JMortensen

Definitely don't do it without a prop valve. The question is whether an adjustable valve be able to turn the rears down enough to prevent the rears from overpowering the fronts (which is dangerous). You'll probably be the first to find that out if you try it.

As with all of my projects, I wouldn't hold your breath. Right now I'm welding mufflers, then I'm going to test fit the engine and figure out the rest of the exhaust, and then maybe do the trans x-member. When all of that gets done, I'll be back into the rad stuff I think.

Don't know on the offset, but there are a bunch of threads on that subject. You might try the Z transmission calculator for tire diameter and gear selection. http://webspace.webring.com/people/cz/z_design_studio/

If you can fit 15x9s, the 225 extreme summer performance and DOT tires work well on a 9. They're really wide for 225. You said roll center should somehow relate to the tire. I think you meant scrub radius. There are lots of race cars running a positive scrub radius. The most immediate effect in a Z is that a big scrub radius will make it harder to steer. AWD is the traction king. Google "traction circles" and you should find some stuff about how much traction each tire has at any given point. Suffice it to say that in a high hp 2wd car the undriven wheels are usually not pushing to their max, and that's why AWD has an advantage. That thing really does look cobbled together though... LOL

Cutting a spring makes it stiffer. Maybe one side sagged more than the other. I'd cut them even with a cutoff wheel (not a torch) and put them in and not worry about it. If you're not racing, it doesn't really matter if your spring rate is 20 lbs different on one wheel or if one corner sits 1/2" higher than the other.

Got all my stuff in and started on this one and my welder liner is finally past it, so got the end of one muffler welded on (crappily) and then had to stop. Hopefully a more consistent feed and speed on the wire will help out. Definitely getting more spatter than I get with normal wire too. Here's a bit of the trial and error I've gone through so far: I wanted to make the muffler serviceable, so I had to figure out a way to get the perforated core in and out. My first attempt involved a harbor freight tailpipe expander in the perf core. I figured it would be easier to stretch and I could slide it over the 2.5" pipe on the other end. That didn't work out so well. As I stretched, the perforations did just what you would expect paper to do, and one line of perforations just split very neatly in half. I didn't buy a whole lot of extra core, but I have enough that I'll be able to cut out the damaged end and weld a new piece in there. Next attempt was to stretch a piece of 2.5 tube, figuring I'd plug the core into that. That failed as the tailpipe expander couldn't handle the force necessary to stretch the tube. Finally I cut about a 1.25" section of the tube and stretched that. I was (barely) able to stretch that, although the expander tool isn't working so hot anymore after doing two of them. When using one of these tools, one thing that seems inevitable is that one end will stretch more than the other, leaving you with a cone shape. I used this to my advantage, sizing the pipe up until I could smack the core into the cone and get it to barely bottom. My hope is that this will keep the core from rattling when it's all together. The cone is sized such that the one end of it is large enough for the perf core to slip into and the other end is a little too small for the 2.5 pipe to slide in, so what I did there was to hog the end of the cone out a bit with a burr, then slid it over the 2.5 pipe and welded it. Then I welded the end plate to that, and welded that whole assembly to the end of the 4" muffler tube. So basically there is a female socket for the perf core in the end of the tube. On the other I'll have a 2.5" tube that sticks through the muffler end plate and the core welded to that. So the ~18" core will come out with that end. To make it serviceable I need to be able to remove this, so I took a 1/2" wide piece of the 4" muffler body tube and cut out a bit so that it slides into the muffler tube, and welded it back together. This piece with its reduced circumference will be welded to the muffler end cap, and then be screwed into the muffler body and sealed with some exhaust pipe sealant. If I didn't want these serviceable, I'd probably be done already. Still haven't decided where to put the angle iron. I'm thinking right in the middle. I think Burns puts them more towards the inlet, but my thought is that they deflect the gas into the packing and I'd do better with that right in the middle. Putting them more towards the exit side would probably work too, but I am thinking that might increase backpressure if the flow ended up getting hurt by the end cap on the exit side. Nice thing about making these serviceable is that if it isn't quiet enough I can pull it apart and play with it some more.

Yes. Another way to say it is that I think that you have to worry about more than just venturi size when it comes to determining where the peak power will be. Runner length and diameter, carb size, air horn length, timing, cam, how the porting was done, etc. Seems way too simplistic to say 36mm = 6800 rpm and 37mm = 7000 or whatever.

I did have a friend who polished the venturis with jeweler's rouge. You might try that before you spend $120. Your cam has a lot of lift and not so much duration. Maybe look at that? I'm just thinking that 1mm in choke size might not even register on a dyno.

Just got these in, they look pretty damn cool so I thought I'd share. It's a collector with a "bullet" or "spike" to smooth the transition from the end of the 4 primaries to the collector. I hadn't ever heard of these but read a page on side pipe testing and they tried them and found a pretty consistent 11 hp on a motor that was making something like 500 hp if I recall. Cone Engineering (www.coneeng.com) makes 3 to 1 collectors too. This is a "merge collector" like Burns Stainless sells as well. I wanted 2.5" collectors, so this narrows to 2" and then tapers back out to 2.5. They have 3 different tapers, and say that the sharpest one has a larger effect on high end power and the slowest taper makes better low end. I picked the middle one. The collector kit with 2 collectors, These parts are mild steel but they have the same thing in stainless, and they have muffler parts too. Really cool stuff, and the mild steel collectors were $115. Seems pretty cheap for a serious looking piece. I don't mind the DIY aspect when compared to the price of the Burns equivalent.

On a 70 there is a rib on the right side but not the left. I believe a 73 has ribs on both sides. My firewall was splitting from the cowl on both sides. There is a seam where the firewall and cowl meet and it's a rust prone area because water gets in the cowl vents and then sits in there. I am pretty sure that putting the STB loads on there is what started separating the panels.

I think it needs more reinforcing than the channel across the firewall to really be stiff enough to support the loads. When you attach to the middle of a span, you're attaching to the weakest part. I did my STB to the dash bar like that and then came to this realization. Oops. If you want to see how weak this part of the car is from the factory, jack your car up on the front crossmember, then put jackstands under the TC boxes and let the jack down. Mine would droop ~1/2" or so with some pretty obvious creaking. That's with the STBs in place.

Don't buy a car that has extra weight to turn it into a racer. Start with the lightest car you can.

Looks like it does better than that, and I'm going to emulate the 2 stage (will put a couple pieces of angle in the flow path): http://grassrootsmotorsports.com/articles/sounding-off/

Sweet drawing. I don't believe that those spots are all that strong. I had my bars going there and it was tearing the firewall up where it meets the cowl. bjhines did a lot of reinforcing in this area for his, you might want to find his pics.

I ran an aluminum tap tube STB for years, worked fine. Tap tube is aluminum tube that is sized right to be tapped, probably slightly smaller than the pre-made turnbuckles.

I was considering welding with carbon wire, and the reason I'm doing this at all is because I wanted a lightweight, quiet muffler and the Burns Stainless unit is $458. I found www.coneng.com and with some of their parts and some generic SS tube, I'm going to make my own 18" mufflers (2 of them) for about $200. It's a race car so it won't see a lot of miles and I'm sure that longevity of the welds wouldn't be an issue. It was cheap enough to do it right that I just spent the extra and bought the flux and the wire.

Why not just screw some pedal pads on to the existing pedals?

Most pedals require you to roll your feet over. There are lots of aftermarket pedal pads you could add to make it easier, but beware. I was once at a track day and overheated the brake fluid and as the pedal got softer my foot was hitting the gas pedal without me being aware, so I ended up boiling the fluid that much faster as I inadvertantly stepped on the brake and the gas at the same time. This was with stock pedals, so adding more to the bottom left of the gas pedal would potentially make that problem worse. I wouldn't try to change the bend in the pedals themselves, that definitely sounds like the hard way.

You can tighten them up. Just loosen up the lock ring and then turn the larger outer part in until it's tight, then tighten down the lock ring.

I've been running the R1R for almost 2 years on my Miata. Treadwear is 140, but I've put 10K miles and probably 15 autoxes, 2 schools and a practice day where my odometer showed 30+ miles of autox on them and they still have some life left and I can safely drive them in Seattle weather. They would be doing a lot better if I had known to keep them cool between runs when I got them. The "extreme summer performance" tires are viable street tires, and they're not that expensive. Real "R" compounds, not so much, but the extreme summer tires work on the street IME.

https://www.google.com/search?q=15x9+6UL&tbm=isch&tbo=u&source=univ&sa=X&ei=iWIqUsSjN-fkiALV_ICwCw&ved=0CEUQsAQ&biw=1680&bih=925#q=15x9+6UL&tbm=isch&imgdii=_

What??? There are a TON of tires to fit a 15x9. It is a very popular size for Miatas. Toyos, Yokohamas, Kuhmos, Hankooks, etc. all come in 225/45/15. The sportier 225's are WIDE and fit nicely on a 15x9.

You could probably part it out for more than $700. I'd do it.

Ha! You'd probably win too.

Don't reduce caster if you want the car to handle. In fact, you'll probably want to increase it for better handling and yes, more positive caster does make the steering heavier.