Should an aftermarket subframe really get forced into tt3+

[Scott Johnston]

I'd like to propose a rule change that would allow aftermarket subframes which retain factory suspension mounting points to not have to utilize the non production car modifier. Either an approved "production" status, or adding st4/5 to the chassis modifier, or an exception to 6.2.1 for subframes which retain oem pickup points for suspension.

Example: K24A2 in a miata requires an aftermarket subframe so the exhaust can be routed out of the engine bay. All suspension pickup points remain the same. On pure power to weight it's a tt4 car all day, and a tt5 car with some detuning or tire choice, however the modifier assessed for the subframe means it can only compete in tt1 to tt3. This has kept me from being a regular attendee at TT events.

 

There is a similar motor (k24z3) that utilizes the stock subframe because the exhaust packaging is easier - it has a single exit exhaust port on the head.  Why shouldn't k24z3 and k24a2 swapped miatas compete in the same class? The only difference is exhaust routing (and I'm eyeing the modifier for side exit exhaust as a similar rule to what I'm proposing). 

What is the thought behind the oem subframe rule, if chassis mounting and suspension pickup points don't change?

[Scott Johnston]

I'd like to bump this topic and ask for a specific request/allowance to the aftermarket subframe rule. K swapped miatas should have parity. I have an NB Miata with a k24a2 kit, the original KPower offering which uses an aftermarket front subframe specifically for exhaust clearance. Because of the non-production modifier, I have to compete in TT3 or higher, which I've done and continue to do however my power to weight is not appropriate for that class. KPower has a newer kit for a k24z3 which retains the stock subframe due to the single exhaust port on that motor, and it allows those cars to participate in TT4 or TT5 since they use a stock subframe. I'd like to make a petition for parity among the kswapped Miata chassis. Cars built using either kit have the exact same suspension pickup points, and the engines make similar power. I would like to compete in the same class against similar builds, and as such am requesting a rule change or allowance. 

[Greg G.]

Sorry Scott, I didn't see this before.  We don't allow it because there is essentially no way to tech inspect this without taking the car apart, taking the subframe out, sitting it next to a stock subframe and performing a meticulous comparison inspection using calipers, etc.  We have been told in the past that there are "no differences" only to find that was not quite true.

[Quigs]

@Greg G.would it be possible for Kpower (the supplier of the K24 swap kits for Miatas) and NASA to get together for a subframe comparison like you mentioned above to where if confirmed the suspension pick up points are indeed the same as OEM the Kpower swap kits could be listed as ST/TT4 legal?

Since it is such a common swap and Kpower is really the only provider of a complete swap package I think this would generate a much better balance of performance for swapped Miatas trying to stay within the proper P:W categories.

[Greg G.]

Scott, I'll run it by the NASA Exec's, but the potential problem that I see is that it is fairly easy to identify that an OEM subframe has been modified, but even if a specific aftermarket subframe is compared ahead of time, there is no way once it is on the vehicle to determine (at least easily) that it was not modified prior to being installed.  I haven't looked at the specific application you are describing, but most that I've seen could be modified, repainted or powder coated, and look very much like the aftermarket part. 

[Greg G.]

NASA Execs also felt that there was no way to facilitate tech inspection, as well as it is a slippery slope to waiver something that is otherwise not permitted.  

[Heavy85]

Adding on to this topic.  Understand aftermarket subframes would be nearly impossible to manage.  But since engine swaps are allowed why can stock front subframes not be modified to allow the swap?  Again as previous example with no changes to suspension points which are easy to check.   Example in my LS swapped RX8 the stock front subframe is modified as follows: 1) notched a corner for exhaust clearance 2) welded on engine mount provisions 3) changed the steering rack so it wasn’t in the crankshaft pulley.  Suspension wasn’t touched unless you consider steering rack part of the suspension but there was only negative performance impact due to steering geometry change in this case.

Thanks for the consideration. 
 

Cameron Lane - Az region (who also takes the 0.4 hit for no performance gain)