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7000 rpm is 131 mph for a stock ratio 915 and full size tires , also you ran to 130 in about 19 seconds
What fun
Nice test road
Ian

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Old 08-25-2020, 04:19 PM
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Originally Posted by Jonny H View Post
^ Default for CDI+ :

Soft limiter set to 7000. This takes out 10 degrees of advance so youíll feel a dip in power. If you push through this, then....

The cyclic ignition cut hard limit is set to 7250. This cuts 4 sparks out of 5 for a rolling burn to prevent fuel wash and backfiring.
Hi Jonny!

I did indeed leave the RPM limit defaults alone (for now). I have on my list of things to do, to get in and add a bit more polish to my spark curve so I'll bump the rev limits a bit. Also need to double check my tacho calibration.

The motor does want to make power past 7000RPM so I'll give it a few hundred RPM more to run out

Thanks as always for the support! Hope you've been able to get out in that beautiful green SC, last we talked you were in lockdown.

I have to say, the only thing I have ever thought this car needs (other than more open road!) is one of your AC systems!!
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Old 08-26-2020, 05:44 AM
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Originally Posted by icarp View Post
7000 rpm is 131 mph for a stock ratio 915 and full size tires , also you ran to 130 in about 19 seconds
What fun
Nice test road
Ian
Hi Ian!

I did change the stock 1.00 4th to a 1:08, so the top of 4th is about 125, based on my calcs using 215/60-15 Pirelli P6000 as a tire model. The CN36 is identical in circumference as far as I can tell.

Here's a "wayback" post on the trans ratios. All that research and calculation has paid off!

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Originally Posted by Jonny042 View Post
One thing I've been putting off for some time is the transmission. Hernia operation (minor, umbilical, no biggie, thanks for asking) in November precluded my lifting anything too big so this has been hibernating under the bench for a while. The plan was, originally, to put in the car and see how it shifts, but this project has evolved to be a nut and bolt sort of affair. Am I going to stick a used, tmu, unknown transmission in this car, after all the work I've done? Nah.

So somewhere along the way I started Autocrossing the Rot Rod and changed out 2nd and 3rd for shorter ratios. The thing is an absolute beast now. This little experiment was a success, and a learning experience, and it only reinforced my opinion that a gearing change to better suit a car for it's intended use is absolutely one of the best things you can do. Yes it seems a little pricey (more on that later) but it's such a huge advantage!

I called my trans for the Rot Rod an SC/RS/Carrera hybrid which is pretty accurate, as the final drive, 1st, 2nd, and 3rd are the same as the SC/RS and 4th and 5th are stock 3.2 Carrera ratios. changing just 2nd and 3rd meant it was a budget friendly proposition, and while I was in there I replaced the 1st gear dogteeth, the 1/2 shift collar, and the 1/2/3 synchros (remember the new gears come with fresh dog teeth). It was previously reluctant to upshift, downshift, or go from neutral into 1st at a full stop, but now it shifts like a dream instead of a nightmare.

One thing that I (predictably) don't love about the stock 4th gear is it's a bit doggy compared to third and the upshift does have a fair RPM drop but for the usage the Rot Rod gets it's a good compromise.

For this car I decided to go slightly longer for 2nd gear, with a 1.933 ratio compared to 1:2.000 for the SC/RS, the same 1:1.381 for 3rd, and a 1:1.08 for 4th (compared to the stock 1:1.000). The 5th gear for the late SC transmission is 1:0.8241 so it's a bit lower than the Carrera (but still geared for 165mph at 7000rpm!!). The 4th gear change gives me one more "good" gear for higher speed backroad driving, and retains the long 5th for cruising between special stages and driving home from the track

The results, in graphical form:



Comparing the before and after on the graph might make you thing there's little enough change that it's not worth the trouble, but after trying this out on the Rot Rod I know it's going to be fantastic! Nice close ratios from start up to 135mph, and a long fifth for relaxed highway cruise. Should be fun!

I should note, this is nothing groundbreaking, in fact pretty familiar territory for many on the forum. Bill Verburg and Matt Monson come immediately to mind for their tireless contributions to any and all gearing related discussions, gliding_serpent for sharing his though process in selecting gear ratios for his track car, Gordo2 did a 2nd gear swap with good results, and I am sure there are many more.

Of course let's not forget Peter Z. and his classic, the 915 tutorial, and Gordo's transmission rebuild thread. Thanks, guys!!!
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Old 08-26-2020, 06:33 AM
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Funny you mention gearing. I was thinking during the video that the rpm drop to 5th was much larger than the rest. You can hear the engine load going into the cruising gear.

Car sounds and runs amazing. Felt like I was almost in the back set listening to the wail in real time.
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Old 08-26-2020, 07:03 AM
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Originally Posted by jpnovak View Post
Funny you mention gearing. I was thinking during the video that the rpm drop to 5th was much larger than the rest. You can hear the engine load going into the cruising gear.

Car sounds and runs amazing. Felt like I was almost in the back set listening to the wail in real time.
Thanks, Jamie!! I really look forward to hearing yours soon!

That wail is just amazing - it's interesting how the pitch and sound of this motor is not entirely unlike a high revving small displacement flat six - I've been watching videos of 2.0L Cup 911's and the sound is similar!:

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Old 08-26-2020, 07:57 AM
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Exhaust + ITB + Cam overlap + rpm = magical noise.

zoom zoom.
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Old 08-26-2020, 08:17 AM
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Bath Time

Thought you guys might like to see a pic of the wheels without the usual coating of brake dust..... I swear every time I look at it, it gets better looking!!!

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Old 08-26-2020, 06:18 PM
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New advance curve

I've been running a really lazy advance curve, and was too lazy to change it. Well, maybe that's not the way to put it. It was very conservative, and so am I. No advance from base idle timing (10 degrees) up to 2000rpm, then 22 degrees advance coming in at 3000rpm. In other words 10 degrees at idle and 32 at higher rpm. It was easy to check and verify.

I recently decided to add some polish to it:



I was getting the occasional bit of kick-back on startup so pulled some timing (-4 degrees) below 800RPM for easy cranking. At all reasonable idle speeds from 800 to 1200RPM it's a flat line at 0 degrees, then rising to max advance of 22 at 3000rpm, with a few degrees extra until higher RPM when the cam comes in and cylinder pressures are even higher, so I drop to 20 degrees advance.

I set the base timing at 12 degrees. With the relatively low compression (9.5) and the cooling brought by the fine MFI atomisation and the rich mixtures again keeping things under control, I think that 32 degrees at 7000RPM is a good choice.

I also bumped up the rev limiter a bit.

It was quite a tuneup, let me say!! Everything about the motor became better. I didn't think that was even possible. Starts easier, idles better, and has a low to mid range punch that's just nuts! It also uses those extra RPM up top. I might bump the limit a little more as it's still pulling hard when the fun stops.

I really want to go back to my test track and re-do that video!!!!
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Old 09-01-2020, 05:44 AM
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Sounds like it’s time to dyno it and get the tune fully dialed in!
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Old 09-01-2020, 07:02 AM
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Sounds like itís time to dyno it and get the tune fully dialed in!
That it is!!! Waiting for the border to open up, I had planned to go to Minneapolis for that sometime this year, so it may have to wait.

I do still have a low to part throttle lean spot around 20% throttle opening, across a large RPM range. I can't always feel it but I know it's there from looking at the AFR. It's keeping me from leaning the mixture out across the range, the curve is pretty good but still in the high 11's at full throttle. I'm pretty much out of adjustment with the part load screws so I am going to have to hack away at the space cam in one area. I've been reading up on that.

I might also try a "T" space cam, for kicks. If it's close to what I need and the fuel delivery is only weak on the high end I might choose to modify it rather than start grinding away at my genuine RS space cam.

In other words, I have a way to go...... but it's a lot of fun.

The latest news is that I've put 1500km on the motor and am now doing the 4th oil change and second valve adjustment, also did a compression check and all cylinders are within 5psi of each other, the oil looks good (I even cut into the filter) and the cam wear patterns are nice and light and even on all the lobes.
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Old 09-01-2020, 08:00 AM
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Quote:
Originally Posted by Jonny042 View Post
I've been running a really lazy advance curve, and was too lazy to change it. Well, maybe that's not the way to put it. It was very conservative, and so am I. No advance from base idle timing (10 degrees) up to 2000rpm, then 22 degrees advance coming in at 3000rpm. In other words 10 degrees at idle and 32 at higher rpm. It was easy to check and verify.

I recently decided to add some polish to it:



I was getting the occasional bit of kick-back on startup so pulled some timing (-4 degrees) below 800RPM for easy cranking. At all reasonable idle speeds from 800 to 1200RPM it's a flat line at 0 degrees, then rising to max advance of 22 at 3000rpm, with a few degrees extra until higher RPM when the cam comes in and cylinder pressures are even higher, so I drop to 20 degrees advance.

I set the base timing at 12 degrees. With the relatively low compression (9.5) and the cooling brought by the fine MFI atomisation and the rich mixtures again keeping things under control, I think that 32 degrees at 7000RPM is a good choice.

I also bumped up the rev limiter a bit.

It was quite a tuneup, let me say!! Everything about the motor became better. I didn't think that was even possible. Starts easier, idles better, and has a low to mid range punch that's just nuts! It also uses those extra RPM up top. I might bump the limit a little more as it's still pulling hard when the fun stops.

I really want to go back to my test track and re-do that video!!!!
There you go! I bet thatís a different car now!
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Old 09-01-2020, 11:28 AM
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There you go! I bet thatís a different car now!
Well, it already felt pretty good, but yes, it was a huge positive change. Love that CDI+!!!!!
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Old 09-01-2020, 02:04 PM
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Just a quick update, the car is buttoned back up after the oil change/compression test/valve adjust, also I had a look at the piston tops and am concerned with the amount of carbon that's built up on them already - so it was with renewed purpose that I removed the MFI pump and made a few adjustments inside.

I was finding a bit of a lean spot on part throttle (say, 15%) over the entire RPM range so there's no real fixing that with the part load screws..... I had previously screwed with the space cam starting point a little trying to lean out the idle mixture when I ran out of adjustment on the idle screw, but I since have figured out that the black screws can overlap and in fact overcome the idle mixture adjustment entirely. So, the adjustment has gone back to close to stock (this is the 45 degree andgle set with a guage inside the front cover, I was at something more like 47 degrees now gone to about 44. This changes the rotational starting point of the fuel map on the space cam by moving the map area left or right a small amount. It seems to have most effect on the fuel quantity change in the first few degrees of throttle opening.

I've also been struggling to get the full throttle fuel delivery leaned out and I had previously "cranked up" the transmission ratio eccentric to get more fuel at higher openings but probably overdid it a bit. So that went back about halfway towards the original setting.

Neither one of these changes are something you'd do with a stock(ish) MFI setup and I'm coloring outside the lines a bit with both of them. The are also most easily done with the pump removed so take a bit of time.

They also require that the main rack be adjusted, in this case several turns leaner (a huge amount). So getting the car started and idling and running requires a bit of fiddling. What fun!!!

Anyway, I KNOW!!!!! I'm supposed to change one thing at a time..... but I think I can seperate the effect of them both, and happy to report the part throttle mixture is much more consistent, I also had a slight rich bump right off idle that is now gone, and apparently the shift of the space cam profile to the right a bit has filled in that lean spot.

I'm finding, now, that with the ignition timing set to my best guess curve with a lot more timing, sooner, the engine feels better when running leaner mixtures. It would previously surge a bit at light throttle cruise if the mixture went above 13.5:1 or so but it feels smoother now.

Overall a good change, and the motor feels more crisp and energetic. Time to get serious about datalogging, again!!
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Old 09-15-2020, 05:17 PM
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Ooops I almost forgot, one of my buddies came over and we spent a few hours polishing the paint which I haven't actually bothered with since I first polished it....... a loooong time ago. Also we applied a sealer to help the paint be a little less grabby.

It looks pretty amazing. Thanks, Cory, for the help! (I promise to get some better microfiber towels for next time!!!)

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Old 09-15-2020, 05:33 PM
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Old 09-15-2020, 06:35 PM
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I really enjoy reading your writings . Well done , I got the cis stuff done this eve and will test the car in the AM
Good to see the progress
Ian
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Old 09-15-2020, 07:42 PM
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Car looks amazing Jon! Is it legal in Canada to put the front plate on the right side of the bumper? When my 73 was on the road I put it there so you could see the S bumper cut out. Not a great pic but like this. My car is the polar opposite of yours.

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Old 09-16-2020, 03:26 AM
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Originally Posted by Shaun @ Tru6 View Post
Car looks amazing Jon! Is it legal in Canada to put the front plate on the right side of the bumper? When my 73 was on the road I put it there so you could see the S bumper cut out.
I'm sure it's fine as long as it's clearly visible, but every province has different rules. Here in Alberta, we don't even have front plates.
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Old 09-16-2020, 04:07 AM
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Originally Posted by Shaun @ Tru6 View Post
Car looks amazing Jon! Is it legal in Canada to put the front plate on the right side of the bumper? When my 73 was on the road I put it there so you could see the S bumper cut out. Not a great pic but like this. My car is the polar opposite of yours.

I don't see anything wrong with that car, at all!!!!

It's purely a personal thing, I actually don't like the "S" cutout and very seriously considered eliminating it!! But I kept it for the same reason the factory did, tow hook access. My plate attaches with wing nuts (actually wing bolts from the electrical panel cover in the engine compartment.)

As for the legality of any alternate positions, the Ontario highway traffic act dictates that it be mounted on the front of the vehicle, so off to the side would be fine.

Quite a few people around here run without front plates but I always go with the approach that if I get pulled over it's probably going to be for speeding, and at that point I don't need to give the OPP another excuse to ticket me.
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Old 09-16-2020, 05:28 AM
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Shaun, when you get stopped in Canada, the cops generally go to the rear to check the L/P as their girth and equipment belt prevents them from bending down to have a good look of the front. On my RST, the plate is approximately as on your car and I’ve never had an issue. In Ontario, lots of older cars have their L/Ps bolted to one side of the bumper. The key is can it be read from the front. Don’t think the Highway Act says how far back you have to stand to read. (Tung in cheek).
Sorry Jon for highjacking the conversation.
So great to see two incredible narrow bodies on the same page!!!
Cheers,
Johan


Last edited by Uwon; 09-17-2020 at 04:38 AM..
Old 09-16-2020, 07:06 AM
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