Don Terrill’s Speed-Talk

We build a similar engine for my shop helper which is about to go on the dyno soon but we made a few changes.
I used the Icon series forged pistons +.040 and a Scat connecting rod set.
The crank was a AMC Rambler 4.2 steel crank with a .010 off set grind and a -.010 deck height.
block was cut about .040 for a .035" piston to head clearance with the aftermarket rods as they had enough strength.
The head was the older large port head with 1.94/1.60 valves with light blending and just a port match.
Sm Blk valve springs having 110 seat and 350 open at max lift.
I machined the heads for 7/16" screw in studs and moved them slightly to allow the use of 1.72 ford roller rockers.
I used a 1/2" thick spacer to clear the taller rocker set up with custom length push rods.
The intake is a late 4.2 direct injected type with the throttle body machined to remove the reduced section so it is the same size without the restriction.The use of multi hole injectors was done for better fuel spray pattern. I think they were ford.
Viper V-10 coil pak with the 6 plug wire section was considered at 1st but went with the coil on plug set up for a 2000 grand cherokee.
The dual outlet header has 1 5/8" tube into dual collectors 3 to 1 X 2 for better exhaust flow and easier placement of O2 sensors.
The cam we are starting with is 216@ 50 on both Int and Exh..293 lobe lift on a 112 lobe center with 1.72 rockers with .504" at the valves.
the ECU we were going with at 1st was a GM unit but ended up able to use the Dodge unit because he got a super deal on a 2000 grand cherokee to put it into.
We will soon see what the power is as we are just loading it on the dyno now after some tuning and injector changes in should be in the 300 hp range which is what we are shooting for.


It is a fairly easy build to do as the parts are cheap as dirt and even though there is a bunch of extra work on the head for the rocker studs and GM spring locators but to just bore the head to .3425" and .343" to use some off the shelf GM type stainless valves and springs retainers are 10 degree comp with +.050 locks.

The aftermarket cranks I looked at the seal surface was on the small side of too small and a few other locales that used them had oil weeping from the rear main seal.

I will post some details when we get it run up and make a few pulls.

Yard that turd out and install a 5.9. What a waste of time and money.

Its lookin good so far.
389/420 at 4500. Should be just fine for wheeling in the bush and still have gas to get home.
Needs more tuning on the ecu but thats all the kid needs for a 1st jeep

peejay wrote: ↑Sun Apr 29, 2018 12:58 pm I would think that a gigantic throttle body like that would be better suited to a smaller plenum. 62mm is huge even for 300hp.

Are you kidding? With long runner helmholz-tuned intake manifold that size of thottle body is just right for 170 hp engine.

That small throttle body might well be reason for low power - BMW M52 has ~64mm thottle body and that starts to be restriction pretty soon after 200hp.

Carnut1 wrote: ↑Sun Apr 29, 2018 9:45 am The later intake has nice curved runners, old one looks like a six tang fork. New one must be an improvement.

That early manifold looks like normal tuned inline-6 manifold, 1-3 and 4-6 cylinders are divided to their own Helmholz chambers. For high rpm tune chamber size is very small and throttle body must flow high to keep that chamber full. Very similar manifold design to BMW M50/M52 designs which are excellent.

That jeep engine don't have MAF? Without MAF that high helmholz-tune is pain in ass for keeping AFR right for emissions so they probably switched to less tuned intake to pass emission tests with cheap engine management....

naukkis79 wrote: ↑Thu May 03, 2018 3:55 am

peejay wrote: ↑Sun Apr 29, 2018 12:58 pm I would think that a gigantic throttle body like that would be better suited to a smaller plenum. 62mm is huge even for 300hp.

Are you kidding? With long runner helmholz-tuned intake manifold that size of thottle body is just right for 170 hp engine.

That small throttle body might well be reason for low power - BMW M52 has ~64mm thottle body and that starts to be restriction pretty soon after 200hp.

I wonder how all those SCCA GT and FIA endurance engines makes ~350hp+ with a single SIR (single inlet restrictor) smaller than that. You can make it work...

hoffman900 wrote: ↑Thu May 03, 2018 5:49 am I wonder how all those SCCA GT and FIA endurance engines makes ~350hp+ with a single SIR (single inlet restrictor) smaller than that. You can make it work...

By making flow constant vacuum over throttle body- increasing plenum size to big enough to lose Helmholz-effect together with shorter runners to achieve constant flow instead of pulsed flow into cylinders.

But at that stock configuration that Helmholz-resonance is tuned to less than 200hp and more power is to be found with bigger throttle body. That 62mm is just the size that I6 Helholz-tuned engines about 170 hp have, and that becomes pretty restrictive at higher power levels - more so if Helholz effect is strong - eg plenum size is small and from pictures it seems that for 5-liter engine that intake plenum is really small.

One thing that can be tested is to make velocity stack directly to TB, so losing original long piping to TB. That should increase TB flow and lower Helmholz-effect - and if TB is restricting power at resonance frequency it should pick up some hp.

corvette90 wrote: ↑Sat Apr 28, 2018 10:55 am hi all

friend of mine likes offroad driving in his Grand Cherokee and decided to build a stroker...

....Harland sharp roller rockers

......another thing, the valvetrain is near quiet with cold engine, and very loud with hot engine..sounds like a diesel...
rockers dont hit valve covers, clearance everywhere more than enough..also no spark knock of course, the clackering is going in line with rpm and is very constant

im open for every input, please respond

thank you

I've had a few sets of HS rockers, and they were all loud compared to SS Comp and Crane Gold on the same cam- I quit using them.

hi all..

all in all very interesting...

if we do another engine, we will also use different rockers...the HS seems not to be the quietest ones...

another thing comes to my mind....as someone mentioned here before...the stock intake, altough its the one used in the late years, can become very well a restriction.... TPI comes to my mind here....so, we have around 780ccm per cylinder on this motor, about 50 ore so more than in a 350 V8...and as we all know, TPI become a restriction at higher rpms...

we will try a different intake with short runners, will post results...

regards

ProPower engines wrote: ↑Thu May 03, 2018 2:45 am Its lookin good so far.
389/420 at 4500. Should be just fine for wheeling in the bush and still have gas to get home.
Needs more tuning on the ecu but thats all the kid needs for a 1st jeep

389 HP and 420 ft lbs torque ? Sounds almost too good to be true on that build...

Truckedup wrote: ↑Fri May 04, 2018 5:30 pm

ProPower engines wrote: ↑Thu May 03, 2018 2:45 am Its lookin good so far.
389/420 at 4500. Should be just fine for wheeling in the bush and still have gas to get home.
Needs more tuning on the ecu but thats all the kid needs for a 1st jeep

389 HP and 420 ft lbs torque ? Sounds almost too good to be true on that build...

Yeah Pro power was that a typo?

ProPower doesn't blow smoke, so he'll be along to clarify, but those are serious numbers for an unported stock iron head with Chevy valves.

PackardV8 wrote: ↑Fri May 04, 2018 6:43 pm ProPower doesn't blow smoke, so he'll be along to clarify, but those are serious numbers for an unported stock iron head with Chevy valves.

Yes thats why I asked if it were a typo as i dont think he would be deliberatly inflating numbers. 389/420@4500 is impressive. I think i better buy a Jeep !

Yup we were getting some better slightly torque numbers playing with timing and injectors/fuel pressures when a cloud of steam filled the cell when the head let go.
Pulled it and I guess my port matching got a little thin in a couple spots near the guide area.
I did sonic the head before doing any work in there but I guess I got it too thin.

Going to try that new aluminum head and some extra squeeze and see what we get. The aluminum head looks better then the old crack prone cast heads which crack in the center of the valve cover area but I liked the 1.72 rockers so I will have to mod the new head.
The EGT's were not consistent which I think is the mod'd stock large plenum intake but that can be fixed up while waiting for the head.
I will let you know how it goes after parts get here

Excellent! Im keen to hear more. I like something a little different. Are these still the same basic engine as fitted to iirc early 80's cherokee. ?