My First stroker with ?'s

[herbiehind]

i thought stock dcr was below 8-1 . you thinking scr ?

[Gorillaxj]

Nope, just an error in the article. its linked in my post....

it is true that the DCR is 7.47-1 according to the calculator for the stock 4.0l and not 8.47 as the article states.

So how do I no for sure what Octane to use?

[Gorillaxj]

Would It be worth it to retard my cam 4* to achieve the same SCR while achieving 8-1 DCR? would like some input or a push in the right direction from someone who has done this... If I need to run premium its not ideal but is ok. Just want to build it right the first time.

Offset key that would allow me to get 8-1DCR http://www.summitracing.com/parts/MRG-988G/

[Retlaw01XJ]

I'm a little lost on your combo....What is your cylinder head CC , piston dish cc, and quench distance?
I'm just finishing my build... near 9.2 Static CR and 8.0 Dynamic. Quench is near 0.057". #0331 heads are near 58 cc.
I expect to run regular or maybe mid-grade gas, with a mild Crower cam, based on what I've read here....

Tighter quench may tolerate more CR. Also depends on what altitude you are at.
You are correct that later closing intake will reduce dynamic CR and reduce octane requirement....
I'll have more REAL data in the coming weeks. BTW, I'm near 450 ft above sea level.

[Gorillaxj]

I'm a little lost on your combo....What is your cylinder head CC , piston dish cc, and quench distance?
I'm just finishing my build... near 9.2 Static CR and 8.0 Dynamic. Quench is near 0.057". #0331 heads are near 58 cc.
I expect to run regular or maybe mid-grade gas, with a mild Crower cam, based on what I've read here....

Tighter quench may tolerate more CR. Also depends on what altitude you are at.
You are correct that later closing intake will reduce dynamic CR and reduce octane requirement....
I'll have more REAL data in the coming weeks. BTW, I'm near 450 ft above sea level.

Right on! I am at 5000FT all day. I Go up to about 10,000-11,000ft on a semi regular basis.

Ok, let me start over with more detail. I will be building my setup using the below setup. (can still change things if needed) based off the "poor man"

Parts list-

258 crankshaft: 4.2L light weight short nose crank
Connecting rods: 4.2L Rods
Cylinder Head: 7120
Pistons & rings: Sealed Power H825CP .20 over (15.8cc)
Timing set: Comp cams kit
Camshaft & lifters: Comp Cams 68-232-4 4X4 cam w/lifters
Rocker arms: still debating if rollers are worth it... Kind of want to because the last set (stock style) I put in is showing wear with about 14k miles...
Mopar Performance 5249464 valve springs
Mopar Performance 4452032 valve spring retainers
Mopar Performance 4529218 valve keepers
Pushrods: Reuse stock 4.0
Head Gasket: going with .051" stock height due to CR (wanted to use Mopar Performance 0.43")
Using Stock Cylinder head bolts
24lb Injectors
APN manifold (for 91-99 to fit 7120 head)
62mm Throttle body

Taken from the calculator on this site...
Bore - 3.895
Stroke - 3.895 (making it square)
7120 head (shaved 0.10" to make flat) lost about 1.3cc per chamber making it 56.6 correct?
Keeping stock deck clearance .0215" correct? (doesn't change with stroker setup)
Headgasket 0.051"
Pistons 15.8cc Sealed Power.
Cam duration 250
Cam separation 113
Cam Deg advanced 3*

Resulting with-
SCR of 9.74-1
DCR 8.37-1
Quench 0.0725"

My fear with decking the block is that my SCR will continue to rise... I could CC my pistons and try to achieve a zero deck and same CR. but is that the ideal choice at this time? would it make the pistons weaker?

[Cheromaniac]

Right on! I am at 5000FT all day. I Go up to about 10,000-11,000ft on a semi regular basis.

Keeping stock deck clearance .0215" correct? (doesn't change with stroker setup)

At those elevations the air is so thin that the engine won't ping even if you run it on catpiss.

With the 4.0 block, 258 crank, 258 rods, and H825CP pistons the deck clearance will actually be ~0.030". I also calculated your stroker's SCR at 9.7:1.

[Gorillaxj]

Ok, thanks. I just wanted to make sure I was going to be ok. Catpiss it is!

I'll just do it how it is is my last post then and give her hell. thanks for all the help and putting up with my annoying questions!

[Cheromaniac]

thanks for all the help and putting up with my annoying questions!

What annoying questions?

[Gorillaxj]

HAHA! well thanks anyway. Its weird being on a new site with a bunch of new info to take in... normally I can figure things out quick and easy... thanks for all the help!