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Mustang rules related questions


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This is on an '89 LX 5.0 hatchback.


Are the HPM MegaBite Jr. lower control arms legal? I'm guessing no since they apparently change the geometry of the suspension.


I have Baer brakes on there now. Dual piston caliper on the front, single on the rear. I don't know the piston bore sizes off the top of my head, but assuming they're inside the spec, is using the Baer setup with smaller rotors legal?


FMS sells a long block that is the "stock" config. That would appear to a legal setup, but is it a smart setup? Are there things that are commonly done to the engine that are legal but not found on that stock FMS block. Not looking for anyones secret recipe here, just wondering if it's worth building one instead of just going with a stock block.


On the transmission, is it allowed to use a Tremec 3550 or TKO in place of the T5? Seems like there wouldn't be any gain by doing this since the extra strength really isn't needed with the horsepower limits, so I'm wondering if it's legal.


Is it legal to use an aftermarket throttle body, EGR spacer, etc? Seems like it might be allowable as long as it doesn't change the torque/horsepower curves.


I'm sure I'll come up with more.


Thanks in advance...

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  • 2 weeks later...



See the rules section of this website for specifics. This should answer the questions in your post. Allowable modifications are listed and if it isn't there, it's not allowed. If in doubt, ask beforehand. We are all willing to help you out.


Look forward to seeing you out there.


Greg Robinson

#12/55 Mustang

Team Hi Line


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I guess I should've asked things a bit differently. I have read through the rules a few dozen times and it does seem pretty clear on what can and can't be done.


Here's my exact situation. I have a car that another person had started setting up for AI and had done some work on. I was going to continue down that road but am rapidly realizing that AI is *very* expensive if you want to be competitive. So, rather than finishing this car off as an AI car, I'm going to try backpedal to a CMC car.


So let me try this again...


The lower control arms were on the car when I bought it. I don't know if they're the same geometry as stock. I guess the better question is if Megabite Jr. control arms change the geometry of the suspension and as a result aren't legal (8.36.3)?? I don't believe they are, but I was hoping someone might have asked or tried this before and would know.


I have a Baer brake setup that I know isn't legal as is (13" rotors on the front), but I'm guessing simply going to a smaller rotor and appropriate caliper arm might do the trick. There rear rotors are 12" already so they should be OK. My real question here is more if anyone knows if this has been done before and if so, which Baer calipers are legal under the piston size restrictions (8.35.9)?? I believe this setup is the "Track" setup on the front and "Touring" setup on the rear.


As far as the engine questions go, I'm new to this. I don't know if there's a huge advantage to be gained by balancing the engine or if a crate motor from FMS is fine. I'm looking for some advice and discussion on whether it's worth the $$ or if a car can be competitive with a simple crate motor.


On the transmission, I don't know if a TKO or 3550 qualified as a T5. From what little I know of them, they're effectively the same transmission, just beefed up a bit. The stock transmission that's in the car now is in questionable shape (had problems with it as WSIR a few weeks ago). If a 3550 or TKO is considered to be a "Borg Warner World Class T-5 transmission", and I'm simply going to replace the tranny instead of tearing it apart and trying to fix it woes, I'd prefer to buy the 3550 or TKO. If I wanted to step up later to AI, it'd be nice not to have to swap transmissions again. So the real question is would a 3550 or TKO be considered a "Borg Warner World Class T-5 transmission" for the purposes of the rules??



On the larger throttle body and EGR spacer-- that's what is on there at the moment. I don't know if they'd be allowed since they really won't have too much of an effect on a stock engine. I know it's implied in the rules that it would not be legal since it's not explicitly allowed, but if such a radical change as a carbureted motor with Edelbrock intake is allowed, it would seem that a simple change like a TB/EGR spacer that's slightly larger than spec might be permitted assuming it doesn't result in the car exceeding the horsepower limit or do anything that would substantially change the torque/horsepower curves. Again, I'm new and don't really know if there's a bit of wiggle room on things assuming it doesn't make the performance of the car change appreciably. I guess that's the real question, is there some lattitude given on things as long as they don't appreciably change the performance of the car.



Thanks in advance.

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Give me a call in the evening sometime so I can help you out on these questions you have.

I think I have some answers on what will work and will not.



916 933-5750

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