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I think I found a lot of my tuning problems. The reason I had to scale the MAF tables.... etc. Check out this log:
MAF grams per second is in yellow
RPM in blue
LV8 in black
Timing in red (advance before TDC, no knock retard shown)
Knock count in green.
Since the MAF stops reading above about 3700 RPM and just flat lines, once the load drops into the lower regions of the timing table it kicks up the timing resulting in spark knock. I'm thinking 42 degrees total advance is likely too much at WOT 5200 RPM
So what the heck is wrong with this thing? I've had two different MAF's on it and they both pretty much act the same. Now both of them sat in parts cars for a decade so that doesn't mean they aren't both bad. Just seems odd.
I'm not sure. Were you driving it or was it in neutral/park? Without load on it, the RPMs can fly all over the place with very little power change, meaning very little air flow changes.
I'm not sure. Were you driving it or was it in neutral/park? Without load on it, the RPMs can fly all over the place with very little power change, meaning very little air flow changes.
Yes it was under load - LV8 was around 200 then dropped because the MAF signal didn't increase with RPM - that was a pull on the freeway. I do have another ECM. I'll give it a shot first.
Changed out the ECM. Didn't change anything. Also checked exhaust back pressure and no issues there.
Am I right that MAF grams per second should increase beyond 145 at some point? Am I floating the valves? What gives here.....
Volumetric Efficiency calculation at 3450 RPM gives about 87%, and the MAF reads correct at idle (5-8 grams). That would seem to point at some mechanical issue post 3500 RPM. Only thing that comes to mind for me is valve train?? Could the stock springs be that shot after 155k miles? Compression is excellent @ 190 across the board.
My thoughts are going toward valve float, and my 700R4 governor needing recalibrated - its a race trans originally built for a hot 355 with 4.10 gears. I'm running the LB9 with 3.70's.... it's holding 2nd till I hit valve float on the little 305 (It feels like) and then at times it will downshift to second (from third) if you don't first get it into overdrive. Once Its been in overdrive it seems to downshift to 3rd find without revving out in second.... Its a 3000 stall non locking converter.....
Rick
Last edited by GeneralDisorder; 05-18-2017 at 01:13 AM.
The LB9 would float valves on the stock 85 pound springs at just over 4,200 RPM when it was new. With nearly 30 year old, weakened springs It would not be beyond comprehension that the valves just aren't getting home in time to maintain any flow at a slightly lower RPM now. Long runner intakes do not like reversionary flow one little bit at anything but the lowest RPM.
The 305 is already challenged with a long stroke/bore ratio and smallish valves, and even a moderate cam isn't going to compensate much. A stock cam is a regular wheezer at less than .400 lifts and the necessarily short duration. It would be marvelous in an off-roading truck since it does a great job at maximizing low-end torque. That's a substantial reason there were no factory rear gears over 3.45 and no converters much over 2,000 stall (most were around 1,575).
Frankly, a 3,000 RPM stall converter behind any TPI without some form of boost may not be a good combination. Resolving all that may not solve all the problems, but even with the right cam, springs, and heads/valves, the stock TPI will start to hit a wall by 4,500 RPM unless it is pressurized with a blower. I've done some conversions which have made respectable torque up close to 5,600 RPM, but not with stock TPI heads and cam/springs. I'm sure it can be stretched further, but I view that as a futile effort with TPI - Your time and money could be spent better elsewhere.
Another consideration is that the OEM system, regardless of the MAF in use (film or hot wire) has a maximum resolution of 254 g/s. If you get an engine combo which can flow more than that (and many do) the ECM goes stupid and can only revert to PE/WOT tables for injector PW. That only happens at your "PE" setting for TPS in the binary tables, and stock bins are usually 70% of max. Unfortunately, stock bins also flatten out the PE enrichment versus RPM starting around 3,600 RPM, which may also not be optimal (but very coincidental).
For sure. I'm aware of the limitations and my plan is a 383 with a procharger. I'm going to run the blowerworks MAF which has a modified BIN file capable of 460 grams/sec.
The 3000 stall converter is definitely not the best combined with the 305 but my trans pump seized and this trans was available from a friend for $1k fully built with only a few months of street driving on it. He spent $1700 on the rebuild about 5 years ago... I couldn't pass it up and it works GREAT.
Mostly I'm using this as learning device for tuning while I build the 383 on the side, etc. I can't hurt the 305 - or rather, if I do it's no great loss. There's a 20k mile 350 in my parts car that will get abused in the name of tuning education if I grenade this little LB9.
I'm just trying to understand what I'm seeing in these data streams and I wanted some confirmation that Im on the right path thinking the valve train is the (first) bottleneck I'm hitting here.
Just educational value. Not looking to win any races just learn something.
Probably wouldnt need to but stock bins cap maf flow nearer 160-170 around 3600-3700 i think. But i didnt know it was all stock. Probably wont be going that high. I know a bolt on L98 can hit near 200 g/s. Mild heads cam stuff 270-300 whp near 240-255 limit. Wild combos max them out 255 way early in rpm pull
I dont know what a 305 typically hits for g/s maf flow at wot
Well I'm going to change the springs and add 1.6 comp magnum rockers this weekend as a cheap experiment. I have 260 lb/inch springs and new stem seals. About $200 for everything. I'll post my findings up here.
So I'm in the middle of doing the springs, stem seals, and rockers. Resting my back for a minute......
Looked up the valve spring spec in the '86 factory service manual. I don't have a spring rate tester but they do give a free length as 2.030". Old ones measuring about 1.960". New springs from my machinist are at 2.017" and he gave me some shims to go under them too. Manual gives an open pressure spec of 194-206 lb/inch. New springs are supposed to be 260 lb/inch.
My peak MAF sensor readings went up about 3 grams per second. I am attributing this to the 1.6 rockers.
After talking to a few people, I'm pretty sure that ~155 grams/second is as much as the 86 305 flat tappet heads, cam, valves, and exhaust will flow. The reading I've done seems to indicate the TPI system itself is capable of more but I just can't put it through the engine and exhaust.
Can anyone refute this with stock 86 305 MAF readings with a higher peak than 155 grams/sec?
My real problem seems to be my 700R4 governor is shifting at too high of an RPM. Apparently I need to install lighter (?) weights and springs to get my shift points down to about 4500 and then I'm going to set a rev limiter to 5000 and play with my timing table to get it to stop pinging up at the top of the range.
I'm surprised that an 89 PROM for a 305/700R4 would allow the engine to go into detonation like it does at 5200 RPM. I guess I should look at the 86 PROM tables and see if they made adjustments for higher flow on the 89. Based on the simple HP ratings and cam specs from the different years it appears that the 89 made 20 HP more than the 86. That might account for the way the 89 PROM acts on this engine?
I think there's more to using the 89 PROM on 86-88 engines than is usually talked about. It's not just a matter of disabling the VATS and removing the cold start injector from what I'm experiencing.
So doing some maths and checking out some appropriate formuli (general approximations, rules of thumb, call them what you like)....
Apparently a rough equivalency for Mass airflow to horsepower (at WOT, near redline) is given by:
MAF grams/sec ÷ .75 = ~Crank HP.
In my case:
155 g/sec ÷ .75 = ~206 HP.
The .75 is sometimes quoted as .80 which is 193 HP. The 86 LB9 was rated at 195 HP. My guess is it's somewhere between 193 and 206. This is with the 1.6 rockers so might be pushing a bit more than stock. Solving for the exact number (about .7795) using 195 for the factory HP rating yields an increase of about 4 peak HP with the 1.6 rockers. Nothing I could feel. Was an interesting experiment though!
Side note - Comp 1.6 magnum roller rockers (non self aligning) fit the 86 LB9 with no mods. Straight bolt on. No issues with the pushrods, etc.
Anyway - the calculation is a good sanity check on the accuracy of the MAF sensor. In case anyone finds this thread in the search.
I changed out my 700R4 governor for a stock (mint green gear) unit. Got a good used one from my local trans supplier for $30. This brought my shift point at WOT down to 4000. I'll play with the weights when my B&M kit arrives to get that up to about 4500 and leave it there till I get an engine together that can breathe a little harder.
I'm pretty sure based on my searches that the 87+ LB9 with roller cam had a 500 RPM higher redline in addition to an extra 20 HP.
Rick
Last edited by GeneralDisorder; 05-23-2017 at 12:23 AM.
05-17-2017, 10:49 AM
