I am looking to pick up a higher mileage 90-93. Having previously owned a 91 (timing guide death) I understand most of the issues with these vehicles. However, I have some cash I am looking to burn, and want to pick up a project car. What I am wondering: Is there any truth to the rumor that the 90s were the quickest between the 90-93s? Also If I get a high mileage one, and am willing to spend some decent money on maitenence can I get the original performance out of the engine? I am basically looking to get a good one, and do some modifying (full suspension/ecu/tcu/maybe more) just a fun car to haul *** in, I miss that on cam rush of my 91. Also, how much does a Level 10 tranny upgrade cost?

They tend not to lose a whole lot, if anything.

Some claim they perform best between 100-150k,and in the 4 Q's I have owned I have seen no correlation between power and low milage.

-It has generally been held, that the 90 and the earlier 91's were the strongest (Some disagree though)

-I think any 90-93 is a fast car, keeping in mind that the 93 have dropped the sodium filled exhaust valves.- I have a level ten tranny upgarde on my car, they come indifferent trims.Mine cost $4500 and includes kevlar lined clutch faces and a higher stall speed torque converter.

Fred...

If you do get a performance loss with miles it's usually almost all to non wear items:-Dirty TB-Plugs-Injectors-old Tstat /radiator making car run warm or hot.

Stuff like that all of which can be easily addressed.

Fred..

Palmer, Did you buy that doctors Q, from B.A.D.? I couldn't find it in members rides, what am I missing?

Yes, I bought Rex's Q.

Fred...

actually ive heard the 93s were the quickest, and the 9os are also SOHC, good luck, my friends got a 93 with 123k and she pulls just fine, harder than my older 89 with 186k that is now gone

The 90's are DOHC (per bank) just like the 93's.

Fred...

AZ - Let me know when you start shopping...

I love looking at old Q's (and helping spend other people's $$$):D

nlzmo400r wrote:actually ive heard the 93s were the quickest, and the 9os are also SOHC, good luck, my friends got a 93 with 123k and she pulls just fine, harder than my older 89 with 186k that is now gone

are you in the wrong forum?

lol

I'm thinking he is...

nlzmo, we're discussing Q45's, not 240's.

If all of the systems are running correctly (ie MAF, o2 sensors, spark plugs, tb, plenum, etc) then there should be no performance loss.

Well, let's not forget the normal wear and tear seen over time. My car is well-maintained (IMO of course). Clean TB and plenum, new O2 sensors, new plugs, all new temp sensors (including that EGR one that costs a freakin $90!). But the car doesn't have quite the pull of other Q's I've been in, and I'm pretty sure it isn't quite as fast now as it was 40,000 miles ago (218k now). Things just plain wear. Valves and guides, bearings, rings. The compression on each cylinder is around 158psi on average. Not terrible, but not 180psi which is what it probably was straight from the factory. I would not be surprised by a well-maintained Q performing its best at 100k, but I don't consider a Q45 with 100k as "high mileage".

factory spec is 185 psi.Minimum factory spec (rebuild time) is 142 psi.My strongest Q engine was 90k miles (I dont remember the exact numbers but supposedly was nearly perfect compression all around).

Fred...

Remember the compression RESULTS changes with barometric pressure and altitude............185 is sealevel and 29.92 and incoming air at 60F plus perfect clean intake and oil viscosity.

A lower reading may not be as low as the rpm increases or the running temperature causes the rings to expand.

http://www.factorypipe.com/Tec....html

Low compression or variable cylinder to cylinder compression shows up first at idle rpm.

After all a 10% drop in peak power 300~~337 lb/ft [or a 28-30 HP drop] will only result in 0.3 seconds increase in quarter mile time. Unless you have accurate progressive data you'll never feel it.

More common is transmission slip [increase in shift time] as 0.3 second cannot be felt or differentiated easily.

I would be more suspicious of a 150k tranny than a 150k engine.

Of course owners can destroy anything.

I notice my 95Q is a littlt slower than my 93Q was at 70 to 90 mph when you drop to 2nd. But the 95 seems to pull a little harder in fourth at hi...hi speeds. Other than that, they seem to both hall pretty good.

I've been wondering about this all weekend. I think that a couple things can affect the performance in DAEDALUS' car that won't be apparent in a compression test.

Namely deposits on the pistons.

I do not tear into engines daily, so I'll suggest this as a theory and someone else can point out the errors.

Recently I pulled the head off a honda with 120K miles to replace a burned exhaust valve. The owner of the car and I cleaned about 1 mm average of deposits from the top of the pistons.

I got to thinking about the Q. With 67 cm2 of surface area on a piston, 1 mm would be about 6 cm3. Hardly signifigant in a 4494 cm3 engine, except that the compression ratio would be increased from 10.2 to 11.5 With the higher compression the results of a compression test would look a lot better. A reading of 160 on a cyclinder with 6 cc's of buildup would mean the same cylinder clean would only read 141 - thus masking heavily worn rings or valve seats.

Of course I don't fully understand the dynamics of compression fully - if sea level pressure is about 14.7 PSI how can a 10.2 compression ratio engine produce 185 psi?

Anybody want to weigh in on this?

dan

Your logic is sound; I'll trust the math. Perhaps a leakdown test is more applicable. I have also pondered buildup on the intake valves. Recently seen a car torn down for a rebuild in class and you would NOT believe the amount of deposits on the intake valves. Fewer miles than my car, but carbureted. The car must have felt like it was congested with a head cold. The next time I pull the plenum off I'll make a point to take a look at the intake valves, and I will be doing an intake cleaning on my car within a couple of weeks.

The actual measurement from a compression test is probably higher due to the dynamics of the test: valve timing, velocity of air, etc. In my text, compression test results should be = (CR)*(atm pressure) + (atm pressure) + 5

This would give 170 psi for the Q, still lower than factory upper. And I honestly can't explain the last 2 terms...why add 1atm again. The value 5 used is called the "volumetric efficiency" term. Perhaps just an attempt to approximate the real results with a method executable by most people.

forecast wrote:Of course I don't fully understand the dynamics of compression fully - if sea level pressure is about 14.7 PSI how can a 10.2 compression ratio engine produce 185 psi?

I would guess that the static 10.2 to 1 ratio is calculated as if the cylinder were perfect (no valves opening or closing).

"1 mm would be about 6 cm3. Hardly signifigant in a 4494 cm3 engine, except that the compression ratio would be increased from 10.2 to 11.5 With the higher compression the results of a compression test would look a lot better. A reading of 160 on a cyclinder with 6 cc's of buildup would mean the same cylinder clean would only read 141 - thus masking heavily worn rings or valve seats.'

Worse yet what brand of gasoline will NOT KNOCK with a 11.5 CR even a 11.0 would be a problem..

Again ABSOLUTE BARO pressure will cause variations in readings as even the electronic peak hold compression testers are calibrated for 14.7 psi base, so Atlanta would be 0.5 lower x 10.2 =0.5= 5.6 psi lower what tv says 29.92 baro [all airports, tv correct for altitude so as not to alarm consumers].

In Denver 3x10.2= 30.6 +3 = 33.6 psi lower would be in spec.

Completed testing on the 28,000 mile factory rebuilt tranny installed currently in my Q.Used Consult to log the parameters just before, during ,and after a series of WOT 1st to 2nd shifts. Tricky since 2 seconds is all you have when you push record.

Essentially what happens is the timing at 7,000 rpm drops from 28 to 8 [rpms had dropped to 6400 in 210 milliseconds] then to 2 degrees then slowly progressively bumps up in 1 degree increments to 23 at 4800 rpms.

resolution is printed in 1/50 of seconds so accurate enough to resolve that the average of 9 shift was 800 milliseconds +- 100 milliseconds from power cut prior to shift, the shift, and the point after the shift where normal advance resumed.......all of this occurred while the speed sensor read 52.0 mph.

Would be a good method of determining tranny health but not as good as an accelerometer where the slack period [acceleration, shift, resume of accel] could be accurately determined.

I went back an got out the calculator. The Q45 engine should have bottom dead center volume per cylinder of 623 cc and a TDC volume of 61 cc (difference of 562 cc's per cyclinder and a ratio of 10.2:1) In a pressure test situation I forgot about the affect of temperature on pressure. While the density of the gas will increase inverse linearly with volume, the pressure won't. Pressure will increase along a slight exponential when compressed rapidly due to a rise in temp.

Q45tech wrote:Worse yet what brand of gasoline will NOT KNOCK with a 11.5 CR even a 11.0 would be a problem..

This might suggest my theory that compression tests can be artifically increased by piston deposits could be wrong.

The "deposit increased CR ratio and knocking problem" consideration might suggest that even thin despoits on the head or pistons could lead to drivability problems - except that these problems would only show up at or near WOT.

Isn't detonation (spontaneous combustion without a spark) a function of high density and temperature. Different fuels have a curve on a graph (temp verses density) where above the curve an air fuel mixture will spontaneously burn. The Q's engine is designed so that with 93 octane fuel the conditons will never exist. Even low octane fuel will idle fine in a Q45 since the amount of air and fuel admitted is so small that the density level won't get very high.

[Assume 675 rpm idle requires 10HP - about 4 gr /sec of air - this becomes .09 gr / cylinder / cycle = 1/7th normal air pressure meaning cylinder pressure before ignition is never more than 20 psi]

It's only as the cylinder pressure before ignition increases to high levels ( 150+ PSI?) that the engine approaches the detonation threshold for lower octane gas - thus in Denver 93 doesn't really need to be true 93 since the CPbi won't approachs the detonation threshold for lower octane gas.

Going out on limb; I might suggest that cylinder despoits if excessive (more than a few CC's per cylinder) might actually be causing detonation at WOT, if the detonation occurs only a couple degress before intended igntion the effect won't rattle the block very much and the only tangible effect is a loss in power - how one would test this theory, I have no idea.

forecast wrote:Going out on limb; I might suggest that cylinder despoits if excessive (more than a few CC's per cylinder) might actually be causing detonation at WOT, if the detonation occurs only a couple degress before intended igntion the effect won't rattle the block very much and the only tangible effect is a loss in power - how one would test this theory, I have no idea.

Well, the deposits do inhibit heat transfer, and therefore contribute extra heating to the intake charge, thus promoting pre-ignition and knock.__________________Brian1995 Q45 & Q45t

See my new topic in Nissan Engineering talk--cycle variations.I knew this would come up so posted around noon.

Knock is only a problem if it occurs beore TDC or a very few degrees after as the ideal peak combustion pressure should occur at 16-17 ATDC.

True the VE at idle or cruise is below 20%..........a cheating short cut is 2.2 millisecs/11.0 millisecs at 4,000 rpm WOT =20% of max fuel times enleanment ratio 12/14.7=0.81 x 20= 16% VE at idle vs maybe 90-95% at torque peak.

You could compare the engine vacuum running 18" vs <1" WOT.

Anyway carbon/additives/burnt oil vapor- deposits can absorb gasoline or restrict air flow, besides raising combustion chamber temperature.

In theory the richer the mixture the slower the flame travels from the sparkplug to the extremities [why you need more advance as the VE declines after 4,000 rpm so if you don't start the enleanment [shorter injector open timing] and add extra 1 degrees advance per 500 rpm all the way to redline......you can get high rpm knock also.

More later.

Since this thread is getting pretty technical ,I will take it out of Infiniti General and into Nissan/Infinit engineering forum.

Fred....

Jumping around: Which would one want, more ring wear or more bore wear. Obviously easier to change oem rings than to add material to bore.

http://www.aera.org/Members/En...3.htmh ... _i...ument

Engine deposits:http://web.mit.edu/energylab/w....html

Something to think about........gasoline is made up of differing vapor point compounds.http://web.mit.edu/energylab/w....html

http://www.mahleinc.com/home_i...ument