Guest ON3GO Posted January 5, 2005 Share Posted January 5, 2005 Okay so i got the L28ET running in my Z but now i have maybe 14psi of vacuum at idle, but i use to have 28 or so before. i did have my head ported and polished so could this cause the less vacuum? is this bad? what are some things to correct this if the port work is what caused this. any help would be great. mike Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted January 5, 2005 Share Posted January 5, 2005 Well... get a normal gauge not the one in your car and hook it up... see how the needle acts bro, then call me and I'll tell ya what it means. lol More important, get that thing leaned out a bit and the BOV workn'. Anybody got a BOV to loan mike till he gets some cash? Quote Link to comment Share on other sites More sharing options...
Guest ON3GO Posted January 5, 2005 Share Posted January 5, 2005 hehe, thanks ed. anybody else have a word on this? mike Quote Link to comment Share on other sites More sharing options...
Sparky Posted January 5, 2005 Share Posted January 5, 2005 engine timing will have an effect on vacuum...... so if its not set to where it was that will give you those results. thats how I used to set the timing on my plymouth, hook up a vacuum gauge a turn the dizzy until until you get the highest vacuum level and then back it off a couple of degrees. Its not something that I would do on a performance engine, but a 69 valiant isnt exactly a performance car....it was a mix of whatever my grandfather could find while he had it, so no timing marks what so ever. Quote Link to comment Share on other sites More sharing options...
Guest ON3GO Posted January 5, 2005 Share Posted January 5, 2005 well i think we got the timing pretty good, but it still does miss abit, but when reved it smooths out so nicely. mike Quote Link to comment Share on other sites More sharing options...
Guest Magnum Rockwilder Posted January 5, 2005 Share Posted January 5, 2005 a 69 valiant isnt exactly a performance car HEY!!! I had a '69 Valiant 4 door with a .060 over 318, 904, and 4.56 gears, and it ran mid 14's @ 95mph with a basically stock motor. It was too rusted underneath to fool with, so I sold it and now I'm getting a '68 4 door in the next month and doing a balls-out 360 buildup. A Valiant with a slant 6 won One Lap of America repeatedly. So don't knock 'em til ya try 'em. Quote Link to comment Share on other sites More sharing options...
Sparky Posted January 5, 2005 Share Posted January 5, 2005 mine was a 69 four door running a 273V8 with the stock carter bbd two barrel carb. Duels on stock manifolds, shaved, slammed, with flames. I miss that car, but it just rode like shiat because it was sooo low, downtown streets are not fun in a car that low. I had plans to airbag it and notch the frame to get her lower but never got around to it. 12k invested, sold for 2k. ARGH!!!!!! Quote Link to comment Share on other sites More sharing options...
Guest ON3GO Posted January 5, 2005 Share Posted January 5, 2005 btw i dont have my vacuum canister anymore, could that cause this? i never thought it worked anyways. Quote Link to comment Share on other sites More sharing options...
Nismo280zEd Posted January 5, 2005 Share Posted January 5, 2005 Damnit mike put it back on! Quote Link to comment Share on other sites More sharing options...
Guest ON3GO Posted January 5, 2005 Share Posted January 5, 2005 i dont think it was ever hooked up anyways.. so i cant see this fixing it. mike Quote Link to comment Share on other sites More sharing options...
JMortensen Posted January 6, 2005 Share Posted January 6, 2005 I ported my 22RE head and when I slapped it back on my idle was at 3000 rpm, so I would say that porting is going go have an effect on vacuum. Of course so will having a fresh engine (probably a lot more than the porting). Quote Link to comment Share on other sites More sharing options...
Cody 82 ZXT Posted January 6, 2005 Share Posted January 6, 2005 I would think that a ported head could certainly have an effect on vacuum. Basically I see it as the air is seeing a restriction and that creates vacuum. The ported head could have less restiction so it now has less vacuum. Also the cam timing and the adjustments on the valves will have an effect on it as well. Quote Link to comment Share on other sites More sharing options...
Clifton Posted January 6, 2005 Share Posted January 6, 2005 A ported head would have no effect at idle. There isn't enough air moving through the head to make a difference with a throttle plate that is just barely cracked open. A vacuum leak and timing, valve or ignition would effect it though. I think you may have missed something during reassembly. Quote Link to comment Share on other sites More sharing options...
wheelman Posted January 6, 2005 Share Posted January 6, 2005 Cody, The vacuum is in the entire intake track from the valve to the throttle plate. If anything a ported head with better flow would increase vacuum, that is except that the cylinder volume filling with air (or actually not filling due to the closed throttle plate or other restrictions) as the piston moves down is what generates the vacuum. The only thing that might be affecting your vacuum other than a leak or missing vacuum canister is a large cam with lots of overlap. Clifton, I can see how valve timing will affect vacuum but how will ignition timing affect it? Mike, IIRC you didn't change the cam so you must have a leak somewhere. Put the vacuum canister back in, it was there for a reason. Wheelman Quote Link to comment Share on other sites More sharing options...
Clifton Posted January 6, 2005 Share Posted January 6, 2005 Clifton' date=' I can see how valve timing will affect vacuum but how will ignition timing affect it? [/quote'] If it is retarded enough to get a rougher/low idle it would pull less vacuum. I don't think it would drop it from 20-14 though. Quote Link to comment Share on other sites More sharing options...
Cody 82 ZXT Posted January 7, 2005 Share Posted January 7, 2005 Cody' date='The vacuum is in the entire intake track from the valve to the throttle plate. If anything a ported head with better flow would increase vacuum, that is except that the cylinder volume filling with air (or actually not filling due to the closed throttle plate or other restrictions) as the piston moves down is what generates the vacuum. [/quote'] I understand that vacuum is from the throttle plate all the way to the cylinder but, vacuum is the measurement of a restriction in the intake track. Right? Better flow = less vacuum. As the piston moves down it is pulling air in the cylinder. If the work of pulling the air in is made easier by installing a better flowing head then the work the piston is doing pulling the air into the cylinder is made easier. Thats the way I see it. Maybe I'm wrong here? Let me know! Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted January 7, 2005 Share Posted January 7, 2005 I would think that the amount of port work you had done would not affect vacuum so dramatically. Double check all of your vacuum lines and make sure all of your injectors are tightened down. Did you replace the injector orings when you had it apart, or didn't you remove the injectors? If all the usual suspects check out, check your valve adjustment again to make sure that none of them are too tight and remaining open. After you have exhausted all possibilities, do a leak down test to make sure your valves are seating properly. I understand that you just had the head rebuilt, but unless you do the work yourself, you never know what may have been overlooked... Quote Link to comment Share on other sites More sharing options...
Guest Magic Posted January 7, 2005 Share Posted January 7, 2005 For my money the vacume is a measurement of the pressure difference between the atmosphere and the area between the throttle plate and the inlet valves/ piston head (depending on if the inlet valve is open). If you have had your head ported (decreased the restriction between the inlet manifold and inlet valve/piston head, then the effeciency of any air flow (either vacume or pressure) is improved. The piston head should be able to suck more air when the inlet valve is opened on a ported head, thus leaving less air mass in the throttle chamber when the inlet valve closes - which means a greater difference in pressure compared to the atmosphere (vacume). That said, the difference in airflow through a ported/non ported head at idle would be marginal (real gains occur at high flow times, see bench tested flow maps of ported heads). Therefore I dont think the porting would effect the vacume that significantly. I would be looking elsewhere for a leak. Quote Link to comment Share on other sites More sharing options...
savageskaterkid Posted January 7, 2005 Share Posted January 7, 2005 whts the big deal if u have a lower vacume on ur setup, r u running sumthin in the car that needs that much of a vacume pull, or is it just the thought of.........hmmmmmmm, it used to b like this, but now its like this Quote Link to comment Share on other sites More sharing options...
yo2001 Posted January 7, 2005 Share Posted January 7, 2005 cam timing effects idle also. also low velocity intake air Quote Link to comment Share on other sites More sharing options...
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