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Author Topic:   Motor placement?
sledgehammer
Dirt Maniac

Total posts: 119
posted December 22, 2005 07:29 PM  
Rules say rear of motor flange no closer than 70" from center of rear axles. Currently at 71 1/2", would it be worth the time to move it back 1 1/4"? How much would that affect the rear percentage?

Thanks

thebomb
Dirt Maniac

Total posts: 162
posted December 22, 2005 09:49 PM  
thats a tough one, every little bit helps, it just depends wether or not your up to it

rocket36
Dirt Freak

Total posts: 247
posted December 23, 2005 02:38 AM  
the guys that win regularly will be the one's that have spent the extra time and effort doing the little things - maybe moving there engine back to the maximum set back rule.

if your winning already, why bother, if your not and you want to, well its the many things like this that may make the difference.

aggressive
Dirt Full Roller

Total posts: 38
posted December 23, 2005 05:20 AM  
IF you have enuff wheelbase length and its a bar car,it may be easier to move the rearend forward....

sledgehammer
Dirt Maniac

Total posts: 119
posted December 23, 2005 06:51 AM  
Thanks for the replies, this is a SIMS limited/Southern Sport mod car. I have not raced it and am looking to do everything I can to make it competative.

Thanks

Dman
Dirt Freak

Total posts: 280
posted December 23, 2005 07:44 AM  
Moving it back is alot of work.Driveshaft length,throttle linkage,shift linkage,exhaust clearance,radiator hoses and fan spacers,motorplate mounts etc..Pulling the rear end forward with the bars can have some definite ill effects on handling.I would save my duckets for a new chassis and run it as is for the time being. I don't think the 1 1/2" will be noticeable on engine set back but would be by shortening the rear links.Check it out on a set of scales this may tell you if it's worth it.

tilley88
Dirt Forum Champ
Total posts: 896
posted December 23, 2005 08:30 AM  
I moved the engine back a little over an inch in an old Shaw mod I had, and it raised the rear percentage about 1%. This was a 110" wb chassis. The shorter the wb, the harder it is to get rear percentage. And it is alot of work to get the engine moved back. You can get offset motor mounts and space your midplate back, but you may have to shorten your d'shaft, tranny rods, throttle rod, etc., etc. You may be better off moving the little things back, i.e.- battery, pwr steering reservoir, radiator, body, fuel cell, lead, anything that you can think of. I did all that with the old Shaw, and only got 2% more rear. Dissapointing, to say the least. I ended up with 56% rear and the car was about 150# heavy. I sold the car and bought a bare DW8 chassis, moved a bunch of mounts to suit me, ended up with a chassis that had 60% rear, and barely made minimum weight(2450) with me in it, full of fuel. I could have made it even lighter by going to lighter headers, radiator, narrower body(mine was 72" wide), removed the 50# stick of lead, gone to a smaller cell, etc. You gotta weigh the pro's vs. the con's. Do the work, spend the money, or get another chassis. But what you have may not be that bad off to begin with. I know several guys around this area that can't get more than 55% rear w/o adding tons of weight, yet they still manage to run up front and win on occasion. You could move the rearend forward, but that could turn into a big job, too. It would also shorten your w/b, which would actually reduce rear percentage. BTW, aren't the SIMS mods set-up with jackers on top of the original spring buckets? P.S.-Excuse my spelling and droning on, I just got home from working a 13 hour nightshift, been up for 22 hours, and think I'll crash now........

sledgehammer
Dirt Maniac

Total posts: 119
posted December 23, 2005 09:50 AM  
This is a full frame metric car with stock rear suspension. Moving the rear is not an option. With current set up I only have 50% rear on the car.

robhbk24
Dirt Freak

Total posts: 378
posted December 23, 2005 11:58 AM  
can someone explain why it ouwl have more effect on a longer wheelbase than short? i was just wondering it seems to me if it's a shorter wheelbase then the rear wheels are closer so the more you move the motor back the closer you would be. my new street stock is a metric cut down to 101inch the same as a 3rd gen f-body i personally like the shorter wheelbase for handling purposes but was just wonderiung why it would have lesss rear percent. i could see if the over all chassis is longer behind the wheels because of the added leverage available

sledgehammer
Dirt Maniac

Total posts: 119
posted December 23, 2005 12:25 PM  
Lets look at a 110 inch wheel base with the back of the motor set 72 iches form the real axle. Now lets say that the wheel bases is 112 iches with the motor the same 72 inches from the axle. Now the motor is 2 inches farther back from the from wheels which removes weight from them an puts it on the rear. The above is in reference to a modified.

If your car has the motor mounted in the stock location then shortening the wheel base will increase the wheel base.

robhbk24
Dirt Freak

Total posts: 378
posted December 23, 2005 02:53 PM  
got ya thanx for the explanation, our rules are the #1 plug with the upper ball joint so in my case the shorter wheelbase will help in your case it's 72 inches no matter what so the longer thew wheelbase the further thew motor is off the front. makes sense. just a ? then in my application my old car was 108 my new car is 101 the motor on my new car will be set back as far as allowed which will gain me another 3 inches + if everything else remained the same what kinda gains in rear percent do you think i can expect.things aren't even close to being the same as overall this new car is being built with rear % in mind. the cage was tacked in today and ended up 9.5 inches back further than the old one. ( i just added onto the bacvk of the frame rail)

jello
Dirt Roller

Total posts: 19
posted December 23, 2005 05:14 PM  
If its a sims car and you only have 50% rear, then yes I would probably move the motor back to the maximum amount. I would also take a real good look at all other placements on the car--battery, fuel cell, ballast etc etc. 50% seems really low to me for a sims. Just curious--how much does the car weigh? I am not saying that 50% is wrong, just out of the ordinary

Billy Gould JR.
Limited mod #GO

sledgehammer
Dirt Maniac

Total posts: 119
posted December 23, 2005 05:21 PM  
2165lbs, the car only had a 12 gal fuel cell which only had a couple of gallons of gas in it. I plan on moving up to a 22 gal cell. The battery is directly behind the driver seat. When I move the mid plate back I plan on cutting all of the cross braceing loose and moving is back also so the trans mount will line up properly. I think that between all of that the rear percentage should come up.

What is a good rear percentage for a sims car?

Thanks

john56h
Dirt Forum Racer

Total posts: 82
posted December 23, 2005 06:51 PM  
Does anybody running IMCA type mods that previously raced a street stock type of car think that maybe the mods just don't have enough weight on the front tires? When I switched from a 3000 lb. streeter to a 2600 lb. modified I felt that I couldn't get the car to corner as well as the streeter had, especially at corner entry. Lap times for both cars were nearly identical, with the mod quicker in the straights and the streeter quicker through the turns. All I could figure was that since the mod was lighter overall, even with better rear weight percentage it still had less weight on the rear tires than the streeter and it had a lot less weight on the front tires. I don't think it had enough weight on the front tires to "stick" the frontend properly on corner entry, thus it would tend to push. Any other thoughts guys?

tilley88
Dirt Forum Champ
Total posts: 896
posted December 23, 2005 11:24 PM  
When I first drove a mod after years of drivin a streeter I thought the same thing, man this thing don't stick like a streeter. After a couple weeks in the mod I figured out you gotta drive it harder into the corner and let it roll over on the tires and TRUST the thing to stick. After that I really started having fun. That push you're feeling may be driver induced. I had to take a ton of wedge outta mine to get it to loosen up going in.

jello
Dirt Roller

Total posts: 19
posted December 24, 2005 10:10 AM  
You might save your money on that fuel cell and just run the one you've got--just add some bolt on weight on clamps (you can move it around to your liking and it won't slosh around like fuel weight). I would probably move the battery back further also. I have 57% rear in my car. It will be a lot of work changing all that stuff. good luck

mod10
Dirt Newbie

Total posts: 3
posted December 24, 2005 11:48 AM  
I think the biggest difference between the street and the modifieds sticking the front tires in the corner is the TIRES, we ran a lot better tires in the street class around here than we run in the mods.

General
Dirt Maniac

Total posts: 157
posted December 25, 2005 12:57 AM  
I moved mine back. Ran into clearance problems. Big pain. Lots of sims cars have had to add weight to the back of the car. Sometimes all it takes is a little extra fuel cell protection or maybe a bigger rear bumper. Now, we can't all be as succesfull as Billy Jr., but we sure can try.

john56h
Dirt Forum Racer

Total posts: 82
posted December 25, 2005 02:38 AM  
The modified that I ran had Identical tires (American Racer IMCA spec 8") as the street stock that I had run previously (actually the tires and engine came from the street stock). I ran on asphalt, so you couldn't toss the car into the turn and get the RR planted, so that could be why it was so noticeable for me. But even on a big dirt track where the turns are driven more than power slid, too little weight on the front tires could be a concern.

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