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Old 02-11-2019, 11:44 AM   #1 (permalink)
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Jeep 4.0 supercharger tuning

Im wanting to lower the engines compression ratio so i can run more boost (vortech v1 super charger). Does anyone have a sorce for the jeep 4.0 head gasket file? My idea is to have a spacer plate cut with water jet to lower the CR from 8.8:1 to 6.5:1. How thick material do i use to achive 6.5 ratio? Im not looking to rebuild a engine/change pistons at this time(that will come later), only to ad a decompression plate under the head. I didnt find decompression plate information on the internet for Jeep 4.0

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Old 02-11-2019, 05:38 PM   #2 (permalink)
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Seems like you are adding in failure points with that. The graphite gasket is thicker than the MLS gasket but not by much.

How much power are you trying to make?
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Old 02-12-2019, 06:05 PM   #3 (permalink)
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Seems like you are adding in failure points with that. The graphite gasket is thicker than the MLS gasket but not by much.

How much power are you trying to make?
Not looking to add a failure point, but blowing a gasket is better than blowing a piston i geuss.

I'm trying to make 100 HP over stock.
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Old 02-12-2019, 06:57 PM   #4 (permalink)
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Not looking to add a failure point, but blowing a gasket is better than blowing a piston i geuss.

I'm trying to make 100 HP over stock.

I am putting a turbo on my 4.0 and plan to make over 100 more than stock without touching compression or really anything else.

With the compression you are looking for that engine will not run worth a flip at idle if it will even start.
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Old 02-12-2019, 07:51 PM   #5 (permalink)
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I have an engine that runs on 6.3 to 1, it runs all day long....
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Old 02-13-2019, 07:10 AM   #6 (permalink)
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How about having a thick copper sheet cut into a head gasket? no need for a spacer, then.

Alternately, you might be able to open up the combustion chamber on the head and make the dish on the piston bigger.

Also, maybe run the turbo on E85 for more octane and leave the compression stock.
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Old 02-21-2019, 11:48 AM   #7 (permalink)
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It's such a common engine, I'd be surprised if Cometic didn't have one on file. They make extra thick gaskets all day, with reasonable prices.
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Old 02-26-2019, 06:25 PM   #8 (permalink)
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It's such a common engine, I'd be surprised if Cometic didn't have one on file. They make extra thick gaskets all day, with reasonable prices.
Thanks for the referral. I messaged Cometic about the decompression gasket. They do offer thicker gaskets and different bores. How do i calculate the thickness needed to reduce stock compression from 8.8 to 6.0? The way i understand it the lower i get the static compression ratio, the more boost i can throw at it to more easily tune horsepower. My Vortec V1 supercharger is capable of 20 psi boost.
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Old 02-27-2019, 06:11 AM   #9 (permalink)
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Old 02-27-2019, 08:35 AM   #10 (permalink)
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Really you are chasing all the wrong things. My 4.0 wasn’t enough and it was far cheaper and easier to swap in a relatively stock ford 5.0 than it was to mess with my relatively low mileage 4.0. I put the 4.0 in a friends relatively stock cj7 and everyone is happier.

Just because your blower can make 22 pounds there’s no way you want it pushing 22 pounds all the time. The heat it will make, plus the wear and tear, plus the load on the engine and the accessory drive is just unreasonable. Realistically you should be looking at 6-8 pounds of boost, it’s the functional limit of what you want to throw at a 4.0 anyways.

The head really doesn’t flow, camshafts aren’t happy with higher valve spring pressures and wipe themselves with fair regularly. Plus they just aren’t happy revving.

My first step if I was really married to the 4.0 and the supercharger would be the thickest gasket cometic makes, 8 pounds of boost and a bunch of work mapping it and working out valve springs, cams and head flow before anything too drastic.
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Old 02-27-2019, 10:21 AM   #11 (permalink)
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Really you are chasing all the wrong things. My 4.0 wasnít enough and it was far cheaper and easier to swap in a relatively stock ford 5.0 than it was to mess with my relatively low mileage 4.0. I put the 4.0 in a friends relatively stock cj7 and everyone is happier.

Just because your blower can make 22 pounds thereís no way you want it pushing 22 pounds all the time. The heat it will make, plus the wear and tear, plus the load on the engine and the accessory drive is just unreasonable. Realistically you should be looking at 6-8 pounds of boost, itís the functional limit of what you want to throw at a 4.0 anyways.

The head really doesnít flow, camshafts arenít happy with higher valve spring pressures and wipe themselves with fair regularly. Plus they just arenít happy revving.

My first step if I was really married to the 4.0 and the supercharger would be the thickest gasket cometic makes, 8 pounds of boost and a bunch of work mapping it and working out valve springs, cams and head flow before anything too drastic.

Chasing the wrong things? Let me elaborate. The jeep that I built goes everywhere i want to go and is super reliable. I hop in and drive all the way through the rubicon and back with no issues. Its been this way for many years. I only have two complaints, both of which dont have to do with offroading. #2 road noise at highway speeds, #1 too slow up the mountain passes hwy 80 and 50 (im still faster than the heavey haulers) all im "chasing" is being able to maintain a reasonably high rate of speed to the trails.
Thank you for the advice, i really only anticipate running around 6-8 pounds of boost.
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Old 02-27-2019, 10:59 AM   #12 (permalink)
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#1 too slow up the mountain passes hwy 80 and 50 (im still faster than the heavey haulers) all im "chasing" is being able to maintain a reasonably high rate of speed to the trails.
Thank you for the advice, i really only anticipate running around 6-8 pounds of boost.

And you could easily accomplish exactly that by simply bolting on a low pressure turbo to your engine now, tune it and run, why not give it a try before removing a perfectly good sealing cyl head ?
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Old 02-27-2019, 11:17 AM   #13 (permalink)
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And you could easily accomplish exactly that by simply bolting on a low pressure turbo to your engine now, tune it and run, why not give it a try before removing a perfectly good sealing cyl head ?
Im going to try it out as is asap. I completed the SC bracketry, and pulled the oil pan, i was going to add oil return provisions, but instead bought a moroso oil pan. I'll be modifying it slightly to allow pinion clearance and i have to redo the exhaust.
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Old 02-27-2019, 11:23 AM   #14 (permalink)
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Shows the bracketry and oil pan
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Old 02-27-2019, 01:21 PM   #15 (permalink)
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Old 02-27-2019, 03:42 PM   #16 (permalink)
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6-8 pounds just get the thickest cometic gasket they sell and run premium. No extra failure points and much cheaper in the long run.

I just set up a Miata that way and it started at 9.4 cr static. 8 pounds of boost no issues.

Just make sure you pull some timing and have a nice reliable way to pump in the extra fuel.

6-8 pounds of boost is much more manageable.
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Old 02-28-2019, 07:40 AM   #17 (permalink)
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Even though a centrifugal SC will make power down low, anything in the 6:1 compression ratio area is going to be an absolute turd when not at a fair amount of boost. 14psi you make roughly double the naturally aspirated power, but a 6.5:1 4.0 is making 100-125hp?

Is e85 available in you area and the areas you travel. That will give you better detonation resistance and run cooler. Don't add failure points with head spacers and extremely thick head gaskets and think you can jam in a bunch of boost.

Good fuel, a good means of tuning (megasquirt?), and conservative timing should make things last.
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Old 02-28-2019, 03:48 PM   #18 (permalink)
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How do i adjust the timing? MAP sensor? Coolant sensor? Will i need a boost retarder? Can i use my stock in tank fuel pump as a lift pump to supply fuel to a bigger pump/regulater setup? Whats recommended?
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Old 03-01-2019, 07:03 AM   #19 (permalink)
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you will need fuel/ignition controller

i got AFE unit i had on my supercharged 4.0
id sell it






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Old 03-01-2019, 07:39 AM   #20 (permalink)
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you will need fuel/ignition controller

i got AFE unit i had on my supercharged 4.0
id sell it
I looked into that. Im obd1, I believe that aem fic is for obd2
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Old 03-01-2019, 08:11 AM   #21 (permalink)
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i wouldn't go down below 8:1, much lower and your off idle tq is going to be next to nothing. I run a V1 on a vw vr6 motor is 100% stock (head/bottom end) aside from a stainless head spacer dropping down to 8.25:1 and a megasquiert ecu. the v1 has cog pulleys and puts 12psi out at 2800 rpm with no issues aside from melting tires. i would worry more about the stock 4.0 rods than drooping to a extra low compression ratio. if your obd1 maybe look into swapping over to a megasquirt ecu, i have put a few on obd1 motors. being able to pull any part out of the junk yard or summit and toss it on a home built mix/match motor and self tune it is a real game changer when adding boost to a motor not normally equipped with forced induction.
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Old 03-01-2019, 10:15 AM   #22 (permalink)
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How do i adjust the timing? MAP sensor? Coolant sensor? Will i need a boost retarder? Can i use my stock in tank fuel pump as a lift pump to supply fuel to a bigger pump/regulater setup? Whats recommended?
I'm not certain on 4.0 tuning options, but being obd1 I'll assume their limited. A megasquirt/microsquirt is 3-400 and gives you full control over fuel and timing. You'd use a MAP sensor with it to let it adjust fuel/timing based on boost/rpm/tps etc. Mega/micro uses a coolant sensor to do all the normal warmup enrichment stuff and can be used to start pulling timing to protect the engine if its running hot. On an engine that is already EFI, it shouldnt be a hard install. I'd upgrade the stock fuel pump just to be safe in boost, but something like a walbro 255 or 450 should do the trick. A base tune or something close can probably be found on the web since the 4.0 is so popular.
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Old 03-01-2019, 11:28 AM   #23 (permalink)
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I don't know all of the details of your engine but if it's bone stock as far as head, pistons, rod, deck height and head not surfaced you are going to need about .220" between the block and head to get down to 6.5cr.

Research what John Kasse is doing with his engine masters builds as he's doing crazy stuff with thick spacers.

Really though you are going about this wrong imo. Look into some form of intercooler/better intercooler and/or methanol injection. Also like others have said look at other ECMs like the megasquirt.
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Old 03-01-2019, 11:46 AM   #24 (permalink)
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The banks turbo kit for the 4.0l adds about 100hp and doesn't include a new head gasket or a spacer. I'd pattern whatever you want to do after what they've engineered.
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Old 03-01-2019, 04:15 PM   #25 (permalink)
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With .plus 22 of head spacing, what about pushrod length?
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