If you are only getting 18mpg hwy then something is really off. You should at least be getting mid-20's with high 20's being relatively common. My 92 which needed a tuneup for sure, still averaged 26mpg (based on miles and fuel needed to fill up again, not the CPU readout) on a 300 mile trip. My boosted c5 gets 30+ mpg on the highway consistently.

You could have a bad coolant temp sensor, stuck injector, bad O2 sensor, etc that is causing the car to run pig rich. Or you need to shift out of 2nd gear haha. Get an ALDL cable, scan software, and an old laptop and log it while you drive for awhile since you're tech-savvy.

 

I'm familiar with that process and I still stand by what I mentioned before. I'm not sure how to adjust the AFR to a "lean" tune for fuel efficiency while cruising.

 

It's definitely running rich, one sniff of the exhaust fumes will tell you that. 113k miles and check engine and service ASR (traction control) lights are both lit. Those will be taken care of right after the oil leak is handled.

Any thoughts on the services provided by that site. The testimonials sure sound good, but you know they will only post the best reviews and none of the bad ones. Basically, for those that don't feel like reading about it, they have give you logging software to use, you drive the car logging the data, email them the logged data, they set-up a tuning profile, email it to you, you load it in the PCM, drive the car and log data, send it to them, and so on, up to three tunes for $115, $35 any additional tunes. Personally, while I am tech-savvy, I am far from knowing what each setting does in the PCM programming. I think this would be a very good learning experience as I'm a hands-on learner. It would give me the opportunity to see the changes being made to the various settings, and experience what each change does first hand.

I'm not expecting a huge change in fuel efficiency, but 3-4 MPG is worth $115 to me. I do a decent amount of driving, put over 50k miles on my truck in the past 2 years. Had 237k miles when I inherited it, now has 293k miles.

 

Hotcam
1.6:1 roller rockers
Long tube headers
rear end gears
Dyno Tune

http://home.insightbb.com/~nathan.pl...rformance.html

 

I've used the software and equipment that he uses. It's good stuff. I believe that anyone wanting to tinker with their C4 should have a scanning software at the very least.

As for his claims on a "stock LT1", I have my doubts. Over 2 tenths, 3mph and 3-4 mpg???? I've never tried to extract optimal power and efficiency from a stock LT1. There are people on this forum that have. Maybe those claims are possible.

 

This thread has a lot of good info. 1st vette your in the same boat I was in. I wanted 50 more HP simply because I believe a 350 should make 350HP or more. But after all the research I did (spend lots of days reading) the best way to make power on an LT1 is to open her up. she needs a cam heads, etc...

The best option for under 1000 is to change the roller rockers (my 2 cents). Good rollers and spring parts w/labor around 700 at a good shop. If you can do it yourself knock off half the price. I have another thread on here that I created asking for advice on the rockers. One of the members even provided a full part list with numbers. The mod adds around 15HP + or - on parts and engine shape.

good luck and if you do find an affordable upgrade please email me and let me know.


Now another question look at these two articles from Super Chevy and please help me out with this performance improvement question.
http://www.superchevy.com/how-to/vem...throttle-body/
http://www.superchevy.com/how-to/vem...injection.html
If I add the open box lid, the Mass air, and a 52mm TB. Will that become 18RWHP like they talk about?? What am I missing is it too good to be true?

 

Yes it is too good to be true. With these types of mods people have a tendency to think cumulatively, that is, everyone adds up the horsepower numbers claimed to create a total gain. But that type of thinking is incorrect here. The numbers you should be concerning yourself are the amount of air that the engine can take in. An otherwise stock LT1 can take in and exhaust only a certain amount of air. You can open up the airbox, modify the MAF for more flow, and put on a larger TB. Now your engine can gulp more air through its "mouth". But you have done nothing about the maximum amount of air the "throat" and "lungs" can take. If you make your mouth much bigger but still have a narrow throat and small lungs you can't breath anymore air than you did before. So you cannot change the maximum throughput of air without changing the amount of air that the intake, heads and exhaust can handle. And to overcome that restriction you have to install a larger intake, heads and better exhaust
such as long tube headers. The cam has to match also. You can get some gains with a cam but that still has it limitations with an otherwise stock engine.

So those modifications may provide some marginal gains but there are definitely not cumulative no matter what the magazine articles imply. Remember they're in business to make money - have to make the advertisers happy.