What sbm stroker to run? Help please

Hello,

Time has come in my build to buy a rotating assembly and with all the options these days I'm left confused on which way to go. I've talked to Tom at Molnar as well with Rod from BPE. Both were very knowable and helped out with some questions I've had. My question is which will make the most power out of my setup? Do I go with a 4 inch stroke or a 4.125 crank? I want this combo to last. It will be a pure drag motor. So that being said do I upgrade to Oliver rod or Callie's ultra rod if I go with the 4.125 crank? Or would the Compstar be sufficient in a 650-700 hp motor? Here is what I have so far:

Virgin bore 59* "R" block
Milodon 4 bolt main caps
Arp main studs
1050 dominator (E85)
Bullet cam: intake lift 720' exhaust lift 712' duration 302/308
Heads are W5's ported by SDSS
Indy 360-3 intake
Harland sharp 1.6's
Dana 60 with 4.88's
4-link rear end
Afco coil overs
I haven't bought a trans yet but I'm leaning towards a A & A 904

Heads flow @ .700" 319.7/242.6

The bore right now is in the 3.90's I don't want to bore the block crazy right away as I'd like this block to last me a long time. I was thinking boring it 4.020 or 4.030 to start. I'll be getting the block sonic checked in the next few weeks so I know what my max bore will be.

Any help or ideas would be greatly appreciated. The car should way around 2850# with me in it.

Thanks! Mark

A lot depends on bore thickness, that said I would bore as little as posible the HP is in the thick walls, as for crank I am leaning to the 4.125, but since your a drag motor only you could go with the shorter lighter piston and 4.250 crank and not have to worry about piston rock and longevity of the short piston.

I would do a 4" crank, with a 6.200 long rod. If that block is a stock deck height.

I would also sonic check that block and see what I had to work with before ordering pistons and boring the block.

Unless you are going to change the gear ratio in the car you should build the engine to match the 4.88 gears. Figure out how fast you want to go and then that will tell you what RPM you'll be at in the lights. Once you know the RPM you can figure out the best stroke. I doubt that you want anything over 4 inch stroke but I haven't done the math myself.

yes, I need to find out what the sonic numbers are first and foremost. There's just so many options and I didn't want to go with a Eagle or Scat set up. There so dang heavy!

Ryan at SDSS said the same thing. Stick with a 4 inch stroke. But it's so tempting to want to run a bigger crank. I understand bigger isn't always better. I've a got a 33 tall tire so I was thinking the 4.88's would be ok. If I change tire a 4.56 or 4.30 would be going in the rear.

4 inch crank is plenty for W 5 heads. I ran a 422 inch W 5 headed motor for years( 4.100 bore) those heads aren't THAT big. Ryan did mine too.
Used the compstar rods( 6.300) with CP Pistons. Raced it 6 seasons, new owner 2 more, then new Pistons beacause it needed a fresh bore. Still together today.
The comps stars will be more than adequate, shifted it at 7, trapped about 7500 hundreds of passes.
Too bad about the small bore, another reason I wouldn't go past a 4 inch crank.

for a 904 of that caliber you might try contacting Chuck Lofgren over in Cedar MN. Not that far from you and he can build you a very dependable trans.

The block is a stock deck hight block.

Thanks for the info on the Compstars. Ya, the bore is a bummer but I'd hate to bore it .80-.100 over right away

I have a 4.125 molnar crank in my 440'' with w2 heads. 653 hp and 590 tq.

Thanks J_BODY! I remember your duster out at Oahe. I think maybe your dad was driving it then. I was always thinking to myself that car is Bitchen through the muffs! Even cooler now with the w8 setup. 👍🏻

Why in the world would anybody build a whole motor to match a 300 or 400 dollar set of gears? That makes zero sense. I would build the motor for the intended use, Dyno it, then match the convertor and gears to what you have. Do you ever drag race?

Nice! I'm building a 79 volare Roadrunner tube chassis car. Nice to see another F body guy on here!

The gears can change easy enough it's just what I had in the rearend. B3422W5 how much did your car weight with that combo? What did you ET at if I can ask?

"UNLESS".... I think you both share the same opinion on the gear deal B3. Personally I'm betting the 4.88 and tall tire will be a dang close fit for that combo. Our W5 ran great with 4.56 gear and 29.5 tire, although we dropped down to 4.30 when we went D60.... wrong choice imho.

Jay, what were you guys running for a rotating assembly on your w5 setup?
Thanks, Mark

Car weighed 3350. Super stock springs. 9.80's at 135. Mild roller, Victor W2 modified by Brett.
The new owner( I am 300 pounds) tossed 130 pounds off it( 3220 now) bumped compression from 13-1 to 14-1, and swapped to a very aggressive bigger roller that isn't streetable like mine was. 727 trans, 4.30 gear, 28 by 10 tire
That all said, the car now has been 9.62@140, still on s/s springs and 10 by 28 quick time pro's. Over this past season the heads finally let go( leaking water and ufixable) and the guy found bare heads (w5)and had Modern CNC them. They are smaller. Best I know of he has been thus far was 9.80, but I suspect it's already run better. It only dynoed about 15-20 horse worse with these new heads, so shouldn't run much worse than he had it running once he has had it out a few times

Very impressive! I think Ryan was pretty conservative with my w5's. Didn't want to turn them into sprinklers lol. There very early w5's, not the blue plug version. I'm hoping to be in that 9.60 area. We will see. Fingers crossed lol

Ours was pretty mundane... Eagle crank and rods. Stock 340 block filled. BCR 2 bolt main caps. Our first set of heads were one of the "cnc group buy" porting sdss did. Our engine builder flowed a port and wasn't impressed, but we left them alone as my dad was looking at running low 10's. Think he was only shifting at 6200. Still had the 8.75 rear with 4.56 gears. He upped the shift to 6800 and run a couple 9.8's at Oahe at 137mph IIRC. We were twisting axles pretty bad so we got a D60 for it and he dropped the gear down to 4.30. Cam was a Comp .658 lift I/.631 E. 275 @ .050 I / .631 @ .050 E. We ran 1.5 Erson rockers..... and I also vote for the 4" arm .

Eagle rod from the W5 VS the Molnar in our W8.

Why waste money on new gears if you don't need to. In fact, why build a motor and dyno it to figure out what gear to run? All it takes is a few minutes with a calculator to sort it all out. The car weighs 2850 and he wants to run 9.60 so that tells you how much power is required. He has 4.88 gears and 33 inch tires so that tells you RPM in the lights. He already has ported heads so that tells you the CSA. Once you know RPM in the lights and CSA then you can solve for engine size. Get the sonic results to figure out the bore size and then that tells you what the stroke needs to be.

Is that a 6.000 rod? Boy, there sure is a big difference between the Eagle and Molner!

the Molnar rod is a 6.00, the Eagle.... stock length. .....so Andy, off the cuff do you think the 4.88 is going to be the "go to" gear? I'm thinking it will be dang close.

Sounds great bench racing. Rarely works that way at the track. No way to know exactly what the car will trap at until you make a pass and account for convertor slip, knowing where torque is helps to buy the right convertor product.
Yes, you generally aren't going to be far off, every gear is 250 or so rpm and you likely aren't going to be wrong more than 1 gear ratio, but your comment to build the motor around an existing gear ration didn't/ doesn't make sense. Build the motor, dyno it( if you can) take it out and run it. Determine the optimal gear for it, and run that gear. If it happens to be the gear in the car, you got lucky.

....and your opinion of the 4.8? You've "been there/done that". I'm just thinking light car, the general outline of the build the op has presented, tire size, 904 trans..... the 4.88 will be in the ball park.

I didn't catch the tire size. I ran a 4.30 gear with 28 tire, and it likely would have run as good with a 4.10, but I never tried it . Before I sold it I strongly contemplated the swap, 7500 at the stripe would have been nice to knock back 200-300 rpm
for more longetivity . Have to be a tall tire to need that much gear(4.88). I depends too how much steam the motor makes. That small bore isn't going to help it any. Mine made peak power 6800ish.

I've got 4.30 gears with a 29.5 tire...... third gear to the stripe is pretty ugly on the data log. Only crossing around 7. 4.56 is the next step since I own a set.

The tire size is 33 tall. I'm thinking with a 4.88 it should be real close to what I need.

Here are a few pics of the build so far

nice


Looks like a really nice car in the works.......

Not crazy about the scoop, I'm going to try and shorten it a bit in the back. With the motor being set back nearly a foot, the distributor is under my cowl and this scoop is probably going to be my choice whether I like it or not. It will definitely be one of a kind. The car is a 79 Volare Roadrunner.

Thanks! It's a lot of work! Lol

Old Pro-stock comes to mind w/that body style.......

Paint it like a Super Coupe!