Cams...

[cj8rckcrlr]

I've got a 99 sport 5speed, i've got all the bolt on power mods, im thinkin about a cam and roller rockers...what kindda cams are yall runnin...this thing is my DD but it see some semi extreme rockcrawling...mainly lookin for low end power...part numbers would help out alot, but i would really appreciate any information yall can give me...thanks

-James

 

[nosigma]

Roller rockers are best for high rpms to reduce friction and improve engine acceleration (can you say drag racing?). I love my Comp Cams Xtreme 4x4 dual pattern, .491 in, .512 exh but its in a flow benched 4.0 HO, ported, big valved, roller rockered, triple 45DCOE Webers, custom header street machine (66 Rambler Convertable). Pulls like hard from 1800 and screams from 3250-5750. The key part of selecting a cam for your needs (extreme rock crawling) is what rpm do you want the engine to perform at? I designed my motor (rods, quench, valves, port flows and gears for a 5100 rpm peak power.

What RPM do you want peak power at? Once you know this everything else (port volume, valve size, port flow and especially cam design and the ever important intake closing angle will fall into place.

What RPM range do you use while crawling?

John

 

[5-90]

Roller Rockers are of limited utility to us - either you're trying to wring every last little bit of power out of the plant (they complement other mods,) or you're building a high-rpm racer (which we're not.)

Note I said "limited utility" - not "useless" - if you've already got them in, it shouldn't be a problem for you.

Cams? I've been thinking strongly about the Blue Racer WG5121 for when I build up - I've only been able to run it in simulation (Desktop Dyno 2000,) but I've been impressed with the numbers, especially under 3500RPM (it looks like a torque MONSTER. It also seems to work well - in sim - in anything from a stocker to a wild stroker. I can't wait to try it in an engine - I'm thinking of whomping up a stroker on the RENIX block, #7120 head, and maybe a Flatlander Racing 4.145" crankshaft. I've got to do a little engineering to make the thing work - they designed it for the 258, and I'm trying to wring information out of them to make it work for the 242... I will, of course, share information once I get it and figure it out...

5-90

 

[cj8rckcrlr]

thanks a ton for the feedback...

yea see, this thing is still my Daily driver, so i'd like to have alot of power midrange, not all on top end, not all on bottom end...offroad im around 2000 give or take 500rpms...i'll probly stroke the motor down the road, but for now, i just wanna get a little more torque for offroad and on the street...so not too wild of a cam...but something that i'll notice a difference...

now, should i change anything else when doin the cam?

-James

 

[5-90]

That's why I keep thinking of the WG5121 - in terms of low-end and mid-range raw power, it's just about the best.

Considering we're working on inline sixes here, we should be more interested in mid-range and low-range power than anything else - the engine isn't designed or built for high-end power, it's built to pull stumps off-idle (and do so all the time.)

People who build their I6 engines for high-end power are missing the point - most inline sixes just don't last at high revs - harmonics in the crankshaft will tear the thing apart, given time (how much is anyone's guess.) The crankshaft is just too long to handle high revs - the complaint of harmonics and bad vibration at 6000-6500RPM is common.

Most cams will be an improvement, tho - even the stock 258 cam, in sims, does rather better than the 242! Go figure...

5-90

 

[nosigma]

CJ8,

Just like S-90 I spent dozens of hours running combinations on desktop dyno and set up dozens of cams using lobe grind data from several manufacturers. I had the advantage of a home built flow bench which allows you to really tweak the cam.

I suggest you purchase a copy of desktop dyno. The absolute numbers are pretty good but the relative differences you see between set ups are very accurate. The most important item for you to pay attention to is the intake valve closing angle. With a five speed you will need to make sure you have good power in the lower rpm ranges 1800-2500 unless you are geared real deep. Overlap will be a bad thing for you. Dont worry about the engine falling off the cam at 4000 to 4500 unless you twist the pee out of it on the highway you dont need power up there, you want to trade it for torque at the bottom end. If you cam it too short you will end up with sky high dynamic compression (not to be confused with static compression) and will be unable to run much advance. Go for a tight running quench distance such as .030 which will put the pistons out the top of the bores about .010 (pay attention to compressed gasket thickness). You can run 9.8:1 with this kind of quench (I run 9.85:1 on mid grade with 35 degrees total advance). You can get away with this tight quench if you run matched length mangafluxed 4.0 rods, light weight hypereutectic pistons and keep the revs down.

S-90 is correct about the torsional instability in the crank. I dont know a lot about the 242 crank but the 258 crank will break at the number 5 rod journal if you spend even a few seconds with it held between 5900-6000 rpm. The drag guys blow through this and get away with it for a few runs. The road racers break cranks constantly without a soft touch rev limiter at 5850. I use to port heads (4.0 HO and 258) for drag and road racers so I have quite a few war stories about busted cranks.

John

 

[Dr. Dyno]

thanks a ton for the feedback...

yea see, this thing is still my Daily driver, so i'd like to have alot of power midrange, not all on top end, not all on bottom end...offroad im around 2000 give or take 500rpms...i'll probly stroke the motor down the road, but for now, i just wanna get a little more torque for offroad and on the street...so not too wild of a cam...but something that i'll notice a difference...

now, should i change anything else when doin the cam?

-James

If you fit an aftermarket performance cam, you'll also need to change your cam sprocket for a '94-'98 version (unless you opt for the Cloyes dual roller timing set). The '99+ cam sprocket won't fit on any aftermarket cam.
Since you have a 5-speed, it's better to go for more torque in the low/midrange so I'd suggest the Crane 750501 cam (248/260 advertised duration, 0.427"/0.456" lift, 112* LSA). The Blue Racer WG5121 that 5-90 suggests is the same as the larger Crane 753905 (260/272 duration, 0.456/0.484 lift, 112 LSA). That cam is great in a stroker but it's not as suitable in a 4.0 when it's attached to a 5-speed.

 

[XJawgi]

I've only been able to run it in simulation (Desktop Dyno 2000,) but I've been impressed with the numbers, especially under 3500RPM (it looks like a torque MONSTER. It also seems to work well - in sim - in anything from a stocker to a wild stroker. I can't wait to try it in an engine -
5-90

Sorry to chime in here, but what numbers do you put in when using dyno2000 under induction : induction flow and manifold type? Thanks

 

[cj8rckcrlr]

alright, all this info is great, im learnin alot...thanks a bunch yall...and yea, i need to get the desktop dyno program...wheres the best place to get it from?...

-James

 

[5-90]

If you get a copy of DD2000, sign up for my JeepPower group (groups.yahoo.com/group/JeepPower) and download my cam archive there - it will save you a lot of data entry, you'll find more cams in there than you think, and I've triple-checked the data so I KNOW it's right. It's the same cam files that are included on the CD with my book (although there's a little more on the CD as well - but most of the companion files are posted at the JeepPower group...)

5-90

 

[cj8rckcrlr]

sweet, thanks man..

 

[5-90]

Sorry to chime in here, but what numbers do you put in when using dyno2000 under induction : induction flow and manifold type? Thanks

I'd have to look at my "baseline" file - I got the numbers from a discussion on "Strokers" - and they're reasonably valid. Of course, head flow numbers are every bit as important - I may have to update the archie I'm keeping at JeepPower - add head flow files and a baseline dyno sim just to simplify things...

5-90

 

[cj8rckcrlr]

Since you have a 5-speed, it's better to go for more torque in the low/midrange so I'd suggest the Crane 750501 cam (248/260 advertised duration, 0.427"/0.456" lift, 112* LSA).

so i would have to get an older cam sproket to run this cam?....should i go ahead and change the chain and crank sproket at the same time...if so what is a good place/brand to get...

-james

 

[5-90]

Yes, it's a good idea to change the timing as a set (3-piece.) As I recall, the crank sprocket and chain didn't change - just the cam sprocket - but there's no sense in doing a partial fix, since you're there anyhow.

Any aftermarket brand should not be a problem - I favour TRW, but you can use pretty much anything.

Where? Follow the advice I'm always giving - find a good local parts house (small store or small chain - NOT Kragen, AutoBone, or anything like that,) and give them all your high-dollar business. It's better for local businesses, and you'll find your prices start to get better over time as well (I now get "jobber-minus" at my local - which is what the shops pay, less 5%. I also get counter catalogues for free, since each catalogue they give me is money in the bank for them anyhow.)

I'll still get my fluids and solvents at big chain stores, since they have better prices (and I go through enough of the stuff. I'm thinking of starting to buy bulk,) but I will NOT go to Kragens or AutoZone for parts - I get better parts and better prices elsewhere.

5-90

 

[cj8rckcrlr]

Yes, it's a good idea to change the timing as a set (3-piece.) As I recall, the crank sprocket and chain didn't change - just the cam sprocket - but there's no sense in doing a partial fix, since you're there anyhow.

Any aftermarket brand should not be a problem - I favour TRW, but you can use pretty much anything.

Where? Follow the advice I'm always giving - find a good local parts house (small store or small chain - NOT Kragen, AutoBone, or anything like that,) and give them all your high-dollar business. It's better for local businesses, and you'll find your prices start to get better over time as well (I now get "jobber-minus" at my local - which is what the shops pay, less 5%. I also get counter catalogues for free, since each catalogue they give me is money in the bank for them anyhow.)

I'll still get my fluids and solvents at big chain stores, since they have better prices (and I go through enough of the stuff. I'm thinking of starting to buy bulk,) but I will NOT go to Kragens or AutoZone for parts - I get better parts and better prices elsewhere.

5-90

yea, i can get discount prices through my work, but i was just checkin on brands for timing setups...cuase i think im gonna do that crane cam, and yea i'll do the whole timing setup. might as well...

and as far as roller rockers, what will they actually do for me, help it rev up faster? or just help it handle higher rpms....any power gains?

-James

 

[Dr. Dyno]

There are minimal power gains from RR's (I recall a magazine (possibly JP) getting a mere 1.5hp gain on the dyno from a 4.0 with the Mopar RR's). The benefit is the ability to adjust the valvetrain if you add other aftermarket parts.
The Cloyes dual roller timing set is probably one of the best. Costs ~$110 from Summit Racing.

 

[5-90]

Concur. Most roller rockers are adjustable for lash (which helps with cam consistency, more than anything else,) and they eliminate parasitic drag at the rocker pivot and the valve tip.

However, that parasitic drag consumes, at most, 1% of produced power - that's why rollerised rockers are a mod for "all-out" engine builders. If you want the engine to rev faster, you'll want to reduce weight in the reciprocating assembly. However, this will accelerate the effects of harmonics at high RPM with the inline six, and since the I6 is intended to make usable torque at low crankshaft speeds (and therefore piston speeds!) it is self-defeating to build one to make high-end power - that's not what it's designed to do.

5-90

 

[cj8rckcrlr]

Concur. Most roller rockers are adjustable for lash (which helps with cam consistency, more than anything else,) and they eliminate parasitic drag at the rocker pivot and the valve tip.

However, that parasitic drag consumes, at most, 1% of produced power - that's why rollerised rockers are a mod for "all-out" engine builders. If you want the engine to rev faster, you'll want to reduce weight in the reciprocating assembly. However, this will accelerate the effects of harmonics at high RPM with the inline six, and since the I6 is intended to make usable torque at low crankshaft speeds (and therefore piston speeds!) it is self-defeating to build one to make high-end power - that's not what it's designed to do.

5-90

yea, that makes sense...i'll probly just pass on the RRs dont' seem like they'd be worth it, maybe down the road if i stroke it and really build it...

but i'm gonna do the cam and timing set in a month or two...and again, thanks for all the info...

ha, oh yea, a buddy of mine is thinking about putting a 50-75 shot of nitrous on his stock 4.0, im telling him not to...but are there any real reasons why not to do something like that...it just seems kindda stupid to me...i can't imagine the motor holding up to all that...

-James

 

[5-90]

Yeah, I'll probably do RR on Project: REDSHIFT - but that's going to be a power wagon, and I'll want every advantage I can get (meaning roller tips and pivots, roller timing (if I don't find a gearset,) five- or six-speed gearbox, and anything else I can think of - including a 400-500 pound diet (more if I can manage it, less if I can't.)

If you're curious about the nascent project: REDSHIFT, try a search - I know I've discussed it here before in general terms.

As far as the 50-75 HP giggleshot, I'd not see it causing any trouble. However, make sure that the kit that he gets can handle supplemental fuel deliver, or that he designs it into the system. Remember - N2O doesn't make power - it just supplies oxygen so more fuel can be burned.

TUNE RICH and work DOWN, do NOT "tune lean" and work up. Even with a mild nitrous shot, it's possible to go from "brake specific fuel consumption" to "brake specific aluminum combustion" - high temperatures and pure oxygen aren't a good mix - unless you plan thoroughly for it...

5-90