It’s time for a new motor!!!

[Bolted to Floor]

The Mustang has
5 speed Tremec with the .64 5th gear
power brakes
air conditioning
3.50 rear gears
245/45 17 tire


Here was the old motor with a broke crank!!!

Using the Wallace racing engines calculator, the static compression is 9.74 to 9.84 depending on deck height of .005 to .0 using the 11.7cc value.

Edelbrock RPM with a 750 vacuum secondary converted for 4 circuit idle. I do have a BT 2X4 for down the road at a later time.
Cam is a Comp Hydraulic roller – Lift is 574/574. Installed at 106 Intake centerline, Duration @ .050 is 227, lobe separation is 112. From talking with Comp this morning, it could be reground. They could move the duration and or lobe separation a few degrees. The lobe could be increased about .010 for a new lift of .591.
Duraspark distributor with factory ignition box
Timing chain Ford Motorsports with 9 position keyway
Standard volume oil pump with ARP drive
Head gasket Fel Pro 1020
Cylinder head – Felony heads from Barry w/ 76 cc chamber, adjustable rockers and POP’s end stands. I might swap over to nonadjustable rockers and new pushrods. 
Bore 4.11
Piston Sealed Power 381NP-.060 over - 10.33 to 11.7 cc depending on where I look.
Pin dia. Stock .975
Compression distance 1.66
Crank Stroke 3.98
Rod length Stock 6.488
Deck height 0 deck to .005 in the hole according to the Machinist

New motor

With only 6600 miles prior to crank break, I will reuse most of the parts I can. I do have another 390 block that should clean up at maybe .020, definitely by .030. I will buy a new Scat crank and rods and I’m leaning toward the 4.125 stroke. It gets me to 429 to 431 depending on bore clean up. I want to be in the 9.5 to 1 range for compression. The block will get decked to help achieve the right compression ratio.

Would the difference in stroke (4.125 vs 4.25) make a big difference in the scheme of things?

Is there a better selection of shelf pistons for the 4.25 stroke vs the 4.125? 

What would a ballpark price be for a custom set of pistons?

If the cam is reground to something different, what should it be? Is it worthwhile for the additional lift?

The intended purpose is to drive it. We drove it to Adrian Michigan for the Mustang Steve Bash with the crank breaking on the way home. The 2020 Bash will be in Surfside Beach South Carolina and I intend on being there. The car was a lot of fun to drive, it pulled from 1000 RPM in 4th gear and never bucked. 1600 RPM was about as low as it would go in 5th gear before it started to act up. The next motor needs to do that too.

Thanks for the help.

[Stangman]

The 4.250 stroker kit it the same price as the 4.125 so it almost dont make sense not to get the larger of the two. And let the machine shop tell you what piston size to get. JMO

[DuckRyder]

Boy this sounds like a familar dilemma ... 

I’m far from an expert, but I agree that it doesn’t make much sense to go anything but 4.25 unless you are limited by some rule...or something like that.

Cam: The only way I can think of to gain lift by regrinding is reducing the base circle, do a bit of research on this.

[Bolted to Floor]

Thanks guys.

Yes, from 3.98 to 4.25, they are all the same price. What a dilemma to have, right??

I’m the limiting factor and probable over thinking it. 

I was hoping to regrind the cam to make it more suited for the added displacement. If I go to a different cam, then I have something I can’t bring myself to throw away or find a buyer for.

[Barry_R]

4.250
No reason to do anything else in your application

[My427stang]

I think I would go 4.25 in a heartbeat, then put a 3.91 or 4.10 gear in it, and re-cam only if you want something rowdy. Rock it back to 109-110 ICL and buy pistons to match. 12% increase in torque multiplication from the gears plus the bigger engine, plus only a 2.50 final drive with a 3.91, plus the mellow cam for a/c and cruising would be very strong

If you really want a new cam, sell yours, regains won’t get you to a modern lobe easily

[Bolted to Floor]

Thanks Guys

[BattlestarGalactic]

Typically that now "small" cam will give you more torque with the increased stroke.  Yes, you are limiting the overall HP,  but is that really an issue if you can shred the tires for 4 gears???

With my new motor in the wagon, I actually backed the duration up a few degrees(but added some lift).  It keeps the workable RPM range down to a more sane level for longevity.

[Bolted to Floor]

Thanks Larry, shredding tires in 4 gears could be appealing.   

I do like the idea of longevity.

[turbohunter]

Roger the longevity John.
Sacrificing a few horses for continued fun (especially in a light mustang) is a thumbs up.
Had to make that same decision and I’m sure my rear tires have zero chance of survival.

[Bolted to Floor]

Well…..I picked up the short block from the machine shop today. It took about 3 weeks from when I started the thread to know what size pistons to buy. By that point, someone had bought all of the 4.25 stroke cranks from Scat!! So….that made it an easy decision to go with a 4.125, I didn’t want to wait till the next batch arrived. Everything for the rotating assemble got ordered around Christmas, arrived at the house, and made it to the machine shop by mid January. The machine shop balanced it, line honed and decked the block, checked all the clearances, assembled the short block, and degreed the cam. He also gave the heads a once over to make sure they were OK. Now I get to carry on with the remainder of the assembly. Happy days are on the way!!!

[Barry_R]

I have soaked up every 4.250 crank I can get my hands on for several months now.  Almost feels like the Blue Thunder business model - if the market needs fifty of something you produce twenty of them and let the customers fight it out.

[Bolted to Floor]

In that case Barry, thanks for helping me in my decision making process.

It’s good to be busy, right?

[Barry_R]

In that case Barry, thanks for helping me in my decision making process.

It’s good to be busy, right?

Not that good - when you need fifteen of something and you only get three or five at a time it ain't no fun.
same exact problem with roller cam cores.

[Bolted to Floor]

In that case Barry, thanks for helping me in my decision making process.

It’s good to be busy, right?

Not that good - when you need fifteen of something and you only get three or five at a time it ain't no fun.
same exact problem with roller cam cores.

Issues like that can take all the fun out of business.