16 replies to this topic

[trey]

Just curious where the time reductions come from ?

More specifically , If someone were to do a slow build FP , what changes yield the best bang for the buck ?

- Tires
- Weight
- Aero
- Engine
- Suspension
- Gearbox
- Others ???

[Think Racing]

Great question. I have the same question myself. I'm glad to see someone else posting here about F cars. I just bought a '91 FP car and it's not a bad little racer all by itself, but I want to take it to the next level.

Where should we focus? Suspension, or engine? Where can you get some of the trick suspension parts I've seen like custom a-arms with heim joints, etc.?

[red986s]

Being an ITA racer I sneak around the the Prod forum for bits of wisdom. You could try asking your question there.

http://prodracing.com/prodcar/

When I started converting my SM over to ITA I did small changes (header, then MegaSquirt ECU, Dyno tuned, then diff changes) Slowly working with my mechanic to get it faster. Plan on doing a full on ITA engine build this winter. The end goal being to have a well sorted FProd.

A good source for all things Miata would be Jesse Prather Motorsports.

[Ken Nesbit]

The answer is all the above, I built mine from scratch, not an SM convert so take my advice for what it's worth, but here's how I would look at it in order:

1 - Tires - almost a gotta have, not cheap but if you're going prod racing a reality.

2 - weight - there's easy horsepower.

3 - Engine - Since there's not a lot you can do, compared to full prep, not horribly expensive (I used to run a full prep MG, so maybe I'm not the best benchmark), but for the most part you're talking pistons, cams and lightening/balancing the rods and crank and a clutch/flywheel.

4 - Computer and dyno time to tune it - again not sure what you can run in SM, but for my car paying for dyno time and someone that knew what they were doing on it was the biggest bang for the buck.

5 - Suspension - The SM setup is probably good enough to start with but delron bushings, again not cheap, work really well...don't worry about the heim joints until you have to start worring about tenths of a second.

6 - gearbox - again nothing really wrong with the stock box, just have to figure out how to deal with a couple of odd spot shifts, but a close ratio gearbox DOES make life a lot easier. Using a 6 speed and blocking out 1st gear (add 50 pounds back to step 2), gives you closer ratios than the stock 5 speed and is a nice option.

The others kind of where you can fit them in.

Like I said, the biggest bang for the buck is the computer and dyno time.

[wheel]

Go to the Prod web sites. Look for posts by Jesse Prather and Sam Henry. This is really like asking the difference between flying a Piper and a Tomcat.
wheel

[Bench Racer]

Just curious where the time reductions come from ?

More specifically , If someone were to do a slow build FP , what changes yield the best bang for the buck ?

- Tires
- Weight
- Aero
- Engine
- Suspension
- Gearbox
- Others ???

- Tires--------------C.= 15 x 7, 9 pound rims or lighter (tire selection will tell you maximum negative camber required)
- Weight-------------B.= 2075 pounds (stock case/gear ratios transmission)
- Aero---------------A.= -roof/-windshield/ keep the body width as narrow as tires allow/reinvent the front air dam/splitter

- Engine

- Suspension---------C.= Start with eccentric delron bushings in OEM control arms/double adjustable shocks with adjustable spring perches/as simple as Spec Miata springs & front sway bar is a good start/Google for control arms/ask Jesse Prather/Rick Harris for control arms
- Gearbox------------B.= stock case/gear ratios transmission
- Others ???---------D.= you may race with the OEM fuel tank, but cell/battery in passenger area to center/lower CG before roll cage petty bar.

- Others-------------D. Differential = Torsen taller than the OEM.
- Others-------------D. Alum flywheel is a MUST/small clutch/pressure plate

Rick Harris/Jess Prather had a couple F threads on the original site.

[trey]

- Tires--------------C.= 15 x 7, 9 pound rims or lighter (tire selection will tell you maximum negative camber required)
- Weight-------------B.= 2075 pounds (stock case/gear ratios transmission)
- Aero---------------A.= -roof/-windshield/ keep the body width as narrow as tires allow/reinvent the front air dam/splitter

- Engine

- Suspension---------C.= Start with eccentric delron bushings in OEM control arms/double adjustable shocks with adjustable spring perches/as simple as Spec Miata springs & front sway bar is a good start/Google for control arms/ask Jesse Prather/Rick Harris for control arms
- Gearbox------------B.= stock case/gear ratios transmission
- Others ???---------D.= you may race with the OEM fuel tank, but cell/battery in passenger area to center/lower CG before roll cage petty bar.

- Others-------------D. Differential = Torsen taller than the OEM.
- Others-------------D. Alum flywheel is a MUST/small clutch/pressure plate

Rick Harris/Jess Prather had a couple F threads on the original site.

Sounds like you could build a decent car by doing :
- Aero
- 2075 #
- Tires / Wheels
- Engine : Intake , Header , Pistons , Cams , Head , ECU , Tune
- 4.77 / 4.88 ??? R&P Torsen
- Solid bushings / AFCO Coilovers / SM bars
- Fire System

I'm wondering how much faster this would be than a top level SM and how much slower than a top level FP ?

[red986s]

This is really like asking the difference between flying a Piper and a Tomcat.
wheel

Nice analogy Jim!

[Think Racing]

Ken, I need to get the name of your dyno.

[Brian Linn]

More specifically , If someone were to do a slow build FP , what changes yield the best bang for the buck ?

- Tires
- Weight
- Aero
- Engine
- Suspension
- Gearbox
- Others ???

My 2¢...Engine is going to give you your biggest gain, but may cost you biggest buck. As others have mentioned, Jesse Prather is the man to speak to. He can give advice on where to start even with a budget engine. The ECU (Electromotive or MegaSquirt) is part of the gains - then dyno time, but once again Jesse will get you closer to your goal.

-If you have a SM, then I would start with the Hoosier slick radials. The camber settings are not that different from the Toyo. The bias-ply slicks require way less neg camber than the radials or Toyo's. SM wheels are fine to use for an FP Miata, but as David points out, there are lighter options which are $$.

-Gearbox options go hand-in-hand with weight options. If you use the stock box, you can weigh 2075. If you install a box with non-stock synchro gear ratios you add 5% weight and if you go to a dog-ring box then you add an additional 5% weight. So the gear box options come with a penalty and the 'bang for buck' is low IMO. The options are costly. I do use a dog-ring box (Ron Olsen) because I was used to them from my previous car and can dial in ratios to stay in the power band.

-Aero - at a lot of tracks I don't think aero is that critical. A front spoiler that limits the air going under the car is relatively in-expensive, but useful. Most of the fiberglass body work is wider than is needed for a FP car. The fiberglass panels do have some weight savings, although the stock hood and fenders are pretty light. Some are using stock panels for a narrow stance with Road America in mind. Taking the windshield and top off reduce your frontal area, but add drag. If you want to run a full cage (as opposed to a smaller hoop), I would consider keeping the windshield/top.

-Suspension- Nothing beyond stock/SM required to go fast. I think Prather won his two FP and one EP championships with stock control arms. They are durable and easy to find replacements. The aftermarket control arms are lighter and should be easier to adjust, but you won't see much change in lap time. The Delrin bushings would be a good start. Many use the SM sway bars and shocks, but you will eventually want to make changes to your spring rates. Jesse also sells the Afco shock package where he specs valving that is not available off the shelf. The Afco's have adjustable compression and rebound- using knobs that are on the body. Koni's and Penske's would be more $$, but worth it to some people.

[trey]

Thanks for a great reply , I guess the thing I'm not clear about is how far behind will a simple build be from the solid runoffs cars ?

Let's say I took a 1.6 SM and :

- Removed windshield & roof
- Modified cage to low drag
- Clean up interior aero drag
- Front aero clean up
- Run stock bodywork
- Hoosier Radial Slicks
- Run SM suspension
- 4.3 Mazdacomp Rear End
- Stock Gearbox and internals
- Engine : Head , Cams , Intake , Header , ECU , Tune
- Anything big I'm missing ?

[Brian Linn]

I guess the thing I'm not clear about is how far behind will a simple build be from the solid runoffs cars ?

I can't really answer that question, but it should be a blast to drive.

The front running FP Miata's (and really it can be said for any class) of Rick Harris, Ken Kannard and Eric Prill all have really good equipment, but also those guys know how to drive them at the car's limit. Front runner's usually are very detail oriented and take a great deal of time and thought into their preparation (again, like any class). Most don't skimp on equipment, but it's not always the most expensive car that is out in front.

[EPrill]

-Gearbox options go hand-in-hand with weight options. If you use the stock box, you can weigh 2075. If you install a box with non-stock synchro gear ratios you add 5% weight and if you go to a dog-ring box then you add an additional 5% weight. So the gear box options come with a penalty and the 'bang for buck' is low IMO. The options are costly. I do use a dog-ring box (Ron Olsen) because I was used to them from my previous car and can dial in ratios to stay in the power band.

Good info posted here. Just one slight correction to Brian's gearbox info is that it's 2.5% for alternate ratios and another 2.5% (total of 5%) for a dogbox.

Brian and I have very similar equipment. Same engine builder, same trans, both on Hoosier radials. Don't need a body kit any more (fenders at least) if you run the radials. For aero I have done some work on the front end of mine, but it's certainly not required and probably not a big help at shorter tracks anyway.

Suspension stuff is all bolt on. Jesse has a great kit but you could run your SM stuff. I put Penskes on my new car and thus far have liked them. I believe that David Bryson has a car with SM suspension (hardtop car) and it goes plenty fast.

I'm not 100 percent convinced a hardtop car is any worse than a convertible. I went with a convertible because I like open cars. There have been a couple of hardtop cars out there so you certainly don't have to cut the cage and windshield out of your SM if you don't want to. Nobody's run up front at the Runoffs with one but that doesn't mean you can't.

I guess my order of converting things would be as follows:

Ignition
Engine
Tires
Weight
Suspension
Gearbox
Aero

Now I built a skinny, low car that is probably the slipperiest FP Miata to date, but that was with RA in mind. It certainly doesn't help me at Hallett, etc. That's why I put aero last, although it was important in my overall project.

Also, I run a stock gas tank. Yes, it's a little higher than the passenger floor, but it doesn't change cross-weights as you run through the tank. The fastest lap ever run at Road America in FP had a cell in the trunk (behind the rear axle), so again, some things may not be ideal but won't relegate you to the last row on the grid!

Eric

PS- Brian, don't sell yourself short on that list of front-runners.

[EPrill]

Thanks for a great reply , I guess the thing I'm not clear about is how far behind will a simple build be from the solid runoffs cars ?

Let's say I took a 1.6 SM and :

- Removed windshield & roof
- Modified cage to low drag
- Clean up interior aero drag
- Front aero clean up
- Run stock bodywork
- Hoosier Radial Slicks
- Run SM suspension
- 4.3 Mazdacomp Rear End
- Stock Gearbox and internals
- Engine : Head , Cams , Intake , Header , ECU , Tune
- Anything big I'm missing ?

Trey- Do you already have the 4.3 in the car? I'd look at the 4.77 or 4.88 if you're putting a new diff together. Also, definitely change to the 1.8 diff. Need the diff housing and a different driveshaft. Holds more oil and lasts longer with the added grip and power.

[trey]

Trey- Do you already have the 4.3 in the car? I'd look at the 4.77 or 4.88 if you're putting a new diff together. Also, definitely change to the 1.8 diff. Need the diff housing and a different driveshaft. Holds more oil and lasts longer with the added grip and power.

Eric , Thanks for the encouraging comments

Yes , I'm in the diff poorhouse , my 1.8 ITA car has a stinkin 4.1 .... my 1.6 car has a mazdacomp 4.3 ... I can live with the 4.1 @ TWS , but it's terrible @ MSRH ... I'm in total agreement , any FP build would need a 4.88 or 4.77.

I'm surprised by your comments in regard to the potential of a windshield car , and I love the fact that you can build a narrow FP ( without fenders ) ... I love open cars too , but it's good to know that I could get semi competitive without cutting up the cage and windshield .

I'm guessing the skinny car helped that monster lap record you have at TWS too ... That's a great lap !

[EPrill]

Eric , Thanks for the encouraging comments

Yes , I'm in the diff poorhouse , my 1.8 ITA car has a stinkin 4.1 .... my 1.6 car has a mazdacomp 4.3 ... I can live with the 4.1 @ TWS , but it's terrible @ MSRH ... I'm in total agreement , any FP build would need a 4.88 or 4.77.

I'm surprised by your comments in regard to the potential of a windshield car , and I love the fact that you can build a narrow FP ( without fenders ) ... I love open cars too , but it's good to know that I could get semi competitive without cutting up the cage and windshield .

I'm guessing the skinny car helped that monster lap record you have at TWS too ... That's a great lap !

Thanks Trey, that TWS effort was actually a wide-body car on bias ply tires. It was Mark Weber's car that I drove in 2010. He's running it this year.

[red986s]

I'd look at the 4.77 or 4.88 if you're putting a new diff together. Also, definitely change to the 1.8 diff. Need the diff housing and a different driveshaft. Holds more oil and lasts longer with the added grip and power.

+1, Your corner exiting will vastly improve.