Head/compression ratio

[Slo-Sho]

How about zero decking the block and using a Mopar performance HG with a compressed thickness of .043" effectively making the quench height .043"?

 

[AlabamaBill]

More or less direct at flash but anyone who knows please jump in. Is the amout milled off the deck be a 1:1 ration of raising the rocker arm or does the geomerty require something different. I am guessing, alignment of push rod is not true perpenidicular to crank and pistons so it would not be a true 1:1 or then again it might be so close you can go with 1:1. I wish i could read blueprints and paid a bit more attention in trig and geometry in High School!

I was also intrigue by the Head gasket/zero deck suggest posed by the last poster.

I have a hesco head on DD XJ with the general air/exhaust mods. I running a stock TB(with spacer) though but fuel mixture is good. I am close enough to B'ham, I ll probably let them do the block though I am sure it will not be cheap. Lord knows the head wasn't.

I was building what I call light/moderate trail rig and had not plan to stroke it. My DD driver is stroker canidate one day and I have learn a great deal off this thread for both engines when the time comes. Thanks

 

[Flash]

How about zero decking the block and using a Mopar performance HG with a compressed thickness of .043" effectively making the quench height .043"?

What is the piston to deck hight of a 4.0 any ways?


Flash.

 

[Flash]

More or less direct at flash but anyone who knows please jump in. Is the amout milled off the deck be a 1:1 ration of raising the rocker arm or does the geomerty require something different. I am guessing, alignment of push rod is not true perpenidicular to crank and pistons so it would not be a true 1:1 or then again it might be so close you can go with 1:1. I wish i could read blueprints and paid a bit more attention in trig and geometry in High School!

I was also intrigue by the Head gasket/zero deck suggest posed by the last poster.

I have a hesco head on DD XJ with the general air/exhaust mods. I running a stock TB(with spacer) though but fuel mixture is good. I am close enough to B'ham, I ll probably let them do the block though I am sure it will not be cheap. Lord knows the head wasn't.

I was building what I call light/moderate trail rig and had not plan to stroke it. My DD driver is stroker canidate one day and I have learn a great deal off this thread for both engines when the time comes. Thanks

I don't know but from what i have read here so far it seam to be multiple Rather the 1:1 but I'm purely speculating here.
need some one with more knowledge then I...........you would thing that i would be 1:1.....well then there is the valve job that can add to the mix too.


Flash.

 

[MudDawg]

Slo-sho put it very well....nothing to add to that.....the stock deck height?? pick a number....you need to measure yours....i have seen them vary widely.

11.3....nah...not stock....but a 2.5 does have 10.2 as stock...and they tend to ping...unless you have one with a knock sensor...I would rather keep the performance by using good fuel and dialing in a bit of ignition lead.

Decking the block and/or head does not change the GEOMETRY of the valve train....just the required pushrod lenght.

You get what you pay for...I use the best machinist I can find for my engine work...if you live close to Hesco....they are the big dawgs.

 

[Flash]

the reason i asked about the 4.0 "piston to deck hight" is that if it was like .070 or .090 down, that would raise the compression up by quite a bit!



flash.

 

[MudDawg]

You need to be careful about overdoing the CR on an engine like a 4.0 in a Heep...It will be tuned basically to bring out the most torque from idle up to 5200 rpm...the cam associated with that sort of tune up will cause high effective CR at low engine speed....hence....detonation....

High CR numbers are best used when you have long duration/high overlap cam numbers....the higher cr helps with low rpm cylinder pressures associated with pumping losses at low speed. In other words...better torque numbers...

Another way to look at CR is there is the THEORETICAL CR based on swept volume and combustion chamber volume.....the other is actual CR based on the trapped volume....this uses the cylinder volume from the point where the intake valve closes...this will always be a lower number than theoretical CR.

In other words....unless you are building a killer normally aspirated street motor....you don't need high CR....in the case of the Mighty 2.5....it is a killer high RPM motor....but you can't take a 4.0 anywhere near where my 2.5 can rev...:sunshine:

 

[jacked]

exactly how much should be shaved to yield a 9.25 cr with using the mopar gasket.

 

[Flash]

exactly how much should be shaved to yield a 9.25 cr with using the mopar gasket.

That depends on to many thing, stock 4.0? stroker! if stroker, what piston it has and compression hight.

Are you shaving the head or decking the block?


Flash.