Hitting a wall at 4200 rpm.

[Cherokee77]

Hi all,
Im new here, been around jeeps my whole life but new to strokers.
Me and my friend just put together a poor man 4.6, specs are as follows. 1990 cherokee with obd 1 comp.
4.2 crank
4.2 rods
Stock 4.0 .30 over pistons.
7120 head p&p with polished chambers.
Comp cam 232.
Neon 703 injectors. Fuel pressure turned up to 40 psi static.
63mm tb.
2.5 inch mandrel bend exhaust from manifold back to new magnaflow cat and muffler.
Borla header.
First we got it running and it pinged which I expected so I made a adjustable map sensor according to Dinos site, and turned up the fuel pressure. That took care of the pinging, and to my suprise this thing runs really well the torque climbing hills is awesome. We pretty much have it all dialed it except one thing, when you go wot and hit 4200 it hits a wall, fuel pressure is ok, afr gauge is reading around 13.2 when this happens. I checked timing we are at 8 btdc base and 32 total. Now from some of the threads I have read this could be valve float. What do you guys think?
Thanks.

[Cherokee77]

One more thing we put champion r9 plugs in. I come from the turbo v8 scene and know with boost and a cold plug and or a big gap you can get spark blowout.
I know the cylinder pressures on this motor are high is spark blowout a possibility?

[bigal389]

If you didn't change the valve springs then that's the problem. You get valve float around 4200 with the comp 232 and stock springs.
Al

[Cherokee77]

Thank you Al.
I was afraid of that. We did put brand new sealed power springs in. When I put the valve springs in the seat pressure was a bit lighter than I'd like.
What is a drop in spring that will cure the problem without machine work?
Thanks.

[bigal389]

Mopar performance 5249464 springs you'll need keepers and retainers to match, they're expensive. Some people have had luck with others but these are tried and true.
Al

[dwg86]

Look at Howards Cams spring 98111; [email protected], coil bind 1.125, and 305 spring rate. This spring insalled at the stock Jeep spring height of 1.640 would be 108.3 lbs on the seat, max lift at coil bind .515.
With your cam exhaust lift of .476, that would give you a .039 safety margin. This spring should fit the stock retainer 1.140 OD/.830 ID. Spring OD 1.240/.860 ID.
Looks like a deal at $29.95 a set.
http://www.competitionproducts.com/Howa ... nfo/98111/
https://www.summitracing.com/parts/hrs-98111

[dwg86]

The problem I had with the Mopar performance springs 1) The seat pressure was a bit high for a flat tappet cam. If I remeber correctly they were somewhere around 125 on the seat. and 2) they hit the valve cover. I had to "clearance" the valve cover to get them to fit.

You can also see what size the mopar 5.2/5.9 magnum, or 5.7 retainers are. I think they will fit the Jeep valves and retainers, and then you can pick a spring from there. Now dont hold me to that, do your research on that one.

[Cherokee77]

Thanks Al, those are a bit exspensive by the time you are done. Might have to do that if I cant find a alternative.

Dwg I might order a set of those just to get some measurments, and other numbers and see if they would work. The price is great.
I will let you know how it turns out.
Thanks.

[dwg86]

Cool. Let us know what you find out. Check your spring installed height. With a valve and seat grind your installed height is probably more than 1.640.
There are some SBC springs I think will work with the jeep retainer (like comp 982) but the spring seats will need machined because of not enough lift and coil bind. And that won't work for you with the head installed.

[Cherokee77]

Looks like the Howards springs will not work. I need roughly .950 id, those are only .830. This looks like it will be tougher than I thought unless I pull the head and have it machined, or the mopar springs.

[dwg86]

What size is the inside step of the retainer and the outside diameter? I don't have a retainer to measure. I thought the dimensions were 1.140 of and .830 inside step.

[Russ Pottenger]

Looks like the Howards springs will not work. I need roughly .950 id, those are only .830. This looks like it will be tougher than I thought unless I pull the head and have it machined, or the mopar springs.

Plus .040 from coilbind is too close.

[Russ Pottenger]

What size is the inside step of the retainer and the outside diameter? I don't have a retainer to measure. I thought the dimensions were 1.140 of and .830 inside step.

The outside of the retainer doesn't matter, but you're correct on the inner step. It'll be .820 to .830
and about .930 for the spring seat step in the head

[dwg86]

What size is the inside step of the retainer and the outside diameter? I don't have a retainer to measure. I thought the dimensions were 1.140 of and .830 inside step.

The outside of the retainer doesn't matter, but you're correct on the inner step. It'll be .820 to .830
and about .930 for the spring seat step in the head

Oh yeah, I forgot about the head side. I just assumed it would work since it fit the retainer. I also thought .040 was close, but wasn't sure what his actual install height was.

[Cherokee77]

For the mopar springs it will be close to 300 bucks, but we could buy some springs and have the head machined for cheaper then you throw in head gasket, and the nickel and dime stuff to pull the head and we will exceed that 300. But then I have read the MP springs are a bit stiff and have wiped some cams out, Has anyone heard of that?