IMCA Stock Car Trends

My brother has decided to try his hand at building race cars, specifically metric full body cars. He has asked me to help him with setting up the front end and driving one for him as a "house car". I've been creeping through the history and have come up with the following trends. Please comment if my summarizing is not correct. 1.)Camber should be set so 1° gain per 1" travel. 2.) Caster should be set to gain a minimal amount during bump. #1 is to maximize tire surface area #2 so the car feels stable during cornering. I have a question when it comes to roll centers. In short, more upper a-arm angle, shorter roll center. Shorter roll center acts like a shorter arm (faster movement & stiffer rate (RF)). Many of the previous threads state that front and rear roll centers work together, my question is where does a guy start and how do you know which one needs to change. For now, we are going to purchase a rear-end from a local builder, but won't necessarily know how the RC compare. How does one go about changing when the car doesn't work well? Start in the front for corner entry and rear for transfer and exit?The other question I have after creeping around the FB classifieds, is it appears most builders are building at max set-back and not building the cars real heavy upfront. In a lot of cases it seems looks like max of 2 1-1/4" tubes tied together around the front of the engine and running back to the main cage. Is this to allow the cars to flex more than previous? Seems like there would be an awful lot of flex in these during bump. Is that the intended to get RF to seem softer until the center of the corner?Any suggestions or tips would be awesome! Already feels like the off season is dragging by.Thanks!Banana

A lot depends on your rules. and what can be changed and cannot.
I am not Familiar with the IMCA rules, so bare with the questions

Do you have to use Stock upper A-arms, and A-arm mounts?
Do you have to keep stock shock mounting locations?
Need to lower the upper a arm mounts, and take out a lot of the anti-dive built into the stock setup.
If you can alter the upper a arm mounts, and use a tubular upper a arms then using a 68-72 Chevy Nova lower a arm will help a great deal.
If you have to use stock upper a arms, then you will have to cut off the a arm mount and move it.

Bump steer on the Metric GM is horrible, that will need a lot of work.
Gen 3 Camaro drag link helps some, but not enough.

Lots of things can be done to greatly improve the front ends. that is where a lot of your gains will come from.





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Thanks for the response.We can use aftermarket tubular uppers, but they have to be IMCA approved. [url]https://www.speedwaymotors.com/IMCA-Spec-GM-Metric-Stock-Car-Racing-Upper-Control-Arms-Alum-Cross,2120.html. We can move the shock mounting location wherever we want. Just has to be single mount location, non adjustable. Rest of front end has to be unaltered OEM, OEM location and match the frame so I'm assuming the nova contol arm and camaro drag links are out at that point. We have to use stock tie rod ends, so limited in what we can do with bumpsteer as well.Thanks again Banana... I don't know how to format this so it's easier to read, it keeps smashing everything together.

The camaro nova parts are still OEM. They are Still Chevrolet parts. As For the Camaro drag link, speedway sells one. They label it as a metric bump steer improvement, and charge you 2.5X what it cost to parts store.

IMCA stock car can move the upper a-arm mounts anywhere you want to.

Tie rods, center link, pitman arm, lower control arm MUST be GM metric G-body parts. No other OEM parts. Spindles can be OEM G-body, or 3 piece replacement arms, Nothing else. no bumper steering spacers allowed, no bending of steering parts.

The only legal part you have to work with is the upper A-arm mounts.

Wow. They keep them in a tight box.
Not a bad think though, everyone has the same parts that way.
looks like about all you can mess with would be balljoints?

Yes, you can also run taller ball joints.

If you think that box is tight.... IMCA hobby stock has the same suspension rules PLUS they have to keep the OEM upper A-arm mounts in the OEM location and use stock mount shocks.

Quote:

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Originally Posted by SRXSRULE

Yes, you can also run taller ball joints.

If you think that box is tight.... IMCA hobby stock has the same suspension rules PLUS they have to keep the OEM upper A-arm mounts in the OEM location and use stock mount shocks.

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Ouch.
That is our pure stock rules around here. Stock location shock, stock upper a arm, and supposed to be in stock location.
but the better driving cars from the better builders are moving the upper mount around, and rewilding back on.
They say OEM parts like I posted above, but rules do not state G Body parts only. Some are doing the gen 3 Camaro drag link, and a few the Nova lowers. That is why I asked about that stuff.
Most of the Pure Stock guys around here have nice looking and well built cars, but handle like crap. They do not know anything about all the front end improvements that can be done with "OEM" stuff.
I am a mod guy so I know all about the nova stuff on metric from the early to mid 2000's when modified chassis builders were doing all that, and the drag links. There is one guy here that has built a car with the nova lower a arms on g body and he dominates everywhere he goes. He is a smart guy, he has built modifieds, and worked at MasterSbilt race cars years ago.

Yeah, tech is everything. some tracks dont check much at all and 1/2 the field is not legal. Makes it that much harder to win with a legal car.
Guys have been moving the stock upper mounts for several years now. They have started taking measurements on those (some tech guys), so now many guys have switched to moving the lower mounts. They are trying to measure lower ball joint location but that doesnt really mean much.... you can keep the ball joint in the same location and just turn the arm.

So after a bunch of reading and creeping through the forums, would it be fair to say a guy needs to find a balance between a consistent chamber/caster curve during bump vs. the effect it has on bump steer? Does a guy just pick a starting spot and see what is preferred or is it chamber curve more important that bump steer (or vice versa)? With the IMCA stock car its pretty limited to what can be done....ThanksBanana