My search for better performance

[Padgett]

Makes sense since the GN makes its power from boost. Suspect the MAF sensor has a higher max airflow and needs a MAP sensor. Also larger jets.

 

Think I'd prefer an L-67, Throttle is on the intake with a supercharger and response is much quicker.

[2seater]

I never flowtested a GN MAF but judging by size and construction it would be probably be comparable to that 3” MAF I am using now. I know the gram/second flow rate maxed out at 255 or 50% more than ours but the frequency output is different so not compatible with ours. 
 

I am putting together a S/C engine to see the difference in feel and performance. It will be very similar to the short block of my original engine to isolate the S/C and the turbocharger from other factors to judge the difference.

[2seater]

I think this will be the last installment for a while and there is one item I have been meaning to mention, even from the beginning. Some or all of the general idea and modifications are applicable to the Series II engines as well. If I had done this with a long range plan in mind, rather than incremental changes, starting with a lighter, more compact and stronger foundation would make sense. Even more important is the fact that the Series II has aftermarket support. Just recently I found the Australians have various performance parts for the LN3. Starting from a higher performing baseline has dividends that payoff even more when force multipliers are added. 

 

This is the latest rear exhaust manifold I modified. It will work on everything but the full turbo installation. Since it is a modification of the standard manifold it may not look very pretty, but it designed to smooth the flow from the opposing flow paths out to the exhaust. Again it is ceramic coated inside and out. The O2 sensor is at the tip of the vee that keeps the opposite sides from crashing into each other. It's first use will be on the engine I want to put together next. It may not be obvious but the center exhaust runner is lengthened from stock and tilted toward the tailpipe opening. 

 

 

These are the different pistons that have been mentioned along the way. The markings are compression height from the piston pin to the crown, and the weight in grams. The piston on the right is the stock piston from my '90, the center one is a Silvolite for an L27 from '93 which raises the compression ratio to 9:1 and zero decks the piston and the piston on the left is for an Australian Holden with a Buick engine. The Holden type will be going in a shortblock that has been salvaged, also from Daves89, which had rust problems in the cylinder bores. The block was bored .030" oversize to clean up and the really bad cylinder was offset bored a little to take out a large rust pit. A crying shame since the engine only had 5k miles on it.

 

 

Last photo is detail of the Holden piston where the small raised area in the center is clearer. The idea behind the flat cone shape is to soften the pressure spike when combustion starts, hopefully suppressing detonation tendencies. The engine will be right at 9:1 compression ratio. The heads will be from the '95 L67 S/C engine I took the supercharger from. The late model heads, the last of the Series I engines, have roller pivot rockers but are otherwise similar to the LN3 heads. This engine will get a new replacement camshaft for an '88 LN3 engine. The purpose is to assemble an engine very similar to the fully turbocharged engine in the car currently, but it will have the Eaton M60 supercharger instead. I have always wanted as close a comparison to see which approach is most satisfying. This probably never ends, maybe combine the S/C with the half turbo?? 

 

[Ronnie]

10 minutes ago, 2seater said:

I have always wanted as close a comparison to see which approach is most satisfying. This probably never ends, maybe combine the S/C with the half turbo?? 

Good write-up about what you have done so far.  I look forward to hearing about the SC installation. If the SC isn't enough you can always throw a bottle in the trunk for some on demand power power. ?

 

I've been wondering about your transmission. Do you allow the converter to lock up when driving with the turbo building boost or do you have a switch to keep the converter from locking? Preventing lockup seems like it would be easier on the transmission.

 

 

[Padgett]

Throttle with the stock PROM needs to be less than 50% for the TCC to engage.

[2seater]

What Padgett just mentioned is part of the difficulty with the old school mechanically controlled transaxle. I have never spent enough time to dial in high load and low rpm timing charts. The turbocharger responds to load more than rpm so cruising along at medium speed, say 60 mph, and get to an incline that loads the engine, but the turbo starts to spool up before the TCC sees enough throttle, if it happens at all, to unlock the converter. This happens in rolling terrain more than you might think. The engine can produce enough power to motor on through the increased load, but because it doesn't take much actual throttle, it holds on to the TCC and the engine may rattle itself. In other words, the modulator and throttle cable to the trans are all designed to work within the normally aspirated envelope, and when adding boost that is a fair piece outside of that, more needs to be done. My partial solution is simply prevent any TCC below 55 mph, and that's fine, but it's not enough at higher speeds. For short inclines, just roll out of the throttle, the TCC unlocks and roll back in with higher rpm and it's happy. But it will relock unless you accelerate a bit. A switch to lock it out manually is a good idea I just have never implemented. 

 

Regarding laughing gas: most of the people that I was exposed to in the turbocharged GN community always mention the bottle could be empty and then you would be "unarmed". It's just something that sort of rubbed off on me. I looked at it, and even if adding some mechanical boost device can be complicated, once done, it is always there. It has it's place, just not for me at this point. 

[2seater]

Your comments above got me to thinking. I never really monitored the TPS signal to see where it was in relation to performance issues?? It was looked at when doing a test run and making sure it would get into power enrichment and things like that but not in the danger zones of light and part throttle with variable load. Always good to have a fresh perspective and ask the right questions?

[Padgett]

The TCC is computer controlled even on an 88. I think we could add a MAP component so if manifold vaccuum drops under (or MAF rises over) a certain point it unlocks. Is that what you are thinking ?

[Ronnie]

I liked the feel of cars with the 350 Turbo transmissions back in the old days when you didn't have to worry about a TCC locking and unlocking.

 

I would add a switch to turn the TCC off so the MAP, MAF and TPS sensors don't determine lockup. Much better throttle response in 3rd and 4th  gears and I'll bet the turbo would spool up quicker and make it even more responsive. If you want to test it out you can just unplug the electrical connector going to the transmission. The ECM will set a code but a warning won't be displayed on the dash. Just cruising in 4th you won't notice the converter slipping until you get back in the throttle and that is where you will feel the difference and I think it would be easier on the transmission. If you like it you can install a switch so you will have converter lockup on the interstate. Yeah it will knock off about 2 mpg driving around with it unlocked but that is a good tradeoff for me.

 

 

[2seater]

2 hours ago, Padgett said:

The TCC is computer controlled even on an 88. I think we could add a MAP component so if manifold vaccuum drops under (or MAF rises over) a certain point it unlocks. Is that what you are thinking ?

Padgett, I don't know enough to ask the right questions sometimes. I have given some thought to a MAP sensor that might be used with the input for the air temperature sensor which has the ability to change the ignition timing but I don't have enough knowledge to implement such a thing. Never thought about TCC. Thanks

[2seater]

1 hour ago, Ronnie said:

I liked the feel of cars with the 350 Turbo transmissions back in the old days when you didn't have to worry about a TCC locking and unlocking.

 

I would add a switch to turn the TCC off so the MAP, MAF and TPS sensors don't determine lockup. Much better throttle response in 3rd and 4th  gears and I'll bet the turbo would spool up quicker and make it even more responsive. If you want to test it out you can just unplug the electrical connector going to the transmission. The ECM will set a code but a warning won't be displayed on the dash. Just cruising in 4th you won't notice the converter slipping until you get back in the throttle and that is where you will feel the difference and I think it would be easier on the transmission. If you like it you can install a switch so you will have converter lockup on the interstate. Yeah it will knock off about 2 mpg driving around with it unlocked but that is a good tradeoff for me.

 

 

I already have the TCC locked out up to 55 mph, and I could set that higher, but maybe there is another path I never thought about? 

 

I monitored the TPS on my way to and from breakfast this morning. Speeds never over about 50mph, so a pretty much urban environment. One thing I noticed immediately is my TPS is set too high, like .44v at idle. I am pretty careful about things like that when swapping stuff around but sometimes the little things slip by. It seems to me it is a small error and would likely not have a big effect, but to be accurate I need to correct that. The other thing I noticed is when accelerating normally, my TPS is around 1.6v or so. If I push harder from a stop, where I am over 1.8v-2.0v it is clearly spooling up, and the faint whistle is more apparent and gaining speed faster than average traffic around me. I will need to get into more rolling terrain out of the urban area to see where the throttle is when getting into the possible problem area. 

 

To be clear, this turbocharger setup is more forgiving and flexible than my original installation. It now has an air to air intercooler and the intake plenum is doubled in size which slightly slows the initial rise in pressure in the manifold which was my goal. 

[Padgett]

How are you handling the need to retard the ignition and fatten the injectors during boost ?

 

Still have my notes from the L-67/Getrag in Greg's 88 but know it is very important not to go lean under boost or may have a holy pistons moment.

 

Just a thought but the TCC max rpm is set to 5500 rpm stock, could drop it to say 2750 rpm (about 80 mph) & remove entirely in 3rd. Right now it drops out above 43% TPS, could also drop that down.

Edited April 7, 2021 by Padgett

[Ronnie]

9 minutes ago, 2seater said:

I already have the TCC locked out up to 55 mph, and I could set that higher, but maybe there is another path I never thought about?

Maybe if I had my TCC lockup set point that high I wouldn't feel a need to switch off the TCC where it never locks.

[2seater]

You both gave me something to think about?

 

There is no specific retard protocol. The enrichment should work normally when above a tps threshold. The injector size of 30# is set in the  Prom. The fuel stock fuel pressure regulator raises fuel pressure in a direct 1:1 relationship under boost. Fuel pump is a Walbro, I forget which model.

 

The whole point of using a larger MAF is to keep the frequency output in a range the ECM can read so the load and timing chart can be adjusted over the entire possible range. I don’t know enough at this point to know how to adjust the LV8 which I am sure is made up from multiple inputs, and is the Y axis of the timing chart?

[2seater]

I did correct the tps to .4v at idle position. Full throttle is 4.52v. The net result when I went out to try a little higher speeds while watching the TPS, is the overall readings in what I call average driving, now occur at a bit lower voltage. There is no such thing as really steady state on the throttle so it is a sort of average impression. The country around where I live was flattened by the last glacial age, so there are no more than gently rolling hills to climb in many places. In any case, I never got above 1.5v on the tps, and that includes relatively brisk acceleration up to 70-75 mph. Cruise at around 70 on the flat is in the .8v range which creeps just over 1.0v from throttle increase to maintain that speed up the inclines.

 

I tried holding the throttle to a tps reading of 1.5v from a stop, which it turns out is much harder than it sounds. Running up through the gears at that approximate throttle input showed 5-6inches of Hg manifold vacuum until it shifted to third gear when the gauge jumped to very close to zero and right on the edge of crossing into boost, terminal speed around 65mph.

I don't want to give the impression this is a quick car, or even a fast one, but I term it effortless in average driving. It requires little throttle to get it rolling and keep it there. Many years ago, and I believe it was before adding boost, that I did an experiment on a long straight stretch of road, and I mean several miles. I just held the throttle to keep the manifold vacuum at 5 in Hg and let it accelerate, which it did fairly well at first but slowed as the forces of friction and other things built up. It was still gaining speed, very very slowly, as it crossed 100mph and I terminated the test. If memory serves it was about three miles.

[2seater]

4 hours ago, Ronnie said:

Maybe if I had my TCC lockup set point that high I wouldn't feel a need to switch off the TCC where it never locks.

I don't know. It really depends on the type of driving, traffic and lay of the land. Most of my everyday (retired) driving is in urban to suburban areas, so speeds over 55 are not common. As Padgett mentioned, there is more than one setting that can be changed, but I took the easy way out and just set the minimum speed to 55. The solution you have now is pretty good and I do believe I will install a lockout switch for special circumstances.

[Ronnie]

19 hours ago, 2seater said:

The country around where I live was flattened by the last glacial age, so there are no more than gently rolling hills to climb in many places.

I guess that might be a reason the switch for the TCC might not matter as much to you as it would to me. My area is much different. It is relatively flat here in the TN Valley where I live but in just a short drive things can change a lot. For example, the Cherohala Skyway (below) and other places in the hills and mountains of East TN are much different. A converter kicking in and out as you get on the brakes and than back on the gas can be irritating and distract from the fun of driving up and down hills and around curves. I think I would really like the extra power you have when I'm driving in the mountains. I believe it would really improve the fun factor. ?

 

[2seater]

I agree Ronnie. Where I have noted similar behavior to what you describe is in the southwest part of the state. This area was beyond the extent of the glacier and parts are called the driftless area, leftovers of what was carried alone. I have quite a few relatives from that part of the state, 150-200 miles away. I can simply drive without overdrive but that is wasteful and doesn’t seem to be necessary. Keeping the rpm above 2000 under high load seems to be just fine.

[Padgett]

Can be adjusted but I would prefer to stay in lock up and not unlock every time I hit an overpass. One thing I have noticed is everything runs cooler in lockup since even 3% slip turn into heat. When thinking about not staying in lockup I would consider an external transmission cooler.

[2seater]

56 minutes ago, Padgett said:

Can be adjusted but I would prefer to stay in lock up and not unlock every time I hit an overpass. One thing I have noticed is everything runs cooler in lockup since even 3% slip turn into heat. When thinking about not staying in lockup I would consider an external transmission cooler.

Aren't overpasses considered "hills" in FL? I agree that lockup is preferred for the majority of the time and I do have a large transmission cooler front mounted. After my little excursion yesterday, I realized what should have been obvious: the small amount of throttle used, effectively renders the normal ECM programming for enrichment, lockup and probably spark timing ineffective ? I do like the idea of a MAP sensor operating a switch to drop the TCC at some preset point, maybe zero vacuum like an N/A engine?? I know the timing map needs work that I just never take the time to investigate. 

 

As near as I can tell from the investigation recently and in the past, the LV8 reading is made up of MAF, RPM and TPS inputs to determine engine load. I am pretty sure the MAF part can be adjusted, or as GM Tuners said, it is a made up number, so that implies it can be remapped?? Opinion?