parish8

iTrader: (6)

thinking about my next project. i want 800-900rwhp thru a locked auto. quiet, smooth, not lumpy.

i am wondering about the positives and negatives of running a stockish cam and low displacement. consider a aluminum block 5.3 with a very mild cam. something that will lug down the highway at 1200rpm at 70mph in a 3000lb car without randomly missing. car should get good mileage.

now when i want the power turn up the boost to whatever it takes. 25+psi if needed. it will be intercooled and e85. the new precision billet wheel turbos will make a ton of boost.

only downside i can think of for sure would be an increase in exhaust pressure pre turbo but with a small cam and minimal overlap the pistons should be able to just pump that exhaust right out. the iat's would be higher but soo what with an intercooler and e85.

i got 17mpg(e85) in my 700+rwhp g8. it was 4200lbs and had a 6.0 in it. seems like 20+ would be easy with a smaller engine and a lighter car.

what are the drawbacks? can i just let the boost make all the power that i want just by turning it up?

wilson34

iTrader: (7)

Man you must be living in my head. Something I've always wanted to do.

HotRodBOB

I was going to be asking the same question later on... I was thinking maybe tuning could solve that problem. have 2 tunes. a nice street cruising tune with very low boost, then a second one when you want to pin it to win it and press the ooooooh hear we go button and later gater! I dunno just a thought

eviltwin_1987

iTrader: (18)

would the mpg really change that much with a 5.3 compared to a 6.0?

98Z28CobraKiller

iTrader: (17)

The small displacement will not really save you much in the way of gas mileage and will make the combo more complicated to put together. For your goals, I would do this:

6.0 with forged rods and pistons at 10.5:1
AFR 215's with inconel exhaust valves and .650 lift springs (due to the boost required to reach your goals)
Stock rockers
LS6 cam
PT47-88
AMS boost controller w/ CO2
Good 120# injectors
4L80 transmission w/ lock up 3600ish converter
3.25 gear

I don't buy into the 17+ MPG on E85 thing though unless you are talking strictly highway. That E85 burns FAST.

stock48

iTrader: (17)

I think your on the right track with the L33 idea. If $ allows you could swap out the 799/243 heads for a set of Trickflow 205/58cc heads, and go with something like the Isky 206/.553'', 114lsa. That cam along with the extra low lift head flow, and compression will skyrocket the effeciency.

skinnies

iTrader: (33)

I think it's completely doable, especially with the right tune and converter/gears. I got 22mpg in my rx7(5.3/tc78), it's lighter(2600lbs) but also is turning the big 33x22.50 hoosiers, surely with a smaller tire it'd get better mpg. I also cruise around 18:1 afr on the e85, even with it lean it doesn't stumble all over itself. This was also with 3.55 gears and a th400, with OD and a good locking converter I don't see it being a problem. I'd think a rods/pistons/small cam 5.3 with a billet 76 would work great, run a 3.23 out back with the OD, tight converter, and run a transbrake.

BigRich954RR

iTrader: (1)

only drawback is more load on the headgaskets and fuel used . but over all a good idea

91blowthru

im very interested in this as well,
a 76mm turbo can be pretty stout on street and can work more to its efficiency, with less than the common 350-370ci behind it.. i think 300-325ci would be sweet with a reliable bottom end and high boost.

(also the aluminum 5.3 would help get some weight off the front end of my gmc sonoma opposed to my iron 6.0L... i like it!)

1320

iTrader: (6)

mpg is all the drag added up. Weight and aero and driveline losses is the mpg winners. The lower you make the needed hp to maintain a speed, the less fuel used. Until the engine you use just makes too much even at low rpm.

I filled up our honda insight (first gen 2000model). It averaged 70.3 mpg....for the last tank. Its 1750 lbs, and shaped like a bullet.....manual trans etc etc etc.
Even 5 psi less in the tires and you see it in the mpg. Its very very sensitive because its very good at what it does.

I wouldnt worry about power......looking at the economy.......I d build the lightest car I could afford too......

23-30 roadsters, a henry j, opel.....cars small and light. The opel would be fun I think. Alum 5.3, coated pistons and chambers/valves, with cylinder kill, and heat the IA with the heat from the exhuast. Try to run super heated intake air like smokey.......then run it lean and boost it, to cause lean burn.

I just want to see someone try it.

hellbents10

iTrader: (10)

Weight, tight converter and small cam are all your friends here. Also the small bore 5.3l is a great way to go for economy, same thing the OEM's have done.

Down sides, getting into boost with a tight converter, and having a small window to make boost with limited rpm and a small cam. It is very doable though, and I would look no further then a LS6 cam for fuel economy.

I got 24 city and 33 highway with my L33 t-56 S10 when I was driving it every day. On E85 I would have seen 19-26 or better I am sure. It also had an LS6 cam and intake and made 330 to the tires. This with a 374 would make 825 to the tires at 5500rpm.

parish8

iTrader: (6)

sounds like i am not the only one thinking about this.

soo the big downside that i see appears to be the delay of getting into boost that this set up might cause. a loose converter with lock up would help you get off the line and at the same time help get better mileage on the highway but i would still go on the tighter side. i agree this would hurt your times at the track some.

then there is variable valve timing and dod. i am not much of a fan of dod but i wonder how the variable valve timing would effect things. probably get more out of just running it on the lean side.

the 17mpg with e85 in my g8 was all highway and running at stoich. more like 11mpg in town. if i could bump that up to 15city/20+highway on my next car and be able to drive to the track and bust off some 9sec runs i will be happy.

old motorhead

iTrader: (10)

How 'bout an LS2/3 block (lite) with a 4.8L crank? About 5.4L's with LS3 bore. Big bore = unlimited head choices. I'm considering this if my LS3 ever grenades. Short stroke should be easy on the bottom end. Less cubes equal more mpg plain and simple. I don't know how durable the long 4.8L rods are. With the longer rods, you can use available LS2/3 pistons. If you have to use the standard length LS rods, it might get complicated...custom pistons etc.

atomic 6

This is exactly what I have been thinking, moving less air at low rpm, no boost, should equal less fuel(even better at +15:1 afr)but more than enough HP to move the car. then higher rpm, and a bunch of boost for power.

Only thing to consider would be the higher boost for more power would equal high HP losses to drive the turbo. It is said that at 2:1 exhaust/boost you are using 1HP per 1 LB/MIN of air(so 10 hp) At 1000 HP you are using 100 hp to drive that turbo. This info is from boost engineer's own tests he posted on The Turbo Forums,

"The normal rule of thumb is that it takes 1 hp (at the turbine) to move 1 lb of air/min at the compressor at a 2.0 pressure ratio. 1 lb/min will make between 9.5 to 10.5 engine hp. "

So now the exhaust design becomes more critical. If you have a inefficent design, and the exhaust pressure ratio is higher than the 2:1 that the guideline is using then you are stealing part of your final hp to drive the turbo.

Then that requires a bigger turbo to get that back, now you have a bigger heavier turbo you have to lug around everywhere.

Next question is will a LS2 block stay sealed at those power levels, or would a L33 with a 4.8 crank(aluminum 4.8) be a better way to go.

Alot of ideas to toss around.

rons 00z

iTrader: (10)

something like that would be really cool. if you could someway use a Exhaust gas recirculation valve or something so if you did want to go WOT you can cut that heated air and get some cooler air in the car to keep the motor from melting down when making power.

Grr

iTrader: (2)

when my current ls1 blows that is my plan too
L33, domed pistons and 58cc heads. Should be around 13.5:1 compression, run it on E85 and hang a Comp Turbo 7271 billet triple ball bearing with 1.32 divided housing and a spool valve. Should be capable of 15psi at around 2800rpm and make an easy 800whp even without going over 6500rpm

rons 00z

iTrader: (10)

i have a similar combo i'm doing like that but it's a 383 with the same SCR. just dont know what induction i plan on using yet

427

iTrader: (3)

I have been thinking about this for my Silverado SS. Been towing a trailer a ton and thinking about fuel mpg. Losing the pumping losses is what I have been thinking, trying to run the engine with no vac and using boost for power. Right now with the 6.0 engine I run between 2 inches vac and 5psi boost with hills and level ground cruising. My rpm is between 2200-2600 most times with converter locked. I would like a small V8 with DOD and boost control on the throttle pedal. Leave the throttle at WOT when cruising and de-activate cylinders to slow down or add boost to climb. Those 12 hour rides get me thinking! I do run my intercooler pump only when I exceed 30% throttle as the hotter intake air helps MPG, I originally tried this in the Nova and it was worth .5 MPG.

Kurt

Fireball

iTrader: (21)

LOL...you just described a turbo diesel engine

427

iTrader: (3)

Close. A diesel uses fuel volume for control of power. This works with diesel but would make lots of good parts into bad on gasoline!

Kurt