IDI diesel powerband manipulation 3

[winfieldblue]

My vintage 1985 Toyota turbo diesel needs more "top end" horsepower, the turbo comes in strong at 2200 revs, and power builds to around 3000 revs and then......nothing !Just a slow trip to the 4000 rev redline. After various attempts to shift the torque peak higher I'm getting a bit frustrated and impatient. So far I've ported the turbo wastegate and freed up the exhaust flow, retarded the camshaft timing(5 deg.), played with various inlet tract lengths, and made adjustments to the injection pump timing and mixture curve. Although some improvement was seen, I want more! I recently fitted a small engine driven blower in place of the turbo, and have picked up power right through the range, however I still need more power from 3-4000 revs (for overtaking on the hyway). The head on these engines is a bit prone to cracking in between the inlet and exhaust valves, so I don't want to risk installing larger inlet valves. I think that the injection pump is the place to look, has anyone had any hands on with the bosch rotary pump? or am I missing something else that is possibly limiting the top end output?...In factory turbo form these engines only put out about 40 k.w. at the rear wheels, need I say more?

 

[70btdc]

If it is a Bosch VE pump have you looked at governor spring modification? The old trick was to replace the intermediate spring with one with a much higher rate, or replace it with a piece of pipe. Leave the full load and idle springs alone, or shim the full load spring if needs be. Doing this alongside lowering the spring rate for the LDA (boost enrichment) under the diaphragm will help. Check your EGT's while doing this though or that cracked head could become a reality pretty quickly...

 

[YvesLLewelyn]

I think the general question is - "Why are diesels so feeble compared to petrol engines of the same capacity".
They just are.

 

[patprimmer]

To increase high rpm power:-
Port the head.
Install higher lift longer duration cam.
Advance injection timing?
Fit bigger turbo.
Fit bigger less restrictive exhaust especially after the turbo.
Don't bother with tuned length.
Increase boost and fuel to match.



Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[70btdc]

Start with the pump. The modifications are free and proven to work. You shouldnt run out of fuel, but delivery profile may suffer if you try to get too much out of the pump. Then you need to look at larger diameter plunger. Fuelling is easier to get right with the turbo setup as extra fuel impacts boost directly as more energy supplied to turbine wheel, which in turn affects delivery rate/timing at pump. Not so easy with steady state SC boost.

Measure EGT's.

 

[BrianPetersen]

Is the engine intercooled? A lot of older turbo diesels weren't.

Installing an intercooler on a turbo engine that doesn't have one, will make a big difference. It will not make any more power automatically, though - but it will let you increase the fuel delivery from the pump.

 

[winfieldblue]

Thanks for the ideas, I have already replaced the intermediate spring with a slightly stiffer one sourced from a newer pump, but should really try another spring altogether, or even a rod in place of it. Which are the "full load" and "idle" springs? I have been experimenting with the screw and locknut adjuster on the lower side of the pump, my local injection pump repairer told me that it adjusts the rate of injection advance, which is where things are getting a bit confusing.When I rotate the pump for more injection advance I get more low end power and less top end, and vice versa, at the moment I'm running less advance than the factory setting, which really makes me wish that I had a programmable computerised injection set-up, but mechanical it is so I will just have to make the most of it!~ What I would like to understand is why the top end power drops off with more advance, it seems to me that the pressure rise during the first part of the powerstroke is happening way too early, and would therefore be placing unneeded strain on the engines internals. Any ideas on how to modify the pump to get around this? I'm thinking about playing with injector opening pressure settings (they are adjustable injectors), but I'm probably opening a can of worms! I read(red?) on a tech site that the pump can supply enough fuel to make 25 kilowatts per cylinder, so am using this info as a guide to the pumps delivery limit. I have purchased a large intercooler but havn't had the time to fit it yet, but am expecting a noticable gain, as I just drove home from work in sub zero temperatures (-1c) and it went noticeably better than what it usually does!

 

[patprimmer]

-1C in July puts you a fair way south of the equator I expect.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[winfieldblue]

Quote[-1C in July puts you a fair way south of the equator I expect.]unquote..

Yes Pat, down southern Vic. on the great dividing range, 600m. above sea level. While we're talking cold, does air have a lineary expansion rate, if so then why does my diesel engine feel so much stronger on a cold evening?.... wouldn't that indicate unburnt fuel going out the exhaust when the engine is inducting warmer air, through a lack of sufficient oxygen to burn the injected fuel? (this engine has no temperature sensors to adjust mixture/timing).

 

[YvesLLewelyn]

Porting the head and increasing cam lift may be OK but the amount of duration increase must only be slight.
Anything like even a slightly "sporty" cam will drop the cylinder pressure to the point where the engine will be impossible to start or run at low RPM.
Presumably a continuously variable duration system (where the duration increases with RPM) would cure this problem.
Even with such a system the slow rate of burning would probably limit the high RPM power.
The only practical method of really raising a diesel's performance is to increase the boost pressure.

 

[winfieldblue]

Yves, cylinder pressure isn't an issue with this engine, it already comes with a 22:1 compression ratio, add the 4-5 pounds of boost from the blower (at idle speed)to the 22:1 to get a running compression ratio. Sure the static compression ratio might be lower, but I can still start this engine on a 0 deg.c. morning using thick cold vegetable oil for fuel. More modern turbo diesels are more likely to have a 16:1 c.r. from what I have seen, I don't think that duration of the cam is going to turn this engine into a no-starter (especially since it runs glow plugs too).If the inlet valve closed so late in the comp. stroke that the compression ratio was insufficient to create enough heat to light the fuel then the cam timing probably wouldn't be suited to a 4000 rev. redline.

 

[70btdc]

Yes, I agree with Yves, dont bother with the cam duration. In fact dont bother with ANY of the standard engine tuning aspects until you have tuned the pump as the cost per PS is tiny in comparison.

Depends on the application, but the governor springs are attached to the mechanism attached to the main throttle lever inside the pump. Some applications dont have a separate idle spring. When the flyweights move, they compress the springs in order of rate, if you have 3 springs, the softest is idle.

Perhaps what you feel with the advanced timing is the fuel drop off more quickly, rather than an actual top-end reduction in power? Are you rotating the pump the right way? Does it get very noisy at idle with it advanced?

The screw and locknut on the side of the pump with the delivery lines is the main fuelling adjustment, not timing related. It is just moving the main fuel lever start point inside the pump, a fuel offset if you like.

Best get freindly with the pump. They are little works of art, very satisfying to tune when you understand what each part/adjustment does. They share a common body, so parts such as camplates and plungers are usually interchangable, and cheap these days. You could also of course change to a much larger pump that has a simlar nose diamter and taper and start from there if you really want. The Cummins 4BT pumps are particularly well regarded.

The manual is here, enjoy:

http://www.htsuk.plus.com/BOSCH_VE_PUMPS.pdf

(Hope it is OK to paste this link)

 

[winfieldblue]

Great link 70btdc, I will have a play with the pump next! I have had the boost compensator apart, and have adjusted it quite a few times in the past, so am familiar with it's internals, and have advanced and retarded the injection pump from the standard setting so arn't going in totally blind! I can't help but notice that the engine makes more or less the same power from around 1/3rd throttle to full throttle,even though at full throttle I have a faint cloud of black smoke coming out of the exhaust, this has me worried about the injection pumps settings (I hope for the engines sake that it's not injecting way too early), hopefully I can use the manuals info to work out the problem. cheers W.