Z3 2.8 final drive ratio change

[PeterJ]

Hi all, I am looking at changing the drive ratio on a manual 1998 2.8 from 3.15 to 4.10 (found on 2.8 auto)...the result should be increased acceleration, but drop in speed in the first four gears. I am not concerned about top speed loss or long distance cruising...just acceration enhancement (the car already has many upgrades). I am wondering if this size of change may be too much and make first gear redundent? or give me the acceleration boast I am looking for. Also, I am being told that the 5th gear is an overdrive gear so the speed at a given RPM will actually increase compared with the other four gears where the speed will decrease at a given RPM (after the final drive ratio is changed to 4.10)...any one tried this before??? (ie, taking the final drive ratio from an auto & putting on a manual)??

Thanks for any comments

Peter

 

[r37]

thats a massive change in drive ratio. Too much i think. It'll give you a massive acceleration boost but the 2.8 will get to 60 in second, with your new final drive you'll need to change up to 3rd which will probobly slow you down. Although 2/3 gear corners will shift to 3/4 which is a straight shift so might speed you up. The back can be quite tail happy anyway and with the lower gearing to them you might find it allmost un-driveable.The most common swap on a Z3 is a e36 m3 back end giving you a 3.23 final drive with an LSD.

 

[PeterJ]

Thnaks Dan. As I am converting a auto to manual + engine upgrade, I was planning to start with keeping the Auto final drive ratio after I convert to manual & alter as appropriate. Do you have any views on "Racelogic Traction Control" (my car has the basic ASC)? It is being reccomened to me in the light of increased engine BHP and final drive ratio change...

 

[r37]

it cant be a bad thing, i find the standard traction controll to be useless. I think completely cutting the power makes the car worse because the back tends to find grip and swing round leading to a tank slapper. If you plan on racing or tracking your car then i'd think the TCS will be turned off, maybe the racelogic will help if driving on a wet surface but for spirited driving i'd leave it off.

I also assume you havnt smoothed out the intake hoses for the extra power. IIRC you use some silicone boost pipe and replace the pipe from the MAF to the throttlebody to smooth the airflow, this removes the traction controll system aparantly as there is a sensor in there. I only had a quick read over this so im not 100% but it might be of use to you.

 

[PeterJ]

Hi Dan, i have just ordered the Racelogic Traction Control System.....thanks again!

 

[PeterJ]

did the calculations, but don't know how to upload a photo of the table (various available final drive ratios with gear speeds) & have gone for 3.64....the engine upgrade & remap will see the RPM red line beyond 7000 (i think 7,500) which should compensate for the reduced gearing meaning red line gear changes will be at about the same road speed as a stock 3.15 ratio .... am not considering fuel economy here!

 

[r37]

what are you doing to the engine, if you dont mind me asking.

 

[PeterJ]

Hi Dan, have done the following (the engine is single vanos non-US version):

1. M50 inlet manifold conversion + throttle upgrade
2. AFE Cold air intake system
3. Rogue Power Pulleys
4. Schrick High Lift Camshafts
5. Eisenmann Quad Exhaust (from stock cat outwards)
6. ECU remap (currently being done)
7. 18 inch wheels
8. Bilstein B6 shocks all round + semi trailing arm bush suspension upgrade (also Bilstein)

Have not driven yet since the upgrade as waiting on a computer adaptor, but hopefully should be all done within a couple of days

Within the next 6 months:
8. Auto (there are no manual Z3's around here!) to manual conversion with 3.64 final drive ratio (just decided the ratio!)
9. Quaife LSD
10. Race logic traction control
11. Loads of other stuff like interior retrim in Italian leather, soft top & frame new sils etc etc etc

 

[r37]

alot of nice work done there, high flow manifold and sportcat should finish it off nicely and make a good track/fast road car. You didnt list an induction kit or any chassic bracing. Front strut bar is an excelent way of stiffening up the front end and thicker ARB and poly bushes would stiffen it up further.

 

[PeterJ]

Hi Dan, yes, I have also fitted a weichers front strut brace, but that is about all the budget will allow for now(!)...had the Bilstein B6's/rear bushes fitted a year ago as the stock shocks were degassed...what a difference in handling!...for the other upgrades...the engine is now all done, but still waiting for the computer adaptor for the remap (don't want to risk driving untill after the remap)...so it is very frustrating not trying it out at the moment.... and the transmission/LSD work should be completed within 3 months I think. We had the engine apart & it is almost 'as new' condition (only 50,000 miles on the clock over 14 years)..lovely. A few people have said I should have purchased an Z3M instead....maybe(?)...but i got the car near 18 months ago very cheap & the M version I saw was 5 times the price (for same year 1998)...& so I got the cheaper 2.8...spent a bit, then a bit more, then a bit more still, then upgrade etc...so when you starting going down that road...you really don't want to part with it! ...you know every part of the car intimately..I could list out all the other work I have done...like brakes etc, but the list is too long!.Totally, the money I have spent/will spend (including purchase price) on totally restoring my 2.8 to perfect order & 'better than new' in terms of performance & handling & conversion to manual; it is about the same price as that 1998 ZM I considered which had a lot more miles (but was manual) and I would have certainly spent a lot of extra money bringing it up to the same 'mint condition' as there was 'worn out this' & 'worn out that' as you would expect from a well used 14 year old car...so all in all, I think my route has been cheaper & it is very exciting & rewarding to restore/modify your own Z & put your personality on it....Also, if I put my modified 2.8 with it's lower gear ratio next to a stock Z3M of the same age, there would not be too much difference (if any) from 0 to 60 mph I would have thought. The stock 1998 2.8 Z3 (single vanos) has a BHP of I think 189 (possibly 193?) & estimates put my current Z3 at just over 250(? - any thoughts on that number Dan?)...maybe more(?) still less than the ZM's 320BHP, but my gearing should be lower.
I have decided against Supercharging as it is a bit obvious when looking under the bonnet & would not pass an MOT with one fitted here (unless factory standard)...high flow exhuast manifold & high flow cat may be next year....anyway, I intend to keep my Z3 2.8 untill I am too old to get in & out of it(!) & I stand no chance of getting my money back if i sold it, but on the other hand, will not lose the much greater amount in depreciation had a purchased say a brand new 2.5 or 3.0 Z4...& am a big fan of the retro styled Z3 & not so much the (technically better) Z4...all personal taste though...

 

[r37]

i have a '97 2.8 single vanos and it came with 193 BHP, s5 manifold gives you another 20, remap another 10, exhaust and induction maybe 10, cams might give you 20 or so, i'd say 250BHP was a good estimate. With that sort of power and the drive ratio you should give a Z3M a good run up to 100 or so, depennding on who's better at changing gears. I too had planned to modify my 2.8 heavily until my insurance company decided otherwise. They will charge me less to insure an M then my very lightly modified 2.8. Even in stock form i love driving the Z3, such a chuckable car and with the roof down its like a big go kart, will definately feel bad selling it when the right M comes along.

 

[Dino D]

Hi Dan, have done the following (the engine is single vanos non-US version):

1. M50 inlet manifold conversion + throttle upgrade
2. AFE Cold air intake system
3. Rogue Power Pulleys
4. Schrick High Lift Camshafts
5. Eisenmann Quad Exhaust (from stock cat outwards)
6. ECU remap (currently being done)
7. 18 inch wheels
8. Bilstein B6 shocks all round + semi trailing arm bush suspension upgrade (also Bilstein)

Have not driven yet since the upgrade as waiting on a computer adaptor, but hopefully should be all done within a couple of days

Within the next 6 months:
8. Auto (there are no manual Z3's around here!) to manual conversion with 3.64 final drive ratio (just decided the ratio!)
9. Quaife LSD
10. Race logic traction control
11. Loads of other stuff like interior retrim in Italian leather, soft top & frame new sils etc etc etc

@PeterJ how did this go on the end?
Be interested to hear how you like the Quaife and the 3.64