Have a 383 with E-tech 200's, Speed Pro 10.2:1, Perf. RPM airgap w/ cust. TBI adapter, Turbo City hogged BBC TBI w/stock 350 injectors, Comp XFI 274/280 w/114 LSA, 1"5/8 to 3" shorties into dual 2"1/2, into flowchamber(where wideband is located)& 2"1/2 dual out w/flowmasters. 4L60 stock stall w/3.73 255/70x15's.

Use moates autoprom & Tunerpro, WB data piped into datastream for logging
along with digital display, 94' 16197427 PCM w/ OD mask & BJLH .bin to start with. Previous 350 w/ vortech heads & perf. cam & modded tune ran strong, lotta tire spin though.

Used the same modded .bin to break in the 383 with only displacement changes made to it. Drivability is somewhat fair with light to moderate throttle in-town.Ran 13.5 across the board in idle AFR table & commanded VE to give those results out of WB all the while trying to keep up with temp increase. After warmup 180-200 got VE in entire table within +/- .2 (except for under 700 rpm)by commanding idle speed w/IAC. Only made slight mods to timing after that to get smoothest idle under no load. Reran & adjusted the same way in gear up to around 1400 rpms.

One problem I have been working on is what I think is Map AE correction when put into gear from nuetral, acts like it wants to stall lean(according to WB)or takes too long to compensate. Have the same issue with throttle AE even after large increases in fuel PW across the board in both Map & TPS tables. And I'm not even in closed loop yet!

You would think too small injectors right? They seem to be OK @ flooding the engine in several areas where my AE,VE,Temp corr. table skills are lacking!

Only have about 2-3 weeks before I pull the engine & sell vehicle for newer model but would like to get close on tune.

 

Also forgot to mention I haven't had a chance to road tune w/emulator but have 5 days starting saturday to get-r-done. My thoughts on this is putting my 3000 lb. boat behind me to help out with loading the engine for possibly ease of tuning. Any quick tips or strategies appreciated.

 

what fuel psi are you at? with 61lb 350 injectors you would probably need around 30lbs of pressure to feed that engine. ive heard with an unheated manifold like the airgap, your ae and transient fueling can be tough to get right.

 

The airgap will be difficult with the stock computer. The AE is based on the temperature of the manifold with that setup, and not the cool temp that the computer uses to generate the AE temp compensation. On top of this, the low velocity in the intake makes it want to go even leaner. With a manual it would be an impossible nightmare, but with an auto, it will be a nusance that pops up every now and then once its tuned. The best thing to do is try to find a balance between cold and hot engine operation.

 

I think thats exactly whats going on. But where is it getting manifold temp from beings there is no sensor. Calculated from begining coolant temp & knowing timeframe engine temp should increase @ if t-stat operating correctly? I see the AE temp corr mult vs. MAT & its set @ 1 across the board. Could the #s be lowered when cold & raised when hot to possibly correct my issue. Will have to try when I get the throttle body back on.

Thinking along those same lines that doesn't explain the stall when put into gear due to the fact the engines already at a stabilized hot temp. Still in the MAP enrich #s perhaps? I did do some prop gain adjustment & was wondering if it affects everything from IAC, TP, 02, etc.,etc.?

BTW phenolic is absolutely the worst material to use as any kind of spacer/adapter, as it warps and creates a nice vacuum leak. Fabbing up 1/2" aluminum replacement & should be back in business before tommorows road tuning expedition.

 

It appears these two holes aren't big enough not to create 3" of vacuum above 4000, after all that time fabbing! Blows me away especially when I know how tiny the head ports are. Oh well the new non-warped version was opened up considerably.

 

If those two big holes aren't enough, than it is time for a single plane manifold with an open plenum.

 

Well as it turns out to my suprise those holes weren't big enough. The new adapter allowed another 3 kPa. PIC's show new opening transition that really didn't affect idle stability like I had feared. Peaking around 96 kPa @ 5600. I Guess thats as good as it gets with this intake.

On another note I simply could not squeeze enough fuel out of the 61#ers no matter what PW they were subjected to. Installed stock 454 BBC supposed 75#'ers & in the process of adjusting all previous figures. Motor still seems soggy for all thats in it, although could be wieght issue....4200 ish?

 

What was your fuel pressure with the 61# injectors. I have run them to over 45 PSI with success.

Too much fuel and improper timing advance make for a doggy running engine.

If you want to make your TBI go further, SINGLE plane manifold.

 

Could only get 16 psi out of stock regulator. Plenty of fuel below 3000, way lean above 4000 @ 12+ msecs. New inj way rich down low(10:1) & still lean above 5200(13:5) but lower PW's (6), still working on #s.Now @ stock press w/ stock reg.

 

Your injectors are way past static, untill you get the PW back down under 80-90% it's gonna run like poo no matter what size injectors you put in it. The injector opening and closing times get all funky when you get past 100% duty cycle and in my experience actually deliver less fuel than if you back off the duty cycle to 80-90%.

You'll most deffinatly need a different regulator, you can use the VAFPR without the vaccume line to get 30 psi. You can also bypass the regulator all together and use an external ment for a MPI setup.

 

A few questions I have about the TBI inj firing scheme is whats the difference between synch & asynch, and the relavance @ wich RPM it swiches over?
Also the max asynch BPW constant is listed @ 11.9 msecs, is this before all the enrichments or is that the final calculation? What msecs can I get away with before hitting 80-90% duty cycle?

 

Synch is firing one injector with every reference pulse. So the injectors alternate. If my memory seves me correctly at 5500 rpm you have around 5 ms to get all your fuel in.

Asynch is firing the injectors on a 12 ms time interaval independent of engine RPM.This cuts down on the number of opening and closing events and allows you to get more fuel. The idea is that asynch fires too slowly at lower RPM's to use effectively, at higher rpm's it doesn't matter much as the injectors are open more than their closed.

It's been a awhile since I played with this stuff.....best to double check yourself.

 

Yeah, the PCM has settings to enable or disable async based on the load and RPMs. You can actually go up to 100% DC without issue, other than going lean. The bigger problem is at low PWs with large injectors. When they get down into the usec range, the opening/closing time really comes into play and you need to really have to set the bias table up properly to allow additional time for the opening/closing.

 

Thats kinda why I was trying to do it with the 61's, now my idle PW is under 1msec @ idle but it still seems to be idleing well in spite of the spray pattern.
It appears if 5 msecs is max @ 5500 then the 75's are still too small as I'm at around 6.5 now @ 5500, but really cant raise FP any more due to the idle PW issue. Whats the solution...?

 

Actually my engine idled fine with .6 msec of on time at the injectors. You can possibly switch to asynch at high loads (my 3.1 runs async always) or use a vacuum compensated fuel pressure regulator. I had one of the cheaper remote regulators on my TBI setup. The vacuum hose was hooked up to it. This drops the fuel pressure when the vacuum is high and allows it to rise when the vacuum is low.

 

I kinda figured that was the only option @ this point. But who makes a decent reliable VAFPR. My attempt at it didn't fair to well, I modified a stock regulator wich was able to compress the spring approx 3/4 inch over stock & only gained 2-3 psi. With the 61's the spray was scatterring outside the TBI, with the 75's I'm afraid it'll dribble if PW is lowered @ idle to compensate the added pressure.

 

Playing around with the numbers this morning it started to make sense. Based on what Bmonte said about Asynch firing every 12 msec, that would be the reason for max Asynch PW being 11.9 in my stock .bin file. And since Synch-to-Asynch happens at 2100 rpm, everything above this is on a 12 msec firing schedule, wich if you do the math says I can get away with up to 10.7 msecs and be under 90% duty cycle correct?

If I'm way out in left some one let me know before waste a lot of time scoping to confirm...running out of time!

 

Any Feedback ????????

 

Well it appears it's a pressure issue not PW, pattern looked good w/ 6.4 msecs clear up to fuel cutoff @ 6000 with room to spare. Put a pump in it awhile back but coudn't remember wich one so I dead-headed it @ the filter & it's good @ 65psi & well over a gallon a minute. Between the 4 TBI's I have the 305's had a bigger spring in it so I put in in my modded regulator & was able to achieve 20+ psi. Now it's back to the VE grind!!!!

 

I was going to say.... you need to get a different fuel pressure regulator. Check out http://marine-performance-parts.com/ for all the TBI GO-FAST parts....

 

After the injector swap and fuel pressure increase I now realize why I should have gone MPFI. For a first timer, tuning in SD, the combo I have is taxing to say the least. To get the fuel right on both the high & low ends is impossible without a VAFPR, no matter how much VE tuning you do.Here's what I know.

Wideband 02's lie.At what point/rpm the data can be trusted I don't know.
Not to discourage anyone from attempting tuning, as what I have learned to me is both unmeasureable and priceless, but IMO the only way to truly
"GET IT RIGHT" is with a 5 gas & a loaded dyno.

 

It's funny to see the light bulb come on for the first time. I'm sure you are just frustrated, but once you tune a few engines you'll be able to replace the 5-gas with a little intuition and your nose. At low engine speeds I tend to ignore the O2 sensors and just tune for max vaccum with the least amount of smell possible.

If it makes you feel any better your combo is one of the "in between" setups that has enough dynamic range to need a lean idle and lots of fuel up top. If you go much meaner you need a rich enough idle to keep your PW's up, if you go milder you won't need as much fuel up top.

 

Not really that funny from where I am, thing all but blinded me !!!!!
I had such high hopes for my TBI setup and wasn't dissapointed on the max power I was able to achieve. 0-60 in under 6 sec's isn't too bad for 4200 lbs. with 3:73's. Gainesville's T-N-T is next, I'll see what it'll do in the 1/4. Still don't have the the fuel right @ 5600 but it's close, just a tad shy.

Problem is that if ambient is anything less than say 70* it's misfiring, fouling plugs, to the point it will barely run. The intake/TBI setup is just too cold.
Curious to know if there ARE any performance gains by using the AirGap over the GMPP manifold, doubt it is worth the drivability nightmare. Wish I had made that fabbed adapter heated.

 

OK, so I arrived @ 25 psi and 75#'ers to get my commanded 12.5 AFR on WB @ 5600 wich is my shift point. Injector constant based off of Witchunter's flow calculator appears to be close enough to what it actually is. Have a hunting problem now & it doesn't matter if it's open or closed loop.


Where to go from here???????