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MG Midget and Sprite Technical - EFI 1500 Updates

Hi Folks, techy post warning! ;-)

Car is finally and properly back on the road after my dramas last summer! Yipee!

Since said meltdown the big change in engine spec is the tubular 4-1 manifold I designed and fabricated, plus a rebuild of the rest of the exhaust, albeit in the same size (1.75") as before. The new manifold replaced a Spitfire MK3 cast manifold, a short, cast iron 4-1 type thing. In theory the new manifold is tuned for a peak around 5100 rpm.

As I drive the car, the ECU is able to "self learn" the fuel requirements based on wideband lambda readings. At full throttle it aims to achieve a lambda of 12.5. The below data/graph shows the ECU fuelling readings before and after the manifold swap. What the numbers mean is kind of irrelevant, they are just a multiplier to calculate the injector opening time. So the volume of fuel injected is proportional to the number.

Cutting to the chase, the ECU is now adding an additional ~8% fuel between 4000 and 5500 rpm. It's all a bit hypothetical without a rolling road but fuel = power (if it is being burnt correctly), so I could assume approx. +8% power from putting a proper manifold on.

Last time it was on a rolling road the engine was on carbs and a dizzy with a Piper 270 cam, and clocked 101 flywheel hp.

The "before" readings in the attached table were for the engine with fuel injection and a Piper 285 cam. Which from data logs. I estimated at ~103 or 104hp. The bigger cam being restricted by the old exhaust.

But now add 8% onto 103 = 111hp! Happy days! I wanted to crack 110 and I think I have done it.

As said, it's all hypothetical of course, one day I will get on a rolling road to check my maths. But it is certainly lively coming off roundabouts in second! :-D I forgot how much fun driving my midget was. I was laughing and wooping all the way home last night! :-)

Cheers,
Malc.



Malcolm

Edit...

As mentioned, the tabulated numbers are just a factor to calculate the injector opening time. It is purely coincidental that they are similar to my estimated power output.

Cheers,
Malc.
Malcolm

It's looking good Malc. A lot of hard work gone into it and with the added bonus of it being great fun to drive.
Any images of your new manifold in situ?
Jeremy MkIII

Nice one Malc--looks like you're on the money there, hypothetically as you say but that should translate to a similar practical result as well you'd thinkk-
The old exhaust sure was holding it back by the looks of it, one little thing i'd like to ask is what is controlling ignition advance , is the pcm setting that via a knock sensor or are you loading it manually---would you have a similar map of that on full throttle-?
Cheers
willy
William Revit

Jeremy, yes of course will get some pictures this evening.

Willy, igntion is a wasted spark system using a VW coil pack triggered from the ECU. The advance curve/map is manually set and simply a copy of how the dizzy was set before the conversion, with 28 degs total @ 3000 or something RPM.

Malc.
Malcolm

All good Malc-
I'd just looked at your fuel requirement map and noticed the slight dip at that 4600 mark and thought it might be ignition related but if it's all in at 3000 ish then I doubt that to be a cause, thinking further about it, it's not necessarily a horsepower dip, it may well be working quite well there and an actual power curve might show differently
OR
It may well be proof that your exhaust design is working exceptionally well in that 4900 rpm area that you worked it out for and that in itself has bumped the curve in your fuel map up in that area instead of being low at 4600

Don't worry it's just pedantic me thinking out loud, I'm sure it's fine

willy
William Revit

I wouldn't get too wrapped up in the detail Willy. It does need a bit more messing with and then smoothing out.

Malc.
Malcolm

Some pics Jeremy, sorry, not the sharpest images. My phone camera is awful!





Malcolm

Coil pack


Malcolm

wow, you've made it look like a very modern engine Malc, impressive. The 4 branch manifold looks an especially neat fabrication.
You should patent/copyright your modifications!
Jeremy MkIII

Agreed Jeremy---impressive
William Revit

Malc,
That looks great. Do you think a little fatter on the rest of the exhaust will reduce back pressure and allow it flow a little better? Might even squeeze another couple of horses out of it :O)

Best of....
MGmike
M McAndrew

It does look the dog's. Very nice.

64 thousand dollar question.

How much has it cost? 😉
anamnesis

Went out for another run on Friday, seems it still wants to add a smidge more fuel. The grey line on the graph is where I am now, at about 11% more at the top end. The gains are now so good I am starting to question them! ha ha.

Whilst it has been ages since I drove it in it's previous incarnation, but it does seem more eagar at the top end. It used to get pretty out of breath by 5500, but now I have kit the soft limiter (currently set at 5600) a couple of times already... oops! That has not happened before.

Need to get booked in with Pete Burgess...

Anam... you really want to know? I keep spreadsheets of what I spend so could easily tot it all up.

Cheers,
Malc.



Malcolm

Malcolm, What is the exhaust manifold wrapped in? Is it for heat shielding? All impressive btw!
Bill Bretherton

Do you use Megasquirt?
a.o. arnold

Looking good Malc, that's a better shaped curve than the earlier one
PeterB will get interested in this for sure---How far from his w/shop are you
A little question--if i can please,
How far down the exhaust have you wrapped it-----

willy
William Revit

Bill, it is "titanium" exhaust wrap. I don't know what is titanium about it, but it is the poshest sort of wrap!

A.O, I am using a Speeduino ECU. It's a cheaper alternative, but uses the same TunerStudio software for tuning.

Willy, just the manifold pipes within the engine bay. Trying to keep bay temps down and avoid the inlet manifold becoming a massive glowing heat sink!! The collector and main exhaust under the car is unwrapped.

It's a couple of hours for me to get to Peter Bs. But I have run on his rollers before so I know results each time are comparable.

Cheers,
Malc.
Malcolm

Malc,
was your runs with the previous or present rollers, I can't remember when they changed but it was a while ago. Each run will have minor differences then there's the fuel changes over the years. How many decimal places do you put on your figures.

I'm getting terrible OCD with those HT leads, can you not remap them to fire in strict order to twin them out to double-V orientation.

I can see you have caught the concours bug.
Nigel Atkins

Hi Nigel,

I am with you on the HT leads, but there isn't a tidier way to do it. The coil is effectivly split down the middle, so 1&4 must come from one side and 2&3 the other. I could turn the coil through 90 degrees, but then that and the wiring to the coil doesn't look right!

Been in touch with the good Dr. Burgess. He confirmed updates for his RR mean it measures slightly lower power at the wheels and greater losses overall. It was 2019 I was last there. Wow, time flies.

Happy spridgeting!
Malc.
Malcolm

Malc,
you could have straight connectors off the coil, longer leads and two combed runs, you could do a technical drawing but nothing beats actual installation so buy a reel of HT lead and connectors and boots and we'll have it looking good. It would also add 2hp!

Well IIRC the 'new' rollers go back a bit more than 2019 so pretty comparable.

Yellow HT leads might give a bit more power, I like your markings but can't approve of your cheapness to leave the lead needing the most cable-ties, true engineer though. I had red mini-cable-ties on blue HT leads, a confirmed 2.5hp increase.

Cheers.

Nigel Atkins

This thread was discussed between 14/04/2022 and 22/04/2022

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