S-10 Forum banner
721 - 740 of 759 Posts

·
Horsepower Addict
Joined
·
326 Posts
Thats a lot of timing at high RPM & somewhat lean.

My take...
13.1 AFR at 100kpa is lean even for a modern engine designed with precise cylinder airflow balance (i.e. an LS1), but most others work better around 12.8 at the leanest.
The unequal length of intake runners will play havoc & at that throttle opening it needs to quickly transition into boost enrichment anyway.
Above that I typically stay around 11.5:1 (or richer) over 5lb boost & carry your 3700rpm timing (or less) into the higher rpm ranges... your chamber design will dictate your limits.

Also those tables do not have a bunch of resolution, meaning it interpolates between them without a lot of adjustment options.
With that said, 12.8:1 at 83 & 100kpa, & maybe 12:1 or 11.5:1 at 124kpa, & 11.5:1 above.

Hope I'm not overstepping my bounds, but I do not want to see you hurt anything.
It's easier to sneak up on a tune than to change blown head gaskets & crushed pistons.

I can show you some carnage from tunes much more conservative than above.
 

·
Registered
1991 Irregular Cab Short-Short Bed
Joined
·
644 Posts
Discussion Starter · #725 ·
Thats a lot of timing at high RPM & somewhat lean.

My take...
13.1 AFR at 100kpa is lean even for a modern engine designed with precise cylinder airflow balance (i.e. an LS1), but most others work better around 12.8 at the leanest.
The unequal length of intake runners will play havoc & at that throttle opening it needs to quickly transition into boost enrichment anyway.
Above that I typically stay around 11.5:1 (or richer) over 5lb boost & carry your 3700rpm timing (or less) into the higher rpm ranges... your chamber design will dictate your limits.

Also those tables do not have a bunch of resolution, meaning it interpolates between them without a lot of adjustment options.
With that said, 12.8:1 at 83 & 100kpa, & maybe 12:1 or 11.5:1 at 124kpa, & 11.5:1 above.

Hope I'm not overstepping my bounds, but I do not want to see you hurt anything.
It's easier to sneak up on a tune than to change blown head gaskets & crushed pistons.

I can show you some carnage from tunes much more conservative than above.
You are not overstepping. I appreciate any feedback I can get!
 

·
Horsepower Addict
Joined
·
326 Posts
Are you able to adjust the table size / steps independent of the MAP sensor range? i.e. 3 bar sensor with the boost table only going to 200KPA
I've tuned many different EFI systems but never the one you are using.

What is your max boost & range of the MAP sensor?
What is the cam size?
Base Compression?
Max RPM?

I'll be glad to help you out.
 

·
Registered
1991 Irregular Cab Short-Short Bed
Joined
·
644 Posts
Discussion Starter · #727 · (Edited)
Are you able to adjust the table size / steps independent of the MAP sensor range? i.e. 3 bar sensor with the boost table only going to 200KPA
I've tuned many different EFI systems but never the one you are using.

What is your max boost & range of the MAP sensor?
What is the cam size?
Base Compression?
Max RPM?

I'll be glad to help you out.
I can't change the resolution or the size of the tables. 16x16 for timing (and VE table) and 12x12 for AFR. I can edit the steps which I did to make roughly 16% increments in the timing table and 22% increments in the AFR table. Maybe that's the wrong approach. I could change the figures for RPM columns and kPa rows if needed.

The Megasquirt has an on-board 4 bar MAP sensor. I'm figuring on max boost of around 25 PSI but not not trying to go anywhere near there until I'm confident of the tune. It will be plenty fast with 10-15 PSI boost.
I'll attach the cam card at the bottom.
Static compression is 7.9:1
I don't plan on spinning it over 6000.


The intake runners are pretty close to equal but also pretty short.
 

·
Horsepower Addict
Joined
·
326 Posts
Guessing an idle speed of approx 900-1000rpm.
It will like a lot of idle timing with low compression.

It is easier to start out simple so you can easily see what it likes instead of making the theoretical ideal table to start with.
Initially change areas of the VE table instead of individual cells to keep the table smooth & flowing.

Get your part throttle/cruise VE table worked out, then move to timing in this area.
Once you get the timing close, you may have to do the VE again & then go back to timing.

Once you are happy with drivability, then cautiously move into the low boost ranges.
You can start out as low as your wastegate will allow & work your way up.
Your VE curve will stay somewhat consistent as boost goes up, but will be affected by the reduced airflow as the exhaust backpressure increases.
I usually start around 11:1 air/fuel & low timing to build a safe VE table, then gradually lean it out & then add timing after fuel is correct for more power.

Attached is what I would target as a decent starting point.
Ideal timing could be +/- 5 degrees either way depending on the combustion chamber efficiency.... as I have no experience with your particular engine.
If it was a GM SBC, BBC or LS I could give you something very good... my experience with a Slant 6 is limited to tune-ups on my grandmothers Volare from many years ago.
For example, a typical boosted LS is in the 14 deg range on pump fuel & a Small Block Chevy closer to 20 under boost. NA is normally about 12 deg more.
I'm guessing at 20 deg max for your application, but suggest you start much lower & increase at your own risk/based on any specific boosted data you can find.
Severely retarded timing can alter fueling as the mixture is still burning in the exhaust & rich mixtures crave more timing.

Assumptions were made that the last field on the table will be extended as it goes beyond the table limits, hence the reason to concentrate on the lower ranges with air/fuel tables.
 

Attachments

·
Registered
1991 Irregular Cab Short-Short Bed
Joined
·
644 Posts
Discussion Starter · #731 ·
I got the first start today. It fired right up and idled just like it's supposed to.


Then I dicked around with it trying to raise the idle to be more friendly with the new cam.
Until I fouled all the spark plugs...
Auto part Gas Automotive tire Metal Nickel


Still, that's great progress. I have an issue that the wideband isn't sending good data. It's just stuck on 10.3. Hopefully that's just a ground or wiring connection problem.
 

·
Horsepower Addict
Joined
·
326 Posts
Those are some very long reach plugs for a turbo application... I would be concerned with having enough heat transfer to keep the electrodes cool under boost.

You can pull at least 10% from the idle VE table & try again. You will likely do this 2 or 3 times.
What is the lowest your wideband will read?
 

·
Registered
1991 Irregular Cab Short-Short Bed
Joined
·
644 Posts
Discussion Starter · #736 ·
Those are some very long reach plugs for a turbo application... I would be concerned with having enough heat transfer to keep the electrodes cool under boost.

You can pull at least 10% from the idle VE table & try again. You will likely do this 2 or 3 times.
What is the lowest your wideband will read?
Those are the stock plugs. I'm a long way from running it under any boost. Before I get there I'll find some more appropriate spark plugs.
It's a linear wideband from 14point7. The controller is supposed to read from 10 (0v) to 20 (5v).

I found the problem with getting wideband data. One of the pins had pushed out of a connector at the ECU. Easy fix and now I'm getting good AFR data.

I temporarily tweaked the settings on the idle control to let it idle high for cam break-in. While it was doing that I practiced editing the VE table in the high idle area just to see the effect. It's really easy to make 0.1 adjustments to the AFR. So far it seems the Megasquirt generated VE table isn't far off.

I've got some more testing to do before running it again. I didn't finish setting up the fan control so I need to do that. Once the cam has had it's allotted amount of running in I can start tuning the idle for real
 
721 - 740 of 759 Posts
Top