'98 Trans Am 40mpg

[ksa8907]

So your hybrid runs the engine to provide energy. Not just stand-by with no appreciable benefit, aka idle.

[oil pan 4]

Yeah any modern hybrid will have a high voltage alternator driven by the engine that charges the traction battery as you drive.

[ERTW]

Originally Posted by freebeard

What do you think about the work described in the X-Prize Sonata thread? ecomodder.com/forum/showthread.php/x-prize-sonata-40234.html#post668238

Originally Posted by freebeard

What do you think about the work described in the X-Prize Sonata thread? ecomodder.com/forum/showthread.php/x-prize-sonata-40234.html#post668238

The X-Prize was interesting and proof of basic physics. The winners "All weighed under 1,000 pounds and turned in drag coefficients of 0.15", with 250cc single cylinder engines and just squeaked past 100 mpg. Any 3000 lb gas car that claims 100mpg is bs. Smokey Yunick's "100 mpg" was just hype to get sponsorship money (recent video by dragboss garage with Mike Campbell). Engines today burn over 98% of the fuel, so there's not much gain to be had (wrt combustion efficiency). "Cracking" or "catalyzing" fuel, heating, or any other processes, mathematically can't offer much gain; even if they worked. There's just no way to get around the fact that a vehicle needs a certain HP to move it down the road, which requires a certain amount of fuel to be burned.

I'm not expecting to see a huge increase of mpg with my car outside of a very specific set of conditions. I'm mainly curious to see what the "best" LS head can do, and how lean it can tolerate. With porting and some other mods I should be able to push it a little further.

[ERTW]

Originally Posted by ksa8907

Diesels have low vacuum because they don't have a throttle, they control engine speed with fuel.



I'm going to challenge you on that. The prius uses late intake valve closing which decreases vacuum because it pumps the intake gases back into the manifold, does not increase vacuum.

Hybrids do not need to have high vacuum for idle quality because... hybrids don't idle.

I see where the confusion lies. I'm not referring to "manifold vacuum". I mean the vacuum that the downward piston creates as the intake valve is opening. Fundamentally every engine, otto and diesel, create low pressure inside the cylinder which causes air to flow into it (disregard turbos for this argument). Diesels don't have a throttle, so a sensor in the plenum would essentially read atmospheric; the same thing happens in an otto engine at wide open throttle. Air still flows at WOT, which means there is still a pressure differential in the cylinders. I hope that's clear(er).

[pgfpro]

Originally Posted by ERTW

Hey all,

I bought a 1998 Trans Am with 4 speed auto for cylinder head development, and I'm doing an mpg project in the interim. The key points are decreased pumping losses, increased thermal efficiency, and lean burn.

I'm spring boarding off of Legit Street Cars' 40mpg Corvette. While his engine was basically stock, I'm taking it much further.

The Corvette has lower CdA and 6 speed manual (12% lower final drive), which is certainly an advantage over the TA. fueleconomy.gov actually has the auto TA getting 15/23 vs the 6 sp Corvette at 16/25 (his stock car got 30 mpg @ 65mph). I predict the mods will be worth 30+ mpg highway running stoich, 40+ with lean burn.

To reduce pumping losses I'm looking at a 212* cam on a 118* LSA. This will reduce pumping greatly, while keeping vacuum high for good fuel vapourisation. Overlap leads to low vacuum, which causes misfire, which just dumps fuel out of the tail pipe and kills fuel economy. It should also work fine with 87 octane, which is 20% lower fuel costs vs 91.

I have 1-3/4" headers and will get a free-flowing cat-back exhaust.

I'm using 706 truck heads to bump compression to around 11.25:1, which is a 2.7% increased Brake Thermal Efficiency over 10.1:1. The heads have been ported to increase air speed. This improves mixing and atomisation for a more complete and faster burn. I should be able to remove several degrees of timing for less negative work. The preliminary engine sim is showing around 470 bhp (with no knock) and low .400 BSFC.

Alex talks about lean burn and how it raises NOx emissions. Sort of. If you run 1.1 lambda, like he does, this is true. Most charts end there, but if you keep going leaner NOx (and temps) plummet. I would like to go much leaner (24:1). A key enabler is a strong ignition system capable of 140+ mJ. Stock coils only provide around 80 mJ and ICE Ignition LS1 coils with their 10 Amp booster will generate 142. This will come later.

I should have the car up and running mid-June.

Cool project will be following this one

[ERTW]

This project is progressing much slower than I anticipated. mid-June...2023...maybe I was battling a large vacuum leak most of the summer (from porting the intake manifold) and finally got it running in October...then Canadian winter hit and I put it away in the garage.

The 706 heads are ported, valves back cut, etc. They peak at 254 cfm @ 0.550" lift. Sim says there's no real benefit to peak hp using a higher lift cam. The cam arrived a couple of weeks ago. 264/274 advertised duration, 116 LSA, 0.61" lift. The faster ramp rates of the LSX/LSL lobes should make it accelerate harder.

I still have maintenance items to replace. Timing chain/gear, oiling system, rod bearings, et al. Ideally I'd install lower tension piston rings and plateau hone.

I'll be contacting ICE Ignition soon to get some of their LS1 coils and 10 Amp box.

I believe the stock thermostat is 210F. I'd like to go a littler warmer as well - 230ish.

David Vizard pointed to TFX Engine Technology for in-cylinder real time pressure transducers. Their software will calculate VE, IMEP, burn rates, and ideal spark advance for efficiency. This will help with calibrating fuel and spark. Not sure if I can afford a 4 gas analyzer.

[ERTW]

I'm finally getting all the parts I need to do the head/cam swap. A friend will pick up a bunch of parts from Jegs in Columbus. Short travel lifters, stronger pushrods, beehive springs, Melling oil pump, timing chain, all gaskets, etc.

Stock 29 lb/hr injectors will only work up to about 5000 rpm, and I just found a set of used LS3 injectors on ebay. ICT billet adapters and connectors are next. New O2 sensors are on the way to make sure the ECU is getting good info. I've installed NGK Iridium plugs, and apparently the Ruthenium plugs offer better ignitability and economy.

Next week should begin the process of dropping the engine and subframe and swapping parts. I would like to balance the rotating assembly myself (while I'm in there). I'll replace bearings and piston rings if needed.

I have the 2.73 final drive, so that will help with economy. It should run at 1600 rpm at 65 mph with the 285 section tires (C5 take offs).

[ERTW]

A few snowflakes fell this afternoon, and I still don't have my heads back. I'll try to have my car up on stands, drained, and taken apart this weekend. fwiw, a pitot tube showed the ports have 23.5"/320+fps over the STR, which is the magic number for atomising/mixing the fuel. Along with increased torque, the chambers/pistons should stay a tan colour, instead of being covered with soot. That's the sign of complete combustion.

The LS3 injectors went in super easy. I got the necessary tables off of HPtuners forum. I just cut and paste them into my tune file. The hardest part was the confusion after licensing the wrong tune file, and losing two credits. I've been driving it, and apart from a slight stumble, it works well. The ICT adaptors don't fit snugly (no retaining clips) and I think I have a slight vacuum leak.