4.0 rebuild question

So now the question would be do I go 8.8.1 cr or higher? Russ said he would get back to me in a little bit but advised against running 8.8.1 die to it being to low. Just want to hear your thoughts
 
84jimmy said:
So now the question would be do I go 8.8.1 cr or higher? Russ said he would get back to me in a little bit but advised against running 8.8.1 die to it being to low. Just want to hear your thoughts
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Higher. 9.5 or so. Just watch the squish so you won’t need increased octane. 9.7 needs at least 89 octane with a yj HO head.

Ideally as much as you can without going overboard on squish and absolutely needed 93 octane. High CR without much quench, is bad. Needs some quench to get a good mixture in the squish.

I prefer to run non ethanol bc it’s 89 octane instead of 93 with ethanol.

Yes it costs more per gallon, but 10% better mileage and it’s not as harsh on the fuel system components. Also doesn’t boil in the rail /vapor lock as soon.
 
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84jimmy said:
So now the question would be do I go 8.8.1 cr or higher? Russ said he would get back to me in a little bit but advised against running 8.8.1 die to it being to low. Just want to hear your thoughts
Click to expand...

No matter what anybody tells you. Listen only to Russ, he will explain every thing to you. And you will have one helluva engine.
 
Jeff B said:
No matter what anybody tells you. Listen only to Russ, he will explain every thing to you. And you will have one helluva engine.
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Oh I planned on it but was just curious cause I've heard a lot of "people" say that the 4.0 stoker doesn't do good with higher compression. Wanted to ask here since there are a good amount of you with stroker motors
 
Any engine does better with more compression, but you may have to run different fuel to keep it happy. Like 18:1 needs diesel :D
 
What is a good squish number? I heard .0035 is the normal area you want to be in. Would the machine shop be able to check that without installing the head or would they have to put the motor together?

If I check it at home and it's to high I assume I would have to take it back to the machine shop to have them shave the block down
 
84jimmy said:
I read that the 4.0 has an issue with early detonation with the higher compression
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That has to do with hot spots in the combustion chamber of the iron head. Iron heads require lower compression than aluminum heads in order to run lower octane fuel.

Deburring and polishing the chamber helps prevent hot spots that cause preignition of the fuel/air before the plug fires. This is detonation, preignition, ping, spark knock, etc.

You have to balance the CR with the fuel used.

The higher the CR the more power available out of the same displacement.

Higher CR needs higher octane fuel, that is slower to ignite. Higher octane means less oxygen in the fuel itself.

Less oxygen in the fuel means less power out of the fuel itself.

The increase in power from a raised CR is greater than the loss in power from the fuel with a higher octane.

Decking the block or head can increase the CR and increases the quench and squish.

Dishing the piston can reduce the CR.

A domed piston can increase the CR.

A thinner head gasket increases the CR. Thicker is opposite.

Here is one trick.

Getting the quench height correct, will increase squish and more thoroughly mix the air/fuel in a more turbulent chamber.

This equates to less detonation while creating the most power per the fuel, all while decreasing the need for more advanced ignition timing.

This keeps the ignition from having a slight negative push on the piston as it moves towards the top of the stroke at tdc.

Also means you can get away with the most CR per fuel choice, when the quench is optimized and the squish is beneficial.

Now is it worthwhile to have custom pistons machined to your spec, that’s up to you.

You may want to use the parts readily available to you based on what fuel you want to run.

It’s similar to pick a tire size choice and build axles around that, that fits your budget and usage.

Decide on what fuel (s) you want to run, and see which parts get you to your goal in the best way for you.
 
My understanding was mid-grade was just super and regular mixed together.

I have noticed that the few stations around Raleigh that offer Ethanol free gas, tend to stock it in Mid-grade.
 
Mac5005 said:
I prefer to run 89 bc it’s non ethanol.
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shawn said:
Are you sure about that? I thought 89 was just a blend of the high test and regular tanks.
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shelby27604 said:
My understanding was mid-grade was just super and regular mixed together.

I have noticed that the few stations around Raleigh that offer Ethanol free gas, tend to stock it in Mid-grade.
Click to expand...
Around here 89 octane doesn't mean its non-ethanol, but non-ethanol is almost guaranteed to be 89 octane.
 
Mac5005 said:
That has to do with hot spots in the combustion chamber of the iron head. Iron heads require lower compression than aluminum heads in order to run lower octane fuel.

Deburring and polishing the chamber helps prevent hot spots that cause preignition of the fuel/air before the plug fires. This is detonation, preignition, ping, spark knock, etc.

You have to balance the CR with the fuel used.

The higher the CR the more power available out of the same displacement.

Higher CR needs higher octane fuel, that is slower to ignite. Higher octane means less oxygen in the fuel itself.

Less oxygen in the fuel means less power out of the fuel itself.

The increase in power from a raised CR is greater than the loss in power from the fuel with a higher octane.

Decking the block or head can increase the CR and increases the quench and squish.

Dishing the piston can reduce the CR.

A domed piston can increase the CR.

A thinner head gasket increases the CR. Thicker is opposite.

Here is one trick.

Getting the quench height correct, will increase squish and more thoroughly mix the air/fuel in a more turbulent chamber.

This equates to less detonation while creating the most power per the fuel, all while decreasing the need for more advanced ignition timing.

This keeps the ignition from having a slight negative push on the piston as it moves towards the top of the stroke at tdc.

Also means you can get away with the most CR per fuel choice, when the quench is optimized and the squish is beneficial.

Now is it worthwhile to have custom pistons machined to your spec, that’s up to you.

You may want to use the parts readily available to you based on what fuel you want to run.

It’s similar to pick a tire size choice and build axles around that, that fits your budget and usage.

Decide on what fuel (s) you want to run, and see which parts get you to your goal in the best way for you.
Click to expand...

That just gave me a headache. The more I read about this the more I think I just need to pay to play.....
 
shawn said:
Are you sure about that? I thought 89 was just a blend of the high test and regular tanks.
Click to expand...

I should have phrased it differently. The non ethanol at the shell near my shop is 89 octane. They also carry 87,89,93 with ethanol.

Sorry about that guys. I meant it more like I prefer non ethanol and it happens to be 89 octane that won’t ping.

Not all 89 is non ethanol. Facepalm
 
Yeah around the Foothills and mountains, the 90 REC is non ethanol.. REC - reduced ethanol content.. and yes it does get better mileage and higher boiling point. It used to be only sold in areas with lower population density or so many miles from a city of such density or some such like. They may have changed that law as this station is in Hendersonville proper.

IMG_20190704_140541717s.jpg
 
a_kelley said:
Yeah around the Foothills and mountains, the 90 REC is non ethanol.. REC - reduced ethanol content.. and yes it does get better mileage and higher boiling point. It used to be only sold in areas with lower population density or so many miles from a city of such density or some such like. They may have changed that law as this station is in Hendersonville proper.

View attachment 298382
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Most of the Marathons around the Hendo, Brevard, Mills River area have it too.
I prefer it in my crawler
 
ghost said:
That just gave me a headache. The more I read about this the more I think I just need to pay to play.....
Click to expand...

Cliffs:
Run the correct piston/rod combo OR have your deck machined down to get the proper quench based on head gasket choice and top of piston travel vs deck height. It's really just simple math.
If you nail that, along with proper compression, you'll be golden.

This coming from a guy running pretty dang high compression in his Ranger and spending $25 extra per fill up to boost the octane so detonation doesn't happen. However, my engine in the ranger was build specifically for use as a nitrous motor when I drag raced. Nitrous loves high compression, other power adders not so much.
 
-28
 
-Ghost writer
 
84jimmy said:
So now the question would be do I go 8.8.1 cr or higher? Russ said he would get back to me in a little bit but advised against running 8.8.1 die to it being to low. Just want to hear your thoughts
Click to expand...

Jeff B said:
-28
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It's been a while since I ran the numbers on any of that stuff, so I recalculated the compression ratios with the -24 pistons: 8.9:1 static. That's what Russ recommended when I said I wanted to be able to run 87 octane. I'm curious to know what suggestions he has for @84jimmy.
 
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