Yep! I sealed the cowl plenum on the inside when I built the car. When we did the hood vents I put a piece of aluminum under the factory louver panel to seal it there for better aero performance. Basically trying to force the air to get off the hood and over the windshield by not giving it anywhere to go.

I don't have allot of time with these vents so the jury is out. If I can figure out a way to get a camera on the vents I will tape some yarn around the opening and see where it flows. The hunch is that there is more pressure under the hood and from the wheel wells in that area.

 

Oh man, did you see the prelims from yesterday? Throttle bodies allowed for STU rotaries now, so long as there's equivalently sized chokes.

I'd joke about throwing a Miata together but I'm already down the GT-3 construction rabbit hole.

 

Where are you seeing this. All I see is the May Fastrack

 

https://www.scca.com/downloads/49990...bs-05/download

 

So that would mean EFI with a dual throttle body? I would assume that choke size would be 42mm........
Noticed that they dropped the weight by 50lbs on street port and bridge port

 

Yeah; it looks like it's essentially my "would it really be that bad to allow EFI with equivalent chokes?" thought from a while back. Something like an IDA throttle body with 42mm chokes thrown in instead of just an IDA with 42mm chokes.

Maybe that idea will follow to other classes; would be nice to have an EFI bridgeport option in GT-3 that's not an SIR. The turbo rules from STU kindasorta already migrated to GT-3, albeit terribly.

 

Thanks for a great read! Have you been able to get any more track time since you've finished off the jerico, fixed the tri link mount the second time and cut the hood vents? Turns out I am building a very similar looking tri-link panhard setup. Stole the idea from 82transam,

Curious to know, does your dog box have straight gears or helical?

 

Not much track time. I had another drive shaft failure - 2" steel shaft made for IMCA style modifieds - last year. New shaft is 3" diameter shaft with 1350 u-joints - no more conversion u-joints. Still have some more repair work to do and not planning on doing any racing this year.

Jerico/NASCAR style boxes from that era are have straight cut gears. Sounds kick *** at speed and is so smooth under power. Nothing like a stock box.

 

Can i ask an exhaust question? Have you had issues with continuing header failure? Blowing out/cracking just at the first bend after the exhaust port? We run the standard RB steel header on our street ported 13b endurance car and have gone through two in the last couple years. Looking for long term solutions. Thanks in advance

 

https://www.midweststeelsupply.com/s...steelroundtube

If you have a tube bender and can weld stainless, why not get some thick wall tube (DOM or welded) and replace those two long primaries all the way to the first flange? They usually melt at the first bend near the exhaust flange.

Using an existing one as a guide, you might not get the lengths exactly the same, but you get the option of using much better/more durable materials. I've used Midwest steel in the past and their prices, even with shipping, is very reasonable.

 

The difference between stainless and mild steel headers:

• The original .125" DOM mild steel from Racing Beat lasted 4 years behind a stock port 12A - about 30+ SCCA Regional races with a long primary exhaust
• I replaced it with an ISC stainless header that I bought used from another racer. it has about 90 SCCA Regional/National races on it including a short enduro. As a part of the STU build I had it modified to fit a 13B. This header is still on my car.

More mild steel header hate....I witnessed a wrapped Racing Beat header die in ONE racing season. Don't ever wrap a mild steel header.

For the rest of the exhaust I mostly used mild steel for a long time but it required numerous repairs due to cracks. Starting last year I switched to a short primary merged exhaust with a used NASCAR merge collector I bought off of eBay. This connected via V-Band clamps to 304 Stainless 3" tubing also bought off of eBay. I purchased a 4ft straight section and a combination J and U Bend piece to get it over the axle. I welded it all together using 409 Stainless unions with my Lincoln 180 MIG welder. I had no issues doing this. In fact is is easier to weld than mild steel by a long shot.

Stainless for the win. Also use Stainless fasteners on the every connection.

 

So I ended up having a friend build a header from scratch using the RB header as a guide. We used schedule 40 Stainless for the entire thing.

It weighs 2.5lbs more than the mild steel header.

 

Well yeah, schedule 40 is like, 0.15" wall thickness, thereabouts? You only are going to lose weight by going thinner wall.

 

This wasn't built for weight savings. It was built not to blow out. I was just surprised that it wasn't much heavier than the thin wall mild steel header.

 

Oh yeah, I think the RB stuff is like, 11 gauge or something. I'm just saying that if you're using decent material, you can make 16 or 18 gauge stainless live fine.

 

We're not taking any chances...lol...

 

A "forever" header!!!

 

At least the weight is low and on the passenger side. If the rest of the system is the same, may help CG and corner weight.

 

After talking to people at the runoffs and designing stuff for GT3, got curious and looked at the GCR for STU.

Throttle bodies with an equivalent size venturi restriction are allowed at a *50 pound weight break* compared to carburetor now? That seems ***-backwards.

 

Is this what you are referring to in red? The throttle bodes would be FI instead of carbs? Assuming that is what this says, I see the weight break on the Street Port where the choke sizes are the same for a carb at 42MM. For the Bridge Port, you would be loose 2MM compared to the Carb.

Not the easiest to understand and makes my head hurt. I have seen some dyno tests on V8s between throttle body injection vs carb. The throttle body inject made more power because air flow wasn't interrupted by boosters. Yeah the weight break seems backwards. Of course a weight break is only a benefit if you car is light enough to take advantage of it.

 

Yeah it is, though I forgot that STU gets 44mm chokes instead. I just got curious because the interpretation of the wording in GT3 made me go check and see how Prod and STU word it.

 

@mustanghammer Do you mind me asking what you are running for master cylinder and MC sizes? I read though the thread (super inspiring by the way) and didn't see what you decided for the cylinder sizing for the larger (and no power) brakes.

Thanks,

 

Thanks! I honestly cannot remember what I used so I will have to look later this week. This is something I should know!

 

Wow! 300 lbs extra for the bridge port?!!

 

Front M/C is 5/8" and the rear M/C is .700" The clutch is also 5/8" I am using Tilton series 74 M/Cs

Front and Clutch M/C: https://pitstopusa.com/i-5055570-til...ategory:134804
Rear M/C: https://pitstopusa.com/i-5055572-til...ategory:134804

Pedals are from Wilwood and have a 6.25:1 ratio. Pad material also matters and I found that pads with a little more initial bite make the car easier to drive. I have the brake bias adjuster set to put more pressure on the front brakes.