I'm getting ready to do the 749 Syclone/Typhoon ECM swap on my 91Z because I would like more control over the tuning of my F/I setup. More control than the hardcoded Vortech FMU will give me anyway. Current setup is a stock L98 (SD) w/ a Vortech S-Trim (V1) @ 6psi. Planning a motor rebuild soon and I plan to up the boost. The goal is around 500rwhp @ 14.5 psi. I've been reading alot on the Syclone/Typhoon websites for info on the 749 ECM, and I came across this quote. It deals with MAF vs SD and the 749 ECM, and I wanted to know what you guys think. From what I can tell SD will be the better setup for me because I will be burning a custom chip anyway. But before I start the swap, I wanted to know what you guys thought about MAF vs SD when using a 749 ECM?

From the SyTyArchives.Com ...

A mass air flow system can take into account different modifications (cam/heads etc) that are done to increase power, as the sensor can ‘see’ the additional air going into the engine and will add fuel as necessary. This is as long as the sensor is not maxed out, as mass air flow sensors have a limit to their readings. The speed density system is not as forgiving in its calibrations, as the calibration is usually set for a stock system. When major changes are performed on the engine, the computer reads the same manifold pressure levels as a stock engine, and the same amount of fuel is delivered, when more or less is really needed. So in this respect, a mass air flow system is better. It also does not use a restrictive sensor to meter air, as the mass air flow systems do. As I mentioned before, however, the mass air flow systems can be maxed out, so in a higher performance system, the speed density is the winner (and this is the main reason speed density is used on aftermarket ECM systems). In the syty application, however, this benefit did not exist.....

The last sentace seems to say that it would be better to swap to MAF. What do you guys think? I think SD would be better if you were going to burn a custom chip. MAF would be better if you're running a premade chip from some other company. Does that sound right to you guys? I should stay SD right? Or am I missing something completely? Just had to check ...

Thanks!!

 

The 749 is only capable of speed density with the $58 mask. And for your application with the ability to change the calibration on the eprom there is no need for mass air flow. The mustang guys run into the maxing out the MAF problem all the time with forced induction.

 

MAF systems tend to be more forgiving to airflow modifications. And since it measures actual amount of incoming air, it can deliver a correct amount of fuel. Up til you hit the max resolution of the code, in TPI is 255 grams per sec airflow, or the max volume ofair thru the unit, MAF is better.

Speed Density is more dependant on "known" values and makes adjustments from there. So once you make a change and "X" value is now 30% greater than the ECM is told,the ECM cannot correct completly for the change.

This is how I understand the differences, someone please correct me if I am mistaken....

Since you are going to have a unique combination of parts, you will have to tune either system to get the best performance.

 

I've spent a fair amount of time with the SD, and MAF issues on a Turbo motor.

The inherit flaw with MAF on a non N/A application is that you can have sudden changes in VE. While a N/A engine might struggle to get to 100% VE, and decent S/C or T/C design with instantly cross that at 1-2 PSI, and when it does, you need a huge increase in fuel. What GM did on the GNs, is deliberatly pegged the MAF and basically went Alpha-N mode at the higher boost levels. And while the stock cal was good, the second you changed the motor and moved the *knee* over point of the VE, the cal went to dodo. Dodo being relative.

With a *Normal* MAF setup you can have several areas that flow the same amount of air, but do to the differences in VE at those areas, you'll wind up to lean or two rich at some points.

The best running I got a MAF system was when I added a boost sensing *patch* to it, and it made all the difference.

So much so that I'm now running a full MAP system.

For S/C, T/C applications, MAP wins. MAF with boost sensing is second, but a distant second at that.
HTH

 

BTW, the way GM handles the Boost enrichment is VERY CLEVER.
VERY.
So clever I'm reluctant to even mention it since the aftermarket guys still haven't seen the total genius to how GM did it, yet.

If you look at even the Gen7 stuff, and then read what I've already wrote, and then read thru the Sy code, it's amazing.

What's a real giggle is when you can run all these different strategies and then pick an choise. Not being egosectric, just trying to explain things, and get others to try some of this stuff.

 

So you're saying I should switch from Speed Density to MAP if I use the Sy/Ty 749 ECM? Keep in mind now that I will be burning a custom chip for my motor setup and max boost will be 14.5 psi (1 bar). Lemme know what you think. Thanks man!!

CrazyH

 

I got the 749 ECM for $100 by the way. Now I'm looking to buy a laptop from my friend for $75 (IBM P2 300mhz, 128 ram, Win98). Then I'll need to buy the rest of the stuff and I can get crackin. Thanks for the info you guys!!!

 

The 749 is only used in MAP applications.
There's alot of info., about this sort of thing in the archives, doing a search might give you answers to guestions you hadn't thought of yet.

 

Its true!! Answers to questions I havent even thought of yet. So many of them ... I actually did alot of searching, but when I found that quote on the Syclone/Typhoon website I wanted to know what you guys thought.

Now I'm looking into the Holley 950 ECM because it will come with the StealthRam I'm getting anyway. Looks like with some upgrades I can run a wideband 02 sensor and I'll get everything I want as far as datalogging and tunability. It would replace the 730 ECM I have now. The 749 ECM is the most cost effective solution, but I dont know if it will be a good solution for me (time, reliability, and other concerns). We'll see how it goes.

Thanks for all your input guys!!! I appreciate it.

 

I've decided that the Holley DFI is too expensive. I mean, its worth the money and all, but why pay that much when I can do it for less than 1/2 the price. Besides its kinda sounds like fun learning how to burn custom EPROMS. I think I'll be more 'in tune' with my car and really understand what my EFI system is doing. So My 749 ECM will be here in the mail pretty soon. Ended up being $135 including shipping (749 ECM from a wrecked 92 Syclone). Now I'm deciding on which intake to use, a LT1 intake or a StealthRam.

I wanted to thank you guys for all the info you've given me. I'm reading the Sy/Ty websites looking at the mods they do to the ECM to make more power. Considering the potential of my supercharger (20 psi), I'm thinking about planning ahead and doing this with a 3 bar map sensor from the start. So it'll be $58 code and a 749 ECM.

I'm still kind of confused on the Speed Density vs MAP thing. Yenko is telling me the 740 with $58 code can only do SD. You're saying ditch Speed Density and goto MAP. And I thought U had to have a MAP sensor for both Speed Density and MAF. Ah I just need to do more searches I guess. hehe

 

speed density=MAP, so the 749 $58 combo is only speed density/MAP. MAF or mass air flow is a completely different animal than speed density/MAP. Does that clear everything up for you?

 

Yes now it all makes sense. Thanks guys!