Tuning issues for 383 LT1 motor possibly??
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Joined: Apr 2002
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From: Lincoln, NE, USA
You don't need a vacuum gauge. Vacuum is the manifold pressure referenced to one standard atmosphere (14.7psi = 101kPa = 29.92"Hg). Manifold absolute pressure is the pressure in the manifold, referenced to absolute pressure. Same number, different reference point.
You can figure the vacuum from the MAP..... BAR - MAP = Vacuum. If the barometer (BAR) is 100kPa, and your MAP is 90kPa, your vacuum is 100 - 90 = 10kPa = 3"Hg. Its not likely you would ever get "0" pressure loss in the filter/intake ducting/MAF/TB. But 10kPa loss sounds excessive.
As air velocity goes up, the pressure loss in each component increases with the square of the velocity. Assuming uniform volumetric efficiency, going from 3000rpm to 6000rpm would increase the pressure loss in the intake track by a factor of 4. That's why as air flow goes up, MAP goes down. 10kPa loss is too much. You want to see 5kPa or less.
You are losing 10% of the available barometric pressure. That means the density of the air in the cylinders is only 90% of what it could be with no losses. 10% less density means 10% less HP.
You can figure the vacuum from the MAP..... BAR - MAP = Vacuum. If the barometer (BAR) is 100kPa, and your MAP is 90kPa, your vacuum is 100 - 90 = 10kPa = 3"Hg. Its not likely you would ever get "0" pressure loss in the filter/intake ducting/MAF/TB. But 10kPa loss sounds excessive.
As air velocity goes up, the pressure loss in each component increases with the square of the velocity. Assuming uniform volumetric efficiency, going from 3000rpm to 6000rpm would increase the pressure loss in the intake track by a factor of 4. That's why as air flow goes up, MAP goes down. 10kPa loss is too much. You want to see 5kPa or less.
You are losing 10% of the available barometric pressure. That means the density of the air in the cylinders is only 90% of what it could be with no losses. 10% less density means 10% less HP.
Thanks for the info...I'll keep up to date with the tuner and see what we've got going on. I'll probably try cleaning the air filter first and see what that does. I wouldn't think that the MAF would ever truly be a restriction in the intake system, or at least a big enough restriction to worry about. Probably be looking into a 58mm if that doesn't do anything for me. Looks like a 58mm throttle body and long-tube header installation are on the way for me.
Thanks again!!!
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Are you running a ported MAF? Just curious.
We played around with this at the track on night testing differetn CAI's and such. You could notice a differnce between a ported MAF and a stock MAF(both properly tuned for) with the MAP readings. It wasn't much at all but I'm not nearly at the power level you are.
We played around with this at the track on night testing differetn CAI's and such. You could notice a differnce between a ported MAF and a stock MAF(both properly tuned for) with the MAP readings. It wasn't much at all but I'm not nearly at the power level you are.
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We tried this the same night and there was no differnce between a Granatelli and no intake and PCM set to speed density mode. This might be due to the rought entry for the air getting into the TB.
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Joined: Dec 1998
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From: Cleveland, Ohio
You need a bigger TB. Get the AS&M mono blade and be done with it (assuming your intake is ported for it, if not you should have it ported to match). 3" of vaccume will cost you a big chunk of HP. A vaccume gauge is a good way to make sure you are geting good data, but the parts store gauge is not as sensative as the map. Also, I would go with a set of kooks 1 7/8' lts. I made good power with a set of hooker 1 3/4", but I have been told there is more to be gained from the kooks. Looks like you are starting from a good spot. Get the inlet and exhaust squared away and make sure the valves are lashed properly, you will see a big improvement. Good luck.
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From: Lincoln, NE, USA
On the printout, it was reading right around 13.0 or so...the sensor that we tuned off of was actually reading about 12.5 or so. He didn't want to get too lean with it because we don't have the knock sensors enabled. It would jump quite a lot of horsepower everytime he would lean it out though. What should the A/F ratio be?? Keep in mind that I have a 12:1 compression engine.
Thanks
Thanks
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From: Watertown,CT.USA
Well there is a fine line between safe lean horsepower and breaking something.. The closer you get your car (NA) to 14.7 the more power you will make. If it was Force Induction you would want to be around 11.7. I would get your knock sensor hooked up and lean that baby out. As you can see, as your A/F went closer to 14.7 the more HP your car made. I am more familiar with FI so I think you will have to ask the NA experts on here what they think. Good Luck......John
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They really weren't doing much good anyways. The solid roller valvetrain that I have was playing hell on them. I would feel more comfortable leaning it out a bit if he was more confident in his sensors that he had hooked up and if we could hear any detonation over my loud exhaust.
Anybody want to chime in on A/F ratio on a NA, high compression engine???
Thanks
Anybody want to chime in on A/F ratio on a NA, high compression engine???
Thanks
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From: Lincoln, NE, USA
Cool. I thought it might have been a little rich, because I was running like 13.0-13.2 on my hotcam setup. Wasn't sure if it needed to be a little richer for the higher compression/bigger camshaft or not.
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Well there is a fine line between safe lean horsepower and breaking something.. The closer you get your car (NA) to 14.7 the more power you will make. If it was Force Induction you would want to be around 11.7. I would get your knock sensor hooked up and lean that baby out. As you can see, as your A/F went closer to 14.7 the more HP your car made. I am more familiar with FI so I think you will have to ask the NA experts on here what they think. Good Luck......John
That's the stoichiometric AF ratio used to control the engine fueling in closed loop - part low, low/moderate RPM. I provides a good balance of fuel economy and minimum emissions. Beyond that, it is not going to make peak power or torque anywhere near that lean. You typically want something in the range of 12.8-13.2:1. But that's just a starting point. The whole purpose of tuning is to find the optimum combination of A/F ratio and ignition advance for that SPECIFIC engine combination.
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From: High Ridge, MO
No. You don't want the A/F ratio at 14.7:1 running NA.
That's the stoichiometric AF ratio used to control the engine fueling in closed loop - part low, low/moderate RPM. I provides a good balance of fuel economy and minimum emissions. Beyond that, it is not going to make peak power or torque anywhere near that lean. You typically want something in the range of 12.8-13.2:1. But that's just a starting point. The whole purpose of tuning is to find the optimum combination of A/F ratio and ignition advance for that SPECIFIC engine combination.
That's the stoichiometric AF ratio used to control the engine fueling in closed loop - part low, low/moderate RPM. I provides a good balance of fuel economy and minimum emissions. Beyond that, it is not going to make peak power or torque anywhere near that lean. You typically want something in the range of 12.8-13.2:1. But that's just a starting point. The whole purpose of tuning is to find the optimum combination of A/F ratio and ignition advance for that SPECIFIC engine combination.
Thread Starter
Registered User
Joined: Apr 2002
Posts: 480
From: Lincoln, NE, USA
No. You don't want the A/F ratio at 14.7:1 running NA.
That's the stoichiometric AF ratio used to control the engine fueling in closed loop - part low, low/moderate RPM. I provides a good balance of fuel economy and minimum emissions. Beyond that, it is not going to make peak power or torque anywhere near that lean. You typically want something in the range of 12.8-13.2:1. But that's just a starting point. The whole purpose of tuning is to find the optimum combination of A/F ratio and ignition advance for that SPECIFIC engine combination.
That's the stoichiometric AF ratio used to control the engine fueling in closed loop - part low, low/moderate RPM. I provides a good balance of fuel economy and minimum emissions. Beyond that, it is not going to make peak power or torque anywhere near that lean. You typically want something in the range of 12.8-13.2:1. But that's just a starting point. The whole purpose of tuning is to find the optimum combination of A/F ratio and ignition advance for that SPECIFIC engine combination.
Gotcha...so going a little bit leaner will most likely not hurt the engine. As expected, it was making quite a bit more power the leaner it was getting, but I'm no tuning genius...in fact, I know nothing about it!!!! So, I didn't want to get too carried away with it. I guess a little bit more research before hitting the dyno should have been done. I'm sure I can probably get 15 more hp without complimenting the engine with a new tb or exhaust, but I'll most likely wait until I get everything done before I take it back. The car is in storage now for 6 months so that I can leave for the military so no need to worry about it right now!!!
Thanks for all the help!!!
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