vha27

is a reading of -14 in of hg at 800 rpm considered poor, fully warmed up, mid pipe and farrel catback. can a free flowing exhaust effect this reading?

thanks,
chris

DaveW

IIRC, if you have a stock motor (no porting) that's a bit low. 16-20 is normal, depending on engine condition. However, your vacuum gauge could be inaccurate...

The exhaust will not affect the vacuum reading.

quicksilver_rx7

I've got a stock reman with about 20k on it and vacuum is reading ~20 inHg at idle, just for a reference point.

Joe

1QWIK7

iTrader: (33)

i got about 19in at idle (750-800rpm) and about 17in with the fans on (1000-1100 rpm)

Whizbang

your electrical system can effect it because it changes the voltage the igniton is getting. real noticeable on a FC.

trini

iTrader: (2)

man i have seen brand new rebuilds reading at 14 at 800 rpms. so no thats not low. anyhow thats where mine is at, **** i hope that isnt low. :-)

DaveW

Correct: 14 is not low for a new rebuild, since the seals haven't had time to seat-in yet.

vha27

well im looking at -14 in of Hg with a car that has 51,200 miles on it. Under ebay im covered up to 1,000 miles, however im flying to get the car next week, which will be at least a 800 mile drive. im thinking of asking him to take it to the dealership to get a compression test done just to make sure. should i trust the dealership that they're capable of doing this without breaking any parts to get to the plus along with the test being properly performed?

stevemack

I am sitting at 14-13 in. hg. at idle (750-800rpm). I have a street port and 3" exhaust all the way through with a midpipe. The engine has 4k miles on it. I hope that is not too low for a street ported engine.

93FD3S

depends on what seals you have as well. 2 or 3mm

RotorJoe

Thats where mine sits and I have a large street port. I think some of that has to do with my old *** used housing and irons. Pretty much right on the edge of what people say is good. Although on my piston compression tester I see 105-110psi on both rotors all three faces so I'm not worried. 10,000miles on the rebuild so far.


Joe

yuichiror

iTrader: (1)

From http://www.fd3s.net/boost_test.html :

> My car idles at about 750 RPMs. Is the vacuum reading a sign of how
> aggressive the porting is?

Yes.

* Normal stock motor will show 18" or better.
* Mildly ported motors show 14"-16".
* Heavily ported motors can go down to 10"-12".

vha27

so i should be worried, im on a stock motor, unless theres a vacuum leak somewhere or the boost gauge is faulty

to clarify on the compresion test, i remove the front and rear trailing plugs right, the ones on top, and with a piston compression tester with the check valve removed or depressed, should i get about 35-35-35 or is it at least 85-85-85, ive been trying to figure this out exactly for a while

nopistons94

I told you Ill help you with all this stuff man

RotorJoe

I pull the leading plug and leave the trailings in, although this maybe incorrect.

However you should see 85psi or better on all three rotor faces with the check valve out.

With the check valve in you'll see larger numbers. I'm not sure what these should be off the top of my head, I also never check this part. Seems not needed to me.

MR_Rick

iTrader: (7)

Vacuum reading are going to be different depending on your sea level. So I won't use your vacuum reading as a way to see if you have good compresion.

bdennis

My 93 has a pretty serious street port. It reads about -10Hg at idle.

vha27

whats this i read about 3 pulses being 30-35 psi then, thats whats confusing me

RotorJoe

Are you reading that from here (go to the tech section the click the link for compression test)?:
http://www.rotaryresurrection.com/

Probably testing pressure differential between the tree faces.

Joe

*edit* after reading that again, maybe not. I'll let someone else answer that one.

GoodfellaFD3S

iTrader: (213)

I ported my motor aggressively, and have quite a bit of overlap. I see 12-14 inches vacuum at 900 rpm, oem 2mm 2 piece seals, ~8k on the motor.

XSTransAm

here is a thread of a bunch of guys on heres vacuum readings.

https://www.rx7club.com/showthread.p...ghlight=vacuum

andre sinclair

iTrader: (36)

I have a 1st GEN old school 4 port with very agressive porting, my vacuum is @ 14 -16 in hg.
On my 3rd Gen which has a stock motor I`m around 17 in hg.

If you do your compression test with a conventional tester, shreader valve out, you will need @ least 3 seperate bounces of the needle at 70 PSI in each rotor chamber to consider the motor good.

As long are they are even... just continue to boost the hell out of it.

Good Luck,

Andre

Swolbynos

i have about 4-5 in hg @ 1800 rpms.....


but i also have a half bridge. on my old street port i had about 14-15 @ 900