DTT_Eruc Posted August 10, 2019 Share Posted August 10, 2019 Is it possible that tight valve clearance on the exhaust side can cause little to no vacuum on idle...... This is regards to a RB25DET NEO i got...Re done the head installing tomei 1.2 head gasket and lapp over the valves however after that was done the intake side was at nissan specs of 0.012 and the exhaust is way tighter(0.014 to 0.015) on all 12 of the exhaust... will this cause such issue... secondly my last chance was to check to see if my timing was off Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/ Share on other sites More sharing options...
NEO25T Posted August 10, 2019 Share Posted August 10, 2019 How much vacuum do you have and what cams. I just set clearences to what yours are with type b poncams and mine has 13-14 in vac, still have to set the ecu up properly too so might get a bit more Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913205 Share on other sites More sharing options...
DTT_Eruc Posted August 10, 2019 Author Share Posted August 10, 2019 Actually no vaccum at all just show 0 on all gauges(ecu and boost gauge)....running tomei pon cam 262ex and 260in..... before i did the head work this never happened so i was wondering if is something to do with the clearances or timing .... but since the exhaust side has change was wondering if that would of been the cause Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913211 Share on other sites More sharing options...
GTSBoy Posted August 10, 2019 Share Posted August 10, 2019 Look for the problem elsewhere. 0. Real zero vacuum and idle are incompatible. Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913216 Share on other sites More sharing options...
DTT_Eruc Posted August 11, 2019 Author Share Posted August 11, 2019 10 hours ago, GTSBoy said: Look for the problem elsewhere. 0. Real zero vacuum and idle are incompatible. elsewhere like? engine wont idle at 1000 rpm and if it try to will die and it shows zero value Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913225 Share on other sites More sharing options...
NEO25T Posted August 11, 2019 Share Posted August 11, 2019 What rpm will it run steady while holding throttle open. Are all the vac lines connected properly, might wanna do a leak test Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913230 Share on other sites More sharing options...
DTT_Eruc Posted August 11, 2019 Author Share Posted August 11, 2019 1 minute ago, NEO25T said: What rpm will it run steady while holding throttle open. Are all the vac lines connected properly, might wanna do a leak test checked all lines last time i try to make the car stay steady at idle was at 2000 to 2500 rpm or so.....am starting to think its more to deal with the exhaust clearance that causing it not to idle at lower rpm since the clearance is tight..but i just wanna confirm with yall....dont have leak down tools but only a compression tester Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913231 Share on other sites More sharing options...
Ben C34 Posted August 11, 2019 Share Posted August 11, 2019 That's a big issue you have, but I don't think it's the tight clearances causing it. Unless they are non existant. tight exhaust clearances will lead to burnt exhaust valves, so I would be addressing it first anyway. Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913232 Share on other sites More sharing options...
DTT_Eruc Posted August 11, 2019 Author Share Posted August 11, 2019 9 minutes ago, Ben C34 said: That's a big issue you have, but I don't think it's the tight clearances causing it. Unless they are non existant. tight exhaust clearances will lead to burnt exhaust valves, so I would be addressing it first anyway. well i havent drove the car/ran it for long to say for it to cause any major damages but it ran for a while with no heavy load......but what do you suspect it maybe? Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913234 Share on other sites More sharing options...
Ben C34 Posted August 11, 2019 Share Posted August 11, 2019 Intake leak, throttle not closing fully, timing heaps wrong. Hard to guess Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913235 Share on other sites More sharing options...
DTT_Eruc Posted August 11, 2019 Author Share Posted August 11, 2019 2 minutes ago, Ben C34 said: Intake leak, throttle not closing fully, timing heaps wrong. Hard to guess try a home made smoke machine had a very slight leak to the throttle body/tps......saw no other leaks from the intake(injector seals,gasket,vac lines) just the timing to check .... this engine produce vac before i took off the head but after i lap the exhaust valves(grit to fine) and due to human error on my side forgot to check clearance( first time dealing with head work on rb) lol...... but will the exhaust valve cause this issue being the clearance out of gap... Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913238 Share on other sites More sharing options...
DTT_Eruc Posted August 11, 2019 Author Share Posted August 11, 2019 (edited) p.s this is my personal build and not a customer(dont do mechanical services) so everything am doing is trail and error on this project Edited August 11, 2019 by DTT_Eruc Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913239 Share on other sites More sharing options...
DTT_Eruc Posted August 11, 2019 Author Share Posted August 11, 2019 8 minutes ago, Ben C34 said: Intake leak, throttle not closing fully, timing heaps wrong. Hard to guess oh i did check timing but i dont like using the crank pulley as it tends not to be 100% correct(believe mines getting worn out).... all marks seems to line up perfect and did the screw driver trick to make sure it was tdc and all marks line perfect ...... geeeeeeeez idk why little things does cause big problems lolzzz Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913240 Share on other sites More sharing options...
Ben C34 Posted August 11, 2019 Share Posted August 11, 2019 That could be your problem, you have to line up the dots on the pulleys, I dont recall if that is even at tdc as it doesn't really matter. Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913242 Share on other sites More sharing options...
DTT_Eruc Posted August 11, 2019 Author Share Posted August 11, 2019 2 minutes ago, Ben C34 said: That could be your problem, you have to line up the dots on the pulleys, I dont recall if that is even at tdc as it doesn't really matter. yeah all the dots are lined up perfectly ...just did the screw driver test for additional clarification ...... still my question havent been answered yet " will the current clearance value cause this problem also" or is it just intake related(intake cam,boost/vac leak etc) Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913243 Share on other sites More sharing options...
Ben C34 Posted August 11, 2019 Share Posted August 11, 2019 People don't tend to stuff up the exhaust clearence then post results online. If they are just tighter than the spec, but still exist, I would say no way would it cause your issue. What about ignition timing? Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913244 Share on other sites More sharing options...
DTT_Eruc Posted August 11, 2019 Author Share Posted August 11, 2019 3 minutes ago, Ben C34 said: People don't tend to stuff up the exhaust clearence then post results online. If they are just tighter than the spec, but still exist, I would say no way would it cause your issue. What about ignition timing? havent got a timing light to know... i had it at the neutral position/stock...sooooo .....again i started the engine before i did the head removal and it showed vac and also the timing was at stock position and idle fine just dump alot of gas....reason for head removal had a slight bent valve on 11 and 12 exhaust(idk how it happened) but the engine was bought from someone etc etc etc Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913245 Share on other sites More sharing options...
NEO25T Posted August 11, 2019 Share Posted August 11, 2019 Was it running with these cams prior or were they put in while doing the head. Can you put an air fitting in spark plug hole while at tdc comp stroke and listed to see if valves are sealing. Those clearences will not cause it to have no vacuum Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913269 Share on other sites More sharing options...
NEO25T Posted August 11, 2019 Share Posted August 11, 2019 Did you hold the intake cam on the hex with a spanner while removing/installing the cam gear? If not it might be jammed advanced and could probably cause something like this Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913272 Share on other sites More sharing options...
DTT_Eruc Posted August 11, 2019 Author Share Posted August 11, 2019 5 hours ago, NEO25T said: Was it running with these cams prior or were they put in while doing the head. Can you put an air fitting in spark plug hole while at tdc comp stroke and listed to see if valves are sealing. Those clearences will not cause it to have no vacuum yes it was running with those cams before and the engine ran with vac perfect before i took of the head to replace the valves(two exhaust) ..... so your saying the clearance on the exhaust side wouldnt cause such ? Link to comment https://www.sau.com.au/forums/topic/478240-no-vacuum-at-lower-rpm-rb25det-neo/#findComment-7913289 Share on other sites More sharing options...
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