Calling All Racers Of The Jeep Engine

[I6FAN]

The Swapology thread about the Cam Gear Drive "brought out" comments from alot of the race builders that post here. This group of builders have put their combinations through more rigor than most of us will in a life time.

My question(s) is: What components do you like/favor to use i.e. block vintage, main caps, cranks, oil systems, heads, carb/EFI, custom intakes, header systems, hydraulic/solid cams ect.???

[IH 392]

We've been using the RENIX blocks because we got them for free!, stock main caps and bolts, I don't remember if we're using a light crank or a heavy one?, the heavy ones have better harmonics but the light MAY????? accelerate faster??, I'm NOT convinced that they do?, even though the light cranks have poorer harmonics than the heavy ones they are proven by years of service, so?, STD volume oil pump, if you need a high volume one you need to get your crank machined to get the clearance back into spec, we didn't get a head with the blocks so we're running ported 258 heads, opened up for 4.0 valves, ported, the smoggers have a TON! of meat to work with, our class requires a OE 1bbl intake and a 1bbl carb with a maximum of 2" throttle bore, the header is a heavily modified 4.0 to fit the 258 head, the cam is the biggest hydraulic one Crower made.
On the timing chains , we run the OE style mono rollers, the gears sound neat but they can set up harmonics that can lead to spark scatter and the biggest deal with a chain vs gears if something lets go the chain will likely let go and limit valve train damage where gears will keep turning and destroy it all, so the old time races say.

[I6FAN]

Thanks for answering! On the main caps, I've heard of older 258 caps that are solid? I've noticed the 4.0 caps have recesses on the backs of them, so I'm supposing the older 258 caps are not like this. What years are those "solid" types found on?

[amcinstaller]

i know what you mean, i have a set i think? (they may have disappeared in my many moves) of the main caps from my 80 258 and they are solid where as the 4.0 main caps have two ribs on them. sixpak said he was using a set on his 4.x and all he had to do was a line hone on them and reshape which you probly should do anyway when rebuilding an engine

[4.whoa]

the gears sound neat but they can set up harmonics that can lead to spark scatter

I thought the whole point of the gears was to STOP the harmonics problem?

[IH 392]

I believe the gears were to keep the cam turning when unrealistic valve trains were developed (poor lobe design, 300+lbs seat springs and RPM!) and the chains started to fail.

[SilverXJ]

the gears sound neat but they can set up harmonics that can lead to spark scatter

I thought the whole point of the gears was to STOP the harmonics problem?

Nope. They end up transmitting more harmonics and are heavier.

[I6FAN]

Silver XJ Wrote:
[quote]Nope. They end up transmitting more harmonics and are heavier.[/quote]

x2. The belt would be the best solution, but the hardercore racers are using gears because the reasons pointed out by IH 392.

4.whoa Wrote:

I thought the whole point of the gears was to STOP the harmonics problem?

The harmonic is in the crankshaft. The way the firing order and crankshaft is configured it is basically 3 sets of parallel twins; 1-6, 2-5, & 3-4. Each pair is positioned with, and moves up and down with its "twin". Parallel twins, like the old Yamaha XS650 (and others), have a decent up and down balance with the counter weights, but in between up and down, there is a severe fore-n-aft rocking motion. So in our inline six there is three of these rocking motions going on. The stress that this imparts on the crankshaft is a successive series of spirating motions along the crank axis. I'm not exactly clear why at a certain rpm it wants to go "haywire", but it does. Most likely an interaction between vibrational frequency, mass of the crankshaft, and the strength limit of ductile iron. Hesco says the fix is 14" harmonic balancer which is not practically feasible, and a stronger crankshaft material. The ultimate solution would be a forged, 4340 steel crank (each throw counterweighted) which would inturn make the need for billet/forged main caps (maybe four bolt) soon apparent. At that point, the block would start to see failures, but we would probably be at the 700+ horsepower level by then so.... What would be the best way to drive the cam on such a set-up?

[SilverXJ]

the hardercore racers are using gears because the reasons pointed out by IH 392.

I'm pretty sure the majority of serious racers use belt drives. 1) light, 2) absorbs harmonics, 3) easily adjustable.

[IH 392]

That's why a 12 counter weight crank is better than the others.

And yes, today with improved cam profiles and better materials throughout the valve train, including belt technology, gears are becoming a thing of the past.

But gears sound COOL!

[SIXPAK]

My question(s) is: What components do you like/favor to use i.e. block vintage, main caps, cranks, oil systems, heads, carb/EFI, custom intakes, header systems, hydraulic/solid cams ect.???

Block=I've allways used a 91-96 block.......but I would love to try a newer 2000 or so
Main Caps= I've broke 4.0 main caps but have NOT used the 258 "solid" ones yet, no cash-ola
Cranks=I tried a lightweight crank 1 time in 26 yrs...and broke three main caps...won't go down that rode....I saw no ET gains at all in 300 ft sand drags
Heads=7120...I have one ported with stock valves and it flows 262cfm at .525 lift and one 7120 stock head....91-93 have less material around valve guides in port
Carb/EFI=..EFI all the way for me. I really think I'm giving up some HP with it versus a carb but it's my style.....dumb I know
Custom Intakes= Yes
Headers= Custom
Cams=I don't have the pocket book for a roller....I almost had LSM make me a few but our rules have a huge weight break for cams under .500 lift.....I removed a .585/.594 solid cam in favor of the
under .500 cam and saw no drop in ET..it actually went a bit fast since it allowed me to removed 100lbs from car

[amcinstaller]

you are a mysterious person indeed sixpak. never woulda pegged you a EFI guy i thought you had used the 4.2 main caps but i guess you were asking for them for a later project, my bad.

[Jeepinscott]

I race one in the desert.

Block, NVH, 95-99 I believe, girdle with stock bolts
Intake 2000+ match ported to head
header banks customized collector to dump straight down
Head 7120 massaged, new stock head bolts
Valves, chevy stainless, swirl polished, undercut 11/16
Springs Mopar Performance
Locks and retainers Comp +.050
Harland Sharp non adjustable roller rockers
Cam custom by Painless Performance, best cam ever built
'grey' injectors flow tested and matched
Painless Performance engine management system, relaible tuning that made +58rwhp difference alone on the dino
KB pistons, zero deck .040 quench

[racing89]

Out of 12 blocks, sonic tested, 1991 and 92 only ones meaty enough for 4" bore. Coincidence?

[4.whoa]

Probably because the molds were still new