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MG Midget and Sprite Technical - first ever dyno test

I couldnt believe my luck, on the way to the hard ware shop on Friday and noticed a new garage with the word Dyno on the front.
I stopped to have a look and found that its a guy who's into Drag racing and started this garage to work on Drag cars.
He showed me one with a huge turbo on it and a 3 litre nissan engine which he said gets over 1000 hp....he's running 2.5 bar boost and has a water cooled intercooler...

He has just installed a new Dynojet system he imported from America.

So i asked if i could use it,"no problem just turn up whenever you want, 1000baht a test"

So, here are my results:
Datsun A14 engine, std except for K&N filter and tubular header.
RWHP 57.7 @5170 rpm
Max torque 98.39 @ 3080rpm

The top green line is the Torque, and the bottom one the HP..

Can see me getting to know this guy well.....


Andy Phillips (frankenfrog)

Hi Andy it is always good to be able to quantify things. How many runs did you do to bed everything in, will the guy let you do lots of runs?
I assume the torque is in NM? Maybe if you set it to lbs ft next time it will look more like we are used to seeing where torque and bhp crossover at 5250 rpm.

Peter
Peter Burgess Tuning

Hi Peter,
We did 3 runs, all showed figures within 0.3 hp and 0.5 Torque.
Yes, Torque in Nm.

From a converter i found online, 57 rwhp calculates back to 76 hp at flywheel.

The A14, according to the Datsun website, in standard trim gives 80hp and 77 ft lbs (104 nm)

So it looks like i am a little bit down on the book.
next job is to look at the timing.

We had an AF meter running and it varied between 13 and 15.5 during the run with it getting leaner as the revs increased, so maybe a slightly larger jet in the secondary choke.
Its a downdraught hitachi carb, similar to a Weber 32/36 DGAV.

Does the diff ratio make any difference to the figures you get ?

Andy
Andy Phillips (frankenfrog)

Hi Andy

Yes you will get differences with different diffs especially if you are doing inertia test runs. Don't fall for the mistake of thinking you can add a percentage for losses to give flywheel power as you cannot. Tyre speed, footprint, pressure and compound all make a big difference to power losses. Can you get a coast down loss figure? Not necessarily actual transmission losses but correct ball park and allows comparison from car to car. We look for around 14 losses from midget transmission for road cars.

You need to get friendly with him so you can experiment with timing and fuelling changes. Timing makes quite a difference to AFR figures so you need a softly softly approach whereby you get timing somewhere near and fuelling then play around near those settings. having said that the fuelling may well be very weak with a carb jetted for air filter and then run on K&Ns.If you have say a 120 secondary main try going to a 130 and rerun the car.

Peter
Peter Burgess Tuning

S if this was a duel SU carb how do you account for that on a dyno particularly if we are talking the very fine tuned adjustments

Just for kicks when I did my 10 gauge consel ... I did 2 AFR meters with a senor in the 2 outside down pipes about 4 inches from the top of the header... i had intended to add a 3rd sensor to the middle on a switch so I could do a side by side comparison of all 3 down pipes

I know... Its over the top, buts just more for fun then actual reality... I like to respond you never know during a parking lot guymkana when you might need to make an adjustment buring that 37 sec. Run....haha
Prop and the Blackhole Midget

lots of things to read up on now...

and need to find somewhere to buy jets for this old carb from hitachi....
Andy Phillips (frankenfrog)

AF meter was inserted in the exhaust, however i had, just a few weeks ago fitted one myself.
I welded a connecter in the exhaust manifold where all the pipes join to be one.

Once the car was running i got the same AF readings on both gauges.
Andy Phillips (frankenfrog)

Hi Prop

Let us know what sort of readings you get and we can fine tune those carbies! We are finding a couple of flats can make a difference if we are 'almost' there.

Andy

We have drills from 0.4 mm to 2.00 mm in 0.05 mm increments. If we need to reduce jets we solder and then drill.

Peter
Peter Burgess Tuning

Took my built up engine back to the same place today.
So this is the same Nissan A14 engine but with these mods:


A15 crank (increased throw by 5mm)
77mm Mazda UC pistons (increased diameter by 1mm)
Camtech cams 621 cam(0.266" lift, 264deg)
Dual valve springs
Nodiz crankfired ignition (wasted spark)
C/R 10.5:1 (from memory, need to check that)
38DGAS Weber carb on std manifold
Tubular headers 38mm dia
Standard Nissan 8 port aluminium head with 37mm intake and 30mm exh valves.


max PS 92.46(91.2HP)@5950 rpm ATW (previously 57.7PS,56.9HP)
max torque 128.38NM(94lb/ft) at 4500 rpm(previously 98.39NM/72 lb/ft)

This is using the supplied curve that came with the ignition, i couldnt get the bluetooth connection to work to fiddle with the curve.

Very pleased with the result.

Car has 3.7 diff and will pull from 1000 in 4th gear no problem.


Andy Phillips (frankenfrog)

should make a very capable road car :-)
I guess you are mostly unlocking the benefits of the 8 port head - what does the capacity work out to?
davidsmith

77 dia pistons and 82 crank throw.
1527cc.
Andy Phillips (frankenfrog)

Well done Andy, well worth all that hard work you must be really pleased.
Peter
Peter Burgess Tuning

Thanks Peter and David,
Yes very pleased with the result and it makes a big difference to the car.
I've had the Vizard big yellow book for 30 years now and read it cover to cover many times. Only now had the time and resources to actually try it myself.
Andy Phillips (frankenfrog)

This thread was discussed between 26/10/2015 and 03/02/2017

MG Midget and Sprite Technical index

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