Hi everyone, being no expert in tuning I am hoping people may be able to provide their advice...

The image below shows information logged on my AFR gauge, on the road running two gears to 6000rpm with the gear change evident in between. I am running an HIF44 on my supercharged 1275. The AFR is plotted on the top lane and the boost and rpm are both plotted on the bottom lane.



There is also a time line along the top. The blue vertical line shows where the data points were taken, which are written next to the labels (AFR 12.7, 8.4 psi, 4932rpm).

I noticed it takes around 1 second for the AFR to get from 16.5 to 12.7 and during this time the engine is seeing boost and is under load. My questions:
* Is this normal/expected?
* Is it a problem?
* If it needs to be fixed, what would you recommend?
[edit] * Could this just be a time delay in the AFR reading compared to the other data (due to the exhaust taking a while to reach the sensor) and maybe this is just showing the AFR during the gear change, delayed to make it look like it is from when under load?

On a website (here - clicky) testing a supercharged 1275 he notes:



Do you think this could be a problem - that I am reaching the limit of what you'd want an SU to manage?

I should say the car feels like it drives very well. There can be a slight hesitation when you hit full throttle quickly, I'm not sure if that is what is being visualised here?

[edit: also - the tuner said that when he tuned this engine, his AFR gauge was reading about 1 AFR unit richer than mine. So he said that he thinks I should interpret my data as looking leaner than it actually is. I wonder if I need a new sensor or something, not sure]

Thanks all.

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Build thread for Supercharged 1275 1967 Deluxe Resto
Build thread for Mini ute conversion 998cc Turbo

I am not a tuning expert , so caution advised in heeding any info i spruke. My read though is that is all fine if you feel the acceleration is at the level it should be ). my reasons, the rpm increases at the same time as the afr decreases,, so no lag indicating starvation. But what i dont know is should the rpm increase quicker ( steeper curve). As for afr readings, if you have recalibrated and you and tuner are taking reading from same bung etc , could there be slight air getting in when on road as opposed to static?. I would also say i think the tuner has got a pretty good balance ( doesn't dip below 10s and 11s on power and holds at 15 and 16 on idle, but if you wanted to experiment , a couple of runs back to back with say 2 flats change in su settings, would give some idea........ and as for slight hesitation,,, well some engine / su needle combinations/ springs etc are nearly impossible to get aligned all through the rev range so compromise is required. ( if you were running HSs i would suggest dabble in spring combinations and dash pot oil mixs,if you really wanted to explore further)

one thing , i have found on SUs ( not hif though) check afr on long power runs ( ie over 20 seconds) as in two different minis both leaned out considerably, but on short bursts it wasn't evident,, and if you aren't in the habit of flooring it on long straights it may not be an issue at all.

Great build and i hope you are soon satisfied all is well , so you can relax and enjoy your beastie without always worrying.. I also appreciate how you make such efforts to acknowledge and answer all thread contributors a fine example to all forum members Cheers D

Thanks FNQ, that makes sense to me and the car does indeed feel like it is accelerating well.

Re the difference in AFR readings between me and the tuner, I think he was using the one inserted up the end of the exhaust pipe rather than the bung mine is in, but I could be wrong. Also, you mention possibly air coming in...it made me remember that I changed the exhaust since it was tuned, so perhaps that issue has resolved. When cold, the slip joints in the current setup rattle (very annoying) and leak - the two pipes from the extractors to the collector. I have bought some sealant and also one of those Permatex epoxy bandages to help hold it together tightly when cold.

I certainly am enjoying the car already, it starts first go even on the coldest mornings, it drives very well and is an absolute pleasure and joy to drive, I'm so happy with it. The things I'm doing now are just fine tuning type stuff rather than wholesale changes.

I'm checking at every point that things are where they should be and seek advice where I'm not sure. This is the first time I have looked at the AFR log data, and I'm looking at it to setup my water/meth properly. Basically you know you have the right nozzle/volume of water/meth when there is a .5 to .7 AFR drop when comparing no water/meth and when it is switched on. Then any timing changes (and fuelling changes if required) are made from there. I will do some long power runs and check for lean condition - thanks for the heads up.

The other little niggles are re-bleeding the clutch as it seems to reduce effectiveness over time, and the rattly exhaust mentioned above. But I think I'll always find things to work on on this car Thanks for the nice comments about the build and the forum comments - I do appreciate people taking the time to comment or provide advice so I think it's important to acknowledge everyone. Plus I like it I used to live in Cairns for about 2 years btw, bloody beautiful part of the world. I worked at the Woolshed in Shields street town in the late 90s for much of the time I was there...ah those are some interesting memories

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Build thread for Supercharged 1275 1967 Deluxe Resto
Build thread for Mini ute conversion 998cc Turbo

yep - it's the lack of an accelerator pump - mine did the same so I injected it...

Another person I know with the same blower kit as you has 2 needles, one for street and one for competition... I assume it's for the same sort of reasons

The biggest problem though is that the fuel is coming in the wrong side of the blower, you can't cool it. I wonder what intake temperatures you're getting, mine would cruise at 103°, when I punched it, the water spray would bring it down to around 75°, but still too much

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did I tell you that I won a trophy?

Interesting, it does seem like the lack of accelerator pump is key. When you say the fuel is coming in on the wrong side of the blower, what do you mean? A plus side of suck through is that it does cool the blower and the carby operates normally (under vacuum instead of under pressure like blow through). Similarly all the advice seemed to point to water injection before the blower rather than after it.

I see the MCM guys found that fuel injection pre blower also resulted in more even distribution across the cylinders, so even with injection I was thinking I'd still inject pre blower. I'll have to have another look at your setup.

I have been interested in IATs myself just for interest sake. All the research seems to indicate that much of the cooling effect of water/meth takes place in the cylinder rather than in the inlet track, so it would only tell half of the story. But it would be interesting none the less to see what difference the spray makes.

Sent from my Nexus 6P using Tapatalk

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Build thread for Supercharged 1275 1967 Deluxe Resto
Build thread for Mini ute conversion 998cc Turbo

My clubbie is currently running a 1330 with 1.5 su and MS3 for ign, Inovative o2 and a heavy footed driver.

5 deg morning run to work shows 14 - 15 on o2 ............15 deg run home shows 12.5 - 14

It does have a problem with the damper oil dissapearing which will then give me a 16 - 18 on opening the throttle, yes Iknow that my slip joints all leak which will further throw out the figures

Can't wait till the new power unit is ready to go in .......yes the exhaust leaks will be sorted by that stage}

my afr's are not constant up and down .5 - 1 point while driving under most conditions.

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120bhp with 450kg just fun waiting to happen

We were prob. drunk when we set it up last and thought this will be a good idea

Wow that's a difference in timing depending on the weather

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Build thread for Supercharged 1275 1967 Deluxe Resto
Build thread for Mini ute conversion 998cc Turbo

Re mcm, they commented in the "first drive" video that they had to move the injectors post supercharger to get it running correctly.

5 deg / 15 deg = outside temp Morbo ......I'm amazed how much the denser air changes things .... bring on the self tuning efi

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120bhp with 450kg just fun waiting to happen

We were prob. drunk when we set it up last and thought this will be a good idea

Siloban - oh I must have remembered wrong! thanks.

Justfangin - whoops I meant to type "Wow that's a difference in timing depending on the weather" !

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Build thread for Supercharged 1275 1967 Deluxe Resto
Build thread for Mini ute conversion 998cc Turbo

Ha okay I just realised I did it again, I forgot to change it to "Wow that's a difference in AFR depending on the weather". I must have spend too much time with the acetone.

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Build thread for Supercharged 1275 1967 Deluxe Resto
Build thread for Mini ute conversion 998cc Turbo