Thread: 3.69 gears with 30-tooth (stock) reluctor wheel

I'm working on a 98 Regal GS with an Intense Tranny (installed less than 1000 miles ago). It has 3.69 gears and one of those SRC's wired up to the PCM. I was thinking about removing the SRC and just tuning the PCM for the 3.69's.

Using a spreadsheet I found I have the following set with the PowerTuner:

Stock 30-tooth reluctor

Calculated_Pulses_Per_Revolution: 28.03
Pulses_Per_Mile: 22710
Drive_Sproket_Ratio: 0.89

Now I imagine I need to drop all the Shift and TCC MPH settings by 22-25% (multiply current values by .78-.75).

Am I correct? I emailed Intense (to find out what reluctor they used) and Scott Cook strongly recommend against doing this.....but I'd like to get more input first before believing his recommendation.

It gets a P1811 from time to time and I was thinking that removing the SRC would rule it out as a culprit.

Update:

Well, I removed the SRC and uploaded these changes:
Calculated_Pulses_Per_Revolution: 28.03
Pulses_Per_Mile: 22710
Drive_Sproket_Ratio: 0.89

I also got a copy of someone's 3.69 BIN file and used their shift points. I drove the car around and the speedometer isn't accurate so therefore the shift-points are all screwed up. I can work through the shift-points, but I'm trying to figure out why the speedometer isn't right. Intense said they used the stock 30-tooth reluctor.....dunno if that's not right or what.

So, anyone have any input?

I have not had to personally tune for 3.69s yet as there arent a lot of people that go to that gear ratio, but I have found that the sprocket ratio change in HPT makes no change and there are still problems. What I do for 3.29 gear swaps in place of 2.93s is at the top of the speedo calibration screen I copy the existing tire height and then I insert 3.69 in place of 3.29 and make absolutely no other changes and leave the Auto Calibrate feature ON which corrects all shift points. This makes almost everything about spot on for shift points and leaves the speedo correct, also gives the correct pulses per mile that the pcm wants to see. I have done this since HPT came out in early 04 for these cars and it has always worked every time. Again I have not had to tune for 3.69s yet but you could do the same thing that I do but use a different ratio. Interestingly enough, the 3.69 that I plug in has nothing to do with that being the next up ratio available, its simply a mathmatical equation that works out to 3.69. Because the stock ratio in the GTP tune is 3.29, though uses the 1.121 sprocket ratio, take 1.121 x 3.29 and it comes out to 3.69. 3.29/2.93 comes out to about 1.122 so its pretty close to 1.121 and this is the multiplier I use. 3.69/2.93 comes out to about 1.26, so 1.26 x 3.29 = 4.15. Try to substitue 4.15 in place of 3.29 in the speedo table and leave everything else alone and make sure Auto Calibrate is set to ON. Give this a shot and see what it does. My experience with changing the sprocket ratio has never made it correct so Im not sure if there is a problem in the software or there is just more to it than that for what the pcm wants to see change. The easiest way to see if the ratio I gave you has changed is to put the shifter in "3" and get the car into 3rd gear and watch "Current Gear Ratio" on the scanner. It should read +/- .01 or closely to 1.00:1 or it will throw code P0730 for incorrect gear ratio. Again I have not tried this but its something to try and mathmatically it works out great for 3.29s and I have also helped guys running the 3.05 ratio final drive and it has worked just fine for them also.

Ya, I'm gonna have to fire up the HPTuner that the owner has and use that gear ratio tool. From what I have read on the forums, people use 4.11, 4.13, or 4.15......whatever gives the 1:1 ratio in 3rd gear.

So I'm going to change the settings with the DHP back to what they were (2.93's), then download the file to HPTuners and make the change.

That is what I would suggest and glad others have brought that up too. I know PT doesnt have some of the same stuff for gear ratio tuning and I have never done it by multiplying #s because it is too easy with HPT and the auto calculate feature makes it a breeze, and changing just one number makes it all the more easier even though you have to do a little math to end up at where you want to be and I wish it would work as it should. RWD cars are even worse, at least for 3800 Fbody pcms. You have to enter the ratio between the rearend ratio and tire size, ie if you have a 26" tire and 3.73 rearend that is a 6.97 and that is the number you have to entire for gear ratio changes! Its a pain because it is often not right on and it takes miles of driving to get it dialed in spot on and would be great if it had the same setup as the fwd car where you can add tire and gear ratio seperately and do the math on its own. I did forget to mention above that you may need to make small changes to that number I gave you to get an exact 1.00:1 but sounds but looks like you have been suggested a few numbers to try out and it may take a little playing with.

Trannyman,
Do you change the Drive Sprocket Ratio to match the 3.29 (or 3.69) gears too? The instructions I found on HPTuner's forum just say to put in the tire size and gear ratio and hit commit........doesn't mention changing the Sprocket Ratio though. Should I leave that stock (1.12) or change it to .892 for the 3.69's?

Nope I dont touch anything except tire size and gear ratio, that is why I mentioned changing the sprocket ratio trying it without this never has worked right. Simply copy over the tire size and insert the 4.15 or whichever you choose in place of the stock 3.29 ratio in the table and hit Commit, thats it and HPT will do the rest!

Update, found out that tranny had a 38-tooth reluctor wheel which made the speedo waaaaaay off and the TCC lockup-unlock a lot.

So tomorrow I'm putting in a 30-tooth and see what that does.

That will make a HUGE difference! A lot of people used to do that before pcm tuning was an option and used it in conjunction with an src or similar device to get the speedo correct. Once you put the 30 tooth ring back on then things will make sense and you will be able to nail down the tune

30-tooth reluctor wheel installed and now the speedo is much closer! Scanning the car says a 2mph difference over the speedo and the PCM is right (found one of those police speed read-outs around town and the PCM is spot-on). Is there a way to adjust the speedo in the dash?

I am also having a minor TCC lock-up issue with 4th gear. From a normal stop, it starts in 1st, shifts to 2nd, shifts to third, locks the TCC, shifts to fourth but then unlocks the TCC instead of keeping it locked.

I have a few variations of files that I'm going to play with, but I didn't know if anyone else had these symptoms. (3.69's with 30-tooth reluctor and 3000 stall ATI converter) I used HPTuner's Speedo tool.

When you say the scanner is 2mph off of the scanner you mean the scanner data vs the analog speedo/gauge correct? They typically off a few mph and I have even seen a few that read 5mph off. The HUD will show the digital # that will match scanner data, there is no real way to correct the speed on the dash outside of having it recalibrated so it reads correct. TCC is configured to momentarily unlock during the 3-4 shift, sometimes you can plainly notices this and sometimes you dont. Louder exhaust really brings this out. You should be able to change the mph apply and disengage mph vs load with the tuner to get it where you want.