The Road to Bonneville and back

[Plechtan]

We did go to Maxton on June 26 and 27th 2010, we had to make several license runs. we ended up with 5 runs total. the best was 147.5 mph and Scott was on the brakes going through the lights being carfull not to exceed 150mph. Since it was a license run you are limited on how fast you can go. we did have some braking issues( go figure!) We cracked one rotor, so we replaced them both. They The brakes don't like stopping from 150mph, the rotors turned a pretty shade of blue. I think i may switch the proportion valve around so it puts more force on the rear brakes.

[amcinstaller]

They The brakes don't like stopping from 150mph, the rotors turned a pretty shade of blue.

awesome

good to hear you still gettin out there

[Plechtan]

I pulled the datalogger, the top speed was 150 mph. it was in 4th gear and 6350rpm. the rev limiter was starting to cut in. Looks like my driver ( my son Scott) forgot to shift into 5th. Top speed in 5th should be around 185 mph.

We did have issues with the front brakes, I asked a frew people about this and they told me to get rid of them and my problems would go away. We didn't use the chote at maxton, and probably the chute will take a bigh load off the brakes. The problem we are having is that the front end will shake under hard braking. I think the upper arm bushings are compressing and taking the caster out of the front end. (we have a dropped axle) I had previously put in lower arms with joints similar to johnny joints. Rustys made them up for me, they are just stock XJ replacments. I wanted to do the same thing with the uppers, but the bushing is in the axle and not in the Arm. I called Rustys back, and they do ha a joint and bracket that can be welded to the front axle to replace the rubber bushing, Rusty took an interest in the project and said he would make up something special for the application. He said he is working on ot, but i ned something in the next week or two if i an going to install and test it prior to bonneville

[amcinstaller]

turbo tom actually has no front brakes on his drag spirit as well, just the laundry out back.

[4.whoa]

Are you still using that rear valve over the back axle that is supposed to keep the truck from locking the rear brakes? I lowered my mj am having a bad time with not much rear breaking. I adjusted the linkage to keep the arm in about the same spot,but its still no good. Have the front brakes shook each time,or just after the 1st run? trying to stop that rocket had to have warped those rotors

[Plechtan]

The rear valve is long gone, I replaced it with an adjustable proportioning valve from Summit. The current valve has a line that goes back to the proporting valve under the master. Maybe tou should just swap one in fron a XJ.

[Plechtan]

4 people so far have told me not to bother with front brakes, and to loose the power booster. My driver likes the idea of front brakes in case the chute fails. At Maxton we had a problem with the front end shaking violently under hard braking. Since the front end was fine @150mph and only had a problem under braking, we assumed the braking forces were changing the front end geometery. This can happen when the rubber bushings deform under the braking force. I have a beam axle, like a piece of pipe. In a normal MJ/XJ the lower links are very close to the center of (tire) rotation, and the upper links are about twice the distance away. On our axle we moved the "C" pieces up about 4" , so now the upper links are closet to the tire rotation centerline. When you apply the brakes the entire axle assembly tries to rotate foward, the links hold it in place. since i changed the geometry, much more force was transfered to the upper links, the axle tries to rotate foward, compressing the rubber bushings in the upper links, taking all the caster out. we had already replaced the lower links with adjustable links with forged ends from Rustys prior to out last trip to Maxton. The only rubber left on the front end was the upper links and the trac bar. I talked to Rustys and the came up with somthing special. Normally on an MJ/XJ the front upper link bushing is pressed into a sheetmetal support on the axle. You can make a link that goes into the body using a rod end, but to attach to the front axle you would need a u piece on the end to go on either side of the bushing. I wanted to get rid of the bushing. Rustys sells a kit where you cut off the stock bracket and weld on a support with a Johnny joint, then you can use the stock arm or a aftermarket replacment. For me he came up with a U shaped bracket that you weld on to the axle that let me use a link with heim joints on both ends. We installed them over the weekend and feel we have the front end problems under control.

We are working on the balast and a few other things. We leave for Bonneville next Wendsday, Hopefully things will work out better than they did last year.

[Plechtan]

timeslip 2010.gif

Well maybe that says it all. We could have probably ran in the mid 160's if we had the right gear. When we shifted into 5th it just bogged down. The HP required is based on the cube of the speed, so as your speed goes up, the need for HP dramatically increases. of course HP is not constant either, it has a curve, the best is where the HP peak meets your top speed. We were only able to get to 5,200 rpm and our HP peak is at 6,000. The lines crossed too soon. Still 165 would not be enough for the record, that currently stands @ 173 mph. We have to make some dramatic changes and get 50-100 hp more out of it. Maybe a turbo is the way to go.

[amcinstaller]

thats still pretty effin quick. way to go!

[Plechtan]

I was looking around online today, and i came acorss an article on the Dodge SRT 10 I it holds the Gunnis record for the worlds fastest production pickup truck @ 154.587 We went a little over 155 with the Comanche, maybe this will give you some perspective.

[Plechtan]

Some people on another board made a comment that it was a shame that we did not set a record. Well maybe, but it is rare that we succeed at something the first time you try. you usualy get your head handed to you. Imagine if the first time we tried to walk and fell down we gave up the idea of walking. It is part of the human spirit that when we fall down we get up and try again. Some of us as we get older seem to forget this, or find it more convenient just to give up. Maybe i'm not that old or cynical yet. We are racing against a guy who has engine componants that were designed and used in a nascar Series. Not easy to compete against.

My son and I learned a tremendous amount. It is not just about the engine, you need to build a reliable race car. On our car everything worked, we did not blow anything up, we did not spin out or flip over, we had good traction. All we needed was some more HP. We know what gears to use next time, and about how much HP we need to break the record.

Right now I am out of money (probably like most of us these days). I did contact 505 performance and asked if i could borrow the "insane inline II" turbo motor (690hp) to try a run in the Comanche. No answer on that yet, but maybe the people on the board could help. How about writing an email to [email protected] and tell Zach tha you would like to see what his motor would actually do in a vehicle. Let's see if it would actually hold up on a 5 mile run on the Bonneville salt flats .

[Plechtan]

I got stuck working the Machine tool Show in Chicago this week. If anybody is going and would like to talk about he project, stop by the Toyoda Machinery booth. Ill probably be bored out of my mind and it would hel pass the time. Just ask for me and they will hunt me down.

The Comanche will also be at Great Lakes Dragway in Wisconsin this Wendsday night. My Son will be driving.



Peter Lechtanski
The Worlds fasttest Comanche Project

[I6FAN]

Plectan wrote:
The Comanche will also be at Great Lakes Dragway in Wisconsin this Wendsday night. My Son will be driving.

Man, I bet the weather will be sweet for that way up in Wisconsin. Keep us posted on the drags!

[Plechtan]

Man, I bet the weather will be sweet for that way up in Wisconsin. Keep us posted on the drags!

Well he made 2 runs before he got thrown out, something about salt falling off the car onto the track. His best run was a 13.2 @ 110 mph. Not bad for a comanche with a 3.08 gear and street tires

[I6FAN]

Salt falling off the car?: Who would have thought that would happen? No, not bad at all with that gearing and the power band your running. If you had the right lower gear to get the mechanical advantage for it to go faster in a shorter distance that car would do 11's, at least (just a guesstimate).