914turboford

I'm looking at putting an LS1/Vortec in a Mercedes. I want to know what combo would give me a modest 250hp or so and get close to 30mpg on the freeway with a 4L60E and 3.07 rear axle in a 3200lb 450SL. I don't want to have the ECU reprogrammed. I'd like to use all stock parts and do this on the cheap. I'm thinking about a 4.8 vortec short block with early LS1 heads/cam and a LS1 ECU. Is this a workable combo? Will I likely achieve my goals with this?

TooLateVTEC

iTrader: (2)

Im not sure about the 4.8, but the stock 5.3 already has more than 250HP.

Since your looking for max MPG, I would be looking into a 6 speed instead of the 4L60E. The T-56's have 2 overdrives, im pretty sure with those gears and in 6th gear doing 70 mph, it would be turning about 1500 RPM's.

allngn_c5

iTrader: (3)

my m6 with 3.42's turns 2000 rpms at 90 mph and gets amazing gas mileage for being a 402 that has a few tuning glitches to correct. BTW a stock ls1 puts down 290 + rwhp in an a4 application. An a4 with your 3.07 rear gears should be pretty decent. GM calls the 3.15 ratio their performance ratio as compared to the 2.73's that come without optioning for the 3.15's

RAACCR

Junkyard stock 4.8 out of a truck; get the computer, harness and tranny from the same truck, too. Swap out a pre 2001 LS1 intake for hood clearance; you should be able to find one for close to free, since everyone swaps out the newer LS6 intakes for higher performance. You may still need to do a cheap mail order "mini-tune" to the computer to compensate for gear ratios, tire diameter, etc. That would be a nice cheap high-mpg swap.

NemeSS

iTrader: (127)

4.8 with milled heads, ls6 cam. ls6 intake, and tune. will prolly make more than 250hp as is

jmilz28

iTrader: (13)

Yeah, you're going to need some flavor of tuning - there is no way around it. You're kidding AND shortchanging yourself if you think this can be done 100% without a good tune. If you really want max MPG, you need to do this anyway. In reality, a street tune would be more important that a dyno tune - since that's where the part throttle stuff would be maximized. I don't think you'll get there with an auto, MHO, but any of the 5.3s or 5.7s with a six speed and an optimized tune will. Fact is, the 4.8s get no better mileage than the 5.3s in real world driving. Seen this validated with hundreds of truck owners. This is true also of the 5.7s if you keep your foot out but the 5.3s are much more plentiful, you'll spend a grand less getting a 5.3 package. If you've just got a burr in your saddle to max out MPG, get the 5.3, use an LS1 intake, stock cam, slap on the AFR205s or new TFS205s, long tubes, CAI, and tune it on the street and the dyno. You'll be over 25 highway MPG with an auto, bumping on 30 with a T56. There are guys with 6 speed C5s and AFR205s knocking down 30mpg. Different aeros but similar weight and gearing to your car.
But practically speaking, the added expense and trouble of interchanging internal parts, the aforementioned aftermarket heads, or the cost of the T56 will more than offset the benefit of the added MPG. 5.3 truck drivetrain, LS1 intake, headers, CAI, and a PROPER tune will get you most of the way there for the least cash outlay.
So now you have two routes: one that is economically efficient, the other that will prove your MPG point. Which way you go is up to you.

LS1crazy01

iTrader: (14)

Your gonna have to tune it. A tune is not that much more money when your talking about buying a motor,trans,ecu and everything else needed for the swap. You will spend about 400-450 for a professional dyno tune. Sounds like a great build. Good luck!

914turboford

Thank you for the input. When you say "tune", what you really mean is ECU programming, right? The AFR205's are injectors? What is a CAI? I don't think I'll get a T56, too pricey and I don't want to hang a clutch pedal. But just out of curiosity, if I do decide to hang a pedal how would a T5 or Getrag compare to a 4L60E in terms of mpg. I think they have approx. the same OD. I calculated 1650 rpm at 65mph with a .65 OD. I'm a bit leary about having the ECU reprogrammed partly because I don't think tuning for mpg is something these tuners are into.
Brian

jmilz28

iTrader: (13)

Where are you located? There are some sponsors that do great street tunes: Vengeance, PatG, Icon are but three that pop to mind but there are certainly some other badasses I didn't mention. Frost, edcmat, lots of them.

Yes, tuning via laptop and software playing with the ECM/PCM (HPTuners, EFI Live, LS1Edit, etc).

AFR 205s are cylinder heads, awesome out of the box and a bolt on deal. Search AFR and Tony Mamo.

CAI = Cold Air Induction

If you're going to hang a clutch pedal, go T56, otherwise don't bother. By the time you get a 5 speed to handle your motor, you'd have been better off with the 6 speed.

Yes, a MAF is your friend but if you don't have a pig rich factory tune (though many do), you're missing out on a lot and POTENTIALLY asking for trouble doing serious bolt ons with no tuning. Many people have picked up 10% HP increases and MPG improvements more than that with proper tuning.

Don't worry about power, even the little 4.8 is likely to get your desired power even through the A4. You'll get 300rwhp with no compromises with headers, exhaust, and a good tune with no compromises.


A good tune is a MUST, especially if you start mixing and matching factory components. A basic tune is important for gear ratios, speedo, etc. but you'll benefit huge from it with shift pressures, shift points, spark and fuel curves (as better spark and air fuel benefit power and MPG). Would you build a hipo motor, slap any old carb on there and not spend any time jetting or adjusting? It's MUCH easier with a laptop and wideband. Get a good tuner and that may be the best money you spend, don't be leary - be educated. You don't put together a combination of parts, components, and systems and HOPE that it works optimally. That's would be silly.