Jeep Strokers

Ok so after reading around here all day I think I have narrowed down a lot of my noob questions but still have a few.

My plan is to use the 4.5L Low budget stroker plan. I'm pretty sure that I already have a cracked head, 2000 TJ with cast number 0331, so I'm going to get the Alabama cylinder heads redesigned 0331 head. I will be using the 4.2L crank and rods and my current pistons. I also plan on using the .051" stock head gasket. According to Dino's page this setup will give me a 9.7:1 CR with the recommended cam and a .081" quench height. My question is this seems a little high CR for this engine, will I have a problem with detonation? Will a different cam help? Sorry for the noob question but I've read until I'm blue in the face and just need some straightforward answers.

Did you check out the Compression Ratio FAQ? 9.7 is the static compression ratio, what really matters to you is the dynamic compression ratio. Once you read that you're going to start asking more questions and do some more Googling, at least that's what I did. Hope this helps!

So basically with the right cam I can get the DCR to around 8:1 which should run on normal pump gas but the quench will still be at .081" so do I need to deck the heads to lower the quench? What are the problems associated if the quench is too high?

Yes and that's an option.
The cam choice will play a large role in your DCR, and 8 is okay for pump gas, depending on your elevation and the quench. Nobody will tell you a firm number on what will run on pump gas, but 8.5 is about the limit, and at sea level 8.5 is too high.

To lower your quench you could deck the block or use a thinner head gasket. A multi-layer steel (MLS) Mopar/Victor head gasket is 0.043" thick.

A lower quench will help prevent detonation/ping. With a DCR of 8 and a MLS head gasket you most likely won't have to deck the block.

justin_76 wrote:Ok so after reading around here all day I think I have narrowed down a lot of my noob questions but still have a few.

My plan is to use the 4.5L Low budget stroker plan. I'm pretty sure that I already have a cracked head, 2000 TJ with cast number 0331, so I'm going to get the Alabama cylinder heads redesigned 0331 head. I will be using the 4.2L crank and rods and my current pistons. I also plan on using the .051" stock head gasket. According to Dino's page this setup will give me a 9.7:1 CR with the recommended cam and a .081" quench height. My question is this seems a little high CR for this engine, will I have a problem with detonation? Will a different cam help? Sorry for the noob question but I've read until I'm blue in the face and just need some straightforward answers.

If you use the CompCams 68-231-4 cam that I included in my 4.5L low buck simple stroker recipe, the dynamic compression ratio will be 8.48:1. You'll need premium gas at sea level but at higher elevations you could get away with lower octane fuel.

Cheromaniac wrote:If you use the CompCams 68-231-4 cam that I included in my 4.5L low buck simple stroker recipe, the dynamic compression ratio will be 8.48:1. You'll need premium gas at sea level but at higher elevations you could get away with lower octane fuel.

How does ambient temperature play into this? I'm in Kuwait now, and last month I was in Qatar, and both places are insanely hot. In the UAE you're driving at sea level with 120+ degree weather. I'll be driving my stroker in Washington state, same elevation, but it's "unbearably hot" there this week according to my mom, and it's only in the high 80's (which is very warm for area).

I wan under the impression that 8.5 DCR is pushing it for sea-level, and to expect some ping under heavy load. Go to Denver and you could run 87-octane without issue, just as you said.

Hey Pollo,
I live in Oregon. My stroker is around 9.7-9.8 static and around 8.25 dynamic. I'm having it UniChipped tomorrow. The guy there mentioned that combustion chamber shape can also effect whether or not it'll ping. Mine does on 92 octane, especially as it's gotten warmer here in the NW. I added a water/meth system and that's gotten ride of the problem. That's an option. It really seems to help with power and MPG too.

T~

PolloLoco wrote:

Cheromaniac wrote:If you use the CompCams 68-231-4 cam that I included in my 4.5L low buck simple stroker recipe, the dynamic compression ratio will be 8.48:1. You'll need premium gas at sea level but at higher elevations you could get away with lower octane fuel.

How does ambient temperature play into this? I'm in Kuwait now, and last month I was in Qatar, and both places are insanely hot. In the UAE you're driving at sea level with 120+ degree weather. I'll be driving my stroker in Washington state, same elevation, but it's "unbearably hot" there this week according to my mom, and it's only in the high 80's (which is very warm for area).

I wan under the impression that 8.5 DCR is pushing it for sea-level, and to expect some ping under heavy load. Go to Denver and you could run 87-octane without issue, just as you said.

Lower ambient temps. and higher humidity reduce the risk of detonation. When I had the Crane 753905 cam in my stroker, the DCR was 7.86:1 (SCR is 9.25:1) and I was running 91 octane (95 RON) in 120*F weather with impunity. I'm currently running the stock '92 cam which has reduced the DCR to 7.35:1 so I might even be able to try 87 octane (91 RON) in the cooler months.

Cheromaniac wrote:Lower ambient temps. and higher humidity reduce the risk of detonation.

I was thinking about this today and I convinced myself of the opposite. Higher temperatures means that the air is less dense so when the air is compressed there is less air to be heated up by compression. I just thought that less air means lower temperatures under compression.

PolloLoco wrote:

Cheromaniac wrote:Lower ambient temps. and higher humidity reduce the risk of detonation.

I was thinking about this today and I convinced myself of the opposite. Higher temperatures means that the air is less dense so when the air is compressed there is less air to be heated up by compression. I just thought that less air means lower temperatures under compression.

In theory that sound grate. But theres to many strokers out there that can testify the opposite.

If the air is hotter entering the cylinder, then there is a much better change, that a small isolated piece of fuel will light off(pre ignite) before the spark and flame get there.

If you want to test it. install and open element filter.(will pull all the hot eng air in) then on a nice hot summer day when you get it to ping..............ditch the open element filter, and put your stock filter and box back on(pulls air from out side the engine compartment) and see if the ping goes a way.

Flash wrote:In theory that sound grate. But theres to many strokers out there that can testify the opposite.

If the air is hotter entering the cylinder, then there is a much better change, that a small isolated piece of fuel will light off(pre ignite) before the spark and flame get there.

If you want to test it. install and open element filter.(will pull all the hot eng air in) then on a nice hot summer day when you get it to ping..............ditch the open element filter, and put your stock filter and box back on(pulls air from out side the engine compartment) and see if the ping goes a way.

Yes, I have heard of that too. It makes so much sense that it has to be right! But seriously, I know that you're right, I just don't know what was wrong with my thinking. I think that the Iraq sun really is starting to cook my brain. That and all the crap from the burn pit, it makes for a good fresh breath when going on my morning runs.