[BuddyHelps]

Long time listener, first time caller. I'm new to EFI tuning but have been reading up and trying to learn all I can. Just finishing up my build and I'm currently trying to build a base tune to get the car safely derivable but there is one thing that I am very confused about.

My basic combo in a 1990GT with a 331, trick flow top end, anderson N71 cam, longtubes etc. It has 30# injectors, C&L MAF, A9L and I am tuning with a TweecerRT.

The question has to do with what MAF to use. I have always read that "calibrated" MAFs are bad because they trick the engine into thinking there is less air coming into the engine than there really is and can cause funny things with timing curves, open loop, etc. I have both the 19# and 30# sample tubes for the C&L but am not sure which way I should go. I read somewhere to use a 19# MAF and just change the injector settings in the tune and that using a calibrated MAF will just piss off any real tuner but also read that it really doesn't matter as long as you have the correct MAF transfer data for the "calibrated" MAF so that the engine has a true reading of air volume. I noticed that Caledit has data for the 30#(purple) tube but not the 19#(gold) tube. So which one am I better starting off with and why? I have the 19# tube in there now but part of me thinks I should put the 30# tube back in so I could drive it home on the factory tune in case anything ever went haywire with the tweecer/tune. Any insight from much more experienced tuners is appreciated.

[cgrey8]

...Long time listener, first time caller...

A student of the institute at the EIB?

...I have always read that "calibrated" MAFs are bad because they trick the engine into thinking there is less air coming into the engine than there really is and can cause funny things with timing curves, open loop, etc...

It's not that calibrated MAFs are bad. It's relying on the calibrated aspect of the MAF in an effort to use the stock tune that's bad.

...I have both the 19# and 30# sample tubes for the C&L but am not sure which way I should go...

Without any other info, I'd say go with the 30# tube and put the corresponding MAF curve for your airframe and tube into your tune as the MAF curve. Presumably the engine would max out 19# injectors which is why you upgraded the injectors to 30s. The same would be true if you ran the 19# tube. The 30# tube extends the flow range of the airframe to allow a higher mass/volume of air to pass before the electronics hit their high-limit to represent the flow.

...I read somewhere to use a 19# MAF and just change the injector settings in the tune and that using a calibrated MAF will just piss off any real tuner...

That's either a mis-interpretation of what you read, not the entire story, or what you read was just wrong. Don't do that.

...but also read that it really doesn't matter as long as you have the correct MAF transfer data for the "calibrated" MAF so that the engine has a true reading of air volume...

That's correct.

...I noticed that Caledit has data for the 30#(purple) tube but not the 19#(gold) tube. So which one am I better starting off with and why?...

Personally, I wouldn't trust anything in CalEdit. What's important is that you get the C&L-published curve for your airframe with a purple tube. Put that into your tune OR verify that what CalEdit has for that combination is correct. See the problem is C&L makes multiple different diameter airframes. I believe the smallest is 73mm. They go right on up in various increments to 80-something. The combination of airframe and tube together give a specific curve. So the purple tube in a 73mm airframe is going to produce a different curve than the same purple tube in a 76mm airframe. You need to find out the curve for your combination. If CalEdit is listing a curve for a C&L with purple tube but isn't making reference to the airframe's diameter, then you don't know if that's the curve for your combination or not.

[BuddyHelps]

I have the 76mm with the cast aluminum elbow setup. The data in CalEdit is for the "76mm C&L with 55mm electronics and purple tube" so it matches my setup. I too wonder how close the CalEdit data is but unfortunately I am not to the point of being able to figure it out on my own and I cant seem to find any data out on the interwebs for these things. I have searched high and low for contact information on C&L but have come up dry. I have also heard that they are notoriously bad about giving out data on their products for whatever reason but its all mostly older posts I am finding.

It sounds like the thing to do is to put the 30#tube back in and start off with the data in CalEdit and see how close it is. I will probably get it dyno tuned at some point but I want to get it driveable before that to break it in and sort out any small issues it might have so its as close to 100% as possible before I take it to the tuners. Dont want him to have to waste time on stupid things that I should already have sorted. I appreciate the feedback.

[cgrey8]

Download and install EEC Analyzer. Even un registered, it has a number of calculators and MAF curves that you can reference. It has your combination as well:

Code: Select all

16.000	2038.171
5.000	2038.171
4.800	1630.410
4.600	1375.678
4.300	1080.075
4.200	1018.927
4.000	892.195
3.800	786.373
3.600	686.889
3.400	595.325
3.200	513.899
3.000	438.810
2.800	372.593
2.600	318.732
2.400	261.702
2.200	214.811
2.000	177.108
1.800	140.673
1.600	113.109
1.400	87.762
1.200	69.386
1.000	47.208
.800	34.218
.700	28.832
.600	24.079
.500	20.594
.000	.000