Fuel economy pontiac 535 vs LS3

[Formula400]

Hi!

I'm somewhat in a bind on witch road to take and trying to gather as much information as possible.

The LS3 on a pure fuel economy would be a dead winner but the problem is it requires a ton of modifications before the government would approve of an engine swap like this over here... (Sweden)

So before I plow down a x amount of money in a project like an LS3 in a Firebird 2nd gen I'd like to know what the benefits would be vs taking the AI2 road and 535.

The LS3 would be a Corvette one at 480HP and 475 Torque. In order for me to get it legal I'd have to get the entire setup from a donor car including the catalytic converters and every adapter in the book apart from having to alter the entire front and rear suspension. (The front and rear suspension is a requirement for getting the car labeled as altered vehicle witch would enable me to be able to install a LS3 so as it looks like now it'd be about the same price as a 535 with rollers but with added work to the car)

The 535 would be specced for easy driving aka below 6000 RPM and idle like a baby cause that is what the car will live 98% of the time and jumping around in my seat at the stop lights isn't that much fun in my opinion. (So around 550-600 HP and torque) Carb I'd thought to use is a Quadrajet 800cfm one

The Transmission is a 200r4 prepped with a (lockup converter) for the torque and the rear has a 3.73:1.

So how much would I be seeing in fuel consumption on a 535 VS a LS3 with the transmission combo and rear and described?

Any input is appreciated even stuff not related to fuel economy.

:cheers:

Sven

[ProdigyCustoms]

Project EmtpyNest 535CI gets 10 MPG around town, on the interstate, on the dragstrip, on the autocross. It is a equal opportunity offender!

Michaels 540CI in Project Prodigy is the same way! 10MPG

Big cubes equal big fuel bill.

But god almighty the torque!!!!

[deuce_454]

are you sure about the cats.. i have seen many sweedish cars with new powerplants and no cats that were approved...

pm janneslanne he has a 1. gen with an ls engine.. lives in stockholm, im sure he will answer any question...

and my vote is a 3gen engine,

[Formula400]

Hi!

And thanks for the input so far.

Deuce: Well according to Swedish Vehicle unit it's required as well as from SFRO which would be the one's that can label the car to "altered vehicle"

But just in case I'll send Janne a quick PM... thanks for the tip.

Prodigy: 2.3 liters per 10 km that is a lot... but that is also what my 389 took on the street sadly enough (old worn th350), by going with a mild cam and low highway rpm wouldn't that help the fuel economy well below 2 liters per 10km or 11MPG on a 535? my aim would be 15-18MPG wold that even be possible with a 535? (LS3 would easily beat that to my knowledge a 480hp 475torque wold give like 25-28MPG with my setup?)

I'll check out the projects you mentioned, thanks for the tips!

//Sven

[camcojb]

It is possible to get 15-18 mpg on the freeway with a 535 and efi, when tuned well. My Procharged 540 made over 800 rwhp and got 19 mpg on steady state freeway driving (70-75 mph) on a couple of 100-200 mile trips. But it didn't do so well in town, so it'd be tough to average 15-18, but doable for freeway driving in my opinion.

Jody

[Vegas69]

If you are concerned with fuel effieciency then a 500 cubic inch motor probably isn't the ticket. It has to be injected, holley and fuel mileage don't go together. I get 10 on the freeway with my 489! Of course that includes some romping here and there. Injection is in my plans eventually.

[Formula400]

Hi!

Well I'm concerned about fuel economy to a point at least.... since gas isn't getting any cheaper and I use the car as a daily driver during summer time.

But having 550HP/Torque at the flywheel vs 800 at the tires should do a lot to towards fuel economy?

And yes if I went BIG I'd go the EFI road in a year or so for sure. (plans would be to use my Quadrajet carb that shold flow 800 cfm until the EFI got installed)

How is the LS3 handling in a heavy car? (3968 lbs)

//Sven

[Pantera EFI]

Yes, I agree the the correct EMS choice will make the difference, so "do it now".

The MOST important factor is the Weight Difference.

The lighter car (LS-3) will be faster.

Lance

[72blackbird]

You can get 550-600+ hp from a Pontiac motor without resorting to an IA II/500+ CID setup. Plenty of Pontiac guys just use their 400 block (preferably a no.481988 or earlier model), buy a 462 stroker kit, solid roller cam, and some KRE's or E-heads. This build can be bought in the USA for about $10-12k or built at home for less. Plus keeping it pure Pontiac gets the official seal of approval from everyone at any Pontiac meet.

I would only run a 535 if I wanted a 750-800+ hp Pontiac- that much power is overkill for the street unless you want to go 200+ mph or 8 secs. in the 1/4 mi.

Fuel economy is another matter, especially with big bore carbed engines- there is no way an IA II 535 will pull down better mileage than a 462 stroker, since the bigger motor needs more carb. The 535 will eat more gas, even with the same carb as the 462. The LS3, on the other hand, is the true winner in this category- the latest in GM technology lets you run a 480-500 hp motor and still get 25-27 mpg.

Geno