I currently have a 355 in my car that is carburated, the engine has the following setup: 9.5:1 compression, fully ported and polished 487X casting heads with 2.02/1.60 undercut valves, Comp Cams xtreme energy 268H cam 224/230 duration @ .050" and .477/.480 lift with a 110 LSA, 1.5:1 roller rockers, 1 5/8" full length headers with a full dual 2.5" exhaust system. The engine made 260 horse at the wheels though a 700R4 with far from optimal timing settings and while spinning a mechanical fan. This was with a street avenger 670CFM carb and an Edelbrock perfomer RPM intake. I want to switch to EFI for better driveability and better mileage since this is my daily driver, so I picked up one of John's converted LT1 intakes and ported it to match my heads. My question is I have two options to control this setup, either Megasquirt or a 165 ECM and MAF (I have a 165 ECM and a MAF sensor and harness from an 1986 vette laying around). I'm on a budget, and am fairly new to EFI so I'd like to know what you all think would be the best way to go. If I go megasquirt I have a couple questions, I have a new billet conventional mechanical advance HEI distributor that I can use (since I clearenced and welded the back of the LT1 intake to clear) so I don't need megasquirt 2. However MS 1 doesn't control an IAC motor, is there a way to tune around this so the IAC can be deleted or just left closed all the time (I'm using a TPI throttle body)? I can't see how the fast idle will work with no IAC. If I go with the 165 ECM is it worth trying to get the car going on the stock tune and go from there or will my combo need a chip change right off the bat? Thanks for any help.

 

There are many IFs and BUTs,
If you go with MAF and stock tables, it should run good enough to begin tuning - IF YOU HAVE STOCK FLOWRATE INJECTORS (or close to it - 22 lb/hr stock) and run the code from 1989 - $6E, because you have no cold start injector. In fact, probably pretty well, with some accel enrich tuning, but if you do have 22 lb/hr injectors, you won't have enough fuel flow at high RPMs and full throttle. Another BUT, you'll have to use a stock electronic distributor, and will want the knock sensor and knock module.

You can pick up an 89 $6E memcal (chip cluster thing - super easy to change) for cheap (ebay, or classifieds here). But I'd recommend getting something to burn chips with. My only experience is with Moates Autoprom - go to moates.net. But there are other more budget oriented burners available. With MAF, it'll run pretty well with just changing the injector constants (for bigger injectors) and turning off VATS. There's also an army of experts about this on the DIY Prom board here.

If you go aftermarket (I'm a fuel injection engineer for an aftermarket company, btw), you'd better get a wideband meter to tune with - LM1 from innovate motorsports is $350, and a MUST have, even if carbed. And an hour or two on a dyno can save so much energy, and is a lot safer than road tuning.

If you get an ECU that can't control idle speed, you can adjust the throttle blades to hold your desired RPM, but I'm not sure how you'll get the IAC closed (could block it off, or remove it and wiggle the pintle out a few steps at a time and reinstall it until it's closed enough). Of course, your cold idle speed may be a tad low, which can be compensated by either holding the throttle open with your foot, or living with a tad bit higher warm idle speed.

Downsides of Aftermarket - no quick replacements, fewer features = little less drivability, fewer experts. Upside, simpler, don't have to defeat certain features for different applications, don't require as many inputs.

What method of torque converter clutch lockup are you using? And do you have a vehicle speed sensor for the tranny? Do you have a park/neutral switch in your shifter?

I'm leaning towards aftermarket ecu if you don't have a vehicle setup that is close to factory already. You could have it up and running in a weekend vs a few weeks of parts scrounging, and information seeking.

Either way, factor in some money for a wideband meter, you will NOT regret it.

Good Luck.

 

Thanks for your reply, currently I have my own custom made torque converter lockup kit. I used a pressure switch in the 4th gear circuit that is wired through the brake switch and a vacuum switch. It works great, if I ended up using the 165 ecm then I would probably continue to use this system and just set the converter constants to a high number so the ECM wouldn't try and work the converter (provided I can do this?). I'm running a Hurst 1/4 stick shifter which has a neutral safety and backup switch on it that I should be able to wire through for the ECM signal. The car is an 1984 Monte Carlo SS so I believe I still have a VSS sensor in the IP from the original CCC carb system, however if I remember correctly its a two pulse and I need a three pulse or something like that. I'm running 30# SVO injectors so I guess I'll have to bump up the injector constants and go from there. I downloaded tunerpro and an ARAP bin and $6E ECU that I've been playing with. So far I bumped the injector constants, upped the idle a bit, set the EGR and vapour cansiter purge constants high since I'm not using either, unchecked the VATS, and set the TCC and Fan Temps high so the ECM won't run them (I have a separate electric fan controller as well). I have an 86 corvette harness that I'm trying to custom make, since I don't need any emissions functions or the TCC and Fan control I'm going to remove these wires and connectors from the harness to clean it up and simplify things. If what I'm doing sounds like it will work then great, if not I might look into the megasquirt and a WB O2. Thanks.

 

Sounds like you have it all covered, except knock. You can disable that in the code, also. ARAP spark tables are quite excessive in some areas though, so I would recommend copying in AUJM spark tables as a starting point.

ARAP also does PE a little bit differently than AUJM, in that it uses mostly the PE vs Ctemp, and adds and subtracts a little with the PE vs RPM. AUJM does more with PE vs RPM. Either way works the same, but don't mix and match between ARAP and AUJM, or else you'll be way off.

I have a .ECU for $6E for tunerpro that I modified a little to fix an error in the PE calc, and give access to some other things not normally found in the .ecu's that I've been able to find. I used a $32 hack to find the algorithms that I wanted to play with and noticed that many of the algorithms (other than the fuel calculation) are the same, and even have the same calibration, so it was easy to find the same pattern of numbers in the $6E and add ecu items to edit them. If you want it, I can email it to you.