Hemi mods? - JeepForum.com
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post #1 of 8 Old 09-15-2019, 06:30 AM Thread Starter
mr312712
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Hemi mods?

Im looking to get some more torque/power out of my 5.7. So far I tuned It with Superchips on the 87 tune (still running 89 octane) and really notice a difference In the trans. I tried the 91 tune with some 93 mixed In and didn't notice any difference from the 87 tune. On the 87 tune I got It up to 134 MPH (trans manually locked In 4th) and It was still slowly pulling but I let off as I started getting some vibrations and I didn't know how good the driveshafts are good for. On the 87 tune I Increased the rev limiter by 250 and the 91 tune I Increased It by 500. For now I think Im gonna go back to the 87 tune and keep running 89 octane and drop the rev limiter back down to 6050 RPM Instead of 6300 RPM. I plan on doing a SRT8 CAI and possibly switching to the 6.1 throttle body. Exhaust Is there any restriction In our exhaust? I love the way It sounds stock. Any other engine mods? 2008 Overland. Not really looking for more speed just more acceleration.


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post #2 of 8 Old 09-15-2019, 08:14 PM
90grandoneer
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Quote:
Originally Posted by mr312712 View Post
Im looking to get some more torque/power out of my 5.7. So far I tuned It with Superchips on the 87 tune (still running 89 octane) and really notice a difference In the trans. I tried the 91 tune with some 93 mixed In and didn't notice any difference from the 87 tune. On the 87 tune I got It up to 134 MPH (trans manually locked In 4th) and It was still slowly pulling but I let off as I started getting some vibrations and I didn't know how good the driveshafts are good for. On the 87 tune I Increased the rev limiter by 250 and the 91 tune I Increased It by 500. For now I think Im gonna go back to the 87 tune and keep running 89 octane and drop the rev limiter back down to 6050 RPM Instead of 6300 RPM. I plan on doing a SRT8 CAI and possibly switching to the 6.1 throttle body. Exhaust Is there any restriction In our exhaust? I love the way It sounds stock. Any other engine mods? 2008 Overland. Not really looking for more speed just more acceleration.
IIRC, to get to 134 mph you must have raised the speed limiter too, as a stock 5.7's speed limiter is set lower than that. Also, I can see where the engine would start laboring if you still have the stock exhaust logs on the engine. I've had my somewhat modified 5.7 WK (see signature) up to 137 mph with the speed limiter set at 140 mph. Mine was pulling strong at that speed and was smooth as glass. I won't try it again though.....too many possibilities of something to go wrong

Raising the rev. limiter with a stock cam IS NOT wise as if you "float the valves" you could encounter piston to valve collisions, as the valve springs aren't rated for that kind of RPM. The stock cam gets it's most power/torque somewhat lower than 6000 RPM On all 3 of my Hemi's (two 5.7's and a 6.1) with mild performance cams and 6.1 valve trains using PAC valve springs, I have the rev. limiters set to 6400-6500 RPM and have my WOT up shift points set to 6000-6200 RPM.

An SRT CAI is not necessary, but I'd recommend removing the stock baffled silencer in favor of either an SRT intake tube or an Airaid Jr. tube, and also add a low restriction high performance air filter element. On both my 5.7's I have modified LX (Magnum, Charger, 300C) SRT airboxes and intake tubes, AFE air filters, and a second air inlet into the boxes that draws air from behind the grill.

The stock 6.1 throttle body is exactly the same as the one on your 5.7. I run 90mm (Arrington and BBK) on my two 5.7's, but it's really overkill and probably doesn't add any power. They do improve the throttle response though. At most, but not really necessary, an 85 mm TB may help a little, but only after you've addressed the crappy exhaust system.

The exhaust system, specifically the exhaust log manifolds is the biggest choke point that takes a lot of potential power away from the 5.7. A good set of headers and a low restriction 3 in. cat. back will do wonders for it. Add a mild cam and 6.1 valve train and you'll see about a 70-80 hp. increase and about a 3 mile per gallon increase in fuel economy......if you can keep your foot out of it. I've had all of mine (except the 300CSRT) modded for quite a few years now and every time I drive them they get at least one WOT run up to 40+ mph, depending on speed limits and conditions. We just got back from an 1100 mile trip and the LX got lots of good exercise.....especially love the acceleration performance when passing....~60-100 mph.
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06 GCO, Dk Khaki, QDII, Flshing Hi 3rd Bk Lt, MDS "ON" Lt, Airtab Vortex Gens, Debadged, Fumoto Drain Valve, BT Catch Can, Chopped EGR Tube, SRT8 CAI, AFE Air Filter, 6spd 545RFE, Sonnax Trans Line Press Booster, SC Tuner W/Adv Trans Tune App, DS and HP tuners, Transgo Shift Kit, ARH Long Tube Hdrs w/3 in Magnaflow/Xlerator AP Exh Sys, Bilsteins, SRT Springs/Sways, Cust Eng Cvr, SRT8 frt/rear bumpers, FRI Sidewinder Cam w/6* advance/6.1 valvetrain, SLP 25% UD Pulley, BBK true 90mm T-Body, SOS Ign Coils w/.060 spark plug gaps, TEA ported/milled heads w/new valve seats, SRT Reps with 265/45&295/40X20's. Also 05 Hemi LX modded exactly like WK and, SOLD Comp Cammed 06 300CSRT8 just replaced with 2021 Tesla Model S Plaid with 1020 hp and 1050 lb. ft. of torque.
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post #3 of 8 Old 09-17-2019, 03:39 AM Thread Starter
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Ok cool Im gonna drop the rev limiter back down and look for a 6.1 Intake tube. I wanna eventually cam It but wanna do little things now. The vibration I was getting Is the front driveshaft. I was gonna rebuild It but Im just gonna get a new Mopar one, cause I heard the rebuild kits don't last and new aftermarket ones have vibrations. Far as exhaust could an exhaust shop get me some custom piping? Cause I know the LX manifolds fit but you gotta cut some of the tranny and play with the cross member.

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post #4 of 8 Old 09-17-2019, 08:33 AM
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Quote:
Originally Posted by mr312712 View Post
Ok cool Im gonna drop the rev limiter back down and look for a 6.1 Intake tube. I wanna eventually cam It but wanna do little things now. The vibration I was getting Is the front driveshaft. I was gonna rebuild It but Im just gonna get a new Mopar one, cause I heard the rebuild kits don't last and new aftermarket ones have vibrations. Far as exhaust could an exhaust shop get me some custom piping? Cause I know the LX manifolds fit but you gotta cut some of the tranny and play with the cross member.
If you plan to do a cam down the line, do it after you do a header back exhaust system. If you do the cam first, you won't get near the full benefit because of the restrictive stock exhaust manifolds. Also, when selecting a cam, be sure to do your homework. All performance oriented aftermarket cams will kill the bottom end hp/torque to some extent. Generally, the more radical, the bigger loss. For the heavy Jeeps, you'll want something with higher lift, slightly longer duration and a lower rather than higher lobe separation angle.

Most good muffler shops can build you a custom cat. back, but almost none will tackle custom headers. My first set, the silver ceramic coated ones above were custom built, but after done, the guy said he'd never touch another Hemi WK. The LX manifolds WILL NOT fit the WK, I've tried it. The collector hits the frame rails. In the pictures above, the one with the different exhaust manifolds are, left to right, the stock WK (1 3/4 in.), the stock LX (2 5/8 in.) and the collector on my first set of headers which is 3.0 in. You'll want to end up with a complete 3 in. "straight through" system....no switchbacks in the muffler(s) and you'll want to keep some sort of resonator to avoid the MDS drone. One other thing on headers for the WK....IMO, a set of LX shorty headers (don't cost very much) could be modified to fit by cutting and repositioning the collector to clear the frame. I've suggested this before but, to my knowledge, no one has given it a try.

If you can get your hands on a set of stock WK SRT8 headers, those are probably the ones you're talking about. You'll also need the WK SRT mids. to make the install easier. The SRT system will fit, but do require a little cutting away of the bellhousing. Any aftermarket WK SRT8 set of headers will also require the same mod. When I put my ARH long tubes on (the black ceramic coated ones in the picture above), the passenger side header looked to be the easiest one to install but trial and error cutting made it more difficult. The driver's side went right in, but interfered with the starter and knock sensor wiring which all had to be re-routed. Putting ANY header on a WK is a real PITA, and I'll never put long tubes on one again.

06 GCO, Dk Khaki, QDII, Flshing Hi 3rd Bk Lt, MDS "ON" Lt, Airtab Vortex Gens, Debadged, Fumoto Drain Valve, BT Catch Can, Chopped EGR Tube, SRT8 CAI, AFE Air Filter, 6spd 545RFE, Sonnax Trans Line Press Booster, SC Tuner W/Adv Trans Tune App, DS and HP tuners, Transgo Shift Kit, ARH Long Tube Hdrs w/3 in Magnaflow/Xlerator AP Exh Sys, Bilsteins, SRT Springs/Sways, Cust Eng Cvr, SRT8 frt/rear bumpers, FRI Sidewinder Cam w/6* advance/6.1 valvetrain, SLP 25% UD Pulley, BBK true 90mm T-Body, SOS Ign Coils w/.060 spark plug gaps, TEA ported/milled heads w/new valve seats, SRT Reps with 265/45&295/40X20's. Also 05 Hemi LX modded exactly like WK and, SOLD Comp Cammed 06 300CSRT8 just replaced with 2021 Tesla Model S Plaid with 1020 hp and 1050 lb. ft. of torque.
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post #5 of 8 Old 09-17-2019, 11:07 AM
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One time, I tuned It with Superchips on the 91 tune (running 91 octane) and I noticed a difference in the trans. Most of the time the trans shift back to 4th gear while driving on the highway (60-70 mph). So, I returned to stock setting. I don’t want to stress the trans.
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post #6 of 8 Old 09-17-2019, 05:09 PM
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On mine I run a modified (by HP Tuner) Superchips 91 tune with the Advanced Transmission Tuning App. and my custom up/down shift schedules and torque management settings. I've been hammering mine for almost 10 years now with about 100 hp. more than stock and it still works as good now as it did when I first set it up. I think I'll knock on wood though....just in case. With my setup though, I always run it in 4th gear on the highway.....only shift to 5th when above about 70 mph. I also think the Transgo shift kit and Sonnax Line Pressure Booster help quite a bit too.

06 GCO, Dk Khaki, QDII, Flshing Hi 3rd Bk Lt, MDS "ON" Lt, Airtab Vortex Gens, Debadged, Fumoto Drain Valve, BT Catch Can, Chopped EGR Tube, SRT8 CAI, AFE Air Filter, 6spd 545RFE, Sonnax Trans Line Press Booster, SC Tuner W/Adv Trans Tune App, DS and HP tuners, Transgo Shift Kit, ARH Long Tube Hdrs w/3 in Magnaflow/Xlerator AP Exh Sys, Bilsteins, SRT Springs/Sways, Cust Eng Cvr, SRT8 frt/rear bumpers, FRI Sidewinder Cam w/6* advance/6.1 valvetrain, SLP 25% UD Pulley, BBK true 90mm T-Body, SOS Ign Coils w/.060 spark plug gaps, TEA ported/milled heads w/new valve seats, SRT Reps with 265/45&295/40X20's. Also 05 Hemi LX modded exactly like WK and, SOLD Comp Cammed 06 300CSRT8 just replaced with 2021 Tesla Model S Plaid with 1020 hp and 1050 lb. ft. of torque.
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post #7 of 8 Old 09-17-2019, 06:34 PM Thread Starter
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A cam will be way down the line. Exhaust will be first, and yeah I meant the SRT manifolds. I already have a sonnax pressure booster from my WJ that I never Installed. Also Is porting the stock manifolds an option?

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post #8 of 8 Old 09-18-2019, 11:17 AM
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I've only heard of one guy saying it'll help, but I don't believe it'll do much. The problem is that the log manifold runners and collector are too small....period. They restrict the exhaust flow too much, probably at any RPM above about 2500-3000 RPM. The Hemi engine is really pretty well thought out and has very good flow through characteristics and the lousy exhaust logs pretty much kill it. You'll notice in the pix above showing the various manifolds, the LX one (middle one) has larger runners and nearly an inch larger collector. When I put JBA shorty headers and high flow cats. on my Hemi LX it didn't really make that much difference.....maybe only 10 hp. or so. This is because the logs were half way descent and it already had duals.....fairly low restriction. Contrast the WK with the tiny logs and a pretty restrictive muffler, the headers and cat. back make a significant difference.....I am guessing maybe 30-35 hp. or so.

06 GCO, Dk Khaki, QDII, Flshing Hi 3rd Bk Lt, MDS "ON" Lt, Airtab Vortex Gens, Debadged, Fumoto Drain Valve, BT Catch Can, Chopped EGR Tube, SRT8 CAI, AFE Air Filter, 6spd 545RFE, Sonnax Trans Line Press Booster, SC Tuner W/Adv Trans Tune App, DS and HP tuners, Transgo Shift Kit, ARH Long Tube Hdrs w/3 in Magnaflow/Xlerator AP Exh Sys, Bilsteins, SRT Springs/Sways, Cust Eng Cvr, SRT8 frt/rear bumpers, FRI Sidewinder Cam w/6* advance/6.1 valvetrain, SLP 25% UD Pulley, BBK true 90mm T-Body, SOS Ign Coils w/.060 spark plug gaps, TEA ported/milled heads w/new valve seats, SRT Reps with 265/45&295/40X20's. Also 05 Hemi LX modded exactly like WK and, SOLD Comp Cammed 06 300CSRT8 just replaced with 2021 Tesla Model S Plaid with 1020 hp and 1050 lb. ft. of torque.
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