421 4 MIL

[RippinShee]

I want to go 4 mil long rod on my stock jugs and stock cases. What will i need to do? It looks like i just need to have a 68mm bore with 795 pistons, and the 4 mil long rod from fast. I already have drag ported jugs. So besides the crank, rods, and pistons; what else am i going to need to go 421 4 mil?

[firebanshee]

If you allready have drag ported cylinders you might not be able to use them on a 4 mill crank, unless you had them decked and reworked, which means you would probably be better off selling those and getting a fresh set and have them ported for a 4 mill set up.

[RippinShee]

Why cant i use my stock jugs?

[firebanshee]

Why cant i use my stock jugs?

If they are allready drag ported the port timing and durations will be off and you wont have any power. If you have a set of non ported stock cylinders then all you have to do is drop the floors of the transfer ports and exhaust ports 2 mills and you would be good to go.

[dajogejr]

They don't have 795 series pistons bigger than 66mm (.080)

You'll need a big bore blaster piston for that.

 

You'll need big bore sleeves for it and domes cut for the big bore AND stroker crank.

 

To be honest...the big bore kit and sleeves would be a waste of money...

Unless you personally have the knowledge and resources to heat up and install the sleeves, re-match the porting done...

 

The cost would be not worth it.

In my opinion, get the correct size 795 series piston for your current bore and get a set of domes cut for a 4 mil stroker (the domes will have 2mm recess cut into them to run the piston into the head)

 

Now....the porting SHOULD be matched for the 4 mil stroker crank durations.....

 

Before aftermarket cylinders were available...this is pretty much all you could do.

 

Now...with the abundance of cylinders available cast with bigger pistons...it's just so much easier to buy the cylinder with the casting for your chosen crank.

[RippinShee]

So i guess ill just forget the 421 and just go with long rod 4 mil. So i need the 4 mile crank and rods, 795's to my bore, cool head with stroker domes cut. Im very very happy with the drag porting done on my stock jugs. What is the big difference in porting in stock jugs for a mil? Do i need to do anything to the cases?

[dajogejr]

A 4 mil crank is drop in, no case work required.

 

Port Timing.

In Simplest terms...

When you increase the stroke of a motor, you're changing the timing of the piston sucking fuel/air in and letting burnt exhaust out.

 

It'll run as is. But to get the most out of a 4 mil crank, the porting needs to be matched to the longer stroke.

Keep in mind when you add stroke to the motor, the compression raises also.

 

A 20 cc dome on a stock stroke might yield 150 to 160 PSI, that same dome on a 4 mil could put it in the 170 to 180 ball park.

 

Just food for thought.

[RippinShee]

So technically i can still keep my full drag port with boost ports on my stock jugs, get a cool head with stroker domes, and it will run very good. If i want it perfect, get new jugs 4 mil ported. If i get 795 series pistons to 66m, according to the displacement chart, it will be a 397?

Edited September 3, 2009 by RippinShee

[dajogejr]

795 series pistons.

To be honest...without knowing your port layout/timing and durations as they are setup for a stock stroke, it's impossible to tell you how it's going to run with a 4 mil crank.

 

It'll run.

Could run very well...could also run the same or worse with a 4 mil and you'd have wasted your money.

At the very least, get a degree wheel and measure where the exhaust, transfers and intake open up...and talk to whomever ported your cylinder, they can tell you what to expect.