Does 15.28 MPG's sound ok?
10-03-2012, 10:46 PM
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Does 15.28 MPG's sound ok? Just wanting to see if I'm out of touch, or if there really is a problem with my car... Guess I'll start with specs:
Stock LT1 short block.
Ported heads and intake.
Hotcam.
58mm TB, and bigger MAF (not sure the size, but the MAF tables in the tune were modified for it).
Longtubes, ORY, non-stock muffler.
3000 rpm converter (rear gears are 2.73's though).
If some of the specs sound off, there's a reason for that. This was a build with a buddy who helped me out a lot on parts and putting everything together. He threw a basic tune on it to get things going, and after driving the car for a bit i noticed it was getting pretty bad mileage compared to what I figured it should be getting. We tried some tweaks to the tune that didn't help a ton.
I mostly want to do this myself so I can start to learn how to tune. I'm basically seeing what I should look into to get things running good, and then start to play with things that will maximize the cars potential. I have a couple of logs already in case anyone is interested in checking them out.
Also, I have a wideband on the car (in the passenger side of the y pipe). It hovers around 14,7 when cruising (though it seems to spend a lot of time in the high 13's), but when I stop and get out it smells like someone dumped a can of gas. I've also been told from co-workers that they start to get a headache driving behind me, lol.
Any advise is more certainly appreciated!
Stock LT1 short block.
Ported heads and intake.
Hotcam.
58mm TB, and bigger MAF (not sure the size, but the MAF tables in the tune were modified for it).
Longtubes, ORY, non-stock muffler.
3000 rpm converter (rear gears are 2.73's though).
If some of the specs sound off, there's a reason for that. This was a build with a buddy who helped me out a lot on parts and putting everything together. He threw a basic tune on it to get things going, and after driving the car for a bit i noticed it was getting pretty bad mileage compared to what I figured it should be getting. We tried some tweaks to the tune that didn't help a ton.
I mostly want to do this myself so I can start to learn how to tune. I'm basically seeing what I should look into to get things running good, and then start to play with things that will maximize the cars potential. I have a couple of logs already in case anyone is interested in checking them out.
Also, I have a wideband on the car (in the passenger side of the y pipe). It hovers around 14,7 when cruising (though it seems to spend a lot of time in the high 13's), but when I stop and get out it smells like someone dumped a can of gas. I've also been told from co-workers that they start to get a headache driving behind me, lol.
Any advise is more certainly appreciated!
10-04-2012, 06:00 AM
#2
I would say that is some bad mpg. And if your smelling fuel....I'd say you are way to rich. Stock LT1 with hotcam should still get you into the 20's mpg out on the highway. I got 25mpg on interstate doing 85 mph with a supercharger on it. I'd so a mail order tune from pcm4less and dial it in from there or do datalogging and have them fine tune it for yeah.
10-04-2012, 10:12 AM
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15mpg on highway would be horrible my car is running real rich and im seeing around 20 mpg on highway which is still kind of low, but i have a lot that needs to get replaced and tweaked... i agree with above though get a mail order tune and then fine tune from there, best way to do it...
10-04-2012, 10:36 AM
#5
The point I was trying to get across is that even with the supercharger on there everything else was bone stock it was still pulling good MPG. It was pulling 17 vac while on cruise so the supercharger wasnt being used at that point and maybe/or not more of a parasitic loss at that point.
10-04-2012, 10:44 AM
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Plugs an wires are brand new. Opti is also reasonable new. Everything was put on when we dropped the engine in in July. I'm actually pretty light on the throttle, and most of my commute is on the highway. I know there should be some smell of gas since I don't have cats, but would it be to the point of giving people headaches?
10-04-2012, 12:01 PM
#7
The raised stall and the 2.73s is a mistake, it will not stay locked up very well with the bigger cam, unlocked slips creates heat and hurts economy. Though with a HOT cam smelling like fuel I would say it is excessively rich too.
Any exhaust leak before the O2 can let in fresh air and make the O2s think it is leaner than it is causing it to add fuel.
The bigger MAF was stupid and the only thing it will do for you is make tuning more difficult. What MAF was it, some of the aftermarket stuff is really unreliable and some of the GM stuff uses a higher frequency range making a heads/cam car actually need to be tuned speed density at higher rpms.
My advise is get at least a 3.42 gear in it, a stock MAF unmolested and then work on the tuning.
Any exhaust leak before the O2 can let in fresh air and make the O2s think it is leaner than it is causing it to add fuel.
The bigger MAF was stupid and the only thing it will do for you is make tuning more difficult. What MAF was it, some of the aftermarket stuff is really unreliable and some of the GM stuff uses a higher frequency range making a heads/cam car actually need to be tuned speed density at higher rpms.
My advise is get at least a 3.42 gear in it, a stock MAF unmolested and then work on the tuning.
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10-04-2012, 12:48 PM
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Gears are on the list, probably the next thing I do after my finger heals (gates and fingers don't mix well). I don't think there are any exhaust leaks, since my wideband is hovering around stoich. The MAF is a stocker with big ends on it. I've thought about swapping a stock on in, and resetting the MAF tables to stock. The BLMS on the passenger side seem to be staying right around 128 (which coinsides with what my WB is saying). Drivers side reads a little lean (130's). I don't think the IAC mod was done to this TB, since the blades are cracked to bring the counts down (not sure if that's the reason for split BLM's). I can probably pick up a stock MAF at pick-n-pull, throw it in with the stock tables, and see what it does. When I'm cruising it stays locked (I thought that the TCC was vehicle speed dependent, and not RPM).
10-04-2012, 02:20 PM
#9
The wideband would read the fresh air of an exhaust leak the same as a narrowband would and both could report 14.7 because the pcm is using the narrowbands to keep it there at cruise..
The cracked blades means the front cylinders are likely lean and the rear rich at cruise/idle and would contribute to split BLMs.
The BLM being near 128 just means the O2s aren't causing a lot of correction from what was programmed. That does not mean it was programmed right. It would be odd if the programming was exactly as much too rich as a freshair leak made it read lean and the canceled eachother out, but if you smell fuel there is something going on. The HOT cam does not have so much overlap it should smell strongly of fuel.
Could it be a dead cylinder on the "lean" side, if it isn't burning it sends fresh air into the exhaust as well as unburned fuel, could explain the BLM split, bad mileage and fuel smell.
The TCC is based on a handful of criteria and programable. If you are keeping it steadily locked at cruise with 2.73s it is likely lugging with a HOT cam which isn't good for anything.
The cracked blades means the front cylinders are likely lean and the rear rich at cruise/idle and would contribute to split BLMs.
The BLM being near 128 just means the O2s aren't causing a lot of correction from what was programmed. That does not mean it was programmed right. It would be odd if the programming was exactly as much too rich as a freshair leak made it read lean and the canceled eachother out, but if you smell fuel there is something going on. The HOT cam does not have so much overlap it should smell strongly of fuel.
Could it be a dead cylinder on the "lean" side, if it isn't burning it sends fresh air into the exhaust as well as unburned fuel, could explain the BLM split, bad mileage and fuel smell.
The TCC is based on a handful of criteria and programable. If you are keeping it steadily locked at cruise with 2.73s it is likely lugging with a HOT cam which isn't good for anything.
10-04-2012, 02:40 PM
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The first thing I would do is put a pressure guage on the fuel rail, turn the key to run, do not start the engine, & watch that pressure. It should come up to 40 or so & stay there forever. If it starts to fall rather quickly, then you're dumping gas somewhere. You've got a leak.
If it falls slowly, it probably isn't your problem.
If you have to ask, is that quickly, or slowly... it probably isn't your problem. But just watching it for a few minutes.... 5, you should not see any drop in pressure.
If it falls slowly, it probably isn't your problem.
If you have to ask, is that quickly, or slowly... it probably isn't your problem. But just watching it for a few minutes.... 5, you should not see any drop in pressure.
10-04-2012, 02:42 PM
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Gotcha. I'm looking at picking up a set of gears here in the next week or so (GM 3.42's). Would the lack of cats cause some smell of fuel? I'll try and do the IAC mod ASAP. I'll also start looking for any type of exhaust leak. I think the only area it could be leaking would be the flanges on the head side. The gaskets on the collector flange didn't look like it was leaking when I installed the LC-1 (I had an AEM in there before that wasn't reading right). How could I test for a dead cylinder (besides a temp gun). I'm not hearing a miss anywhere. Would a datalog pick it up?
10-04-2012, 02:44 PM
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The first thing I would do is put a pressure guage on the fuel rail, turn the key to run, do not start the engine, & watch that pressure. It should come up to 40 or so & stay there forever. If it starts to fall rather quickly, then you're dumping gas somewhere. You've got a leak.
If it falls slowly, it probably isn't your problem.
If you have to ask, is that quickly, or slowly... it probably isn't your problem. But just watching it for a few minutes.... 5, you should not see any drop in pressure.
If it falls slowly, it probably isn't your problem.
If you have to ask, is that quickly, or slowly... it probably isn't your problem. But just watching it for a few minutes.... 5, you should not see any drop in pressure.
10-04-2012, 03:21 PM
#14
oh np didnt take it that way and pm'ed yeah back......its all good. Kind of hard to explain things sometimes and try to keep it short. Somethings I could write a page on but gzzz by the end I would proof read and say 
to myself.......lol
to myself.......lol 
10-04-2012, 10:50 PM
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And that's a lot bigger cam than what I have. I know the tune is off, but could the converter be hurting me some? It's a re-stalled stock unit. Would swapping to something like a Yank help? I'm trying to figure out everything that could be affecting my mileage.
10-05-2012, 07:24 AM
#19
A locked stall converter wont hurt highway mileage.
Thing is a HOT cam and 2.73s needs more cruise rpm to keep from lugging due to the raised powerband of the cam. Lugging the engine could hurt mileage or cycling in and out of lockup because the cam is below it's powerband could hurt mileage.
Thing is a HOT cam and 2.73s needs more cruise rpm to keep from lugging due to the raised powerband of the cam. Lugging the engine could hurt mileage or cycling in and out of lockup because the cam is below it's powerband could hurt mileage.
10-06-2012, 04:53 PM
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I think that's happening a lot while I'm driving down the freeway. Would swapping to shorter gears allow me to bump the TCC speed down a little?