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Home > Help Needed / General Tech Chat > quick throttle position change not smooth

remko

75 Posts
Member #: 1956
Advanced Member



Hi All,

I can't get the final bit of tuning right for my supercharged 1275 Pickup.
Specs:
eaton M45
MR2 intercooler
blow through metro turbo Hiff44
Mechanical dump valve (VW G40, connected to throttle)

The problem I have is the following:
Quick increase of throttle doesn't work well. Engine hesitates for a while and then suddenly it picks up and the wheels starts spinning due to the 160Nm waking up :) Hesitation is too short to see how the mixture is on the wideband lambda, but my ghess is too lean.

With smooth increase and decrease of throttle the mixture is almost perfect thanks to my LED piston height measurement in combination with wideband lambda and hours of needle sanding.

I already tried different oils in the dashpot. Carb has had a complete overhaul.

Anybody any suggenstions what to do/check?

Thanks in advance!

Regards,
Remko


Turbo Phil

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4584 Posts
Member #: 20
My sister is so fit I won't show anyone her picture

Lake District

Does putting thicker oil or a heavier spring in make any difference?

On a side note, any more info on your LED piston lift indicator?
I made a mechanical one, but a nice electronic one would be better.

Phil.

WWW.TURBO-MINI.COM


hazpalmer

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1633 Posts
Member #: 9038
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Carlisle, Cumbria

On 25th Feb, 2021 Turbo Phil said:
Does putting thicker oil or a heavier spring in make any difference?

On a side note, any more info on your LED piston lift indicator?
I made a mechanical one, but a nice electronic one would be better.

Phil.


Would be interesting to see. Need to sort out how I'm going to tune my mini


remko

75 Posts
Member #: 1956
Advanced Member

Wouln稚 a havier spring or thicker oil make is more lean? I paid extra attention to my lambda. It goes in the direction of lean. I値l try some different springs.
I think it has something to do with the suddenly rise of boost, due to supercharger instead of turbocharger. Is it possible that the pressure rise in carb is quicker then pressure increase in fuel bowl?


remko

75 Posts
Member #: 1956
Advanced Member

And I値l post some pictures of the LED system


metroturbo

806 Posts
Member #: 989
Post Whore

North Yorkshire

There is some info on the excellent LED system here: http://www.turbominis.co.uk/forums/index.php?p=vt&tid=617324


shane

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2501 Posts
Member #: 1246
Post Whore

Lowestoft, Suffolk.

While searching for info for a side project recently it appears historically there has been mixed feeling on here with dashpot springs with some members stating that the (I believe green strongest) was sufficient, others saying that swapping springs made no difference. I recently read of members using two standard springs.
Are you using a plenum of any sorts to incorporate the restrictor ring?

Shane


remko

75 Posts
Member #: 1956
Advanced Member

Thx Metroturbo, saves me finding the pics 😊


remko

75 Posts
Member #: 1956
Advanced Member

I知 driving with the standard plenum with the g40 recirculation valve in front.


DILLIGAF

123 Posts
Member #: 9128
Advanced Member

What have you done with the part throttle lean off pipe ? If you've still got it connected as standard try either disconnecting it and blocking it off. Or leaving it as is and restricting it, with a clamp.


metroturbo

806 Posts
Member #: 989
Post Whore

North Yorkshire

Thicker oil will make it run momentarily richer as it restricts the rise of the piston on a snap increase in throttle opening. Restricting the upward movement after opening the throttle has the affect of increasing the air velocity over the bridge of the carb, which reduces the air pressure over the bridge, and means more fuel is drawn out of the needle.

Personally I'm not a fan of using a stronger spring to solve problems of running lean on acceleration unless you have exhausted all other possibilities. The stronger spring changes where the piston naturally sits in cruise conditions, which will mess up all the work you have already done with your needle.

Are you using the standard turbo fuel pressure regulator? If so, it should have no problem keeping the fuel pressure high enough in the bowl. Might be worth plumbing in a gauge temporarily to see what is happening to fuel pressure. If you have the gear, a differential gauge measuring fuel pressure and boost pressure makes it much easier to see that fuel pressure is keeping ahead of boost.

DILLIGAFs suggestion is definitely worth checking as the part throttle lean off can cause this exact issue. I installed a solenoid in the part throttle lean off pipe to solve the problem of my carb going lean as it came on boost, whilst still allowing the carb to lean off on cruise. Megajolt takes care of opening and closing it, but I do need to add a time delay relay so that it stays shut when accelerating through the gears.

On 26th Feb, 2021 remko said:
Wouln稚 a havier spring or thicker oil make is more lean? I paid extra attention to my lambda. It goes in the direction of lean. I値l try some different springs.
I think it has something to do with the suddenly rise of boost, due to supercharger instead of turbocharger. Is it possible that the pressure rise in carb is quicker then pressure increase in fuel bowl?


stevieturbo

3474 Posts
Member #: 655
Post Whore

Northern Ireland




On 26th Feb, 2021 remko said:
Wouln稚 a havier spring or thicker oil make is more lean? I paid extra attention to my lambda. It goes in the direction of lean. I値l try some different springs.
I think it has something to do with the suddenly rise of boost, due to supercharger instead of turbocharger. Is it possible that the pressure rise in carb is quicker then pressure increase in fuel bowl?


No.

You do not want the dashpot to rise quickly, that is what causes the lean condition if that is the problem you are experiencing.

Log fuel pressure, MAP/boost and AFR's at a minimum. Type of boost does not matter.

9.85 @ 145mph
202mph standing mile
speed didn't kill me, but taxation probably will


remko

75 Posts
Member #: 1956
Advanced Member

Thanks Dilligaf and Metroturbo! Plugging this pipe solved my problem for 90%!
Next step is trying different thickness of oil to solve hopefully the last 10%, but I知 already very happy with this improvement!


remko

75 Posts
Member #: 1956
Advanced Member

Once this is solved I値l switch over to a smaller pulley. Boost will rise from 0,5 bar to 0,75 bar!

Edited by remko on 2nd Mar, 2021.

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