89 Tpi Vacuum ?
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From: West Vancouver BC
89 Tpi Vacuum ?
What's the normal expected vacuum at idle. I can't get it it to run at 450-500 rpm spec. and it normally idles at 600 rpm producing 18.5 ? on the vacuum gauge with no adjustment of the throttle plates. When I redid my manifold gaskets I got about 19.5
on the gauge at start up then went back to the normal range. (and minor erratic idle) I tried checking other ports and systems to see if there was a leak elsewhere to cause this low reading but didn't find anything. From what I understand this is within normal operating vacuum though a the very low end, most other vehicles I've had produced numbers above 20 this hasn't changed since I got the car with 55K and it now has 100+K.
on the gauge at start up then went back to the normal range. (and minor erratic idle) I tried checking other ports and systems to see if there was a leak elsewhere to cause this low reading but didn't find anything. From what I understand this is within normal operating vacuum though a the very low end, most other vehicles I've had produced numbers above 20 this hasn't changed since I got the car with 55K and it now has 100+K.
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From: Kempner Texas
Re: 89 Tpi Vacuum ? (robvan)
Vacuum at idle depends on a lot of variables.
Idle rpm is determined by what's burned into the PROM; if your PROM is burned for 600 rpm idle speed, the IAC will extend or contract to maintain that speed. Diacom or one of the other ECM readers will tell you what's burned into your PROM.
I don't believe I've ever seen a list on what is "normal" but yours seems to be in what I would accept as okay. That is, as long as the vacuum reading is steady and does not flucuate.
For example, my engines pulls 14" in park, closed loop, at idle at 850 rpm, which is where my PROM is burned to idle the engine. If I raise the engine RPM to 1000, my vacuum increases to 18".
You should also be aware that as the vacuum reading rises, the fuel pressure drops. It drops on a rate of approximately 1 psi for each two inches of vacuum increase.
Don't know if this helps, but I tried.
Jake
[Modified by JAKE, 8:12 PM 12/23/2003]
Idle rpm is determined by what's burned into the PROM; if your PROM is burned for 600 rpm idle speed, the IAC will extend or contract to maintain that speed. Diacom or one of the other ECM readers will tell you what's burned into your PROM.
I don't believe I've ever seen a list on what is "normal" but yours seems to be in what I would accept as okay. That is, as long as the vacuum reading is steady and does not flucuate.
For example, my engines pulls 14" in park, closed loop, at idle at 850 rpm, which is where my PROM is burned to idle the engine. If I raise the engine RPM to 1000, my vacuum increases to 18".
You should also be aware that as the vacuum reading rises, the fuel pressure drops. It drops on a rate of approximately 1 psi for each two inches of vacuum increase.
Don't know if this helps, but I tried.
Jake
[Modified by JAKE, 8:12 PM 12/23/2003]
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Re: 89 Tpi Vacuum ? (JAKE)
Thanks ! I have steady vacuum so I was kind of sure it wasn't a problem with the cam or valves and was I beginning to think it was the characteristic of the factory tune, cam grind. though because of getting higher readings from other vehicles I expected more. I have a basic Superchip in it, but think the the idle has been the same even before the chip, wanting to idle best at 600 rpm stock and same with the vacuum. A new IAC and throttle body are planned in the future to hopefully cure that occasional erratic idle. ( it's actually welcome when it's high due to power pullies and low Alt. voltage output ) New to the forum and thanks to everyone for your inputs on everything !!
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From: Kempner Texas
Re: 89 Tpi Vacuum ? (robvan)
Thanks ! I have steady vacuum so I was kind of sure it wasn't a problem with the cam or valves and was I beginning to think it was the characteristic of the factory tune, cam grind. though because of getting higher readings from other vehicles I expected more. I have a basic Superchip in it, but think the the idle has been the same even before the chip, wanting to idle best at 600 rpm stock and same with the vacuum. A new IAC and throttle body are planned in the future to hopefully cure that occasional erratic idle. ( it's actually welcome when it's high due to power pullies and low Alt. voltage output ) New to the forum and thanks to everyone for your inputs on everything !!
Is so, 1 inch difference in vacuum is a blessing; most performance cams - even mild ones - will drop it a lot more than that.
Jake
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Re: 89 Tpi Vacuum ? (JAKE)
No ,I still have the stock cam and had expected with my milage signs of wear showing with timing and vacuum fluctuations. A new cam is on my wish list, I'll be looking for one that delivers max power and still pass emissions testing and compatible with minor engine mods, maybe 1.6 rockers and bored TB, hogged out intake runners and plenum or big tubes. I have an MSD6 waiting to go in also. I've already done the gutted main cat and K & N with cut air cleaner box, MSD wires, Accel Module, power pulleys. Air foil. Jobber free flows, chip. I might gut the MAF again when I get another backup. Still debating on the power band as most of my driving is in town and I don't know what gears I have.
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From: Kempner Texas
Re: 89 Tpi Vacuum ? (robvan)
TPIS's ZZ9 would be an excellent choice for a 350. It's a hydraulic roller. Another one is LPE 211/219, also a hydraulic roller. HRs are the best bang for the buck and are very streetable. CompCams sells them too.
Keep the duration around 212 on the intake @ .050 and the lobe seperation angle wide, no less than 112. You can go to all their websites and check their offerings.
You can determine what rear end gear you have by jacking up the car, (PUT IT ON JACKSTANDS), put the trans in neutral, crawl under and count how many times the drive shaft turns for once complete revolution of the tire.
If it turns just over three times, you have a 3.07, etc.
Jake
Keep the duration around 212 on the intake @ .050 and the lobe seperation angle wide, no less than 112. You can go to all their websites and check their offerings.
You can determine what rear end gear you have by jacking up the car, (PUT IT ON JACKSTANDS), put the trans in neutral, crawl under and count how many times the drive shaft turns for once complete revolution of the tire.
If it turns just over three times, you have a 3.07, etc.
Jake
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Re: 89 Tpi Vacuum ? (JAKE)
Thanks' Jake, I'll definitely be shopping around when I'm ready to get a cam and for the amount of times I've had the back end up I don't know why I haven't checked it out yet. A Corvette slalom racer I know suggested one of the crane cams, one of the milder of the selections for emissions compatible cams but he runs a custom grind in his. usually running on small track set ups, I presume he doesn't need the high rpm. I'll be doing a little more research before making my decision as there are a lot of variables to take into consideration and I'll welcome any input from others as to their experience with different cams for daily drivers. - Robvan
[Modified by robvan, 1:07 AM 12/25/2003]
[Modified by robvan, 1:07 AM 12/25/2003]
