small 1/4mile oval tips, transitioning from road racing

[rob burgoon]

"Take the 850 out of the RF, its keeping you from getting over on the RF and letting the LR travel to add drive and sidebite."

bcollins, let's dig into this a little if you don't mind.

Let say I soften RF from 850 to 650. On entry the car will rock further towards the RF, drooping the LR a little. However, mid corner, the softer RF means more weight from body roll on the RR which can overload the RR causing oversteer.

How does a softer RF create drive and sidebite at mid and exit? Seems like it does the opposite.

[Bcollins82]

"Take the 850 out of the RF, its keeping you from getting over on the RF and letting the LR travel to add drive and sidebite."

bcollins, let's dig into this a little if you don't mind.

Let say I soften RF from 850 to 650. On entry the car will rock further towards the RF, drooping the LR a little. However, mid corner, the softer RF means more weight from body roll on the RR which can overload the RR causing oversteer.

How does a softer RF create drive and sidebite at mid and exit? Seems like it does the opposite.

I understand that the underrail bar is welded in. You are dealing with a chassis that was never designed to travel that far. Same as the ride heights, things are being done differently now. Cut that underrail and bend up a new one and weld it in... Don't worry, all older underrail cars have had this done. Bolt in sections work well also, just in case you don't go far enough the first time. Things have progressed, and even though it may have been designed for it then, it doesn't mean its the best way to do it now. 42 degrees at full drop is close, I usually aim for 44* with both sides hanging, car up and level. Its the only way to do it consistently IMO, but its at 42* when dropped because it is probably starting at a steeper angle than most to begin with. Softening the RF by itself will not add forward drive or sidebite. It is part of a package most cars are running now that uses a softer RF to get the LR up easier, farther, and keeping it up. Dynamic bar angle in the LR also seems to load the LR harder than stiffening the RF spring. And by letting the LR drop farther will raise the rear of the car, and that raises not only the LR bar angle, but also the weight, spoiler height, and adds J bar angle dynamically increasing drive and sidebite.

As far as the gear, you said it was hitting the chip more when you describe the track as dry and black and with the rear hung out all the way down the straight. That leads me to believe that you are hitting it by spinning the tires. 5500 rpm seems incredibly low for a limit. Is that really the high end safe RPM or is that just where power falls off?

[RRR_Products]

Hey Rob what springs do you have? We will def ditch the 850 though. Depending on the night you want to run dry vs tacky have a few springs available for the front end and let's see the valving on the shocks. Depending on what shocks are at or springs we can go from there. Throw a 175 in the RR and 200 LR. Don't recall if you have a brake floater or not on that car. Get rid of the LR under slung and put a strap on it. 4.5-5.5" drop you can start with. With the amount of power you're running you'll be fine on a dry night and tacky may struggle. Nothing wrong with less hp as most of the time too much can mask handling issues anyways. If I were to suggest where to start and what I know works well is a 750 RF and 550 LF in dry or if very dry also lighter RF but again the shock valving is something we would need to see. Just get a 550 LF though to start and get those shock numbers.

[rob burgoon]

Sounds good, looks like I'll be cutting the bar out and adding a droop chain soon then.

5,500 is where GM says to stop.

"RPM limits are critical to engine life. Catastrophic engine failure can occur if the engines are run
above the factory recommended limits. Extensive dyno & track testing has determined the limits of
the engine. Under no circumstances is it recommended to exceed these limits. GM recommends
that all sanctioning bodies, track operators or promoters have rev-limits written in their rule book.
Maximum limit for 602 engine is 5500 rpm."

If I was spinning the tires hard, I'd expect to zing the engine at corner exit when there's still a side load, not at the end of the straight when I am the most hooked up out of the entire lap. As the track got blacker, I was playing with a more diamond driving pattern and driving in deeper rather than trying to rotate early. (since sliding in became impractical). That might have extended the straight a little.

[oldtrackchamp4x]

Does the car have a metric or chevelle front clip? If it is chevelle then the 850 is way to stiff.JMO

[rob burgoon]

Does the car have a metric or chevelle front clip? If it is chevelle then the 850 is way to stiff.JMO

Chevelle I think, but I'm just guessing. What would the symptoms of a way too stiff RF be?

[rob burgoon]

602 crate produces nice useable power past 5500.. around here they run 6200 chip in them so they are chiping at approx. 6000.. just because the sticker from gm says 5500 doesn't mean that's the way to go.

Nice usable power is good. How long does the engine last going to 6k?

[rob burgoon]

Just checked droop on LR, 3 inches of droop travel.

[rob burgoon]

I see them for sale all the time around here 100 plus nights...

the speed limit is 55 on a lot of highways, you don't actually drive around at exactly 55 do you? same thing with gm sticker on these made in mexico motors.

Doesn't the strain on engine parts go up with the square or cube of RPM? My street car isn't at redline at 55mph!

But broken analogy aside, there's probably a safety margin to exploit. I'll consider upping the limiter instead of a gear change once we get the handling issues sorted and the speeds go up.

[charcoal01]

Many times I've dropped my total rpm by adding a taller gear, why? Because you're able to control wheel spin better and keep tires hooked up. I went to barona with my open motor ina mod and ran a 6.2 gear. You should be in the high fives at least.

[Bcollins82]

Just checked droop on LR, 3 inches of droop travel.

Thats not enough IMO... 4.5 to 5 is a good starting point. Make your limit chain adjustable, and don't just remove the underrail, replace it with one that is bent for clearance. Throw the original setup book in the garbage. Set the ride heights like I explained before, Take the spring out of the RF and cycle the suspension to be sure a 2" body shock will clear at full travel or you will junk shocks after you make the car travel. Youll probably want to add a couple degrees of camber to both sides (more pos on LF, neg on RF) since the car will roll more. Change the RF back to 650, LF to 750, LR 175 or 200, RR 225. Jbar in bottom hole on pinion, 5" of rake from center of pinion bolt to center of frame mount. A brake floater works well on this style setup if you arent using one already. Go up to 30 or 40 lbs of LR bite, add a couple percent of left side, and another percent rear. Post the rest of your full setup and include as much info as possible. Shock valving and location, bar lengths and angles, rearend square or trailing, wheel offsets, pullbar info including spring, and if possible a pic of each side the rear suspension LR pics at static and droop. There are a lot of great guys on here that will help if you are willing to give the info, and listen to what is being said.

[rob burgoon]

Many times I've dropped my total rpm by adding a taller gear, why? Because you're able to control wheel spin better and keep tires hooked up. I went to barona with my open motor ina mod and ran a 6.2 gear. You should be in the high fives at least.

Everyone here is saying my gearing (4.7) is too tall, not too short. You're telling me I need to go taller. High fives is shorter, not taller.

[charcoal01]

I'm sorry, for some reason I always screw that up. Shorter is the direction, not taller. Just a for instance, sport mods running a 602 at cocopah run almost the same gear as the a mods running open motors do.

[JustAddDirt]

rob burgoon

you are asking for assistance with a car. several have chimed in to offer advise. I being one of them.
1.You have an older car that was never designed to move like newer cars do. you need to have the option to go to 5" of drop on the lr. Frame will need to be altered to accommodate that. With that being said, you are basically lifting the LR tire off the racetrack when car does roll over with side bite.

2. You need to change the gear. I have 20 + years of dirt car experience, I know when a car needs a gear change.
you can say we are talking crazy talk, that is fine if you do not want to listen, that is your choice, we are just trying to assist. You might want to go ask some front runners what gear ratios they are running. By listening to your video, the competitor's are probably in the 5.67-6.0 range. Listen to their cars, and listen to yours. big difference in RPM's, and acceleration off the corners.
3. I would suggest you ask someone local for help, that has knowledge of dirt cars, and setups. Someone there is bound to assist you. even one of the frontrunners will probably help you. Just got to ask.
4. I would suggest a chassis seminar, if available in your area.
5. If you can upload photos of what the a arm angles (low front view),and some photos of the attitude of the car just sitting there from front and back, that will help us help you as well.

[rob burgoon]

2. You need to change the gear. I have 20 + years of dirt car experience, I know when a car needs a gear change.
you can say we are talking crazy talk, that is fine if you do not want to listen, that is your choice, we are just trying to assist. You might want to go ask some front runners what gear ratios they are running. By listening to your video, the competitor's are probably in the 5.67-6.0 range. Listen to their cars, and listen to yours. big difference in RPM's, and acceleration off the corners.

I feel like there is still some sort of misunderstanding here. My competitors are running claim engines. They can rev to nearly 8,000 rpm. I am the only person in my class using a 602, and I have chosen to believe GM when they say to set your limiter at 5,500.

With a 5,500 rpm limit, of course my car is going to sound different. It should.

I reach the limiter once in a while at the end of the straight. Unless you want me bouncing off the limiter down the straight, my gearing sounds correct. If my rears are spinning (I doubt they are), won't shorter gear ratios add torque and make the wheelspin worse?

[oldtrackchamp4x]

All i have to say is, don't ask questions if you aren't willing to listen to good advice. JMO

[rob burgoon]

All i have to say is, don't ask questions if you aren't willing to listen to good advice. I'm done. JMO

I'm sorry you feel that way, but asking for advice does not oblige me to blindly follow all that is given.

I have several books on dirt track setup and they disagree with each other on fundamental issues. The trick with the books is figuring out who knows what they are talking about.

[RRR_Products]

Rob revving 5500 will be just fine. Especially on a dry night there. If the car is too tight though it may be tougher to drive on a tacky night and may struggle. Also I know what spring set up works well at your track and the valving to get you in the ball park.

[charcoal01]

You're not taking into account the fact that lower hp generally needs more gear. You can keep believing that you only can run that 4.7 gear and you're going to keep struggling. Having an improperly geared dirt car can cause just as many issues as poor setup. Sportmod guys using 602's at cocopah run 5.14's and up and cocopah is almost twice the size of barona. You are spinning your wheels because something isn't right in your setup, you could probably get wheel spin with a set of 4.10s at that track.

[JustAddDirt]

I agree with charcoal01
Not to mention, lugging of an engine is worse than hitting the chip. You will probably end up spitting a rod out the side of the block, or a broken crank.