Jeep Strokers

Looking for some clarification on this as i have discovered not all stock 4.0 valve springs are created equal.

From this link, it roughly indicated the changed in the 4.0 over the few "generations". the writer explains how the heads changed (7120, 0630, 0331) but also the subtle changes in valve springs and cam choice made by Jeep

http://www.enginebuildermag.com/Article ... heads.aspx

My problem?
i rebuilt a 7120 head for my 4.6 stroker which will be going into my 00 xj, using a 99 donor block. i had my machinist install the stock valve springs from the 0331 head i was junking (was not a better tupy version) into my fresh 7120 head as i had assumed ALL 4.0 valve springs were the same. i was wrong in that they were the same specs, but they did install just fine.

I also had my machinist give me the specs from the head (see below).

what i now have come to realize is the 0630/0331 stock valve springs are not sufficient in coil bind or pressures. they would be sufficient if you were still running the later style stock cam, but not most aftermarkets or likely the earlier stock cam. the article notes that Jeep went with a softer valve spring for these heads as the cams were changed to a lesser profile and these newer valve springs will not give me the claimed .450" of lift that most reference or the proper pressures.

my rebuilt head specs:
free length Int/Exh 1.8760
install heights Int/Exh 1.6400
open pressure Int/Exh 202.218 @ 1.2160
closed pressure Int/Exh 71-79 # @ 1.6400
Coil bind @ 1.239

using these numbers, my coil bind either works out to be .341" or .401". Not enough for my cam choice (Comp 68-201-04), and the closed pressure is low.

I have found that Sealed Power (vs1456) & Melling (vs1298) make a stock replacement spring for the 7120 head. Im unsure which spring will be a suitable replacement to give me the correct coil bind/max lift and pressures.

http://www.fme-cat.com/PartDetailWindow ... LV8lqD4KNd

http://www.omnitek.co/mellingweb/Partde ... 298&From=A



Can anyone suggest which stock springs i should be running?

i found a local parts store had 1 Melling vs1298 in stock surprisingly, so i went and picked it up, then stopped by my machinist.

vs1298 results:
closed pressure was 80# @ 1.64"
open pressure was 180# @ 1.216"
coil bind was 1.10" approx
(1.64 - 1.10 - .060 = .480" roughly)

this gave me a rough coil bind of .480". that's a tad higher than what most claim the earlier stock springs are good for (.450") but shows its in the neighborhood of where i need to be with my Comp 201 cam... And much better than the springs i have in the head currently. the pressures were on the low side compared to the Melling Catalog figures so we added a .030" shim and retested.

vs1298 with .030" shim:
closed pressure was 90# @ 1.64"
open pressure was 190# @ 1.216"
coil bind does not change.

I havent found any Sealed Power springs locally to test, but based on the Melling test results, this looks to be the stock replacement spring i need. coil bind and closed pressure are more in line.


Can anyone chime in on this?

I would ask the cam grinder what spring specs they recommend and go from there.

prior to purchasing my cam, i had several emails back & forth with Comp cams tech department regarding a custom grind which had the same lift as the 201, but the Comp tech dept did confirmed the 201 will work with the stock springs which should be a pre 1996 stock spring or a vs1298 likely.

im just trying to confirm the pressures/coil bind figures based on my latest findings. then order the correct stock springs.

going to Mopar performance springs (or other) is not an option for me as i want to keep my setup as simple as possible and balanced. a stock or close to stock 4.0 works very well imo, so a close to stock 4.6 stroker should be the same. i believe the Comp 201 will still work, however with the machining that was done my estimated scr/dcr with the 201 now 9.0/7.7 ... my target was 9.3/8.0. Going with even less lift would help raise my dcr back to my target 8.0, its just another quick delay and cost.

any feedback would be appreciated

604rail_king wrote: Going with even less lift would help raise my dcr back to my target 8.0, its just another quick delay and cost.

any feedback would be appreciated

An earlier closing intake will raise the DCR. I measured my stock 2001 cam and intake closed at 25 degrees @ 0.050" (published spec is 28 deg?). Looking at available cams, I chose the Crower 44243 which also closes at 25 deg. The Comp 201 cam closes at 33 deg, so you'll lose some DCR there. Some other choices would be Crane 750501,or Erson E720111, or even a stock cam.
You could advance the 201 cam a few degrees for higher DCR. Offset crank keys are avail to do it easily.

I used stock 2001 springs and it'll rev to 5000 without problems. I don't do that very often, but it does feel good! Passing power is impressive.
I wasn't able to find many specs on the stock springs (thanks for posting). Jeep did change springs around 1996 to the conical design.
I did post before that my stock springs would bind at 1.125" in a vise. With install height of 1.65", that leaves 0.525" and subtracting the 0.060" safety margin leaves 0.465" for valve lift.

i cannot use the stock cam that came out of my 99 block as i went with a JP adj timing set, which can only use an earlier style cam. the earlier style stock cam will actually lower my dcr quite a bit from the 7.7 using the Comp 201, so i wont be doing that. the Crane 44243 is fairly close to the Comp 201 in terms of lift, so its good to hear that you were able to run it with the 01 stock valve springs.

you are right, i could advance the cam another 2 deg (for a total of +6 deg) to bump up my dcr, but it only made a .10 increase on the stroker calculator. im unsure how this would further affect things overall though...

my concern was with the coil bind and closed pressures figures that my machinist gave me (posted above) using the stock 99 valve springs, which is why im posting. the lower closed pressure could be solved with a shim, but the coil bind is the main concern. the vs1298 i tested has a lower coil bind figure which i believe will eliminate my coil bind issues i calculated i would have using the stock 99 springs.

i guess at this point i could pull a stock 99 spring out of the head, and retest it. OR order a new set of vs1298's.

as for changing from the Comp 201 cam, its still a thought. having my dcr a tad higher would be better in my opinion. my xj is lifted, on 33's, and stock 3.55 gearing ... it rarely see's high rpm.