Jeep Strokers

Here are some pictures I took of my 7120 head with 1.50/1.94 SBC stainless valves installed. I ended up using the Mopar performance 5249464 valve springs. They are stiffer than Mopar advertises. My machinist said they installed at 130 psi and 290 psi at .501 (that is my cam lift). I measured the valve springs as best I could with a caliper and they are installed around 1.675-1.680. So if they were installed at the 1.640 that Mopar says they should be installed at, the pressure on the seat would be alot higher.

By the way, sorry for the blurry pictures, I had a few margaritas before I took them!

Oh yeah...My combustion chambers ended up being 62.8cc.

Whats the reasoning for using SBC valves? Are they bigger than stock (i would assume so). If so, than what kind of benefit would that give you?

I would also assume some kind of extra machine work had to have been done to make the SBC valves work. Would the cost be worth what you gain from it?

Muad'Dib wrote:Whats the reasoning for using SBC valves? Are they bigger than stock (i would assume so). If so, than what kind of benefit would that give you?

I would also assume some kind of extra machine work had to have been done to make the SBC valves work. Would the cost be worth what you gain from it?

The SBC valve sizes are 1.94/1.50, the stock jeep valves are 1.91/1.50. So the intakes are a little larger. Maybe help the bigger stroker take a deeper breath.

I used the SBC valves because the 4.0 valve stems and guides were worn. The stock Jeep valves cost around $8.00 a piece. The guides were something like $4.00 a piece and $5.00 labor a piece to replace. So to replace the valves and guides would have cost $204.00. I got the stainless undercut swirl polished valves off ebay for $60.00. I got a reamer at work and reamed the valve guides close to the 11/32 SBC valve size. The machine shop honed the guides to the final size. The shop charged $250.00 for the valve job(that included opening up the intake throats for the 1.94 SBC intake valves (they charge $200.00 for 6 cylinder valve job). S0 I paid and exta $50.00 for opening up for 1.94 valves and honing guides to size. The shop did reccomend replacing the valve seats(not necesary but reccomended), so I had them replaced. It probably came out to costing around the same price to use the SBC valves as having the stock valves and guides replaced(To convert to the SBC valves cost around $210.00 That includes the new seats), but I have alot more valve spring options available to use now. I bought the Mopar Performance valve springs because I liked the specs that Mopar "advertises", but the advertised specs aren't accurate to what they measure at in real life. I'm still not sure If I am going to use the MP springs or change them.

BTW, the SBC valves are the same length as the stock jeep valves. The lock grooves in the SBC valves are lower on the stem than the Jeep valves, so I used +.050 locks. This made the valves realy close to each othe(within a few thousands). The spring seats have not been cut. The SBC valves with the +.050 locks and the retainers I used put the installed spring height at 1.675-1.680. The stock Jeep valve springs are 1.640 installed.

I also gained about 1.5cc's in the combustion chamber. This was after milling the head. Something I wasn't counting on.

You wouldn't happen to know what the coil bind height on those springs is , do you ?

Some rough math ............... You're stated installed height 1.680"
Subtract You're Cam lift - .501"

What is left over 1.179"

Let's say you're coil bind is 1.125" for example


Subtract 1.179"
1.125"
This only leaves you .054" ! before coil bind , that's cutting it close , .100" would be better .

I'm not trying to be a dickhead or know it all here but ..................... I noticed some comments being discussed in another thread and thought I'd mention,


Since when were 4.2's 11/32" valve stems , any 4.2's I've ever seen have 3/8" valve stems ( .375" ) , 11/32 = .3438"

4.0 l valve stems are 7.9 mm = .311" aka 5/16" ( .312") .

Small block Chevy , yes those are .343"

I do this for a living , at work and at home .

Here's a few pics of some stuff going on at home .

Installed height being checked , this is quite important on 4.0 Jeep heads especially when running a cam with .501" lift.


Valve travel , making sure that the seals are not going to get mashed.


Cutting the spring pads , this time to accomplish two things , get some additional installed height and to reduce the diameter of the guide boss to use beehive springs.




Some port work I have done recently

I need to find my paper work from the shop. I think he said I was good to .600. Mopar says those springs are good for .525 lift installed at 1.640, mine are installed at 1.680. So 1.680-1.640=.040 .040+.525=.565. So I should be good for .565 lift. I'm not even close to that.

Since you do this for a living... do valve springs loose some spring rate after they are broken in? The reason I am asking is my valve spring pressure on the seat was more than what Mopar advertises them to be. I remember someone else posting about having the problem with the Mopar springs. my spring rate is 130 installed at 1.680. Mopar states 120 @1.640.

dwg86 wrote:I need to find my paper work from the shop. I think he said I was good to .600. Mopar says those springs are good for .525 lift installed at 1.640, mine are installed at 1.680. So 1.680-1.640=.040 .040+.525=.565. So I should be good for .565 lift. I'm not even close to that.

Since you do this for a living... do valve springs loose some spring rate after they are broken in? The reason I am asking is my valve spring pressure on the seat was more than what Mopar advertises them to be. I remember someone else posting about having the problem with the Mopar springs. my spring rate is 130 installed at 1.680. Mopar states 120 @1.640.

Springs can lose some tension initially , usually not very much and certainly not enough to worry about , any kind of tension reduction that is of concern to us ( as in , us Jeep fools ) would happen over a very long period period of time. What's important is that quality springs are chosen ,they are well set up to begin with , allowing for sufficient travel , making sure that the springs do not come close to coil bind allows for a service life that is less stressfull and unlikely to fatigue .

130 lbs of seat pressure is not unreasonable , Comp's #926 spring , based on their chart in the catalog installs @ 150 lbs if the installed height was 1.700".
I just finished a big valve 4.0 head , used Comp #26981 , a smallish beehive spring ,these are for small block Chevrolet with a cam that has around .500" or less lift . Those installed @ 1.680" on this head @ 130 lbs , with the cam I'm using , the spring clearance is , .104" of travel left before coil bind , which is safe. Yes I cut the spring pads , had to , beehive springs need to be positively located on the bottom , requiring a lower collar / locator , these ones ( #4693 ) are .060" thick , which is how much was milled off the spring pads.

Keep up the good work


I feel obligated to make sure , if I post something , particularily specifications and other like tips n' such , that the information be accurate to the best of my knowledge , hoping others feel the same. I wouldn't want someone to mess stuff up cuz they read some bad information.

What type big valves did you use...LS1?

dwg86 wrote:What type big valves did you use...LS1?

Mopar performance , sadly , some of these parts , and likely many more are being dropped from the catalog , a sign of the recent economic times. I ported a 2.5 head and tried ordering some Mopar stainless steel valves for it , the exhaust valves are no longer available , intakes , I was able to get , these were standard sizes and the same as what you would order as a heavy duty / performance replacement for a 4.0 , 2.5's and 4.0's share many components.

It seems LS1 stuff is more commonly used for this type of work , I do have some LSI / Comp cams stuff around here , with the intent of using it on a Jeep head , a set of 10 degree locks , I had some titanium retainers but have broken up the set to do some Harley Davidson Heads. Some other stuff went on ebay. I use primarily comp cams stuff for automotive performance work , and will be using more of it on the Harley stuff now that Crane is out of it , used to use quite a bit of Crane springs , pushrods , the odd cam & set of lifters on the Harley stuff too.

Hi there,
I normally read and try to learn quietly but I couldn't resist asking this time.
Briefly I have some stuff that I intend to use it on a slow but undergiong stroker project, right at this moment I do not have all part numbers records and specs, but I have the head machined to accept Chevy valves ( 2.02" and 1.6" ) , I have the comp cam 68-239-4 that has a lift of 0.512", I am willing to take my chance despite of the warnings, I read somewhere that it runs great and does not really negatively upset the PCM.
Now closer to the point: compcam recommend the 926 springs that are rated 415 lb/in, and have a seat pressure of 109 lb/in at 1.8" installed height.
Golen Engines website shows that they do undercut the spring seat to accomodate the diameter of the valve and to have the right installed height without binding.
Question1: is that seat pressure really too high for the cam used?
Question2: Compcam shows different springs pressures at different installed heights for the same spring including the 926. At maximum lift, the spring load would not exceed 317 lb/in. If the spring rate is too high, what would be a reasonable pressure for such a setup? By compcam, the 926 is rated 88 lb/in at 1.850" installed height. Would that be more desirable?
Thank you for the advise

hatem61 wrote:Hi there,
I normally read and try to learn quietly but I couldn't resist asking this time.
Briefly I have some stuff that I intend to use it on a slow but undergiong stroker project, right at this moment I do not have all part numbers records and specs, but I have the head machined to accept Chevy valves ( 2.02" and 1.6" ) , I have the comp cam 68-239-4 that has a lift of 0.512", I am willing to take my chance despite of the warnings, I read somewhere that it runs great and does not really negatively upset the PCM.
Now closer to the point: compcam recommend the 926 springs that are rated 415 lb/in, and have a seat pressure of 109 lb/in at 1.8" installed height.
Golen Engines website shows that they do undercut the spring seat to accomodate the diameter of the valve and to have the right installed height without binding.
Question1: is that seat pressure really too high for the cam used?
Question2: Compcam shows different springs pressures at different installed heights for the same spring including the 926. At maximum lift, the spring load would not exceed 317 lb/in. If the spring rate is too high, what would be a reasonable pressure for such a setup? By compcam, the 926 is rated 88 lb/in at 1.850" installed height. Would that be more desirable?
Thank you for the advise

How do you intend to achieve an installed height of 1.800" or 1.850"? , having never used chevy valves on a jeep head yet , are these longer ? . There are limitations to what can be safely removed from the spring pads and sinking valves to increase installed height is not recomended either.

I don't believe 109 lbs @1.08" is excessive at all , probably safe for normal driving teqnique but might be a little soft for hammer down style of driving , so you wouldn't want to be doing any high rpm , sustained , bouncing off the rev limiter type of driving . The big concern around here is todays motor oils , the changes to additives in oils , running aggressive valve springs and messing up lifters and cams . You will see differing opinions on what is safe or unreasonable , in terms of valve spring tension.

My intention to use the stroker as a daily driver, no much hammering so it would not see even the 6000 rpm mark. Occasional NOS shots will be optional. Want to make it more exciting on the highway. I purchased the valves ( and many other stuff ) off Summit racing long time ago. I shall go in the next dayor two fetch the head and the valves and do some measurements and post them. I remeber the valves were Manly Street Flo series with undercut stems and swirl polish stainless steel valves. The spring pad is my only way out. I was inspired by the Golen build, however they mentioned that the recommended spring installed height is 1.7" ( if they meant the 926 ), on the other hand, compcam mentioned the installed height as 1.8". Here is the link: http://www.golenengineservice.com/html/jp_mag_1.html
And I rekon I shall review some basic units because I can read the spring rate in Lbs/in, but the spring loads are given in lbs or lbf, so obviously they are two different things....

Hi again. Please anyone, if I got it all wrong, then go ahead and clarify and I will be more than willing to listen, it won't upset me.
Starting with definitions :
Spring rate is how many pounds of weight are required to compress the spring by one inch, so taking the 926 compcam spring rate of 415 lbs/in as an example means we need 415 pounds to compress the spring by one inch.I do not have this spec for Mopar springs.

Load at installed height refers to the amount of pressure in pounds created by the spring with the valve closed at a given installed height, so comparing 926 compcam springs to the 4.0L stock springs, it is 109 Lbs at 1.8" installed height and 71-79 Lbf ( this is pounds force ) at 1.64" installed height.
At approximately the maximum lift ( 0.512" with the 68-239-4 ), the compcam spring is rated at approximately 320 Lbs, whereas the stock Mopar would be 202 - 218 Lbf.

Someone with more knowledge than me would please advise if THEORETICALLY it would be more desirable to go to 1.85" installed height for the 926 compcam springs? at that setup, the load at maximum lift would then be closer to 300 Lbs. Is this too much?
I can try to locate a scrap head and see how much meat can be machined off the spring pad.

Now the intake valves on the Manley street flo looks the same length as the Mopar stock, there might be a thousandth or two difference Mopar being shorter., Manley says it is 4.911" length and 0.250" valve tip length, the groove on the street flo is about 0.120" lower than the Mopar.

hatem61 wrote:Hi again. Please anyone, if I got it all wrong, then go ahead and clarify and I will be more than willing to listen, it won't upset me.
Starting with definitions :
Spring rate is how many pounds of weight are required to compress the spring by one inch, so taking the 926 compcam spring rate of 415 lbs/in as an example means we need 415 pounds to compress the spring by one inch.I do not have this spec for Mopar springs.

Mopar spring rate is is 270 lbs, on a used set.

Load at installed height refers to the amount of pressure in pounds created by the spring with the valve closed at a given installed height, so comparing 926 compcam springs to the 4.0L stock springs, it is 109 Lbs at 1.8" installed height and 71-79 Lbf ( this is pounds force ) at 1.64" installed height.
At approximately the maximum lift ( 0.512" with the 68-239-4 ), the compcam spring is rated at approximately 320 Lbs, whereas the stock Mopar would be 202 - 218 Lbf.

At 1.64" the Mopar spring would be 113 lbs. I have read that you want 100-110 for a street driven engine seat load at installed height with a mild cam. I went on the side of caution and installed them at ~1.69, which gave me installed 100 seat load, 232 seat load on the exhaust side open (.485" lift). I also talked with my machinist and he agreed that was the best route for the Comp Cam 68-231-4. He also agreed that the Comp Cam springs were too aggressive. Also, from my research open load should be no more than 250 lbs open, again for a street engine.

Now with the Comp Cam springs, using the given numbers, we are looking at an installed height seat load of 174 lbs at the stock 1.64" Jeep spring height. Over the nose is 386 lbs on your 68-239-4 cam. I am no expert but these numbers are high from my extensive research.

Using the installed height of 1.80" on the comp cam springs we get a installed seat load of 109, and an open load of 320 lbs. Using 1.85" installed height load is: 90lbs closed, 299 lbs open.

I have never heard of anyone complaining about valve float or any other issues using the Mopar Performance springs. Myself, either I don't know what signs of insufficient spring rate are or I have no problem. Even when turning near red line I have no problems. The engine doesn't come on a brick wall like one would expect with valve float, and I have no backfiring or other problems using the Mopar springs.

With the oil issues and accelerated cam wear we see today I would go with a weaker spring over a stronger spring to be on the side of caution. I have ran the same set of springs on a comp cam 68-232-4, and on a few 68-231-4 and never noticed a problem. From my perspective I see no reason to go for a stronger spring unless you are doing all out racing where the engine will be turning high RMPs constantly. and in that case you won't expect your cam to last very long anyhow.

I am no expert on ideal spring pressures. What I know s from my personal experience and a lot of research (some clowns tried to tell me that the Mopar springs were too aggressive, so I spend hours upon hours researching).