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Go Back   Madabout Kitcars Forum > Mad Build Area > Marlin Sportster, Cabrio, Berlinetta and Roadster builds

Marlin Sportster, Cabrio, Berlinetta and Roadster builds Enthused or Confused about your vintage Marlin build? Ask away here or show off your build.

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  #1  
Old 26th April 2017, 20:28
mcramsay mcramsay is offline
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Default The sportster.... things have finally clicked

So a 3 year slightly fustrating build and then quite a few short trips only to return home and undertake some major modifications. Tonight things finally clicked and I've fallen in love with the car.

Nice cool evening and I went for a 30 min trip through some wide country lanes and gave it some proper stick. Initially driving the car it didn't meet my expectations speed wise. However I have realised over the last few trips with the exhaust being so loud that I have been shifting through the gears at 3000 rpm and then flooring it in 4th expecting to be flung back in the seat...the m3 engine doesn't work like that.

Tonight I shifted down into second at 30 and floored it.... 1 the car stuck to the floor and 2 it was like some one had just fired a jet engine up behind the car, it went like absolute s***t off a shovel. I was in 3rd at 80 before I knew it. The car felt stable and the temps seem to be much lower keeping the revs up on the car, I guess the coolant flow is much higher when not pootling around any 1500RPM

I have been excited about the sportster, then frustrated, got bored and ended up hating it.

One good drive tonight and it's the best thing I've ever driven, no car comes close to the sound of the m3 lump at 5000 RPM!!
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  #2  
Old 26th April 2017, 21:49
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Glad you're enjoying it Nothing better than dropping it down couple of gears and giving it full throttle
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  #3  
Old 26th April 2017, 22:11
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Quote:
Originally Posted by mcramsay View Post
So a 3 year slightly fustrating build and then quite a few short trips only to return home and undertake some major modifications. Tonight things finally clicked and I've fallen in love with the car.

Nice cool evening and I went for a 30 min trip through some wide country lanes and gave it some proper stick. Initially driving the car it didn't meet my expectations speed wise. However I have realised over the last few trips with the exhaust being so loud that I have been shifting through the gears at 3000 rpm and then flooring it in 4th expecting to be flung back in the seat...the m3 engine doesn't work like that.

Tonight I shifted down into second at 30 and floored it.... 1 the car stuck to the floor and 2 it was like some one had just fired a jet engine up behind the car, it went like absolute s***t off a shovel. I was in 3rd at 80 before I knew it. The car felt stable and the temps seem to be much lower keeping the revs up on the car, I guess the coolant flow is much higher when not pootling around any 1500RPM

I have been excited about the sportster, then frustrated, got bored and ended up hating it.

One good drive tonight and it's the best thing I've ever driven, no car comes close to the sound of the m3 lump at 5000 RPM!!
Delightful read.
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  #4  
Old 29th April 2017, 21:16
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That was exactly my first experience of my m50 engine in the sportster. I was expecting it to fly like my m3 but was underwhelmed. I was also shifting too soon as the exhaust note was telling me it was time. Once i realised the problem, i let the revs hang on to 6000 and the smile was on my face as it should have been all along
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  #5  
Old 30th April 2017, 10:36
mcramsay mcramsay is offline
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What scares me even more is I'm running with a fault code that sets a 5500 rpm Rev limit on the engine! I havnt got round to addressing the issue yet which is basically the mss50 ( m3 ecu) requires a vehicle speed input in the m3 this signal comes from the diff speed sensor as an analogue signal, then goes into the dash clocks and comes out as a digital signal which goes to the ecu.

Basically the Rev limit is there to stop you going over 155 mph. So by lowering the Rev limit to 5500 there's no way you could reach that speed in the higher gears.

There are boxes on sale to replicate the signal if you are using non standard clocks but they are around 400! I did read up and find you can splice into the car sensor which has the correct output!
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  #6  
Old 30th April 2017, 11:33
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Could you have the ECU patched to ignore the speed limiter?
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  #7  
Old 30th April 2017, 11:38
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I think it can be recored to raise the Rev limit cut from 5500 to the normal value. So it still thinks it doing its job! I'm not really fussed at the moment will get it sorted at some point!
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Old 30th April 2017, 23:36
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Quote:
Originally Posted by mcramsay View Post
What scares me even more is I'm running with a fault code that sets a 5500 rpm Rev limit on the engine! I havnt got round to addressing the issue yet which is basically the mss50 ( m3 ecu) requires a vehicle speed input in the m3 this signal comes from the diff speed sensor as an analogue signal, then goes into the dash clocks and comes out as a digital signal which goes to the ecu.

Basically the Rev limit is there to stop you going over 155 mph. So by lowering the Rev limit to 5500 there's no way you could reach that speed in the higher gears.

There are boxes on sale to replicate the signal if you are using non standard clocks but they are around 400! I did read up and find you can splice into the car sensor which has the correct output!

If you are only running up to 5500rpm, you have got no where near the full on power output from this engine - it is literally just getting going over 4000rpm, and keeps pulling harder and harder upto 8000rpm.

Get it sorted - you are missing so much more fun!!!!!!!!!!!!!!!!
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  #9  
Old 30th April 2017, 23:42
mcramsay mcramsay is offline
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Stock Rev limit is 7600 I think! I'm still getting used to it so I haven't hit the 5500 limit in any gear yet! But yes I do need to get the limit removed!
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  #10  
Old 1st May 2017, 08:59
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a quick and dirty solution would be to (if you still have them) take the main board out of the original clocks and sneak it under the scuttle to provide the signal to the ECU. You should just be able to provide the board with some power to get this working. At least then if you split the signal between the new speedo and the old board, you'll know that what is being passed to the ECU is the correct signal (that may not be the same form or voltage as that from the diff). It would be cheaper than getting the ecu reprogrammed.
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  #11  
Old 1st May 2017, 09:55
mcramsay mcramsay is offline
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Unfortunately I don't have the clocks from the car, and looking online they are 200 quid second hand. It would be good to know what the actual output from the clock to the ecu is I would be able to replicate it then!
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  #12  
Old 1st May 2017, 16:27
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Quote:
Originally Posted by mcramsay View Post
Stock Rev limit is 7600 I think! I'm still getting used to it so I haven't hit the 5500 limit in any gear yet! But yes I do need to get the limit removed!
How are you determining your RPM?
If you have not been up to 5500RPM, how do you know you have hit a limiter?
Have you calculated your speed in a lower gear at high RPM?

It might be worth checking that your Rev counter is showing the correct numbers. My impression of the M3 was that it had only just come on song at 4000rpm, so if you were not going up to 5500rpm you've barely been in the power band. Yet you say you went out and floored it, and hit 80mph in 3rd?

Could it be that your Rev counter is understating your revs?

What size tyres and diff are you running?

My quick maths check suggests standard tyres and diff would require 5900rpm to achieve 80mph in third?
(assuming 3rd gear has a 1.67 ratio, that your diff is the standard 3.23 Evo diff, and your tyres are 245/40/17)

You will certainly know when you have hit the limiter as it feels like it has gone horribly wrong! It just changes from a long push in the back as you get there, to a sudden dying sensation - horrible.
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  #13  
Old 1st May 2017, 17:37
mcramsay mcramsay is offline
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Mike my tacho is spot on, it reads the same as the laptop hooked up and reading direct from the ecu.

I have been at around 5000, I know there is a limiter set at 5500 as it's normal on most bmw's that could reach over 155. And I have the fault code standing which sets this limit. Been reading up on it loads. Very common in the racing world that use these engines.

My diff ratio is either 2.18 or 2.35 which are the ratios used in the e39 530d. Couple this with 225/50/16 tyres and this gives the ability to reach 80 in third without hitting the limiter.
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Old 2nd May 2017, 14:24
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Quote:
Originally Posted by mcramsay View Post
Mike my tacho is spot on, it reads the same as the laptop hooked up and reading direct from the ecu.

I have been at around 5000, I know there is a limiter set at 5500 as it's normal on most bmw's that could reach over 155. And I have the fault code standing which sets this limit. Been reading up on it loads. Very common in the racing world that use these engines.

My diff ratio is either 2.18 or 2.35 which are the ratios used in the e39 530d. Couple this with 225/50/16 tyres and this gives the ability to reach 80 in third without hitting the limiter.
Are you planning to swap to higher ratio diff? - you'll never get out of Third gear!
You are currently geared to a theoretical maximum of 235mph - in a Sportster!!!!!!?????
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Old 29th May 2017, 18:12
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Are you planning to swap to higher ratio diff? - you'll never get out of Third gear!
You are currently geared to a theoretical maximum of 235mph - in a Sportster!!!!!!?????
Bump ............... I was not joking about your theoretical top speed!

Using a very low ratio diff suited to a high torque diesel is killing your S50 engine which needs to be revved hard to perform at its best.
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  #16  
Old 29th May 2017, 18:26
mcramsay mcramsay is offline
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Apologies for the late reply, I have to admit after your recent post I've been doing some research / testing. I can confirm my diff ratio is 2.91, it seems I was misinformed by the owner I bought the rear axle from.

Also I can confirm my rev limit is standard on my car despite having the error code up. I know the ecu was previously chipped so I think that it may have been played with in the past.

Current figures are I can pull from 30-80 in 4.5 seconds in second gear, shifting at 7400 into 3rd.
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Old 29th May 2017, 22:41
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Mike, i think the rev limit on the S50 engines was quite a bit lower than the S54 which you're comparing to on your E46 M3. It was still about 500-800 higher than the M50 though.

McRamsey, I've been driving around in my sportster this weekend tuning my new 3.0 franken-engine made from random bits of M5x series engines and control by a megasquirt. Even with my un-dyno'd tuning efforts, I think I've hit the sensible limit for a road going sportster. The acceleration/torque is definitely an improvement on the old 2.5 and by the time you're passing 5000rpm you're well and truely pinned back in your seat and having to really concentrate on keeping it straight, especially if there are any bumps in the road. The tyres don't let loose but there's a definite lose of steering weight. I probably need to look at the suspension setup again as I've lost 20Kg on the front with the change to an ali block plus the extra power could well affect the handling.

God knows what it must be like trying to control the power on an S50 engined car, even one that only goes to 5500. This has of course only deepened my resolve to upgrade to a V12 asap as I don't believe in stopping at a sensible limit.

Btw, I've a set of M50 clocks up on ebay. I don't know if they could help and are a lot less than 200. The original wiring had the same set up with the vss coming in from the diff and on to the dme, though I never connected that up in the marlin
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  #18  
Old 30th May 2017, 13:09
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Quote:
Originally Posted by mcramsay View Post
Apologies for the late reply, I have to admit after your recent post I've been doing some research / testing. I can confirm my diff ratio is 2.91, it seems I was misinformed by the owner I bought the rear axle from.

Also I can confirm my rev limit is standard on my car despite having the error code up. I know the ecu was previously chipped so I think that it may have been played with in the past.

Current figures are I can pull from 30-80 in 4.5 seconds in second gear, shifting at 7400 into 3rd.
You'll still not get out of third!

Have you considered 3.46, or 3.73, or even 3.91 diffs?

I am assembling an E30 with an S54 M3 swapped engine and gear box for a track car/fast road, and deliberating what will be the best diff ratio, so am interested to hear how your Sportster performs. The S54 certainly performs at its best when it is revved hard, despite Dual Vanos .
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  #19  
Old 30th May 2017, 21:32
mcramsay mcramsay is offline
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Remember I am running the e39 rear subframe so the choice of diffs may be different, also the diffs have different case sizes,so I need to research what will fit. The car is def geared for top end rather than acceleration, I would like to change this but for now I'm happy with the car but a diff change is on the cards for the future.

The vanos kicks in at around 4500 rpm and you can instantly feel the power kick
The car is great fun to drive and sounds awesome mike if you pm me your email I can send a video across.
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  #20  
Old 30th May 2017, 21:33
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I'm running a 3.91 with the M20 - I did bump the tyre size up from E30 rolling radius (205/55/R15) to E36 rolling radius (205/60/R5) which brings the RPM down a bit - 3.3% difference. With extra torque from the stroker rebuild it sometimes feels like you don't need first.
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