Max RPM of Jeep Engine

[TurboTom]

Here is what I asked at the Hesco forum, and Lees response.
Cleared up what I needed to know. I thank him for the response.
We ran into the same sort of thing with the BMW 6's...it was fine if you did not stay at a certain RPM. Otherwise it would over heat the stock dampner until it started chunking rubber bits out of it. BMW made a race dampner with a different durometer rubber, and we had no more problems..but still avoided that rpm if we could.

I asked:

"I am building a 4.0 for an AMC Spirit drag car.

Megasquirt fuel injection, controlling an MSD box. Old TO-4 turbo with birficated housing, home made headers.

During my first stock engine test on an engine dyno I have made 465 ft/lbs and 395 HP at 4500 RPM (14 pounds of boost) Promply cracked 2 pistons and pushed the head gasket out. Just part of testing and I knew these things would happen.

My big question is what is this 5400-5700 harmonic all about. Some drag racers have run in the high 8000 rpm range. So what do I believe? I would like a real explanation of the problem. What kind of testing has been done? Are there any true hard facts? Any data? Can someone from Hesco help?

Thanks, Tom"

Lee's reply:

"The harmonic problem came about with a ROAD RACE vehicle where the driver wanted to let the engine speed (under power) stay the same rpm so he would not have to shift two extra times.

The engine broke the timing chain on first try. Second engine broke with in 10 ft of the first engine.

At this time I had 5 race cars running the engines. all but one broke the timing chain at the same place on the race track that race week.

Back at the dyno I tried to simulate the problem. With some success I was able to break timing chains by holding a load at 5375 rpm and the chain would break. With a cut away timing cover on the dyno and watching with a strobe I could see the chain start to wrap up and break.

The next project was to watch the cam do a harmonic warp. Added two extra cam supports with little help. Still broke!

I don't believe I have any video or photos left. I am sure there is not any engineering data that would be of any help.

I did make a gear drive set up that would not break. But all of those are long gone.

The drag car does not seem to have the problem as the engine will go thru the harmonic range quickly. I have turned the 3.0L engine 7500 for long periods with out a problem."

[John]

By page eleven of this thread, I am back to the vibration exists. Around 5400 it is significant, as additional bearings did not eliminate it's existence, it may originate elsewhere. And still it can be ran through quickly. Custom timing sets can take more abuse through this zone. (I will be pursuing a fluid dampener, hope to modify someones presently marketed unit). But still we have not addressed the 1st question. What is the maximum rpm for our I6. I know my brain goes to the rod length, anyway, it is a good question.
Kudos to Tom and Lee for bringing this info to light and sharing it.
John

[Plechtan]

See this thread on the Fluid damper issue http://www.jeepstrokers.com/forum/viewt ... lit=damper I think the ATI unit is superior to a fluid damper, I ordered one and it should be here shortly. It was a little less than $500.00 and it was a direct bolt on for a 4.0. When i ordered they even asked me what diameter my crank was, I said standard, they said, no should it be over or undersize slightly!

[TurboTom]

While I am sure the ATI stuff is great. (they have always had quality stuff) A harmonic dampner based on rubber will only work in certain RPM bands. While the Fluidampr has a viscous fluid that will dampen harmonics over all RPM's. I called Fluidampr today and they recommended the 7.250" dampner until I said I had a straight 6. He then said I should go with the 8" model dampner ring for a BBC. They sell the 8" dampner ring for $312.95.(no hub) so I will have to adapt it to my crank hub. SixPak did this by machining the stock dampner hub to fit the Fluidampr. I will be at the Performance Racing Industry show ( Booth 1737 Davis Technologies, Traction Control) and will get some more info.
Stop by... if anyone is going... and say Hi. It's a great show, and I will buy 1 beer for everyone who mentions this forum!!
I am sure your dampner will work well, and you can just bolt it on, but a rubber dampner is not as good as a viscous fluid one.
Ask for Turbo Tom

[Plechtan]

I agree with everything you said, but does the BBC damper have a 5 grovepulleyy on it? As for theargumentt that the rubber damper is tuned to work over a specific range, i agree, but since the biggest problem seem to be around 5400-5800 rpm, maybe that is what you tune it for. If you are at PRI, maybe you should also stop at the AT booth and hear what they have to say.

[Plechtan]

I noticed that the crank thrust bearing was located on #3 main, well the support for #3 main has one of the cam bearings in it. I thought it may have something to do with the cam harmonic. I sent at email to Lee Hurley, and here was his reply:

Peter,

Don't waste your money on moving the thrust. I have moved it to read an make
steel caps, still no help at 5375rpm. The problem seems to be more related
to the 4.0L and the elder 232 (close to the same stroke). I have not seen
the same res at 5375 when using the 258 crank. This crank has 12 counter
weights. I believe that the crank is more of the problem than the cam. The
cam is just the results of the harmonics. I have used a test damper from
Fluid Dampers that did make a change in the range (raised to 6600rpm) but
still had the harmonics.

The thin spots can be as thin as .085 as long as they are below the ring
travel and 90 degrees from thrust.

I would suggest trying to stay below 5300rpm.

Lee

So it looks like you stroker guys may not have a problem.

[Flash]

I noticed that the crank thrust bearing was located on #3 main, well the support for #3 main has one of the cam bearings in it. I thought it may have something to do with the cam harmonic. I sent at email to Lee Hurley, and here was his reply:

Peter,

Don't waste your money on moving the thrust. I have moved it to read an make
steel caps, still no help at 5375rpm. The problem seems to be more related
to the 4.0L and the elder 232 (close to the same stroke). I have not seen
the same res at 5375 when using the 258 crank. This crank has 12 counter
weights. I believe that the crank is more of the problem than the cam. The
cam is just the results of the harmonics. I have used a test damper from
Fluid Dampers that did make a change in the range (raised to 6600rpm) but
still had the harmonics.

The thin spots can be as thin as .085 as long as they are below the ring
travel and 90 degrees from thrust.

I would suggest trying to stay below 5300rpm.

Lee

So it looks like you stroker guys may not have a problem.

Thats Vary interesting!!!!!!!! has any on, had a stroker timing chain failure......or one that stretched way out of spec, in a short period of time.................That would be Quite Ironic, if the stroker could out rev the stock(short stroke) 4.0L.

Has any one, rev there 4.L to this mysterious 5375........???????? can you fill that you doing something bad to you engine............or is it something that just the engine Feels????????

Flash

[yuppiexj]

Has any one, rev there 4.L to this mysterious 5375........???????? can you fill that you doing something bad to you engine............or is it something that just the engine Feels????????

Flash

I have taken my stock Renix 4.0 to 6000 before (85+ in 2nd, I was bored).

Still ticks along, 201,000 miles tomorrow on the way to work.

[1bolt]

This thread has definitely come full circle there's a LOT of power to be had by expanding up into 6500 to 7000 RPM's for those with the right application (Sand, Mud drags, street/strip etc.). Not exactly a revelation to crawlers, but

In my years on the internet I can't say I've ever seen a 11 page thread (or equivelent) expand and evolve and become MORE interesting. Let alone arrive at what appears to be an actual conclusion of sorts... <drum roll please> The max RPM of a Jeep stroker is: The same as any other well built push rod engine, something less than 10,000 and limited mostly by money/time and imagination. Well ... at least we know the max RPM is well past the 5375 RPM cam harmonic anyway...

Now wasn't somebody talking about a "rev kit" made for Jeep I6's? I may need one for my 8000 RPM street/strip Comanche well... some day...

[SIXPAK]

In my opinion you can't just say the max rpm is..... there are just way too many variables. Inheritly the smaller the stroke the greater potential for more RPM's. Shorter stroke, less friction, rotaing mass..blah blah..blah. A stroker by it's own nature [ almost 3.900 ] has a significant obstacle to overcome, the stroke it's self and the piston to wall friction which turns into how much HP it takes to spin the motor over at that RPM. Run a few test on an engine program and tell me which has a higher piston speed, 4.0 or a stroker. Which stroker will self destruct first ASSUMING rod strength was somewhat equal, a stroker with 258 rods or one with 4.0 rods?

Look at it this way.. ...it comes down to speed. If you have enough cubic dollars you can do all kinds of fun stuff, which includes spinning a 4.0 to 9000 grand. just a few wondering thoughts.

[Plechtan]

The idea of the thread was to find out what the limiting factors were, the cam harmonic seemed to be a big one, probably the next one is valve float, followed by head, intake. If you look at a 6,500 rpm application, all the cam manufactures recommend solid lifters and bigger springs. Now you need adjustable rockers to adjust your solid lifters. probably need machine work or a valve cover spacer for the lifters. so how much did we spend here?

Pull the head ??
Head work $300.00 ?
Lifters + springs $200.00
Cam $150.00
Rockers $500.00
Gaskets $ 50.00
Valve cover spacer$ 80.00
Replace the head ??

So someplace around $1,300.00 to rev to 6,500 RPM. that may even be risky for the stock rods and pistons, and probably beyond what the stock oiling system can handle. So you beef those up for another grand or 2, then you will not be able to get enough air through the stock intake, so you need a turbo, or supercharger. So i guess we can go as fast as we want if we have enough money. The sprit of this board is to do thing on a budget, the best bang for the buck and do it yourself if you can. I am building the Bonneville engine out of my pocket, and it is not cheap, It will be cheaper than buying a race engine from Hesco. We would like our engine to rev to 7,500 rpm and produce about 420hp NA . so we will need more than double the airflow and double the injector size than a stock 4.0 Hopefully some things that we develop for the Bonneville engine will help others looking to build a motor with similar performance.

I guess i only have 1 thing left to say, if you are building a stroker, make sure you have a 12 cw crank!

[John]

Peter it has already helped. Through this discussion a lot of information has been brought to the table, a few questions are left regarding dampeners and timing sets for example but the cam, crank harmonic relationship answers really have not seen this much public airing in my memory. Yes many on the board have limited build goals, and if costs vs need balance out at low buck, so be it. But there is also some of us who have much higher performance goals and are willing to address limiting factors as required. This is the Performance tech section not the bargain basement after all. We are doing pretty good at pooling thoughts and resources and we have gathered here for less than a year now.
John

[TurboTom]

Less than a year???? I thought this place had been here for longer than that.
What I believe is there is no cam harmonic, just a crank harmonic (as there is with every engine). Our 6's have a longer crank so it will have a more pronounced harmonic.
Just like every I6 out there. Understand it, do what you can to avoid it, Absorb it, then stand on it!!

Plechtan:
No the chevy one does not have the 5 groove pulley on it. And while that is a bummer, I will put one on it. I like machining stuff so no biggie to me.
I will try to talk to the ATI guy's at PRI if I have a chance. Did they tune your damper for you when they built it? If they did that would be great.
But IMHO it will never work as good as a fluidampr...just the nature of the beast. Would I change it now? No, not without testing.
I believe your Bonneville engine goals are reachable, 105HP per liter on a pushrod engine is doable. I would like to go and help if I can, if my money train arrives.
We have a really nice Dyno here already set up for AMC 6's if you need some numbers.

This a pretty amazing thread, On most 11 page threads we would be disscussing the advantages of larger rear speakers by now

[Plechtan]

The suggestion I had from ATI was to run it on a dyno, then change the orings( they had some recomendations), They said if it is right, I should see about a 10hp increase. Hopefully most of the time i will be running WOT and near maximum RPM. The requirements of a street or desert truck would be quite different.

[TurboTom]

What is invoved in changing the O-Rings? they used to take a special tool I believe.
Not a big problem, just sounds like a bit of a pain.