Engine SetBack Information

[racefastnow]

I run a steel dart block with aluminum heads and have had the same car for 2 years. I just recently found out what the setback on the engine is. It is 5 inches from center of ball joint to front spark plug. My rules allow this measurement to be 10 inches. I have talked with some drivers around my area and they all hav it 8 to 10 inches. I would like some explanation on how this is affecting the car. steering and traction???
I am thinking of moving this back. My car is built to be 5 inches. So i need to do some modifying to make it work if i should decide it would help.

[zeroracing]

Yes you should move it back... Moving 5 inches may be some work, I moved one 2" easy with blocks, 5 would be extreme for just adding blocks to backside of motor mounts, you may want to add some bars and some tabs for a mid plate, also your front mounts will need moved back also, again, done it for a few in he's but never 5". I would be concerned with the strength of using a standard block spacer set up to get 5".

You will notice less nose weight, and a lower polar moment.

[racefastnow]

Understanding Thrust from this change

I am trying to grasp how a car uses rear weight for traction. I believe generally its rear percentage, but when the car is in dynamic stage and up on the bars and massive hold down on RF with a soft spring. I feel like this has to be causing some loss in rear traction in order to gain better steering. but anything can be overdone. How does the rear weight in dynamic state effect the top rear bars as they provide the traction. What ive also done is when car is on scales i jack up the left rear till its at full droop and i have been paying attention to how the weight is being distributed during this. The left Rear wheel becomes almost 0. I was wondering if anyone has some thoughts on this.

Im thinking of releasing rebound until i loose exit steering ability, which should gain rear traction. And my 5 inch engine setback is causing and helping the car get on the RF nicely, but at what cost. Maybe looking for a engineering technical explanation, and some on track experience with engine setback and some cross-weight and rear percentage issues from this. Trying to learn from what i have done and what to expect. I have had very good success on dry slick tracks, but not on tacky or muddy tracks.

[jedclampit]

What kind of car is this? A production late model or other?

[racefastnow]

its a production car. The cars are designed for open rules. Our rules allow for a 10 inch setback. Most people have told us we should be moving it back. but looking for some more info related to whats happening(read above message).

Im wondering how the top rear bars create the thrust and how its determined. Ive read most people like 45 degrees for top left rear bar when its up on the bars. where is the thrust coming from. What point or angle of the car? is it correct to say if you extended the bars imaginery angle thru the car, so the bars are pulling from the weight from the car that is distributed a couple feet ahead of the rear links. so if you move the setback back 5 inches. This changes that weight at this imaginery point. Also, if you change the angle of the bar, height of droop. this also effects this imaginery point and therefore the weight its pulling?

Hopefully someone can understand what im trying to ask. ha

[4bangerhotrod]

the reason your LR drops to 0 when you you jack it up is because your jacking the car up and taking the weight off it. you cant check the weight like that cause there's too much going on on the track that you cant simulate on the scales like weight transfer and trust from your bars. the bars are holding the LR up on the track then the weight is transfering back and pushing down on the back of the car while the bars are pushing against it, thats what makes the tire dig. the further back large amount of weight is the more weight that will be transfered back because the weight is closer to the rearend and you have less front weight to allow better transfer.
thanks,
4bangerhotrod

[racefastnow]

I agree with the scales problem. that its not telling you the force on the left rear wheel. but its giving you a static idea of where the weight is on the car when being raced. This can be controlled by car attitude. Thats what i was trying to learn when i move the car around on scales. Ive just noticed the difference in car attitudes, some cars are flat. some have fronts slammed and rear maxed out and any variance in between.

[JustAddDirt]

bar angles and weight at LR tire

you might try this:
Use a ratchet strap to pull and hold LR axle forward. Make sure to fully extend the LR. this will give you a general idea what the weight is doing without cornering forces, and thrust angles.