Max RPM of Jeep Engine

[Alex22]

The rev kits are used to make sure the lifter follows the cam profile in the event of a pushrod or rocker arm failure. Without them the lifter will leave the lifter bore and the engine will loose oil pressure and force the driver to drop out of the race instead of finishing on 7cylinders and not being out of the points race (circle track and endurance/road race and such). The rev kits are not meant to act as a helper spring for the valve spring.

~Alex

[Plechtan]

The rev kits are used to make sure the lifter follows the cam profile in the event of a pushrod or rocker arm failure. Without them the lifter will leave the lifter bore and the engine will loose oil pressure and force the driver to drop out of the race instead of finishing on 7cylinders and not being out of the points race (circle track and endurance/road race and such). The rev kits are not meant to act as a helper spring for the valve spring.

~Alex

The bottom line is that they do assist the valve spring and probably let an engine rev higher with less valve spring pressure.

[Mgardiner1]

Less valve spring pressure on what? on the rocker arms? Certianly not on the cam lobes.... Wouldn't spring pressure A + spring pressure B be greater then spring pressure A by itself? If using stiff racing springs and then these "Helper" springs as well, doesn't that just put more strain on the cam?

[Alex22]

http://www.compcams.com/technical/Catal ... 07/279.pdf

I wouldn't spend the time or money to make one of these rev kits fit or make my own kit. Just use a stronger valve spring and replace it more often.

~Alex

[Plechtan]

I was talking to an engine builder yesterday, he has been doing work on imports, and suggested using roller bearings on the cam and fitting the tight, probably need to go with a billet blank.

anybody got any experience with this?

[dwg86]

I was talking to an engine builder yesterday, he has been doing work on imports, and suggested using roller bearings on the cam and fitting the tight, probably need to go with a billet blank.

anybody got any experience with this?

I did a search for "roller cam bearings". I found this web site http://www.holbrookracingengines.com/ma ... llerb.html Maybe you could call and talk to them about roller cam bearings.

[Alex22]

I forgot to mention that the rev kits can only be used with roller lifters, the springs wouldn't allow the lifter to rotate properly.
If you want to have a billet cam made, bore your cam tunnel, have custom roller bearings made and use an AMC roller lifter you should check these Jesel keyway lifters out http://www.jeselonline.com/v2/index.php?categoryid=16. We are using these in a few of our engines, pretty dam sweet.
FYI, roller cam bearings don't necessarily fit tighter than a stock bearing, the benefit of the roller cam bearings is reduced friction and reliability. It will take longer for the cam to melt a roller cam bearing in the event of oil issues.

~Alex

[Plechtan]

How do you get the keyways into the lifter bores?

[Alex22]

For a few years the V6 Ford rangers had the keyways cut directly into the iron block, I havent seen one myself and I'm not sure how the factory put them in. If you want to install bushings Jesel sells bushings with the keyways cut in them. They aren't cheap.

~Alex

[Plechtan]

SO not only are the lifters not cheap, you have to pay sombody to bore out the cam bores, right? What would all that cost?

[Alex22]

SO not only are the lifters not cheap, you have to pay sombody to bore out the cam bores, right? What would all that cost?

Lifter bore bushings aren't too bad to do in a V engine because there are fixtures available that have set spaces and angles for each lifter bore. I'm not sure if anybody makes a fixture for doing an inline engine, so your machinist would have to make their own piece then buy the reamers and buy/make a tool to install the lifter bushings then re drill the oil passage holes. Since every machine shop is different you will have to talk to your local guy and find out how much it will cost.

I'm not sure If this was covered in this thread yet because its been a while since I've read through the entire thing. Light weight valve train parts will put less stress on the valve train and the camshaft. Ti valves, keepers, retainers lightweight rocker arms and a good beehive valve spring will help out a lot by allowing you to run less tension on the valve springs.

I hope you have a large budget for this build, 7-10K

~Alex

[1bolt]

Yeah budget conscious Jeeping and speed do not mix... If you want to have the worlds fastest Comanche you'll either be spending serious coin or you'll have to be a wizard at low buck mods, and maybe rebuilding every couple runs. I'm not trying to insult the Jeeping comunity but we are some low buck junk yard sommmmbiches (that was a smokey and the Bandit style "son of a bitch" right there ).

I think people are willing to Take Lee Hurley (HESCO) at his word when he says the timing chain tends to break from a cam harmonic around 5600 (or whatever the exact number is) and the crank has bearing oil starvation issues around 6000+ RPM's. One reason his word is plausible is he doesn't sell much of anything targeted at eliminating either of those problems (to fix them according to him would be extremely high buck), he caters to Hill climbers, Mud racers, Sand railers, Jeep Speed racers and other Jeepers who have to use the I6 due to class rules... those guys have found the weak links in the 258 and 4.0.

I don't doubt them because I don't have a lick of evidence to suggest its wrong. So reasons to doubt the cam harmonic = zero trust me I'd love to read someone disproving the harmonic...

For one thing It would mean that making HP would be exponentially easier and cheaper than it currently is. We could just lighten the valve train, open up the breathing, and rev it to 7500 or 8000 RPM's. Instead we're stuck below 5000 RPM's and without the ability to rev, there's not much point in even putting an aftermarket fuel and timing computer in there.

Sure it would be nice to see some case studies of broken timing chains or distributors that were torn up so we knew for sure. But this is Jeeping, we're still in awe of Barney Navarro for getting a 232 to put out 600hp with a Turbo. We have to pay $400 for roller rockers and no one will even make a roller cam for us. If rockers were so trivial to bolt on (and thus easier to sell) I doubt anyone would even make them for us.

[Plechtan]

I think most people on this board ,ad the majority of the population is looking for a good value, doing things as low buck as possible. However somehow, Hesco got 50 people to order an engine and put down a $1,000 deposit for it, and they did know the final price and what the delivery is. These people are looking for performance first and the cost is a secondary consideration.
The vibe I am getting from your post is " don't even bother trying, we already know it won't work" Did you know that Hesco makes a 3.0L motor that goes to 7,500 rpm and does not have a cam harmonic? Very strange, I assume this motor would have bigger valve springs that a 5200 rpm motor, and the cam would be under a bigger load, but no harmonic. The Navaro motor was 188 cid, gee that''s around 3.0L . So if the Hesco 3.0L doesn't have the cam harmonic, maybe the Navaro motor didn't either. Do we have any information from anybody involved with the Navaro Motor that says he was fighting the harmonic?

I believe the cam harmonic exists and also believe it can be overcome. The other issues such as oiling, would have to be addressed on any motor that turns in excess of 6,000 rpm.

[1bolt]

The vibe I am getting from your post is " don't even bother trying, we already know it won't work"

Well I can only tell you the Vibe you're getting is wrong what I was feeling when I posted was "man I'd love to find out its wrong it would open up a whole different approach (one of the easiest ones at that) to making more power". No offense but the vibe I get from you is "I don't want to believe it and I've got no evidence, but I'm still going to anyway"... I think you'll find no warm fuzzy's here for HESCO but there's precious few authorities on high performance Jeep engines and say what you will but Lee is one of them.

Did you know that Hesco makes a 3.0L motor that goes to 7,500 rpm and does not have a cam harmonic? Very strange, I assume this motor would have bigger valve springs that a 5200 rpm motor, and the cam would be under a bigger load, but no harmonic.

Not familar with it, Assuming it has two fewer cylinders, its cam is not as long, which means its natural frequency would be much higher.

The Navaro motor was 188 cid, gee that''s around 3.0L . So if the Hesco 3.0L doesn't have the cam harmonic, maybe the Navaro motor didn't either. Do we have any information from anybody involved with the Navaro Motor that says he was fighting the harmonic?

He ran his fuel pump (at least it looks from pictures that he did) off the front end of the Cam, which we here have speculated could have had a harmonic damper effect. Who knows, maybe the cam tunnel on a 188 is much beefier... I would suspect it is considering they didn't use thin wall casting back then. It also may be that our current longer throw Cranks somehow reinforce the cam harmonic while the tighter journal overlap and much smaller stroke of that engine didn't.

I believe the cam harmonic exists and also believe it can be overcome. The other issues such as oiling, would have to be addressed on any motor that turns in excess of 6,000 rpm.

I agree if it exists it can be overcome, I'd love to find out it was some rumor but.... Again, there's nothing out there to even suggest that its anything but true.

Keep us posted, there are several ways to counter or improve the harmonic, they are expensive but you're out for a land speed record, so expense certainly can't be high on your priority list

[Mgardiner1]

CUSTOM OVER HEAD CAM FTMFW!!!

I used to love blitzin' my little honda engine to 8000 RPM!

Has anybody ever thought about using something called a "Lost motion assembly"? My idea would consist of a follower that rode on the BOTTOM of the camshaft with maybe 50PSI of spring pressure.