 octane pump gas it makes 474 LB-FT @ 3,000 rpm, 574 LB-FT @ 5,100 rpm and 629 HP @ 6,400 rpm.

The owner is a little wild and the first time it left the shop it had an ignition box with no rev-limiter. It came back in 6 hours with bent exhaust valves. As it is making over 600 HP @ 5,800 rpm, we installed a MSD 6AL-2 and I set the rev-limiter @ 6,100 (619 HP). So now, damn it, he uses the rev-limiter as a shift light.....you know.....winds it until it hits the limiter and then shifts. If I set the limiter at 7,000 rpm he'd still do the same thing. It's just one of the many small reasons I've decided to not build anymore engines after I finish the ones already here.

La Roy engines, what did you do for a cam?

I have a couple in use. First one in my 72 Demon is a 13to1 CR 418/360. 4.03 x 4.100. Bottom end has 2600 passes on it and pistons have never been removed from block since new. Just broke a valve a month back on a friday night. Stayed up late and put a different set of heads on and raced it on saturday night and sunday, same weekend. Won a race with it on sunday. Production heads, 1973 587 "smog" castings, 73 block with no fill, Flat tappet cam, racer brown STX-22. Car weighs 3050#. Been 9.68 at 136mph--1/4 mile and 6.09 at 111 1/8th mile-- 1.26 60ft. I put 30 more passes on it this weekend at Memphis Int. raceway and made it to a final in S/P, 9 rounds. Still went 6.28 at 107.6 after 2600 passes,with lesser ported heads.

Other one is 4.25 x 4.07. 442 c.i. Same 587 production "smog" heads. STX-21 Racer brown flat tappet cam. 11.5to1 CR. 11.20s at 118mph 1/4 mile and 7.20s at 97mph 1/8th mile--1.52 60ft. In a 4200# 79 Chrysler "300". Has 3" exh all the way to the rear bumper with 4 mufflers. Runs on 80% 93 octane mixed with 20% 110 race gas. Made the 1100 mile dragweek trip a couple years ago with no issues.

Both engines have produced best E.T.s with 28* fixed timing. The 79 "300" got around 14mpg on highway during dragweek, when I bought this car in 1987 it only got 12/13 mpg on a vacation to colorado, still 100% stock. Engine in "300" is shifted at 6400rpm. Engine in Demon shifted at 7000 after the first couple months, first couple months I shifted it at 7800rpm. Actually was a couple hundredths quicker at 7800 but I figured longevity was worth more than a couple hundredths. Getting close to $100,000 in winnings with engine in the Demon, $12000 was from wheelie contests. Youtube--dodge demon wheelie 2.


Actually have a third one that is 4.04 x 4.00. Same 587 smog heads. ST-21 Racer brown flat tappet. 93 octane pump gas. 4300# 1990 Ram D150 short bed. 2 3" muffs an X pipe and one stock appearing tailpipe. Muff without tailpipe had an electric cut out at exit. with cut-out shut, the X-pipe worked like a y-pipe and made a single exhaust. Went 12.20s single and 11.80s dual exh until the 727 grenaded and killed the truck and broke 5 bones in my foot. I still have engine but truck is gone. Waiting for the magnum 318 to blow up so I can turn my replacement 92 D150 into a hotrod. Will probably run forever. OK then, when the AC quits blowing cold, maybe then I will put the 410 in, of course with a billet high gear drum in the 727.

I spec'd a custom solid roller for it.

I have two BPE 4.250" cranks the first one is 468cid 4.250" x 4.185" R3, 59deg, W9 deal. Very fun to drive and it get about 15-16 mpg and all kinds of torque and it doesn't beat the valve train up. I put it together in 2014 for DW and the first pass on the motor it went 10.11 @135 through the exhaust on a concretive tune up in a 69 Dart. That motor is in the Cuda now. The second motor is still in the works short block is done, 4.250" x 4.200" R3 48deg deal, 6.320" carillo rods nice light pistons thin rings.

I had never thought about offset grinding my current crank, that is another option I wasn't considering before.

Fuel mileage doesn't matter to me, I will use my daily when miles per gallon is the concern over smiles per gallon lol

Reading some of these posts really makes me wish I could find an r3 for a good price, but I am stuck with the stock block for now, which means smaller bore sizes I.e. 4.030- 4.060.... cool to see what some of these aftermarket block combos can do, but also nice to see guys out there using these larger cranks in the stock blocks.

Doing some test fitment and clearancing is nothing I don't mind doing. I don't run a windage tray, so that's not something I am too concerned about.

I would probably go with a bigger stroke. But I am happy with my 3.79 stroke small block. It is a 1973 340 block that is not filled or has a girdle. I am running the 360-2 heads like you have but mine were ported by Brett Miller. It is only 10.9 comp. and a roller (255/266 a.050) I have never ran anything but pump gas. It made peak hp at 7300 but I only shift at 6800. It would probably run faster if I shifted at a higher RPM and it didn't have my home made headers on it. I have never built headers before.

Very good topic of interesting

Indeed an interesting topic. It’s cool to see who is doing what and what there doing it with.

Mshred, I can only find short deck race blocks. Mostly the 9.2 and mostly a 50mm cam tunnel.
I’d love a standard height & tappet block myself.

Very respectable small blocks. Makes me want to do another one.

I have been looking for a while myself and have been finding the same thing, mostly short deck stuff....hoping my poor mans race block with half fill can hold up to whatever I throw at it for as long as possible.

So far so good, fingers crossed

I’d do a short deck but an intake is impossible to find. I’m not interested in building my own sheet metal intake or the 50mm cam expense. It’s a bit much dollar wise at this point. I just can’t throw money at like the U.S. government does its problems. (Real or Perceived!)

LMAO

Any idea what contributed to the low timing at 28* locked? Im thinking those smog heads must have a fast burn chamber for one. Curious to know.

These actually come up on e-Bay more often than one would think.

Bill