Air flow through a stock head

Hello all,

I'm new to jeeps, just bought mine a month ago. Its a 96 XJ sport with a 4 inch lift.

To the point. I work in an automotive machine shop, so I am planing on building a new engine to replace the one with 148k on it. Has anybody here done any flow testing on stock heads? Also, Which casting number/year heads are the best to use?

I am planing on building a 4.6 HO stroker, not sure which kit or if I will put my own together.

~Alex

Look around Dr. Dino's site here: http://www.jeep4.0performance.4mg.com/index.html
Head flow info in the Tech Spec's link. Also check the Ported Head link.

'91-99's (castings 7120 or 0630 are the best flowing).

The earliest heads and the surprisingly the latest heads flow worse than the heads in this performance sweet spot.

IN order of preference...

#7120
#0630
#2686 (RENIX. I know - but they don't crack...)
#0331 (OBD-II with COP ignition. Get a "revised" head if possible, the first run of these tends to crack between #3 and #4. Since I don't know how to spot them - yet - they rank below the RENIX head, which I've found reliable.)

WOW. That site has alot of good info in it. :yelclap: It answered just about all of my questions about the 4L.

Is there a minimum bore size I need to use the chevy valves in the jeep head?

alex22 said:

WOW. That site has alot of good info in it. :yelclap: It answered just about all of my questions about the 4L.

Is there a minimum bore size I need to use the chevy valves in the jeep head?

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Me being me, I'd see if it can't be taken out to 4.000" even (RENIX block - ChryCo blocks won't survive this, and RENIX blocks still need to be checked...)

However, I think there are still some shrouding issues with the 2.02/1.60 valves in the stock 242 bore (3.875",) but I'd have to crunch some numbers to figure out just what sort. But, if you insist upon putting in 2.02/1.60 valves, you should massage the sides of the combustion chamber and probably 'flare out' the top sides of the cylinder bore to help airflow.

And, even the #7120 is borderline to support the larger valves, unless you do some serious porting and flowbench work, methinks. I'm not saying it would be impossible - just difficult, and you may end up seeing very little return for large capital outlay (porting on any head that the shop doesn't do all the time - like AMC sixes - is done by the hour, not by the job. A lot of "on and off" on the flowbench to check work...)

Might one ask what you're trying for? It's easier to give advice on performance buildups once one knows what is being done - and you'll have an easier time knowing when you've gotten where you want to go once you know where that is. First thing I tell anyone wanting to do a performance buildup - sit down with a three clean sheets of paper. 1) Write down your "ideal goal." 2) Write down the "minimum acceptable." 3) Look at those two, and write down a "happy medium." What you end up with will probably be closer to the middle than the other two - but at least you'll now know where you're trying to go...

if someone had big valve ported heads for sale, how much would they be worth to you?

streetpirate said:

if someone had big valve ported heads for sale, how much would they be worth to you?

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Look up an archived version of Accurate Power's site - Mike used to do "big valve" heads on your core.

I'd probably rather go for more lift - or, ideally, a rollerised cam/lifter setup (wich allows a more aggressive ramp profile and you can get more dwell time at full opening. Both of these can give more airflow for less work than going to a larger valve.)

What would they be worth to me? I don't know - it would depend highly on how much additional porting and massaging they'd had, and what casting they were based upon.

When you say that the #7120 "is bordreline to support the larger valves" do you mean that the head is thin around the seat and there might not be enough iron to keep the valve from crushing into the water jacket?

The porting and flow bench work is not really a problem for me since I am the one who would be doing the work. The shop has a Superflow SF-600 with the flow com computer and Performance Trends software hooked up to it.

I am mainly concerned about how low the flow on the exhaust is. I would like to put the 1.6 Ex valve. The stock flow numbers on Dino's site say that the exhaust only flows 68% of the intake.

The XJ will be a daily driver and might see some offroad/haulin down dirt road paths once in a while. I want to build it more for low end torque than high RPM HP, within safe power limits of the 5spd and DANA 35. I don't actually need the new engine but since I can do all the work myself and get the parts through work I really don't see why not.

I saw on Dino's site that the 00-06 intake manifold has smaller runers and is better for torque. Will that manifold fit on the 7120 head with a port match or are the bolt holes in diferent spots?

~Alex

alex22 said:

When you say that the #7120 "is bordreline to support the larger valves" do you mean that the head is thin around the seat and there might not be enough iron to keep the valve from crushing into the water jacket?

The porting and flow bench work is not really a problem for me since I am the one who would be doing the work. The shop has a Superflow SF-600 with the flow com computer and Performance Trends software hooked up to it.

I am mainly concerned about how low the flow on the exhaust is. I would like to put the 1.6 Ex valve. The stock flow numbers on Dino's site say that the exhaust only flows 68% of the intake.

The XJ will be a daily driver and might see some offroad/haulin down dirt road paths once in a while. I want to build it more for low end torque than high RPM HP, within safe power limits of the 5spd and DANA 35. I don't actually need the new engine but since I can do all the work myself and get the parts through work I really don't see why not.

I saw on Dino's site that the 00-06 intake manifold has smaller runers and is better for torque. Will that manifold fit on the 7120 head with a port match or are the bolt holes in diferent spots?

~Alex

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Later manifolds should all swap (1991-up,) but a quick way to tell is to check the gaskets. If you can lay them all one on the other and see through the screw holes, you're good (I don't think the ports moved past 1991, but the exhaust ports were reduced slightly in 1999/2000 to improve catalyst light-off.)

If you have access to a number of heads, I'd like to see raw flow data for lift in .100" increments, including .100" (I've got some flow data, but it's different heads, different operators, and different benches. So, some error has to be assumed...) I'm also trying to collect heads for analysis - if you get any warped/cracked heads in for the AMC six, I'd like to hear about it. If your PT software also supports cam measurement and you get access to OEM AMC six cams, I'd appreciate data on those as well (since definitive data on OEM and MPP cams is difficult to find, and I'd like to flesh out both sections of my book...)

By "borderline," I'm more meaning that the head just isn't designed to flow that much air. I'd really want to put seats in anyhow (I don't think you'll hit the water jacket, but I'd rather "hit and fill" than guess...) but it would take an awful lot of massaging to make the big valve work useful - especially at low RPM (which would benefit more from an aggressive cam than valve opening anyhow.)

So, you're not trying to build a stump puller - that should help (although you should make sure that your Dana 35 isn't the "C-clip" version...) And, since you've got a 1996, you've got the AX-15 5-speed, which will support some mild engine improvements. At least it's not the damned Peugeot... If you go too far, you're going to want a better box - the NV3550 comes to mind - but you shouldn't have too much trouble with the AX-15 (provided you keep it on a steady diet of GL-3.)

I think you'll find that most production heads in the last 15 years or so don't have the exhaust flow that they really should - mainly, to reduce catalyst light-off times (keeping the ports small helps the hot gasses get there faster, which gets the catalyst up to its operating temperature faster. Not entirely sure I like that solution, tho - it increases pumping losses and parasitic drag, reducing specific power output and specific fuel consumption...)

The only "real" manifold change that I can think of happened 1990/1991, when the ChryCo OBD-II system was added, the #7120 head was introduced, and the intake ports were raised about 5/8" to improve intake airflow (by reducing the angle that the flow had to go through to get into the chamber.)

If you want to discuss this at length, we may have to go backchannel - but this has a lot to do with why I've written the Power Manual (information on my website and at groups.yahoo.com/group/JeepPower - it's a "support group" for the book.) There's a link in my sig.

I think I do have the C-clip style, is there a quick way to tell without taking it apart?

I have only seen a handful of 4L heads in the almost two years I've worked at the shop so I don't have alot of information about them. We do not have the Performance trends program for the cam information, only the flowbench program.

The shop is no stranger to extensive porting research. I have spent days on a cylinder head going from the flowbench to the porting bench, discusions with the boss and other porting guys, and back to the flow bench. Epoxy, weld in port stuffers changing seating angles from 45 to 30 and vice versa. A few months ago I put about a week of porting, clearancing and Chamber resizing into a set of Gurney Westlake heads.

You mentioned a backchannel, I'm new to this forum so I am not sure what exactly that is.

~Alex

alex22 said:

I think I do have the C-clip style, is there a quick way to tell without taking it apart?

I have only seen a handful of 4L heads in the almost two years I've worked at the shop so I don't have alot of information about them. We do not have the Performance trends program for the cam information, only the flowbench program.

The shop is no stranger to extensive porting research. I have spent days on a cylinder head going from the flowbench to the porting bench, discusions with the boss and other porting guys, and back to the flow bench. Epoxy, weld in port stuffers changing seating angles from 45 to 30 and vice versa. A few months ago I put about a week of porting, clearancing and Chamber resizing into a set of Gurney Westlake heads.

You mentioned a backchannel, I'm new to this forum so I am not sure what exactly that is.

~Alex

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C-clip axles can be readily identified by looking at the side gears in the differential - you'll see a "C" shaped washer in there if you have them (if you don't, you have "retainer" axles where the shaft is held in by a retainer plate.) The C-clips are usually a bit weaker than a retainer plate, and you can lose the shaft if a C falls out - a retainer plate will hold it in place, since it holds against the outer bearing - which is itself pressed onto the shaft. You'll still need to remove the cover (you could look for the retainer plate under the brake drum, but it's a pain and usually too dirty to tell...)

"Backchannel" means an alternative communication channel. Here on the boards, we're a bit limited - there's a maximum post length (I'm not sure what it is,) there's an inability to use attachments inline, and they'd be limited in size anyhow. "Backchannel," on a board like this, usually refers to direct email - which has a much higher length/content limit, supports attachments and larger files, and what-have-you. So, if you hear someone ask you to "take it backchannel," get an email address if you want to do so. Make sense? Telephones can also be considered backchannel comms - but I hate phones, and need to keep my line clear anyhow.

So, if you'd like to dig into this any further than we already are, you can ping (another technical word...) me at dragonland2001 AT yahoo DOT com, and we can really dig into this. Engine theory is something I've long enjoyed, and I've had to do a lot of research lately to update my first book while writing my second... It keeps me busy!

Thanks for clearing that up for me.

Tomorow I will talk to my boss about the chevy valves in the head and see what he thinks. Time & money vs flow & power. I will send you an email sometime tomorow.


~Alex

alex22 said:

Thanks for clearing that up for me.

Tomorow I will talk to my boss about the chevy valves in the head and see what he thinks. Time & money vs flow & power. I will send you an email sometime tomorow.


~Alex

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Cool. I'll be around - I try to respond to all email within about 24 hours, so I may need you to be patient...

I have to go back to my notes.

The short list. I used a 7120 head. Put in 2.00" LS1 or LT1 valves...can't remember. I put in 1.5? or 1.6 exhaust. The 2.02 were too big and shrouded too much. 2.0 was the biggest for effcient use.

I ported the hell out of my first head. Doing everything possible to cut down the short side. Its THIN there. I found out the hard way.

All you can do is port match, smooth out the walls, smooth the short side but not completely reshape it. Polish the chamber and deshroud the valve walls.

Keep in mind the bigger valves going in with have a larger seat...thus it will create a shroud as the valve seat is cut. So you need to open it up a bit to eliminate the shroud.

I wish I would have gotten flow numbers to compare. All and all...I am using a 1999 intake. I also ported it to smooth down the injector bosses and removed casting flash from the runners.

On the low rpm side, its a little laggy but once you hit the throttle, it really rips along. I am still having trouble with running mega rich with my 24lbs injectors though. So it wont run too long before dying.

5-90 said:

Cool. I'll be around - I try to respond to all email within about 24 hours, so I may need you to be patient...

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Don't shut this conversation completely down............Inquiring mind want to know too


Flash.

Flash said:

Don't shut this conversation completely down............Inquiring mind want to know too


Flash.

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Oh, I know - it's just that going backchannel can open up comms. I may ask about adding people to get messages via email and summarising later - I don't mind, if other participating parties don't mind either...

Its not always nesescary to cut down on the short side. some head designs actually benifit form epoxy on the short side. What often helps is widenig the short side radius and a nice polish.

While boosting the flow is very important you should also think about the fuel/air mix. A slightly rougher floor before the short side may decreace the flow by a few numbers at high lift, but it will produce turbulince on the floor which will prevent the gas from settling. I know this comes into play on carbourated engines, i am not sure how big of an effect it will have on a fuel injected engine.

~Alex

alex22 said:

Its not always nesescary to cut down on the short side. some head designs actually benifit form epoxy on the short side. What often helps is widenig the short side radius and a nice polish.

While boosting the flow is very important you should also think about the fuel/air mix. A slightly rougher floor before the short side may decreace the flow by a few numbers at high lift, but it will produce turbulince on the floor which will prevent the gas from settling. I know this comes into play on carbourated engines, i am not sure how big of an effect it will have on a fuel injected engine.

~Alex

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With a carburetted engine or an engine with throttle body injection, that's true. However, using port fuel injection frees up intake design - usually because the fuel injector sprays directly into the intake port (and also usually right on the back of the intake valve.)

So, fuel "puddling" isn't as much of a concern - since the manifold is "dry" (no fuel.) Therefore, you can work more toward laminar airflow, and pay less mind to controlled turbulence to keep the fuel droplets in suspension.

I was able to flow test a stock, untouched #0331 head off a 2002 with approx 7000 miles on the stock valve job. The head did vacume test good and had no leakage when it was mounted to the flowbench; a Superflow SF600 linked to a laptop using Performance Trends "Port Flow Analyzer." The bench's calibration was verified last month with the calibration plate provided by Superflow.

Dino,
I checked my numbers with the numbers for the #0331 on your site and there is a large variance. Not trying to slam you with my results, I would like to find out why there is a diference in our results. Do you have any information on the head used in the test for your site or what flowbench was used?





*** The graph is just a connect the dots, the straight portions do not acuratly represent the flow.


5.9, Did you get the email?

~Alex