goldhunter_2

so what RPM is to low ? 1300 , 1500, 1700, 1900 ?????????


I am doing Ls1 engine swap/build in a 1980 C3 vet and I'm struggling with figuring out what rear end ratio I need , the stock rear end is 3.07 and I'm using a 2004r tranny with 0.67 OD gear so I need to figure out what RPM range a 1998 ls1 corvette motor should run at normally and at what point is the rpms to low (lugging engine) My goal is available top end high speed with fuel economy on average highway driving (70-80mph) and would say maybe only 10% of the time is town driving. I was thinking if I could set the rpms lower I get better mileage on average highway driving and can always push the pedal if I want to go more, but at what point am I hurt the engine and my fuel mileage?

I know this isn't a great comparison but was just to try getting a idea. My old 97 suburban has 3.42 rear end , 350 (non ls) motor and 700r4 (.70 od gear) here is the rpms I wrote down today to try to get a idea ........but it gets bad to no gas mileage is why I am asking about how low of rpms the ls motor can go.

at 50 mph = 1200-1300 rpms
at 60 mph = 1500 rpms
at 70 mph = 1850 rpms
at 75 mph = 1950 rpms
at 80 mph = 2150 rpms


Does the LS1 motor need to be this high of rpms or can it be lower at these speeds ?
.

RPM WS6

iTrader: (3)

I see rpms as low as about ~1100 at certain cruise speeds in OD/lock-up with my 2.73s, .70 OD ratio and 25.66" tall tires. This is not a problem at all. But that is with a stock LS1 engine, if you plan on a big cam then then you may have issues cruising at that low of an rpm.

When doing the math on this, remember to keep tire diameter in mind. If you've got stock wheels on your C3, then you've probably got 255/60/15 or 225/70/15 tires, which are quite a bit taller than the 275/40/17 or 245/50/16 tires that would have come on an F-body with an LS1.

goldhunter_2

perfect just what I needed , thank you !

I was hoping for around 1300 in od to save gas but just got worried I would hurt the motor that low

777

iTrader: (21)

Normal day to day driving, I shift 1st gear at ~1500rpms (to try and avoid the stupid skip shift) and all the others <2000. The engine makes great low end torque in stock form. I'd say the lowest I would go in overdrive is 1200. I usually cruise sixth around 1300 and it's plenty, sometimes I'll even go close to 1000 @ ~50mph, but then I don't really have much power to pass or anything, nor do I want to push the engine at that low of rpms.

goldhunter_2

yep I do have the 255/60/15 (27.04) tires

Arctic2002ss

Yes, a stock cam has no problems with the rpms you listed and is close to normal for an LS motor. My cammed LS1 did not like to go under 1700 while cruising.

goldhunter_2

my ls motor is all stock I'm not really looking to do any upgrades the way I figure it is this is already 115 hp more then original and fuel injected and that's enough upgrade for me

usafws6

iTrader: (10)

3.42 will be fine, your suburban gets bad mileage because of its weight. And besides with tall tires like that you should have no problem cruising on the highway.