Bit of an update - I bought a daily driver, so now I can play without the pressure of worrying about having to do jobs that only take 2 days!
Got the rest of my trumpets, relocated the brake booster tap and been working converting the Megasquirt ECU to run Alpha-N which everyone seems to recommend for ITB’s. Alpha-N uses Throttle Position Sensor (TPS) instead of manifold pressure (MAP) as the engine load for the fuel and spark tables. As a starting point I am converting my MAP based tables into TPS, I plan to do some road tuning and then dyno tune at a later stage.
Tunerstudio is great - plug in your laptop and it uses the signal from the wideband to tune the car for you - you can get it very close just by driving around, and then a trip to the dyno for the last few %.
I took it for drive around the block, it drove surprising well with my MAP to TPS converted fuel and spark tables. Nice ITB growl - it gets quite a bit louder at WOT.
Only issue so far was an electrical gremlin with the Megasquirt ECU and the MTX-L wideband sensor, which meant I had to redo some of my ECU wiring. I had to make sure this was right as this is the most important thing for getting the fuel maps dialed in.
Will post some videos later when I have had a chance to do some more tuning.
great progress! and good job on making the transition to Alpha-N so easily! that can be a real ball ache at times
looking forward to seeing (and hearing!!) some video of it being driven in anger… mine’s due for a trip to the dyno very soon, in preparating for the next season of racing… we really need to make a plan to meet up at an event this year!
Not sure if this is useful to anyone else - but this is hard found knowledge I don’t mind sharing!
When setting up ITB’s with Alpha N (TPS load) - there are big changes in fueling at small throttle increments, and from what I have read (and experienced) it pays to set up your fuel table with many increments at the smaller throttle openings. If you don’t do this when you open the throttle the AFR will end up being lean or rich during the transition and give poor throttle response or stumbling. Particularly not nice on your daily around town.
MAP based systems (like the standard Charade ECU) for ITBs are not recommended, the main reason being that often with an ITB setup the intake pressure will be the same for varying throttle angles and give poor fueling.
Megasquirt S1 has 12x12 fuel and spark tables, and uses raw ADC (voltage data from the TPS) which I have converted into %TPS opening. I set my tables up with the following increments - see below.
TPS%
ADC
0
56
2
59
5
64
7
67
10
72
15
80
25
97
40
121
60
154
80
187
90
203
100
221
The more advanced MS2 and MS3 use % and have bigger tables - lucky you if you have one of these over the MS1.
Here are my fuel, spark and AFR target tables (this is a reasonable road tune, the fuel map still needs some work in some infrequently used places):
Some other pointers - make sure you get the right sized bodies for your engine. For my car (1.6 HD) I got 38mm diameter GSXR600 bodies. I had read many reports of these being used in Peugeot 106 1600 motors. Smaller bodies will give more low down power and better response. The other thing to get right is the correct intake length - too short will rob you off low and mid range power. The intake length is measured from the back of the intake valve to entry of the intake trumpet. Also be aware that just running the ITB with no trumpet will normally result in too short an intake length and poor mid range power.
For my car I am running a 425mm intake length, which is quite long. Somewhere between 350 and 400mm seems to work for most people. There are a number of online calculators and charts, but the best way to get this right is to experiment with a dyno.
some good info there, Jason! Don’t suppose you made allowance for a spacer plate to add or remove runner length for tuning?
acceleration enrichment is worth a mention, too… not sure what ability you have to adjust this on the MS computers but it’s fairly common to see a 250% accel enrich for a 10% throttle opening over a 0.02s period (enrichment is proportional to the rate of throttle opening with respect to time) this plays a huge role in smooth transitions of throttle, particularly at low rpm
your target AFR at cruise is quite lean… have you tried using stoich at cruise loads for comparison? also, if you don’t mind me asking, why the 13.0 AFR band at high load?
this is the target table I use… different engine of course and note the Y-axis is pointing in the opposite direction to yours… and it’s in lambda (1.00 being 14.7AFR)… but you’ll get the picture https://photos.app.goo.gl/R5tasTHiYSrAZcS37
Not much gets past you Tim! We are into proper car nerd stuff now.
For the AFR’s would you believe if it if I said fuel economy? Probably not much of a consideration in your turbo race car, but for my daily driver it mattered. Thanks for your lambda table, I will see what I can use.
MS does have accel enrichment, funnily enough the settings I had with the old plenum manifold have worked quite well with the ITB’s. MS just adds a pulse width figure to the injector time depending on the rate of change of the TPS. On MS1 it is constant at all rpms, which means it is a bit of a compromise.
A spacer plate, I did not design one, but I will be thinking about how to graft an extra 1" in to see what effect it has - it would be good swap it in and out when I get it dynoed.
Had a great week tuning the car - it drives almost like stock now - at least until you put your foot down and the bellow from the under the bonnet reminds you that there are ITBs in there.
Finished it off with an Autocross event at an old BloKart track - was great fun. Didn’t set any records, but I wasn’t the slowest either.
I do think the tumpets are a bit long- it pulls really well between 3500 and 6500 rpm, which is great around town and on the autocross event, but shorter would be better for a track day on a long circuit. I am looking at a design with trumpets around 40mm shorter (tuned length will then be 385mm instead of 425mm it is now)
Great work, and it sounds very nice! You’ve done an excellent job, makes me want to make a set of ITB’s but my knowledge with CAD and ecu tuning is lacking any other plans with the car, maybe some headers?
The car has headers - they are a modified set of Detomaso headers. It’s reasonably quiet as I have it setup for street use.
Don’t worry about a lack of knowledge - I knew nothing about fuel injection or engine management 7 years ago - I learnt from reading Megasquirt documentation on how it all works.
I could probably do with some of your knowledge on the suspension side of things. Apart from a few of urethane bushes and some front camber bolts the car is stock. Felt like I had alot of understeer on Sunday. There was another guy there in a 205 1.9 Gti, he set one of the fastest times - just shows what a well sorted small fwd setup can do.
I’ve been reading up on your mods. Very nice buddy!!
I am doing a head swap this weekend on a Detomatso. Will take some pics later.
Have compared the std injectors to Mazda Familia Efini 1.8 BP DOHC and they’e exactly the same fitment and ohms rating. Flow rates are std Daihatsu Denso 195500-2040 186cc/min. Mazda 1.8 Denso 195500-2180 256cc/min.
1 of the Dai injectors has a damaged cap which wouldn’t have been helping.
Will try the Mazda injectors to see how it goes. I hope they won’t be to rich. The engine isn’t std by any means now lol. The head has been extensively ported and polished and the cam is a hot rally/race spec. Hopefully it’ll still idle nicely. Bottom end has been freshened and new high comp pistons fitted as well so it should go alright.
The goal is to at least hit triple digits on the dyno. Factory specs are a load of bollocks. This car was making 40hp less than what they’re supposed to, according to specs. It better make close to factory now!
Yeah I would have loved to have dropped a stock Detomaso motor into my car and got 92kw at the wheels! With all my mods I might crack 90kw at the wheels if I am lucky.
The guy who dynoed my car has had many 1.6 MX5’s (factory rated at 86kw or 115hp) only put out around 95hp - it seems it is quite normal for a car to dyno less than the manufactures claim.
If you are running an ECU that allows you to adjust fueling the Mazda BP injectors will work well - mine idles good, probably somewhere around 70% duty cycle at WOT. You may find a rally spec cam needs less fuel at idle and at low rpm compared to stock, and at the mid range and top end it will need more. An wideband in the exhaust with an AFR gauge is a great tool - I run an Innovate MTX-L.
Out of interest what cam are you running? Which valve springs? Did you do a cam lift vs crank diagram? Be great if you have - and any pics of your porting. There is not that much info on there motors - I do my best to share what I find.
and good job on making the transition to Alpha-N so easily! that can be a real ball ache at times
I’m thinking maybe more like Taupo motorsport park 
any other plans with the car, maybe some headers?