Anyone considered this head swap? - Cherokee SRT8 Forum
WK1 General Performance Discussion If you are planning on modifying your Jeep Grand Cherokee SRT8 with a performance enhancing modification, this is the section to post about it.

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post #1 of 35 (permalink) Old 03-07-2007, 08:52 AM Thread Starter
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Anyone considered this head swap?

I was thinking that although the 6.1L HEMI is an amazing engine that although impressive in a 4200lb LX car that maybe it isn't the best candidate for a 4700-4800lb GC. I am willing to bet that a nicely set of ported 5.7 heads when bolted onto a 6.1L shortblock and mated with the GC platform would create pure magic! Just looking at the 6.1 heads and their flow of close to 300 cfm from the factory makes me think RACE head! for a RACECAR! There's a reason Dodge hasn't relinquished the 6.1 to truck duty yet. I was thinking that 5.7 heads when ported, regularly flow 300-315cfm which is still about 20-25cfm more than a factory 6.1 casting.
Hmm---much larger port 6.1L head=290-300cfm
---much smaller port 5.7L head ported=300-315cfm
The smaller the port with the same or better flow at the same valve lifts = VELOCITY!! Velocity= throttle response and TORQUE, which = awesome driveability and FUN FUN FUN! I would have a hard time believing that no one has tried this yet and would love to hear the results if anyone has. Like I said the 6.1 and 5.7 for that matter ARE amazing engines but I think the 6.1 is more race engine than truck engine and it was pure marketing that got them put under the hood of GC's. I am so convinced that this would be THE swap that I will be trying it on my own GC SRT-8 in the very near future.

Last edited by RAMM; 03-07-2007 at 09:02 AM.
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post #2 of 35 (permalink) Old 03-07-2007, 09:02 AM
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Re: Anyone considered this head swap?

Quote:
Originally Posted by RAMM
I was thinking that although the 6.1L HEMI is an amazing engine that although impressive in a 4200lb LX car that maybe it isn't the best candidate for a 4700-4800lb GC. I am willing to bet that a nicely set of ported 5.7 heads when bolted onto a 6.1L shortblock and mated with the GC platform would create pure magic! Just looking at the 6.1 heads and their flow of close to 300 cfm from the factory makes me think RACE head! for a RACECAR! There's a reason Dodge hasn't relinquished the 6.1 to truck duty yet. I was thinking that 5.7 heads when ported, regularly flow 300-315cfm which is still about 20-25cfm more than a factory 6.1 casting.
Hmm---much larger port 6.1L head=290-300cfm
---much smaller port 5.7L head ported=300-315cfm
The smaller the port with the same or better flow at the same valve lifts = VELOCITY!! Velocity= throttle response and TORQUE, which = awesome driveability and FUN FUN FUN! I would have a hard time believing that no one has tried this yet and would love to hear the results if anyone has. Like I said the 6.1 and 5.7 for that matter ARE amazing engines but I think the 6.1 is more race engine than truck engine and it was pure marketing that got them put under the hood of GC's. I am so convinced that this would be [B]THE [B]swap that I will be trying it on my own GC SRT-8 in the very near future.
Doing that steps the compression up into the 11's and some change(trouble on pump gas)The 5.7L pistons are dished,the 6.1L are flat. There is a few companies working on this very idea with a twist, but I'm not telling right now.

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post #3 of 35 (permalink) Old 03-07-2007, 09:05 AM Thread Starter
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Re: Anyone considered this head swap?

I was aware of the comp ratio increase and although it wouldn't be a true back to back test in my case as I was going to convert over to E85 (105 octane) at the same time. Should be a killer!

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post #4 of 35 (permalink) Old 03-07-2007, 10:03 AM
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Re: Anyone considered this head swap?

Quote:
Originally Posted by gculver
Doing that steps the compression up into the 11's and some change(trouble on pump gas)The 5.7L pistons are dished,the 6.1L are flat. There is a few companies working on this very idea with a twist, but I'm not telling right now.
Damn, this could get expensive!
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post #5 of 35 (permalink) Old 03-07-2007, 06:33 PM
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Re: Anyone considered this head swap?

You have a great idea, but there are some things that need to be cleared up.

5.7 head +/- 80cc combustion chamber
6.1 head +/- 70cc combustion chamber

6.1 heads on a 5.7 raise compression (I have done this) and 5.7 heads on a 6.1 would lower comression IF THEY FIT.

You CAN make them work if you:
Machine the 5.7 heads to allow the clearance needed because the 6.1 piston comes out of the bore and would hit the head

OR

Run some custom thick Cometic head gaskets ($200 or more)

You will also need to port match the intakes on the 5.7 heads to fit the 6.1 manifold (no problem either I have done that too).

Also any 04-up 5.7 HEMI uses EGR in the pass side head. You can either find 2003 truck heads (not too hard to find) or just tap and plug the holes (I've done that too).

Also you MIGHT need 5.7 pushrods, but they are super cheap. I know when switching to 6.1 heads on a 5.7 we went to 6.1 pushrods, so the opposite swap might require the same. The 5.7 pushrods are shorter by a little bit.

Another thing to watch out for, the truck heads do not have the holes for the P/S pump on the pass side. It's an easy fix though.
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post #6 of 35 (permalink) Old 03-07-2007, 07:24 PM
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Re: Anyone considered this head swap?

So clearancing the 5.7L combustion chamber to work on a 6.1L would lower static compression even further. I wasn't looking at it that way. Is the 5.7L piston flat top are dished(was going on word of mouth), how much of the 6.1L is outta the hole(10cc less or more?)
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post #7 of 35 (permalink) Old 03-07-2007, 08:11 PM
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Re: Anyone considered this head swap?

The 5.7 is actaully domed. The 6.1 is flat top. I am not sure exactly how far out of the hole it comes, but I can ask my partner (he does all our engine design and assembly) or measure one.
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post #8 of 35 (permalink) Old 03-07-2007, 08:49 PM
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Re: Anyone considered this head swap?

Quote:
Originally Posted by Beast 2
The 5.7 is actaully domed. The 6.1 is flat top. I am not sure exactly how far out of the hole it comes, but I can ask my partner (he does all our engine design and assembly) or measure one.
Was Just curious for furture reference. Does the Hemi shop have any plans on a new head casting on the lines of this discussion???.
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post #9 of 35 (permalink) Old 03-07-2007, 09:10 PM
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Re: Anyone considered this head swap?

We could probably CNC a combustion chamber on the 5.7 that would work, however I bet our CNC 6.1 head would still outperform our CNC 5.7 head on a 6.1, we know it does on a 5.7.
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post #10 of 35 (permalink) Old 03-07-2007, 09:55 PM
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Re: Anyone considered this head swap?

Quote:
Originally Posted by RAMM
I was thinking that although the 6.1L HEMI is an amazing engine that although impressive in a 4200lb LX car that maybe it isn't the best candidate for a 4700-4800lb GC. I am willing to bet that a nicely set of ported 5.7 heads when bolted onto a 6.1L shortblock and mated with the GC platform would create pure magic! Just looking at the 6.1 heads and their flow of close to 300 cfm from the factory makes me think RACE head! for a RACECAR! There's a reason Dodge hasn't relinquished the 6.1 to truck duty yet. I was thinking that 5.7 heads when ported, regularly flow 300-315cfm which is still about 20-25cfm more than a factory 6.1 casting.
Hmm---much larger port 6.1L head=290-300cfm
---much smaller port 5.7L head ported=300-315cfm
The smaller the port with the same or better flow at the same valve lifts = VELOCITY!! Velocity= throttle response and TORQUE, which = awesome driveability and FUN FUN FUN! I would have a hard time believing that no one has tried this yet and would love to hear the results if anyone has. Like I said the 6.1 and 5.7 for that matter ARE amazing engines but I think the 6.1 is more race engine than truck engine and it was pure marketing that got them put under the hood of GC's. I am so convinced that this would be THE swap that I will be trying it on my own GC SRT-8 in the very near future.
I don't think you're going to make more power. It seems quite a few people claim that the intake ports on the 6.1 heads are too large, but at right around 210cc (from what I've seen), that's really not the case.
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