First Goal: 550hp LS1 Getting 30mpg

[bazman]

Originally Posted by drmiller100

smaller cam and more boost.

That does make sense on the surface however the goal was great power and throttle response at large throttle openings, and very fuel efficient at small throttle openings. I must put a video together so you can hear how crisp this thing is ;-)

A small turbo produces a very small orifice for gas to pass through and therefore more back pressure. I chose a medium size turbo because it offers less pressure drop, easier smoother flow, and more cfm per lb of boost. I also plan to drop a new LS3 or maybe an LS7 in there later so wanted a system that will easily adapt over. Both LS3 and LS7 will get better mpg than my LS1 for the following reasons:

1 - LS1 is old - done over 100,000 miles
2 - A new LS3 or LS7 blueprinted and built right is very fuel efficient at part throttle - esp with some tricks to ensure very low leak down and friction reduction etc
3 - The LS3 or LS7 would go with a 6sp to get mpg up as the larger engines will see little (if any) mpg gain on an auto over what I have.

[bazman]

Originally Posted by ecomodded

I like the comfort of a 4 door, your car sounds like a rocket, I do feel that 15% increase in your car's fuel economy is to high of a penalty for the 50 more hp you may or may not use. Offhand my suggestion would be to throw a medium size turbo on it and use the boost when you feel like it a.k.a put your foot down..

The 15% mpg drop is because car now mainly does city commute where-as it used to be mainly highway. On highway cam is only costing 5%. That is not worth losing 50rwhp.

Your idea re medium turbo is exactly what I have ;-) I don't want boost at 1500rpm.

[bazman]

Originally Posted by ecomodded

Rather then a low boost set up, a 20 lb boost medium size quicker spooling turbo, although a twin turbo would be more fulfilling.. a small turbo for acceleration and a big turbo to pass losto air for top speed

The old LS1 with over 100,000 miles still has a good leak down, but 20lb it would not like

The low boost is because I have empathy for the engine and so wanted plenty of cfm per lb of boost while still spooling full boost by 3000rpm.

I get boost starting from 1800 (converter stall is 2800) - so it is perfect. Any more and it'd all go up in tire smoke. As it sits I can throw the keys to my partner even in the rain and know she will be safe. Try driving a high boost V8 auto in the wet.

The key to keeping a boosted big engine safe in the wet is intelligent diff (Harrop Tru-Trac for me, but a Quaife is even better), a stall converter (mild for street) to soften part throttle (remember big engines make massive torque at low rpms), a boost gauge to read what your right foot cannot feel, and a progressive throttle (1st 50% of movement might be only 25% throttle). Low boost makes it even easier.

A manual is easier to keep off boost than an auto

[bazman]

Originally Posted by vskid3

I think you're getting to the point where diminishing returns will really start to kick in as far as engine efficiency goes. You would probably get much better gains-per-dollar with some aero mods, pumping up the tires as much as you can, or a manual transmission swap. My GTO has a 6sp and will putt along at 1600RPM at your 62MPH cruise speed, the RPM difference between auto and manual would be at least 10% (0.7:1 to 0.57:1 with the transmissions offered in the GTO).

However, if saving money isn't your main goal and you just want to see how far you can push the engine, I wish you luck doing what most people would consider crazy/impossible. I love that my stock LS1 can hold its own compared to cars with smaller engines when cruising, I hope that you can make a more powerful one crush them.

I agree re the 6sp helping. I'm at around 1650rpm at 62mph due to my higher diff, but drivetrain losses are significant with an auto.

Right now the car is my company daily driver and the auto is a much better commute. When the car can retire from commute duty I'll put the 6sp in.... along with a built bigger LS engine that will push the limits more than the current set up can. STS get 35mpg out of their 700hp LS3 in a C6 Vette without all the tricks that I'd plan to add, so I hope to get at least 90% of that in my heavier less aero car.

[bazman]

Originally Posted by mcrews

I would first ask if you have increased the psi in the tires?
Since you are obviously VERY mechanicly inclined , have you thought about a slightly taller tire or working w/ the rear ratio?

I run around 38psi which is about as much as I want to for traction and handling balance. The car has big front and rear sway bars, Bilstein shocks (as good as shocks get), diff brace w/Harrop Tru Trac, poly bushings everywhere and new stiffer springs - it handles very well.

For a one off economy drive I would run tire pressures up to max.

Current gearing is tall for a 5.7. I'd go taller with an LS7. I may very slightly lift it via going from 235/45 x 17 tire to a 245/45 but the extra width increase in rolling resistance will partly offset the taller gearing. The height would be mainly for extra clearance more than mpg - some speed bumps around here are brutal.

[mcrews]

wow....I'm enjoying all this 'v8 hotrod talk' although it is over my head!

I have an Infiniti Q45 Sport w/IMPUL Body Kit. Bone stock 4.5 liter w 340hp, 5 speed auto, 2:76 rear ratio.
I run 245/50/18 (27.7") on stock rims instaed i=of the factory 245/45/18 (26" dia).
I also have 265,000 miles. My best hwy mpg has been 32MPG

[bazman]

Originally Posted by mcrews

wow....I'm enjoying all this 'v8 hotrod talk' although it is over my head!

I have an Infiniti Q45 Sport w/IMPUL Body Kit. Bone stock 4.5 liter w 340hp, 5 speed auto, 2:76 rear ratio.
I run 245/50/18 (27.7") on stock rims instaed i=of the factory 245/45/18 (26" dia).
I also have 265,000 miles. My best hwy mpg has been 32MPG

I love Nissan engines, done many 100,000 miles on them from the old 180B Datsun which was turbocharged to the Skyline FJ20 DOHC 8000rpm screamer to the turbocharged R32 Skyline straight 6. Bullet proof engines all of them.

32mpg US is 38.4mpg imperial - that is outstanding for a 4.5 V8 making 340hp.

[bazman]

Originally Posted by Iexpedite

Sounds like you have done almost everything possible to maximize the efficiency of your horsepower motor. Some aero mods would help (I'm thinking belly pan). I am sure you don't want to ugly up your cars profile in the name of efficiency.

I was thinking about a higher overdrive gear in the transmission. How many RPMs are you running at your desired speed? My guess is they are quite low and there is little to be gained here.

I know the Holdens are typically overbuilt to deal with the bad roads found in your neck of the woods. Is there any potential for weight loss?

The lifter thing is interesting. Didn't know that was out there in the aftermarket. I would make the changes you mentioned and see where you end up. If that didn't do it...Like the other guy mentioned, a smaller cam with the psi turned up may be your best option. The boost would cover the reduced power being made on the motor. PM me or post the changes you see with the lifters, that’s just cool that they have those. I am picturing an adjustable screw that bleeds oil based on how far you back it out. Is that correct?

I am looking at a belly pan under the front, I think that'd be easy enough for someone who knows what they are doing (not me lol). My fabricator would cry if I covered his work of art stainless exhaust and air intake plumbing under the rest of the car

Weight loss? Later yes, when it stops being a daily driver I will cage it and lose weight plus add a 6 sp. We'll get great highway mpg then plus have a club car for fun.

The lifters bleed down via some proprietary hole (technical term ) that pump up under higher rpms as the holes are too small to handle the rise in pressure is my guess so then they become anti-pump lifters. That is my take on this... but I could be wrong

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[bazman]

Originally Posted by smokey442

I think the Rhoads lifter is going to hurt you. If you're going to try it do it on intake only. The exhaust closing ramp on all cams is very gentle. If you're running a knock sensor its going to hear the noise and pull out some advance. High intake vacume=higher pumping losses. Open waste gate at low throttle to reduce exhaust back pressure. I'd try retarding the cam 5deg. keeping exhaust valve closed longer extracting more usefull work from still relativly high cylinder pressure. Later intake closing lowers vacume. Pull an 8"hg depression into crankcase via intake vacume. Don't pull any more as gaskets and seals don't like it. Last heat the fuel to 180deg. F This will extend your lean burn limit and slighlty higher flame speed. It may tend to vapor lock on hot restarts. Turn off fuel pump while cranking cures that.

Thanks for your insights here Smokey, you are more advanced than I in what you are describing and you may be right. I'm hoping that other factors will compensate so we achieve an overall gain, we will certainly find out.

In any event you've given me food for thought and I will run it past my tuner to see what we can do here.

I'm thinking that something like this could compensate for extra pumping losses from more low rpm cylinder pressure NanoTechnology Lubrication Breakthrough

at $800 for a treatment I'd bloody hope it works lol

I have used Militec before and believe that is the reason I now have such good leak down despite 110,000 miles.

[bazman]

Thanks to all for your thoughts BTW - that was cool!