Compression ratio

[Cheromaniac]

Here's an article worth reading:

http://www.popularhotrodding.com/tech/0 ... index.html

David "The Wizard" Vizard's hit list looks like this:

15 COMPRESSION BOOSTING MOVES

1. Feed cold air to the induction
2. Keep water as cool as possible (170 F or less)
3. Keep the air cool in the intake ports
4. Put a heat-reflective shine on the outside of the intake manifold
5. Minimize heat transfer through the common exhaust/intake port wall
6. Keep fuel temperatures down (cool can)
7. Run with plugs a little colder than the minimum required
8. Use an ignition system that is gross overkill
9. Utilize as large a spark plug gap as possible
10. Use no more ignition advance than is necessary
11. Maximize quench action
12. Minimize head chamber volume
13. Use flat-top pistons if possible
14. Minimize under-hood exhaust heat--use coated headers
15. Do not ram in but vent out hot air through hood vents

[YJ_and_Corey]

I have two guys out there now with 10.6:1 and 10.5:1 SCR on stock ODB1 computers. They are both running the KB 945

They are both running mid-grade pump gas without any detonation issues.

I wasn't aware people were having problems getting more 4.0L compression
No problems to report here...

[SilverXJ]

What is their DCR?

[Cheromaniac]

I have two guys out there now with 10.6:1 and 10.5:1 SCR on stock ODB1 computers. They are both running the KB 945
They are both running mid-grade pump gas without any detonation issues.

Which cams are they using? A long duration cam could reduce the DCR enough to allow the use of mid-grade fuel.
Which head? The Hesco aluminium head will allow more compression without detonation.
Which plugs?
Any cooling system upgrades?

[Jeepinscott]

I have a 4.0 with 10:1 SCR and 11:1 DCR.

My max timing is 34 degrees. Pistons stick out -.003 with the .043 gasket I have .040 quench. I have a 100 octane fuel limit and size limit to +.060 bore, stock crank. I tried to stay within the realm of pump gas, but the agressive cam put me into the 95-100 octane range.

I run the Painless Performance Hi-Torque cam and ECM.

It's expensive, yes, but worth every penny. Dyno tuning in Socal on a 'current eddy' dyno cost $300. The Air Fuel Ratio adjusted by the stock computer just doesn't cut it. You can only fool the stock computer so much. I have my fuel trim adjusted for racing, but in what I do had to have economy and reliability. You would be amazed what a properly tuned ECM with a built motor will do. The ECM and tuning added 46 hp, over 25 in just dyno tuning.

[gradon]

You might want to correct your DCR # there(it's always lower than SCR).

[YJ_and_Corey]

I have two guys out there now with 10.6:1 and 10.5:1 SCR on stock ODB1 computers. They are both running the KB 945
They are both running mid-grade pump gas without any detonation issues.

Which cams are they using? A long duration cam could reduce the DCR enough to allow the use of mid-grade fuel.
Which head? The Hesco aluminium head will allow more compression without detonation.
Which plugs?
Any cooling system upgrades?

I only spec one cam for Jeep stroker engines unless it is a race engine. I now have over 15 engines out there.
Comp 68-232-4

That aluminum head is a big waste of cash IMHO.

The big key is in the cooling system upgrade. I make the guys who want the higher compression
run Evans waterless coolant. NO detonation with mid-grade. It negates the possibility of hot spots
developing within the head or block by nature of how it extracts heat and it's "wet-ability" due to a surface
tension significantly less than that of water.

Gimmick? It works, that what I know.

[SilverXJ]

Is the waterless coolant the only upgrade to the cooling systems you use?

[YJ_and_Corey]

Is the waterless coolant the only upgrade to the cooling systems you use?

Pretty much, although I recommend a "ported" thermostat housing as well - increases flow.

In my race buggy I am using a Hesco high output pump, but only because the radiator is in the back.

[Cheromaniac]

That aluminum head is a big waste of cash IMHO.

You're not the only one who has that opinion. I think most Jeepers would want to "invest" $2000 of their hard-earned cash elsewhere.

[SilverXJ]

I'll have to look into that waterless coolant. Are they still using a stock rad?

For the "gains" on the aluminum head it is so not worth it. Now if they actually did a major change when they made it that may be different.