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Turbocharging a 5MB petrol?


twodoorgaz

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Hi folks. This has been touched on a while ago - in this thread for one.

I'm awaiting my house purchase to go through, wherein I'll get a big garage and will finally be able to start my build.

I have virtually all the parts I need to build my hybrid drivetrain

  • 2.5 17H Petrol block with a mixture of series and metric ancillaries to dress it up to look like a 2.25
  • Stumpy R380 (050A ratios 1st-4th and a TD5 5th gear)
  • Series Transfer box (ashcroft kit)
  • A nice strong 4.7 diff from MSV8 (yet to get)
  • 24spline rear shafts
  • Heystee front discs
  • Stage 1 stub axles, CVs and shafts at the front

 

Now the above drivetrain will handle plenty more power than even a tuned 17H will make. And I keep looking at the turbo parts from a 19J or TDI and thinking... why not?

 

A turbo'd petrol would surely have a far, far lower compression ratio than a similar diesel (19/20:1) so I can't help but feel that a turbo'd 5MB petrol could be a very tough little unit - as I'm building the engine from the parts I've sourced (once machined) I could also easily swap out some more bits to get the pick of the LR 4-pot crop.

 

If a diesel intake manifold could be used then surely it would be a nut and bolt swap. Not looking to set the world alight, but anything north of 100BHP feels spritely in a Series and I think that even a stock build could reach 120+BHP relatively easily without the pitfalls of the 19J. Yes I could fit a V8, TD or TDI but this is more about having a nice little LR project.

 

Any input would be very welcome.

Edited by twodoorgaz
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Go for it, subscribed, popcorn at the ready.

With 8:1 or 7:1 compression you could get quite high pressures in there without detonation, the thing I'd be more worried about is the ring end gap, melting pistons and blowing head gaskets....

I seem to remember asking the question about the tdi manifold and it was no bueno, same for 19J, but how hard can it be? Proof of concept is a few bits of plate, some tube, and some time.

 

But in all cases, the very best of luck to you!

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As a minimum, you would need variable timing control.  Really EFI and EDIC would be the safest.  You need to retard timing with the boost and enrich the mixture.  EGTs are much higher with turbo petrols than diesels, so it is easy to completely kill the engine.

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I'd assumed carbs and dizzy was doomed already! Yes, you need spark control and either efi or hours and hours tuning a carb to sort of run right turbocharged, before realising it will never be and fit efi anyways.

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Lowering the compression-ratio is a mug's game - it will only result in lower overall thermal-efficiency/poorer-combustion/higher-emissions for the majority of the time - when the turbo's not blowing hard.

Better to stick with a base compression-ratio that's good-to-go with modern fuels (let's say 9.5:1) and then use knock-sensors to calm things down if the turbo's blowing hard and you get instantaneous pinking.

[You ideally need one knock-sensor per cylinder, and the processor-power to knock-back the timing for each cylinder the next-time-round spark after it's knocked]

To be honest, I'd see if you can find a 2-litre Discovery "MPi" and steal its engine/electronics - they were strangely unloved but actually had a higher top-speed than the similar-era V8 Discos! 135BHP at 6000RPM might not suit everybody, but if you knew how to drive one properly [like modern cars there's a rev-limiter there to tell you when you should go for the next gear...] they could be rather fun.

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I wonder if the compressor is a smarter choice? Something of an mini cooper, perhaps? Turbo petrols used be a bit bi polar back in the late 80s. 

I'm watching with interest, as I've a 2.5 p with acr head to go into the light weight.

I've a variety of manifolds in the workshop from TDi 200s if you want measurements.

 

G.

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21 hours ago, Tanuki said:

Lowering the compression-ratio is a mug's game - it will only result in lower overall thermal-efficiency/poorer-combustion/higher-emissions for the majority of the time - when the turbo's not blowing hard.

Really, I was on about the stock compression ratio which I couldn't remember, if it is higher, yes leave well alone unless over 10!

A draw through carb on a supercharger is way less work and plumbing though.

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Reply 1-of-2 "Existing plan and parts"

 

Thanks Guys - it will be a very slow process here, and might end up going nowhere but I'll keep up the thread. If I can't get to a sensible plan for forced induction, I will stick to plan A which is to build it up as a 2.25 5MB-lookalike using the parts as follows:

  • 17H bottom end, including flywheel housing and oil filter (Got)
  • 901-serial SIII (8:1 but imperial) head, timing cover, sump, thermostat, mounts, alternator bracket, etc (Got)
  • Webber 32/34 DMTL carb and inlet/exhaust manifolds (Got)
  • Steve Parker off-the-shelf exhaust system for the 2.5p into a SWB Series (Need)
  • oil bath air filter from a 2.6 6-cyl (slightly higher CFM, but looks stock) (Got)
  • custom cast aluminium plenum to allow standard carb elbow fit vertically to the later carb (to make)
  • Single pulley, part number ERC5349 (Got)
  • Metric starting handle crank dog (Need)
  • Complete cable throttle assembly from a Stage 1 V8 (Got)
  • Standard 90/110 2.5 petrol throttle cable (Got)

The above plan is in the bag. But as I have a drivetrain that will comfortably handle anything a 2.5 petrol can throw at it - even with forced induction. So I can focus exclusively on the engine.

I've built a fair few Series Land Rovers now, but have always outsourced the engine build. For this project, building the engine myself is the part I am most looking forward to - a new engine crane, numerous measuring tools and Rick Voegelin's rather wonderful book on Engine Blueprinting is standing by.

So, going through my existing engine parts in the garage, I already have:

  • 17H block with flywheel, flywheel housing and oil filter housing. It currently has a double crank pulley and a bracket on the front, which I think is a power steering pump bracket.
  • A 17H single groove crank pulley, part number ERC5349
  • A 17H inlet/exhaust manifold with heat shield
  • Two Webber 32/34 DMTL carbs - one from a 2.25 and one from a 2.5
  • Accelerator cable

from a '901' Series III petrol engine...

  • Sump
  • 8:1 head (will be recon'd to 9:1, U/L and 17H spec valves)
  • Rocker cover
  • Side fill oil tube and baffle
  • Rocker cover
  • Dipstick (I can straighten and re-use the metric dipstick tube from the 17H)
  • Timing cover
  • Water pump
  • Fan and pulley
  • Thermostat housing
  • Engine mounts
  • Rocker assembly, timing assembly and a big heap of fasteners
  • An inlet/exhaust manifold and Zenith 36IV carb (won't be using this)

from a 2.6 6-cyl series

  • oil bath air filter (will be fitted into a dropped battery tray from a 4-cyl).

from a 2.6 6-cyl Santana

  • A 38IV Zenith Carb (was planning on using this but couldn't get a set of manifolds that would suit the 2.5 petrol)

from a 3.5 Stage 1 V8

  • Complete cable throttle assembly

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Reply 2-of-2 "other parts in the eBay parts bin and works available"

 

So, lets look at what we have access to via eBay:

 

From any 2.5 diesel

  • Forged crank (its the same part number as the 17H petrol, but I'm told that from the factory the petrol ones were cast not forged)

From 19J Turbo Diesels:

  • Inlet and exhaust manifold
  • Garrett T2 Turbo
  • Block - which I think is similar to the 17H but strengthened
  • Pistons/Rods

From a 200 or 300TDI

  • Block - could be very interesting if I could use a diesel block as long as it was a direct fit with the correct oil ways etc
  • Inlet and exhaust manifold (300TDI only - I'm not going to try and track-down a 200TDI defender one)
  • Garrett T25 Turbo
  • Pistons/Rods

From a Mini Cooper S

  • Eaton M45 Teflon Supercharger.

From a Jeep Wrangler 2.5

  • Inlet manifold with a nice throttle body or multi-pint injection. If I go MJ, the plan would be to have the LR manifold modified to take Jeep components cos I like them.

 

In terms of additional things:

 

  • Machining - I have two machine shops lined up and also live quite close to ACR. I'd prefer to just get the machining done and assemble myself to keep the costs down.
  • Balancing - overkill on a low-rev land rover, but I'm doing it anyway as the cost of having all the rotating components balanced is peanuts (<£100).
  • Casting - I play with a bit of aluminium casting, so I can make simple parts and have them machined. I'd struggle with a manifold as it needs cores which I haven't pulled-off yet, but simple castings are easy.
  • MJ/MS - I'll definitely be going MJ, but open to MS too.

 

One further note:

  • it has to retain a chain driven timing setup. Its my one line in the sand as it makes the installation that bit more pretty than pushing the crank pulley and fan noses out.
Edited by twodoorgaz
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Early ideas:

As I'm not married to the block I have (and its quite valuable), the temptation is to go directly to a 2/300 TDI block which had already had the benefit of LR's learnings from the 19J issues (resulting in cylinder block cracking and crankshaft bearing failures until a redesign of the block and crank bearings in 1988). Q: can a turbo diesel block be changed to petrol spec as I understand that there were differences on oil pathways?

The TDI crank could be retained.

I would guess that I could then use all the same ancillaries from the SIII I had planned to use (sump, timing cover, bracketed etc)

Head - I have a choice of 7:1, 8:1 (standard) or 9:1 (ACR). Q: Would forced induction place additional stresses on the head, or are they all much of a muchness?

Pistons - no idea. Surely these are going to need a different shape. It would be phenomenal if the TDI ones turned out to be ideal for this as I could use a complete TDI bottom end. But the 2.5 petrol ones were specific to this unit, so doubt I'd get that lucky.

 

 

 

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17H and 19J may have slight oilway variations - the 19J and 200Tdi had the turbo oil feed and return but the 17H didn't, and the diesels ack the timing system lubrication system, but this can probably be sorted quite easily.  The 200tdi, 12J and 19J all share the same crank and cam shafts.  Not sure if they fit the 17H timing case and pulleys, but you could compare side by side if you have them.  Tdi pistons have large bowls in the crown that will render them useless for the 17H, but 19J pistons may work; their "v" is far shallower and would have less impact on CR and gas flow

I'm not sure your gearing is going to work well with R380 and the rest standard SIII ratios, unless you meant HRTC by "Aschroft kit".  5th gear is considerably lower than 4th with overdrive, so you'll need something else to step it up or you'll be revving the nuts off the engine most of the time.

Sounds like an interesting project.  I have no idea about fitting the turbo or how to sort the fuelling with a turbo bolted on, but look forward to seeing it.

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I'll try and rake out my Allan Allard book on turbocharging for you and have a look through for some info on a few of your questions. 

A few thoughts:

No problem using an NA head for forced induction. I've turbo'd a fair few NA lumps. 

If you're not looking to go mad with boost (bit pointless on a T25 anyway!), aim for 8.5-9:1 compression. Much lower and you're just dropping efficiency. 

Forged stuff from diesel obviously fantastic, you may even get be able to get the crowns machined to hit the right CR once you've worked out what head to use. An adult at a decent engine shop will be able to tell you what's possible or not. 

Timing/fueling: Tricky setting up a carb to run ~9.5:1 under boost, then dial back to 14:1 cruising so you're not dumping fuel in for no reason, but not impossible. Red90 is right on the money that timing should retard as boost increases too - this is often ignored. Can be done on a standard dizzy with clever use of push/pull vacuum advance/retard. Either way is easy with EFI. But where's the fun in that? ;)

I have a vague recollection of reading about being wary of using diesel turbos for draw through petrol apps due to lacking some extra seals at the cold end, but I'll have to get back to you on that.

The conservative cam timing/duration on the petrol block should suit a turbo app well, but you might find a diesel cam a bit too restrictive. Whether they're swappable between blocks, I don't know?

Great project, I'll be following with interest! 

EDIT: Just saw your MS thread, so ignore comments on carb/dizzy :)

Edited by lo-fi
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13 hours ago, lo-fi said:

Timing/fueling: Tricky setting up a carb to run ~9.5:1 under boost, then dial back to 14:1 cruising so you're not dumping fuel in for no reason, but not impossible.

11.5:1 or similar, surely? 9.5:1 is VERY rich...

BTW - Mini Supercharger may be too small for a 2.5 - I think it will run out of puff and not be able to shift enough air to be useful...

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True, it is pretty rich, though I've found that older turbo cars often run that low on their standard tune. Modern stuff dials it back quite a bit closer to what you've quoted, of course, but with far more sophisticated management systems and knock sensing. Better safe than knocking! You can always refine it later and see how it likes going a bit leaner. Some will, some won't :) Finding out is half the fun on a project like this!

 

 

 

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