Injector Pump Tweaking

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Rick Cobley
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Injector Pump Tweaking

Post by Rick Cobley »

Hi, Have any of you ever gave any thought as to the power output of 38T & 38TD engines?

The 38T first saw light of day in the Nuffield 4/60 and produced 58-60hp, turning up the fuel produced a little more power but with plenty of smoke.

The engine went on to be used in 4/65, 270 & 384 and was producing 70hp before the 4/98 came along and replaced it. So how was the extra 10hp produced without all the smoke!

I started to investigate engine fuelling and discovered the later injector pump delivered less fuel, injected it slightly later and yet produced more power!

During my investigations Welham Diesel Injection Services in Leicester have been very helpful in supping me with pump data which revealed the internal parts of the early and later pumps are very similar ( Except P4801/5 & P4801/6a which have 8.5mm plungers) the main difference being how the pump is set up and thus the rate at which fuel is injected.

My aim is to reassemble a pump in the later spec and test the power output on a dyno and possibly measure rate of fuel used to confirm the improved efficiency.

The work involves using the spill timing method to measure the revised pump settings and it is to this end that I am thinking of building some kind of test rig over a tray to collect spilled fuel, has anybody ever attempted this or have any suggestions?

I also plan to build a P4801/6a as used on the Marshall 904 and try it on my turbocharged Nuffield 10/60.

Regards Rick Cobley


Nowtnew
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Re: Injector Pump Tweaking

Post by Nowtnew »

I wonder if the valve timing was changed too?

Just a thought.

Also I think all the 270s were 4/98 engines. Didn't the changeover come during the reign of the 384?

Regards
Paul
Jazo
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Re: Injector Pump Tweaking

Post by Jazo »

This will be interesting, what size plungers are in the 10/60 4/65 pumps?
3/45 with faster reductions and turbo
Rick Cobley
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Re: Injector Pump Tweaking

Post by Rick Cobley »

Hi, I'm not quite sure when the 4/98 replaced the 38TD. I thought the first 270 tractors had the 38TD and it was soon replaced by the 4/98 perhaps JVP has documents on this?

All injector pumps fitted to 3.8 engines ( as opposed to the 3.4 engines) have 8mm plungers untill the arrival of the P4801/5 and P4801/6A pumps which have 8.5mm plungers. My belief is the extra power and economy comes from changing the part of the cam that injects fuel thus increasing the speed of injection.

Regards Rick Cobley
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JohnP
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Re: Injector Pump Tweaking

Post by JohnP »

The 98 series engine was fitted from September 1972. I don't have the exact chassis number but it was somewhere between 165600 and 165800. This applies to both 344 & 384's.

Engine numbers started at;

4/98DT 101
4/98NT 101
JVP

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Rick Cobley
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Re: Injector Pump Tweaking

Post by Rick Cobley »

Hi, Thanks for that John.

So the last 344 & 384 tractors had the 98 series and then the usual model change.

Had I thought about the Leyland 255 having the 4/98dt then I would have realised the 270 had the 4/98nt

Regards Rick Cobley
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