Feedback on Megasquirt Tune?

[Rojoryu]

Can anyone check out my tables and provide feedback? This is a built bottom end, 8.5-1 CR, 775cc injectors, Precision 5831 turbo. I blew the head gasket the first time on the attached tables at 20 PSI on the street, dyno tuned at a local shop, stock head gasket and ARPs. Most recently had the head rebuild, decked (block included), o’ringed, welded channels, ARP and stock HG and it blew again in the dyno at 25psi (don't have those tables.) I'm curious if the timing or fuel is causing it to chew up head gaskets. Thanks in advance.

[82eye]

what are you using for head gaskets ? maybe time for a cometic or other mls gasket.

[Rojoryu]

what are you using for head gaskets ? maybe time for a cometic or other mls gasket.

Stock HG the first time it blew and stock HG this most recent time. With the block o'ringed I should be able to use an OEM gasket with much more than 25psi from what I have read.

[82eye]

Stock HG the first time it blew and stock HG this most recent time. With the block o'ringed I should be able to use an OEM gasket with much more than 25psi from what I have read.

there's a couple boosted guys that i hope will chime in. they'll know better.
busting a head gasket isn't that uncommon on even a stock m20. there's a definite consensus that the available choices aren't as quality as the originals anymore. if i went through a couple boosted i'd look at copper or mls just as a standard. at least that way you'll know it will hold those levels.

edit : if it went again you'd know it was an issue with a warped head and not the gasket.

[Panici]

Let's start with the basics.

Did you/the shop verify base timing matches the megasquirt when in "fixed" timing mode. If not, your timing table doesn't mean squat.

Do you have the "incorporate AFR target" option turned on? If not, the AFR table is only for reference and not used in the fueling calculations.
Note that if you turn this option on, you'll need to retune your VE table.
With the option on, the VE table will more-closely resemble the real volumetric efficiency of the engine.

Either way, the VE table has to be tuned properly to match the engine.
How do your logs look? Is the wideband AFR following the target AFR?


If that AFR table is real and in-use, it is too lean under boost for an engine you care about IMO.
If you have an uneven injector or a bad tank of gas, there is no room for error and you'll melt a cylinder.


Two points of data:
--On my turbo miata (for which I have a spare engine) I run high 11s (11.5-11.9) at 10psi.

--On my M52B28 E30, I run 11.5 just getting into boost, down to 11.0 at 160kpa.


I would be running into the 10s at 20psi, you're still at 11.5.
Extra fuel should help cool things down and prevent detonation. If you don't have knock sensors to pull timing, you want to run on the safe side.


There are other "gotchas" as well like acceleration enrichment, Timing pull for IATs, etc.

[Rojoryu]

Do you have the "incorporate AFR target" option turned on? If not, the AFR table is only for reference and not used in the fueling calculations.
Note that if you turn this option on, you'll need to retune your VE table.
With the option on, the VE table will more-closely resemble the real volumetric efficiency of the engine.


If that AFR table is real and in-use, it is too lean under boost for an engine you care about IMO.
If you have an uneven injector or a bad tank of gas, there is no room for error and you'll melt a cylinder.


Two points of data:
--On my turbo miata (for which I have a spare engine) I run high 11s (11.5-11.9) at 10psi.

--On my M52B28 E30, I run 11.5 just getting into boost, down to 11.0 at 160kpa.

Extra fuel should help cool things down and prevent detonation. If you don't have knock sensors to pull timing, you want to run on the safe side.

I can confirm when I get back to my other computer at home, but I am 99.9% sure that AFR table is being used. Again, I did not tune this myself. I am considering switching tuners or learning how to. Oddly enough, based on smell and sight alone I would have guessed it was too rich. It blows a moderate amount of black smoke at WOT and smells rich too.

[Panici]

I can confirm when I get back to my other computer at home, but I am 99.9% sure that AFR table is being used. Again, I did not tune this myself. I am considering switching tuners or learning how to. Oddly enough, based on smell and sight alone I would have guessed it was too rich. It blows a moderate amount of black smoke at WOT and smells rich too.

Note: I added a few points to my post above with an edit.


Let me know what you find.

I learned to tune on my E30 when it was N/A, and now have tuned two boosted engines.
If you take things slowly and make sure you understand all the concepts, it's not rocket science.


As an aside, I would not expect any black smoke on a WOT run. Perhaps a puff on an upshift if the acceleration enrichment is really aggressive.

How do the plugs look after a WOT run?

Have the injectors been flow bench tested for balance?

[Rojoryu]

I pulled the plugs several times and they always appeared healthy. But I will admit I never did a WOT pull then immediately shut it down to check the plugs. Injectors were bench flowed after the first HG blew. Here is a dyno run with lambda if that helps identify anything with fueling.

[Panici]

Here is a dyno run with lambda if that helps identify anything with fueling.

Not seeing lambda on there?

[Rojoryu]

Not seeing lambda on there?

I attached the wrong one. Just edited it.

[Dj Buttchug]

OP What is your required fuel? Im wondering why in the meat of boost your adding 122+ % fuel. That seems over duty to me.

[Rojoryu]

OP What is your required fuel? Im wondering why in the meat of boost your adding 122% fuel. That seems over duty to me.

I'm running 93 octane.

[Dj Buttchug]

I'm running 93 octane.

What is the required total amount of fuel you are putting at the engine? If you go into engine constants/ fuel I want to know what the required fuel number is.

[Rojoryu]

What is the required total amount of fuel you are putting at the engine? If you go into engine constants/ fuel I want to know what the required fuel number is.

Ahhhh, I misunderstood the question. I can check once I'm back home.

[Panici]

I attached the wrong one. Just edited it.

Yikes, I see 0.8 to ~0.83 lambda (at peak torque) in that chart which corresponds to 11.8 to ~12.2 AFR.

WAY too lean at 20psi IMO. Like I said, I'd be down in the 10s at that boost level.

Was the dyno operator/tuner wearing DET cans (assuming you don't have a knock sensor?)


I could see running that lean on a racecar application where fuel consumption is a concern. But I'd want both EGT & knock sensors to do it.