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Unread 09-04-2009, 01:18 PM   #1
suntzur
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4.0 Performance out of Cylinder Head?

What head work will give me better performance in a 97 4.0?

I'm running a 97 TJ with the 99 style intake, aftermarket header, 2.5" exhaust w/ flowmaster 40 series (actually being installed tomorrow) and no cat (may add it, but the PO gutted the stock cat). I am installing 4-hole 24lb injectors because I have them from a different project and I know that the computer will adjust the fuel rate accordingly so they shouldn't kill my MPG or foul out my plugs.

I know that some engines benefit greatly from larger ports, usually exhaust. Does anyone have good recommendations of upgrades to the head on a 4.0? The engine ran fine until one injector stopped working and having to swap in the larger injectors got me to thinking about upgrades. Is decking the head a good idea for compression gains? How far, if so? I'd like to keep it under 10:1 so I can run 87 octane still (I tihnk that's the cut-off typically isn't it?).

FWIW, I am going to try to swing a supercharger in the next year or so. That'll require some significant saving of money for me, but it is a desire that might impact what I do with this head.

Thanks, in advance.

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Unread 09-04-2009, 01:29 PM   #2
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1- larger injectors won't do you any good unless you do something with the computer. the computer will simply adjust the pulse width to delivery the same amount of fuel you were getting before.

2- depending which header style you have it may crack. if its a one piece design with no flex joints, it WILL crack very soon. then you'll need a new header, which will then crack. a 2000+ stock manifold is the best bet here.

3- for head upgrades, your best bang for your buck will be roller rockers, heavy duty valve springs and a Hesco cam

4- you could also go with a completely new performance Golen/Alabama head or an aluminum Hesco head. the aluminum head would allow you to run about 9.5:1 on 87 octane, but you'd need to dyno tune.

4- at 10:1 you'll need 100 octane or so. 10:1 would be go for running E-85 exclusively. for 87 octane you need to stay at 8.8:1 compression with a cast iron head.

5- for larger injectors, head or cam work, a supercharger or compression ratio changes, you'll need to dyno tune to ensure adequate a/f ratios.

PM "Robert J. yates", he has done the Hesco aluminum head, Hesco cam, roller rockers and heavy duty valve springs + dyno tuning with a Unichip piggyback. hes got all sorts of info
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Unread 09-04-2009, 03:23 PM   #3
suntzur
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Thank you,

I knew about the lack of improvement from the larger injectors but it was the only option available with no additional cost so they are in.

I went with the flex-tubes on the header so I'm hoping it lasts a few years.

I don't have $2000 to spend on a new head so I was hoping to do something common like oversized valves. I'll look into rollers though. Thanks again.

Any other thougths?
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Unread 09-04-2009, 03:33 PM   #4
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Yea if you do the head, you'll need to do a good camshaft also to make it work.
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Unread 09-04-2009, 04:23 PM   #5
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Quote:
Originally Posted by suntzur View Post
Thank you,

I knew about the lack of improvement from the larger injectors but it was the only option available with no additional cost so they are in.

I went with the flex-tubes on the header so I'm hoping it lasts a few years.

I don't have $2000 to spend on a new head so I was hoping to do something common like oversized valves. I'll look into rollers though. Thanks again.

Any other thougths?
unfortunately real 4.0L performance is expensive. a cam swap is the best option, and a cam swap requires removing the head. any cam over .450" of lift requires heavy duty valve springs.

the best bang for your buck, and cheapest solution, like I already mentioned above, is a Hesco cam, roller rockers and heavy duty valve springs. no head porting required, but it wouldn't hurt to get a 3-angle valve job and some port matching to the intake and exhaust manifolds.
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Unread 09-04-2009, 04:59 PM   #6
suntzur
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I had completely forgotten the camshaft option. The last time I bought a cam was for my race car back in the early 90's. Can I rely on someone at Hesco to spec a cam for me?
I'm going to call around for a shop that will do the roller rockers and springs for me. Any ideas on the prices for that? Nobody will be around until Tuesday and I'd like to set-up a budget this weekend.

Thanks again
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Unread 09-05-2009, 08:28 AM   #7
cfmiller58
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actually the 95 97 and 98 jeep 4.0s have the best stock head flow. the 95's and 97's are almost the same. the 24 lb injector is actually the proper injector to use as the stock injector runs 23.something pounds (i have a site for that ill try to find it, but you can find it by searching the threads on this site).
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Unread 09-05-2009, 08:49 AM   #8
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Quote:
Originally Posted by suntzur View Post
I had completely forgotten the camshaft option. The last time I bought a cam was for my race car back in the early 90's. Can I rely on someone at Hesco to spec a cam for me?
I'm going to call around for a shop that will do the roller rockers and springs for me. Any ideas on the prices for that? Nobody will be around until Tuesday and I'd like to set-up a budget this weekend.

Thanks again
Hesco Inc. - High Performance Engine Service

Call them, they will spec everything for you. Buy what they say, they're the experts in 4.0L performance.
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Unread 09-05-2009, 09:05 AM   #9
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Quote:
Originally Posted by suntzur View Post
I am installing 4-hole 24lb injectors because I have them from a different project and I know that the computer will adjust the fuel rate accordingly so they shouldn't kill my MPG or foul out my plugs.

I know that some engines benefit greatly from larger ports, usually exhaust. Does anyone have good recommendations of upgrades to the head on a 4.0? The engine ran fine until one injector stopped working and having to swap in the larger injectors got me to thinking about upgrades. Is decking the head a good idea for compression gains? How far, if so? I'd like to keep it under 10:1 so I can run 87 octane still (I tihnk that's the cut-off typically isn't it?).
FWIW, I am going to try to swing a supercharger in the next year or so.
Its a bad idea to swap injectors without retuning. The ECU can only adjust the part throttle steady state conditions, at WOT and during transitions you will be rich and down on power.
10:1 is too much for 87 octane, but should work with 91 octane. There are 2 options if you are getting a blower, low compression and "high" boost for max power in boost. If you have a blower with lag, or low boost at low rpms you will suffer off boost performance (actually all off boost performance will suffer). Then high compression low boost. That will require higher octane, but you will get better economy and off boost performance. I would go that way in the jeep, maybe 9.3 to 9.7:1. There really is no solution to reprogram the ecu on the TJs (except maybe 06-now). I would use a rising rate FMU (normally i hate them) and adjust the timing by breaking off the tabs and turning the distributor to back off the timing for boost. (Did you hear that Jerry?) A standalone is the best option but they start at $1000-2500 and go up from there! The best mod for the 4.0 is a 5.7 hemi swap.
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Unread 09-05-2009, 04:56 PM   #10
suntzur
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The 24lb injectors are pretty darned close to the original 23.2lb injectors, even with the additional 7PSI of fuel pressure, assuming that the stats of 23.2lb/hr @ 49 is accurate for the 97 4.0 HO.

I'm not sure how long it takes the computer to make the "corrections", but this thing runs 10x better and stronger than it ever has (since I've owned it anyway). It may be that my old injectors were just really clogged, but man what a difference!

jgorm, what is an FMU? I will be getting some software and a tie-in with the supercharger, is that adequate? I have to admit ignorance on tuning but the seller is local and has promised to help if I need it. He says it's really easy to change the tunes.
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Unread 09-05-2009, 04:59 PM   #11
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Quote:
Originally Posted by suntzur View Post
The 24lb injectors are pretty darned close to the original 23.2lb injectors, even with the additional 7PSI of fuel pressure, assuming that the stats of 23.2lb/hr @ 49 is accurate for the 97 4.0 HO.

I'm not sure how long it takes the computer to make the "corrections", but this thing runs 10x better and stronger than it ever has (since I've owned it anyway). It may be that my old injectors were just really clogged, but man what a difference!

jgorm, what is an FMU? I will be getting some software and a tie-in with the supercharger, is that adequate? I have to admit ignorance on tuning but the seller is local and has promised to help if I need it. He says it's really easy to change the tunes.
FMU = fuel management unit.

To correctly tune your OBDII 4.0L you need a piggyback. The Unichip Q and the SplitSecond FTC-1 are the most used on a 4.0L. They both would require dyno tuning, however the FTC-1 can be 'half-arsed' tuned somewhat close with a laptop and an A/F meter in the cab.
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Unread 09-05-2009, 05:47 PM   #12
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You profile says you are running 33's with 3.07 gears. Changing your gear ratio will make a big difference, and be a lot cheaper than any engine mods that would really do anything.
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Unread 09-05-2009, 06:09 PM   #13
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Porting & polishing and gasket-matching can add a small but noticeable bit of improvement (I'd leave the head to the pros and do the intake & exhaust myself), and there's a company called "Extrude Hone" that will pump an abrasive paste through your intake to smooth out the casting and remove impediments to smooth airflow.
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Unread 09-05-2009, 06:13 PM   #14
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Quote:
Originally Posted by cfmiller58 View Post
actually the 95 97 and 98 jeep 4.0s have the best stock head flow. the 95's and 97's are almost the same. the 24 lb injector is actually the proper injector to use as the stock injector runs 23.something pounds (i have a site for that ill try to find it, but you can find it by searching the threads on this site).
Sorry to disagree it's a 91-95 HO head!
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Unread 09-05-2009, 06:14 PM   #15
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Quote:
Originally Posted by cfmiller58 View Post
actually the 95 97 and 98 jeep 4.0s have the best stock head flow. the 95's and 97's are almost the same. the 24 lb injector is actually the proper injector to use as the stock injector runs 23.something pounds (i have a site for that ill try to find it, but you can find it by searching the threads on this site).
Stock injectors are 19 lbs?
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