Marder Goes OnRoad!

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MonsterAir

Lone Racer 🤠
Messages
2,369
Location
Long Island NY
Had the buggy on some asphalt today. First run with my new grp tires. Finally went thru a trouble free tank! Now I can get into tweaking and tuning the car for different scenarios starting with onroad. I was not very impressed with my top speed and really have no reference to judge my acceleration. Here is my setup-

ESP Champ 27.2 (2-bolt) w/ a obr 27.2 race ported head, 18/46 gearing, viscous dif w/ 30k fluid, 3k shock oil in the rear with 2 or maybe 3deg of toe in.

What do you guys think of the 30k dif fluid? Should it be heavier? Before I rebuilt w/ the obr head I remember it being quicker, though this is going back a while and I never had anything to clock the speed. Just remember being able to get the wheels off the ground pretty easily. I'm wondering if it's the fluid not locking the dif enough. During this run I wasn't able to get the car past a measly 26mph. I think she's running a tiny bit rich but it's been in the 80s and the motor will creep to around 300 after a hard lap or 2.

 
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I can tell you by sound alone that the engine is not tuned correctly for any kind of top speed.
Not nearly reaching high RPM, which would indicate possibly rich, or possibly lean.
Reason I say lean is by the temp. you indicate it is reaching.
These engines should NEVER go over 270, and if you have allowed it to do that damage has possibly already occured.
Possibly air leak, or tuning issue, but it is definitely not correct.

What are your needle settings ?
 
It almost sounds like a possible intake block air leak, and I say that only because of the tempratures your reaching.
At those settings you should be around 220 - 240 Tops
 

The yellow buggy in this video is mine from Several years ago now.
I still have it, and 4 other HPI models + 3 FG models + ... Oh well. ;)
You can hear the higher RPM achieved by these cars, and none of them are running above 250 to 260 degrees.
I did have this exact car on radar, and it would run almost right at 49 mph.
Definitely seems like you have a problem that needs to be found before any damage occurs to your engine.
 
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I'm gonna try richening it up a bit and see what happens. Most def have overheated the motor in past to above 300deg. Would a ring swap help?
 
We have a nice go kart track here that just closed down. Would be perfect for a fpv race, parts of the track you wouldn't see the car.

Going to make a better vid of a speed run now. Maybe you can hear or see something I don't. Thanks for the help looker!
 
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Ok so I did one run with the settings from yesterday and one with it 1/8-1/4 turn richer on the high speed needle. Low is still at 1 1/4 out. When I ran it 1/4 turn richer it started to gurgle and bog so I leaned it out an 1/8..... Is it possible that I used to thick of a head gasket when I rebuilt? Don't remember exactly which one I used but I remember it being a HD copper gasket..... Both runs here didn't get past 26 again.


 
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O.K. - Awesome videos BTW

I think we have a couple things determined here.
First I think your taking a temp reading in the wrong spot.
In order to get a correct reading on the temp., you need to check directly at the base of the spark plug.
If you get anywhere to close to the exhaust port, you will definitely get a high reading like you are seeing.
Secondly, and possibly most important, it does appear that you are running rich for sure from what the video looks like.
Having the temp gun, should help you in not getting to lean, but by listening is really Always best.
If you are not real fimiliar with the sounds it gets tough to know for sure, but it sounds like you have a decent handle on how it should run, and the sounds it makes when tooi rich, and too lean.
When my cars are tuned to Max performance, " Most "of the time my low needle is around 1 1/8th, and High between 1 1/2, and just a slight adjustment either way, but very slight.

Now for the one thing that I am 100% sure is your problem.
Gears !
By moving to the extremely smaller diameter tires, you are running out of gear Extremely fast.
I would look for some On-road car gear combos, and see where that gets you.
I am positive that it will get you WAY more speed, and it will actually make the whole car happier to be in the correct range gear wise for the tire size and engine perfrmance.
 
Thanks for helping me out. I really appreciate you taking the time...... I have been taking temp readings where I find it the warmest which is just above the corner of exhaust port. When you say take the reading at base of the plug do you mean the very top that is covered by the motor shroud or 2 or 3 fins down from the top?..... Your right and I was thinking the same, sounds as if I'm running through the gears at like half throttle and thinking back a few weeks ago when I posted that "can a blown engine gasket do this" thread I clocked 29mph on some med tall grass with baja tires. I still thought that was a bit slow though. I just got about all of the gear combos last week and the bonehead I am I forgot to order the carriers so it'll be Monday or so til I can play around with the gearing..... I found a local group that meets on Sundays for some parkinglot racing. Most of them run fg sportslines and the track they setup doesn't seem to have too long of a straight so I won't need all that much speed to stay competitive. I want to stay with these tires for asphalt cause the handling is loads better and I'm sure nobody with a sportsline would want to be racing into a corner with a guy running big offroad tires lol. Thanks again and I'll report back with my progress.
 
Cool, and your very welcome.

http://www.trailtech.net/digital-gauges/tto/723-et1

These can come with a piece that allows the reading to be taken Right at the base " where the sealing ring hits the head " of the spark plug.
It is the true way to see how the actual combustion is taking place in the cylinder.
Exhaust side of the engine temps. will alwasy be higher, and Intake side always cooler.

You know I'll be watching for replies. ;)
 
Oh boy we got another from suffolk! Ya man thats the one I'm talkin about. How much fun would a fpv race be? You wouldn't even need to stand close, throw the cars on da track walk outta sight and race. lol
 
Hey looker I got the buggy running semi decent now! Ended up trying all of the gear combo's and 26/38 ended up being a winner. Topped out at 53.7mph w/ grp onroad tires last I had the gps on it. I come to realize that I forgot to extend the throttle travel after break in! Was only at 55% or something. I also ditched the temp gun and went down to 32:1 oil mixture. Ran 3 hard tanks last weekend and she purred every time I brought it in for an idle. I'll get some vid up over the weekend next time I tangle with the onroad cars...... Still tweaking the suspension, have some terrible under steer along with my front inside tire coming off the ground and my diff keeps spitting out the oil I put in it. Was such a nightmare getting it apart and back together last time I really don't wanna mess with it til the offseason but I may just have to.
 
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