MADJAK's NA8 - 200+HP N/A

[mrpham]

4.778 is the best!

[madjak]

I ran my car up at Barbagallo on the weekend and the 4.78 and 6 speed combination is awesome. It's moved all my gears up one but also made the shifting much easier. 5th to 6th are actually quite close ratios so the revs only drop down a bit which keeps the engine in the power band.

The track was very wet all morning with 3 cars going into the wall. It only just started to dry out on my last run and I managed to drop over 1 second off my previous best time with the track still cold and slippery. No-one else was close to their PB so that's a good indication that there is lots more time to drop yet. The diff has helped a bit, as well as the short shifter, but mostly the extra 40 HP or so in the upper rev range due to the Honda intake and e85.

I'll post up a video of my second run (in the wet) tomorrow. I left the go-pro running which filled up the card so I didn't capture my final faster runs.

[greenMachine]

There will be a fair bit of drilling required which I'm not really looking forward to especially into the 4140. I think around 1.8 meters of drilling in total. If they work out I can organise a group buy through a machine shop to make them because I doubt I'd have the patience if it wasn't for my own car.

I'd be in that!

[madjak]

Its probably better to wait to see how mine works out. The big question for me is if these composite bearings are strong enough to hold together in the suspension or if they break up over time. I have a sample and they are basically feel and look like delrin but you can get them in a range of grades and friction levels. They seem pretty strong but they are so light my brain is telling me they might not work.

The bronze sintered bearings will be a much safer option. However for a full set it's going to cost $250+ as opposed to $80 for the composites, plus the bronze would need a different sized 4140 rod due to the increase in thickness of the bearing. I'll try it first with composites. If they work out good but don't last I'll switch to the bronze.

If your keen to be a 'beta' tester then I can find out how much to get a few sets of the sleeves machined up. I'm happy to test this sort of thing out cause if it doesn't work I'm only down my time and some money, but for me to supply them to others is a bit risky at this stage. Really this is still an experiment and I probably won't know for 6-12 months if this will work.

I have picked up 3m of the 4140 already and was going to try machining it tonight and see how it goes. I'll post some pics.

[Dweezle]

Will be very interested to see how that idea pans out.

I am most likely going to Poly in the next week or so but if your idea pans out i would happily then switch out to something not requiring the constant maintenence and less friction.

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[greenMachine]

Happy to be a beta tester, I'm looking at the racecar here, not the GM. Not even the GM mk2 ...

[madjak]

This was one of my runs on a very wet and slippery track. I was nearly 10 seconds quicker later in the day when the track had dried a bit but my goPro card was full so I missed videoing the run. My gears are a bit sloppy on this lap but at least you can hear the engine rev and see how fast the gear changes are with the 6-speed and 4.78 diff. I was 10th fastest outright with this lap but dropped down the field later in the day as the track dried and the more powerful cars could get traction. 3 cars ended up in the wall at around the 32 second mark in the video, it was that slippery.

[madjak]

One of 26 done.

4140 is fairly easy to machine, it will just take a while. I'll have to buy a few cans of wd40. Everything assembled will fit pretty snug and with the bearing running on the metal sleave giving a nice free rotation. I'll order 50 of the bearings now and start machining the sleaves. It will take a few weeks for the bearings to rock up from Germany.

[Dweezle]

Looks amazing.
So do you need to grind out some of the bushing??

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[madjak]

No need to grind out the bushing... The Urethane stays the same, I'm just switching the supplied sleave with one that has a bearing over the top. The net size of the new sleave plus bearing is the same as the stock sleave, so it just slides into the bushing. Its made out of 4140 because its a fair bit thinner and they are under a fair amount of load from the torque I have to apply to the suspension bolts to hold them in position.

A couple of the bushings have thin sleaves already. I don't think there is enough meat there to machine room for the bushing. For these I might try opening up the center hole of the bushing, though I'm not sure if you can drill urethane.

With this setup there will basically be around the same friction as sphericals but still have some give.

[madjak]

It's been a few weeks. Here is my class winning run from today. This is the same course that will be run for the National Hillclimb Champs in Nov.



The course is very tight and I was struggling to get the power down with the Torsen slipping. Might have to look into a better center. I ended up only beating the Honda by 0.24 seconds so it's going to be interesting later in the year to see who wins.

[The American]

The course is very tight and I was struggling to get the power down with the Torsen slipping. Might have to look into a better center.

Are you lifting a wheel?

I had a much stiffer suspension set up in my NA (with Torsen) than I do now. It often 'slipped in tighter corners, and I could not get power down, as it appeared to be lifting a rear wheel (if you watch Simon Gratton's machine it regularly lifts a rear wheel in corners, or at least it did). My current set up has much less roll stiffness, and allows much more droop, and even though there is more power, it's getting to the road much better.

[madjak]

My suspension is pretty soft but this course has lots of elevation changes with sharp corners. It's likely I'm unloading the inside wheel enough so that the Torsen slips. Also I'm placing the inside wheel off the track in a few spots. In the wet it was hopeless... I'll upload my second run so you can see what I mean.

[Ice88]

Hey Madjak,

Did you ever fix the 2/3rd throttle issue you had with the Skunk2 throttle body?

Cheers

[madjak]

I haven't changed it. I'm still using the throttle as is. I can't say I have really noticed much difference, either I'm used to it or I'm on or off the throttle like a switch in most events anyway.

Having said that, I really struggled driving the car in a recent club autocross event. The road surface was very, very wet and slippery and the rear would step out at the touch of the throttle. Having less throttle movement was probably contributing a little to the lack of fine control... but at least I got used to catching the rear every time it tried to kill me.

Having said all that, I'm going to run the rest of the year as is. When I get the time, I might lathe up a larger diameter throttle wheel to fix the issue properly. My main concern is putting too much load on the throttle cable as the pedal stop is at it's max and the bracket can flex a lot when pressing hard on the pedal. The other option is to purchase the Skunk2 64mm throttle body made for the miata, and then make up an adapter plate to fit to a Honda intake... but that would be costly.