Stroker issues have me wondering what's up

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mixedupjeeps
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Stroker Displacement: 4.6
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Vehicle Model: Scrambler

Stroker issues have me wondering what's up

Post by mixedupjeeps »

New member, first post but long time reader of the board. I have a stroker that I had built for my 84 Scrambler. I had Cleggs build the stroker but I did the head install and put it in the jeep. The motor only has 600 miles on it but has left me wondering why the power is not what I expected. I also have to go easy on the throttle or the engine clatters. Here are the particulars of the build as I remember without having the paperwork in front of me.

92 engine block and 7120 head bored 30 over, decked.
Keith Black forged pistons (new ones that are supposed to give 8.8 compression ratio.
4.2 crank, 4.0 rods
High flow air intake, 4.7 v8 throttle body, 99+ intake manifold
High flow exhaust and header
93 XJ OBD1 computer and wiring
24 lb/hr injectors, adjustable fuel pressure regulator set at 48 psi
Don't have the cam specs, I'll add them later but it was the one Cleggs uses most of the time
4.56 gears, 33" BFG MTs
Custom cage, 4 link and other off road goodies that make it a bit heavy

I have three other stock 4.0s in the jeep herd at my house and my son's 87 comanche with a tired engine outperforms my jeep so I know something isn't right. With the other Jeeps at my disposal I have been comparing compression, timing and vacuum. I have a wide band AFR meter that will be used to test it once the gauge shows up that goes with the controller.
The compression I am reading is only 100 PSI which seems too low (my daughters 96 4.0 with 80 K miles reads 110 at our altitude (4600 ft)
The vacuum on all of the jeeps is the same
The motor is still quite tight
Starts great and idles very well
Timing is a bit different: My jeep reads 12 degrees advanced at idle but jumps up off the cast scale on the front of the engine when I give it gas. My kids jeeps both seem to start out further advanced at idle but don't jump as much when the throttle is bumped up. My jeep has always been a bit touchy with pinging even on the old motor that I replaced (99 TJ 4.0). I always had to use premium to keep it from pinging. This problem seems to have been made worse with the stroker. Does anyone have any ideas for me to try ?? I am getting quite frustrated with this motor.
6TIME
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Vehicle Model: CHEROKEE

Re: Stroker issues have me wondering what's up

Post by 6TIME »

So you are getting 100 psi cranking on all cylinders? If you have a mild cam and 8.8 compression you should be somewhere in the 135-160 range at sea level, Not sure how much it will change with your elevation? Some say 8-10 psi/1000ft. Did you confirm the deck height and total quench distance? Was the cam dialed in?
Russ Pottenger
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Re: Stroker issues have me wondering what's up

Post by Russ Pottenger »

6TIME wrote:So you are getting 100 psi cranking on all cylinders? If you have a mild cam and 8.8 compression you should be somewhere in the 135-160 range at sea level, Not sure how much it will change with your elevation? Some say 8-10 psi/1000ft. Did you confirm the deck height and total quench distance? Was the cam dialed in?
^^^^ Totally agree.

It's water under the bridge now and there's nothing you can do about it, but that for circular dish piston is just a horrible design that United machine (KB) makes.

You have to deck .030 to .040 off the block and you get rewarded by having zero quench and to low of a static compression ratio that will give you a greater chance of detonating at a given octane level.

Sorry, ... rant over
mixedupjeeps
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Joined: February 27th, 2017, 4:47 am
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Vehicle Model: Scrambler

Re: Stroker issues have me wondering what's up

Post by mixedupjeeps »

6TIME wrote:So you are getting 100 psi cranking on all cylinders? If you have a mild cam and 8.8 compression you should be somewhere in the 135-160 range at sea level, Not sure how much it will change with your elevation? Some say 8-10 psi/1000ft. Did you confirm the deck height and total quench distance? Was the cam dialed in?
Well I'm at 4600 ft so I would lose about 37-46 psi that along with low miles on it may give me what I am seeing. Cleggs did the short block build and they said they decked the block but didn't say how much. I don't know about the cam being dialed in. Unfortunately I'm new to these strokers and went with what they suggested.
mixedupjeeps
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Stroker Displacement: 4.6
Vehicle Year: 1984
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Vehicle Model: Scrambler

Re: Stroker issues have me wondering what's up

Post by mixedupjeeps »

It's water under the bridge now and there's nothing you can do about it, but that for circular dish piston is just a horrible design that United machine (KB) makes.

You have to deck .030 to .040 off the block and you get rewarded by having zero quench and to low of a static compression ratio that will give you a greater chance of detonating at a given octane level.

Sorry, ... rant over[/quote]

So what can I do ??? they told me they have sold several hundred of these and haven't had problems with them.
mixedupjeeps
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Vehicle Model: Scrambler

Re: Stroker issues have me wondering what's up

Post by mixedupjeeps »

Well I found out I didn't do the compression test correctly, I didn't have the throttle body fully open during the test. So I redid the test on all cylinders and the compression came out at 135-140 on all cylinders. Guess I'm back to looking at air/fuel ratios to see if I am way off.
Russ Pottenger
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Re: Stroker issues have me wondering what's up

Post by Russ Pottenger »

mixedupjeeps wrote:Well I found out I didn't do the compression test correctly, I didn't have the throttle body fully open during the test. So I redid the test on all cylinders and the compression came out at 135-140 on all cylinders. Guess I'm back to looking at air/fuel ratios to see if I am way off.
Also worth mentioning when you're doing a cranking compression test make sure you disengage power to the injectors.
The raw gasoline pumping into the cylinders will wash the cylinder walls down of its oil and will compromise the ring seal

Good to hear at least you know that your compression is in a workable range
mixedupjeeps
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Posts: 15
Joined: February 27th, 2017, 4:47 am
Stroker Displacement: 4.6
Vehicle Year: 1984
Vehicle Make: Jeep
Vehicle Model: Scrambler

Re: Stroker issues have me wondering what's up

Post by mixedupjeeps »

Russ Pottenger wrote:
mixedupjeeps wrote:Well I found out I didn't do the compression test correctly, I didn't have the throttle body fully open during the test. So I redid the test on all cylinders and the compression came out at 135-140 on all cylinders. Guess I'm back to looking at air/fuel ratios to see if I am way off.
Also worth mentioning when you're doing a cranking compression test make sure you disengage power to the injectors.
The raw gasoline pumping into the cylinders will wash the cylinder walls down of its oil and will compromise the ring seal

Good to hear at least you know that your compression is in a workable range

I pulled the fuel pump relay out and pulled the coil drive connector to make sure there were no issues in that regard. I think I should have pulled the fuse for the PCM because I think a bit of fuel did get out of the injectors due to the remaining pressure in the fuel line. The plugs looked fine although I doubt there is enough miles on them to see much. They are Champion RC12 and I have read some people use RC9 plugs to help with pinging.
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