2.5 petrol rebuild and conversion to EFI thread?

[FridgeFreezer]

4 minutes ago, Gazzar said:

That's really useful, thanks. I presume the injector can cope with the workload.

Injector size is more down to HP than anything and there's a LOT of leeway in all this because you can adjust the fuelling via the laptop.

You'll only hit problems if the injector(s) are way under capacity - typically if they're going to spend more than 80% of the time open at max power they're considered under-sized - or vastly OVER capacity when the amount of fuel that goes in even in the smallest of squirts is too much for a stable idle.

There's a lot of stuff out there written on this sort of thing that is only really relevant to the bleeding-edge race car technology so don't get carried away by it - as long as you can get air & fuel into the thing it'll probably run absolutely fine.

Given the HP, you should have a wide range of small SPI units from eurobox hatchbacks to choose from in the 80-100hp range.

[Gazzar]

I was going to try to use this.

[Bowie69]

Yep, they had injector options I think?If in doubt, go a little bigger.

[=jon=]

I *may* have a throttle body injection unit from a US truck somewhere in the garage - I was going to do a very similar conversion on my old Essex powered 90 but never got round to it. 

I'll have a look tomorrow - if I can find it you are welcome to it...

[Gazzar]

Ummmm. Interested! Thank you.

 

 

 

But I've to confess to slight reservations. . .  as the unit in the Screenshot looks, on paper, to be near perfect.

It's mechanical link, built in TPS, almost series carb shaped. Siemens injector.

Happy to save money, naturally, but if the VWspeedshop unit makes the job, well, just work, it's very tempting.

Is higher flow rate better? Presumably it can be turned down?

Is 80 lb per hour too much?

 

 

[lo-fi]

Some sage advice already. Don't get too hung up on the numbers, but the takeaway from doing the calcs is "longer is better" for this application. Hehe my comments on that diesel manifold being less than ideal.

With the injector, larger isn't always better. You can run into trouble with the injection time at very low loads being so small compared to the time it takes the injector to open and close that you don't get consistent injection. Best to size it for 80% duty cycle at your estimated horsepower, plus a bit of headroom, but don't go too nuts. 

[Bigj66]

That TB looks a nice bit of kit. Do you think you’d get away with retaining the oil bath filter with one of those? Subject to the appropriate adapter pipe work of course.

Looks like it would need a return plumbing in back to the tank too but that’s no biggie.

[Bowie69]

3 hours ago, lo-fi said:

With the injector, larger isn't always better.

Agreed, at this power level the opening times and idle stability are unlikely to be a problem though, assuming you don't start with an injector 300% overspecced.

The largest the vwspeedshop sell is 80lb, which is good for 140bhp on an ancient design of flat four engine. The LR engine is probably equally as inefficient, so likely to be fine.

Next one down is 60lb, good enough for 100bhp, which given the tuning going on here may not quite be enough. What are the 2.5s as stock, 80bhp?

https://vwspeedshop.com/product.php?productid=16854

 

 

[Gazzar]

That's what I needed to know, is the 80 lb ball park ish.

I'll just figure out the throttle side and then order.

 

And, yes, I'll retain the oil bath restriction!

 

[Snagger]

On 3/7/2020 at 4:55 PM, Bowie69 said:

Agreed, at this power level the opening times and idle stability are unlikely to be a problem though, assuming you don't start with an injector 300% overspecced.

The largest the vwspeedshop sell is 80lb, which is good for 140bhp on an ancient design of flat four engine. The LR engine is probably equally as inefficient, so likely to be fine.

Next one down is 60lb, good enough for 100bhp, which given the tuning going on here may not quite be enough. What are the 2.5s as stock, 80bhp?

https://vwspeedshop.com/product.php?productid=16854

 

 

95ish, if I remember correctly.  5mb 2.25 was in the 80s, I think, and the 12J 87bhp and 10J in the 60s.  It’s been a long time since I looked at the figures, mind, so they may be off.

[Gazzar]

Fuelling this requires an injector, and I've almost settled on the universal SPI referred to above.

This should fit on the series manifold, I hope.

I'm going to order the throttle body today, so I was looking at a manifold.

There's a ring pressed into the manifold that if I remove leaves a 45mm hole.

I can file this bigger, to 48mm.

But, the carb had a lot of adapters and insulators, do I need that for the throttle body? Is icing an issue? Heat soaking?

[Gazzar]

Some pics.

 

How can I remove the steel insert pressed into the Manifold? The od is 45mm.

[Bowie69]

Yup, remove the collar. Not sure how but it probably involves a lump hammer and a chisel.

Icing isn't likely to be a particular issue, especially with the hit spot right underneath.

[Gazzar]

The new exhaust manifold doesn't touch the intake.

Strategically placed dents.

[Gazzar]

Quote

 

I'm tempted to just get a lump of alloy and bolt to the body and manifold with countersunk bolts. A 10mm chunk would do the job and be neat. 

Do I need a separate manifold pressure take off? Or could I tee into the vacuum take off?

[FridgeFreezer]

4 minutes ago, Gazzar said:

Do I need a separate manifold pressure take off? Or could I tee into the vacuum take off?

You need to be careful about where you take vacuum from, it needs to be manifold vacuum and not too near the throttle or it distorts the reading.

[Gazzar]

Quote

 

So, the servo take off wouldn't do?

[FridgeFreezer]

17 minutes ago, Gazzar said:

So, the servo take off wouldn't do?

Depends - some of them have one-way valves in them which would confuse matters! On the RV8 I take off from the plenum exactly the same as the servo port though.

[Bigj66]

Could that collar be split with a hacksaw blade and then chiselled out like a spring bush?

I’m looking to go the same way with mine and had some initial thoughts about a machined allit adapter to join the TB to the manifold with gaskets in between.

The intake manifold could be carefully dremmelled out to the correct size just like porting a head.

[Bowie69]

12 hours ago, Gazzar said:

Do I need a separate manifold pressure take off? Or could I tee into the vacuum take off?

Does the throttle body have one?

[Bowie69]

First picture on the site *seems* to show a threaded port for vacuum take off?

https://vwspeedshop.com/product.php?productid=16854

 

Also, think you are right, a 10mm plate of ali bolted through the manifold to manifold bolt holes, drilled and tapped and a hole in the middle to suite the throttle body would work simply and pretty cleanly.

 

[Gazzar]

I never spotted that.

 

I've ordered the throttle, so I can get hands on when it arrives.

I'll break the collar out of the manifold next. 

[Bowie69]

If it is a vacuum take off, and if you get a fluttering signal, having a fuel filter in line helps to flatten the fluctuations.

But cross that bridge when you get there

[Gazzar]

The issue that FF raised? Good to know.

 

[FridgeFreezer]

I can't remember the deets of it but if you're too close to the throttle plate the air rushing past causes very odd readings, sometimes the point the distributor takes vacuum from is not the place you'd connect the MAP sensor takeoff.