Webers or EFI

[PyroJim]

Evening All,
As some of you may have noticed I have had a few items for sale recently including a tuned engine and weber carbs etc, as well as the shell that they were fitted to.

An interesting side effect of trying to sell these items is that the person who built up the car and engine noticed it for sale on ebay and got in touch with the history of the build.

To cut a long story short, he had the car/engine/webers rolling road tuned and it produced just shy of 170bhp at the wheels, which was nice to have confirmed. I now know that the engine has too many good parts fitted to sell so I have decided to keep it for my other sprint.

If you are still with me my dilemma is: Should I keep the webers and run it that way or sell the webers and the weber manifold and fit EFi onto a standard manifold (as this will be a cheaper option that throttle bodies onto the weber manifold and easier to use the manifold pressure for the brake servo etc).

If I went EFi onto the standard manifold then I was planning to use twin MGF throttle bodies mounted onto adapter plates which would also hold the injectors. But will the gas flow through a standard inlet manifold be good enough for the potential power output of the engine? I quite enjoy technical challenges so the EFi route sounds interesting but just wondered what peoples opinions were?

[PaulB]

Why not keep the weber manifold and use a DCOE compatible throttle body like Jenvey?
That is what I am contemplating.

[sprint95m]

I am in the process of gathering the necessary bits and pieces to EFI an 1850.
As part of this process I have been doing research to try and understand what works best.
My intention is to try to make improvements to the general running of the car with economy in mind
(hoping for 50mpg or something near to that at least.)

My understanding is that for best power results you want a manifold with separate equal runners, which rules in the Weber manifold
and rules out the Sprint one. These runners should be as long as practical.

For power you ideally want one throttle body per runner. Injectors should be as close as possible to the inlet valves.


There is an Australian based forum user, Stag76, who has successfully EFI'd a Sprint engine (in a TR7).
Paulsprint (in the UK) is getting close to completing a Sprint EFI.


As for my own project, I have made some progress, obtaining a TR7 EFI inlet manifold (from Californa( being the biggest step, so far.)
I am concerned about the ethanol content of unleaded. With that in mind I have obtained a 2006 Fiesta tank (with a suitable integral pump).



I am looking forward to seeing how you get on,

[GrahamFountain]

will the gas flow through a standard inlet manifold be good enough for the potential power output of the engine?

You should get at least some idea from what power you can get with a pair of 2" (51 mm) HS8s on a modified std manifold? But I haven't done that yet, so I don't have much of a clue.

Whatever the figure is, you should be able to get a little more power than that, because you're not using the pressure drop over the step in the carb venturi to pull in the fuel or the partial vacuum in the inlet to hold the dashpot piston up. So the EFI setup should give less restriction in the airflow. But I still wouldn't think it's the 210-220 hp that 170 at the wheels must mean.

I guess it depends if you're just after the most power you can get or have an eye on cost. If it's the former, then I would agree with Ian. But the saving in the MGF throttle bodies, even the 52 mm Trophy ones, over the Webber replacement ones does look huge. Big enough to be worth a try?

Graham

[PyroJim]

If I use the weber manifold then I have the advantage of obtaining maximum power but as this is going to be primarily a road car I want the low end drivability to be good. This can be done with the Jenvey throttle bodies that have the injector port built in (as opposed to injectors down by the inlet valve) but this is a very expensive path. Also does anyone have any experience of using the inlet vacuum from a weber manifold for the brake servo etc. ? Also a steady (i.e. non pulsing inlet manifold pressure would be useful for the MAP reading to be used by the ECU).

I could possibly machine up some adapters so that I can mount the MGF throttle bodies onto the weber manifold?

It would be good to know what power people have achieved using the standard inlet manifold with 2" SUs on?

[GrahamFountain]

does anyone have any experience of using the inlet vacuum from a Webber manifold for the brake servo etc. ?

I have used both the take off for the servo and the one for the vacuum advance. The servo was driving a pair of big princess callipers on the front of a TR7 and 4 speed slaves on the back. Seemed to work fine - possibly a little too well, considering that was the one I was in when I committed that unforgivable sin of "stopping too quickly" in front of a Discovery.

As to using 4 of the MGF bodies (48 mm?) on the 4 choke manifold, I can't see why that would cause the same problems as you get with using carbs that are too large a diameter, as the lower air velocity has no impact on drawing in the fuel. Might have some effect on mixing.

Any more details on what/how/where you're thinking for the injectors with the std manifold? I like the simplicity of SU HSs, but they're not noted for their fuel economy. I went from HS6s to Dellorto 45 ADDHEs with a huge difference to the power and responsiveness, but bugger all effect on the average fuel consumption on the daily drive. And I've already got a std manifold bored out to 2".

Graham

[Carledo]

If you have a problem with getting enough vacuum to drive a servo efficiently (you shouldn't really, my injected Vauxhall engine drives the Sprint servo on my Toledo just fine) you could consider an alternator driven vac pump such as the ones fitted to Isuzu Diesel powered Vauxhall Combo vans, the alternator is a similar bolt fitting pattern to a Triumph one, however the pump will need an oil feed and return, not TOO difficult to engineer.

Steve

[tony g]

Electric vac pumps are quite common on VW now. Just another option.

Tony

[Carledo]

If I use the weber manifold then I have the advantage of obtaining maximum power but as this is going to be primarily a road car I want the low end drivability to be good. This can be done with the Jenvey throttle bodies that have the injector port built in (as opposed to injectors down by the inlet valve) but this is a very expensive path. Also does anyone have any experience of using the inlet vacuum from a weber manifold for the brake servo etc. ? Also a steady (i.e. non pulsing inlet manifold pressure would be useful for the MAP reading to be used by the ECU).

I could possibly machine up some adapters so that I can mount the MGF throttle bodies onto the weber manifold?

It would be good to know what power people have achieved using the standard inlet manifold with 2" SUs on?

Bottom end performance is much more a matter of cam choice (and to a lesser extent exhaust design) but a good EFi map will be much more efficient AND easier to accomplish than anything that can be done with carbs of whatever brand. I would (and do) use a MAF sensor rather than MAP and a single large throttle body with a plenum. it's ultimately much cheaper and, though not quite as good for ultimate power, is still streets ahead of carbs.

Steve

[GrahamFountain]

Keeping the component costs down is good, so the fewer throttle bodies the better. But I would be interested in keeping the engineering to a min as well. So two bodies on a std manifold would sound like a better idea to me than a single one remote from it.

But as a matter of interest, how does one connect the throttle cable to those Jenvey throttle bodies - they don't look to take either the linkages for Webbers or Dellortos.

Graham

[Carledo]

Keeping the component costs down is good, so the fewer throttle bodies the better. But I would be interested in keeping the engineering to a min as well. So two bodies on a std manifold would sound like a better idea to me than a single one remote from it.

But as a matter of interest, how does one connect the throttle cable to those Jenvey throttle bodies - they don't look to take either the linkages for Webbers or Dellortos.

Graham

Clive Senior has Jenveys on his Ford powered Spitfire, perhaps he'll put a pic up! I learned very recently that Jenveys factory is only a few miles from me, I must go up and have a prowl one day!

Steve

[PyroJim]

I should have been a bit clearer on the inlet vacuum issues. This is all based on research as I have not tried it yet. It sounds from you guys that running the servo wont be an issue. As the Weber manifold has individual pipes for each cylinder then the pressure in each one pulses with the operation of its inlet valves. From what I have read this can cause issues with the EFi ECU. In theory the EFi can run off a throttle position sensor alone but this is a bit of a compromise. I have been wondering if a can connect all 4 intakes together to a small accumulator and put the MAP sensor there (a kind of crude balance pipe).

It looks like the MGF throttle bodies will not fit onto the Weber manifold so one other option there is to use bike throttle bodies, I will look into this one.

I have considered the idea of one large throttle body with a homemade plenum chamber but I do not like the idea of fabricating a plenum chamber, I don't generally like the look of homemade ones (hope that doesn't offend anyone it is just my personal preference).

If the standard inlet could realise the power potential then I would like that route as if I design adapter plates that hold the injectors and allow MGF throttle bodies to bolt straight on then this would make it easier for anyone one else wanting to fuel inject their sprint.

Then I have to decide whether to go for Megasquirt or Omex 600. At the moment I am swaying towards Megasquirt as I quite like the DIY challenge of it all.

[PyroJim]

Sorry Graham - to answer your question on injectors on the standard manifold.

My initial idea is to design an adapter plate that sits between the MGF throttle body and the manifold. It will be about 30mm thick so to allow the injectors to be mounted into the plate itself. This would mean that the manifold would not need to be altered. I have to look into this to see if I could use 2 injectors (1 in each plate) or whether each adapter plate would have to hold two injectors.

Still at the thinking stage at the moment as my Sprints are in Bridgnorth and I am in Cornwall. I will rectify this if I get more garage space down here

[sprint95m]

viewtopic.php?f=4&t=16859&hilit=megasquirt
Please have a look at this thread. Stag76's advice and observations are very informative.

Paul has posted a photo of his set up HERE on my thread.




Have you considered an Emerald K6?
http://www.emeraldm3d.com/k6-ecu-info-and-specification



Reference a single throttle body and plenum, this is what I am going to do.
I intend using a Sprint air box as the basis for this because it has a decent dome shape.

Ideally a plenum should have a volume of between 1 and 2 times engine capacity.
Lower size helps low down torque, larger gives top end power.
A Sprint air box is 4.1 litres, so needs reducing for my 1850. I'll cut a section from it in such a way to reduce its volume and make it tapered
away from the single throttle body.
I'll probably make bellmouths from steel tube employing a socket as a former, heat and a hammer.



Originally I was intending to go EFI next winter, but since I have already sourced the fuel tank/pump and an inlet manifold,
once I get a fuel rail sorted, there is nothing stopping me now really.....



Ian.

[AlanH]

Others with much greater knowledge may correct me but I think that if you implement throttle body injection in the way that you are intending, performance gains would be severely limited.

Given the greater complexity of fitting EFI, it could be that Webers , perhaps with a 123 dizzy, are a better option.