SAiamNE

I just bought a 1990 GXL. The previous owner told me it got a rebuild and put some Turbo rotors in..

Is there any Advantages or Disadvantages to this?

Thanks

j200pruf

iTrader: (4)

Only disadvantages, because turbo rotors have lower compression. It could be noticable if you had a S5 N/A (9.7:1 CR) and used S4 Turbo rotors (8.5:1 CR) although to change series the counter weights woudl have ot be changed.

LT8TurboII

iTrader: (2)

Yea, you need to go the other way, NA rotors in a Turbo

Daniel

bejbis

haha dan....you just had to chime in on that didnt you

igottafc

iTrader: (6)

how much HP can the NA rotors handle?

SAiamNE

Ok i don't understand this "RX-7 Specalities" shop in Calgary is doing. Why would they install these rotors if they know they shouldn't be going in? Every thing i hear about them is trash.. I don't think i have heard one good thing about them on this board.

BlackIceGuitar

too many veribles to tell you for sure

SAiamNE

OK. Guys im totelly confused here about Compression #'s.
When i took this car to get an inspection i had my uncle take it since i had an important doctors appointment i could not miss.
Anyways at the Mazda dealership the guy said the compression on the front was "dead on' and the rear was off by something like 1 or 1.5. Is this 1 or 1.5 PSI readings or is there some kind of other scale? The guy told my uncle it was still a good motor and nothing really wrong with it. Although there is a tiny oil leak but nothing to really worry about he said. Could my #'s be screwed up to because the guy before me aparrently said it had turbo rotors in it? The engine only has like 40 000KM's.

So can someone just sum up a little confusion for me?

Thanks

Kenteth

Compression of the rotors and compression of the combustion stage of the engine are different.

Compression of the rotors in an s5 is 9.7:1.

The comrpession of the engine is something completely different, and you see numbers anywhere around 80-120 psi

Edit: Compression of the rotors in an s5 NA is 9.7:1

SAiamNE

So when the guy at the dealership said the rear was off by 1.5 an example might be 115PSI in the front and 113.5PSI in the rear?

SAiamNE

I thought there was some other type of scale?
Where like if you are inbetween 4 and 7 you are good.
Under 4 meaning time for a rebuild and above 7 is awesome compression or something like that?

88ROTARY

so what is the compression ratio of rotors in a n/a s4

rx7_turbo2

OK something's not right here.

RX-7 Specialties should know better than to put turbo rotors in an n/a. As mentioned before I've seen weird stuff come out of there but this one is a no brainer.

I would get a comp test again, and this time record the numbers, that should tell us what rotors are in there.

If they have put n/a rotors in it, it's not going to make the same power as having the "right" rotors in there.

SAiamNE

You mean...

If they have put TURBO rotors in it, it's not going to make the same power as having the "right" rotors in there.

I'm gonna phone Mazda monday and see if they have recorded the #'s onto there computer or something. I paid $80 bucks for the dam compression test and they didnt even write it on the sheet they handed me..

I was also only "told" the motor has turbo rotors in it. So tomorrow when i go work on my car i will check the reciept again and see if it has turbo or something writtin on it..

neptuneRX

couldn't you just add a turbo?

SAiamNE

Dear lord...... absolutly NOT!! HEHE..

Sorry but NO..

RotaryResurrection

iTrader: (8)

I highly doubt any builder would put turbo rotors in an NA engine. It'd be fairly slow, more so than a stock NA engine.

Compression RATIO (8.5:1 or 9.0:1 for turbo, 9.4:1 or 9.7:1 for NA) is different than compression PRESSURE an engine generates. When you run a test, you test the PRESSURE...the measure of how efficiently an engine moves air. You're measuring wear on the internal seals and surfaces.

Mazda and their digital tester measures compression in BAR...the metric standard for large amounts of pressure. 1 bar = 14.7psi as I recall. To convert a reading taken in bar to PSI (what we are accustomed to) multiply the bar reading by 14.7. Expected readings for a rebuilt engine are 105-125psi.

When they told you the rear was off by 1-1.5, they meant bar...30psi or so less. That is quite a difference, if that is the case. The FSM calls for a differential of chambers no more than 20psi IIRC. IT won't hurt the engine too bad, and some difference is normal (10-15) but the more uneven the difference, the less smooth the engine will run and the poorer it will idle.

rx7_turbo2

We pulled apart a turbo motor built by them that had 1 n/a rotor and 1 turbo rotor We drained over 4 litres of excess oil out of a car they did an oil change on, I could go on. So it's not out of the realm of possibilities but still...

SAiamNE

Thanks RotaryResurrection that cleared up everything!
I will double check with my uncle on the excact # he gave me. I've driven it a couple of times and the idle is very smooth and crist. It doesn't bounce at all and idles constant at 750ish. I guess i will just play it by year and see how it does. I will still give Mazda a call and get those #'s from them. Hopefully this will clear everything up and i won't be so worried about a blown engine..
I don't think i will be going to RX-7 specialties anytime down the road either..

Does anyone know of any other shops here in Calgary that do rebuilds besides Mazda?