hi everybody *dr nick riviera style* thought i'd introduce my self and ask a few questions about my newly accuired pride and joy. after having my car written off by a drunk driver end of july, the empty spot in the garage is now taken by the 91 300zx tt 5 speed. car came with coilovers, ceramic clutch, billet flywheel, mags, recaro driver seat, factory fitted crunchy 4th gear, ems ecu and mags and 108,000km. major service was done recently (service records included). I have to admit i was surprised how quick these little beasts are. i always thought they were quick but this is mind blowing. and handling... wooooheee... a couple of questions for the local z gurus the stock boost gauge only goes to 7 psi. in your buyers guide gauge goes to 14 (same gauge different numbers). can someone shed some light on this for me please? crunchy 4 gear i'm aware that nissan used softer materials on the 4th gear syncro. it ocassionaly happens upshifting and pretty much all the time on the downshift from the 5th. double clutching prevents the crunch on the upshift and briefly engaging the 3rd before dropping it into 4th eliminates the crunch on the downshift. my question is, are there aftermarket syncros that are stronger? I know that oil (not sure which one) is supposed to help but i'd rather fix the problem rather than patch it up. i'm aware that it would be a full gbox rebuild. while on the topic, straight cut versus helical, noise aside, could someone give me a quick rundown on pros and cons of each (my knowledge of gearboxes is very limited so spare no detail however small). great forum you guys have with tons of useful information. Thanks in advance Tom
Welcome Tom, the oem boost gauge is measured in millimetres of mercury.... which means the "7psi" you are referring to is actually 700 which is roughly 13.5 psi, so if you are getting a full scale deflection on your oem gauge it's no wonder you are flying because you are running about 1 bar of boost. If you are a long time reader it's surprising you haven't wandered into the FAQ or Tech section, if you do so now you will find a swag of answers to a lot of your future questions.
Welcome ....>> Two things first: 1. Please fill in your profile as it helps us to help you. 2. Most questions aren't new so you can save yourself some time by using the Search function or reading the technical pages. Back to your questions: 1. The stock boost gauge is not in psi but mmHg X 100. Refer to the FAQ for more info. 2. 4th gear crunches can often be cured with Redline synthetic gear box oil. I have successfully used Redline MT-90 (for over 5 years) while others have had no success with MT-90 but good results with Redline Light Weight Shockproof. For mor information on this use the search function or see this FAQ. A full rebuild will cost minimum of $1k, if you want straight cut gears or a dog box then at least $10k.
i have wondered through the tech section but could not find anything about aftermarket synros or straight cut gears (or i might've missed it) and the boost gauge. the gauge doesn't shoot up all the way to 7 so i doubt it's running that much boost. i haven't had a chance to test it coz, like mentioned in the original post i'm unsure of the gauge calibration and coz i've only had the car for a couple of days and it's been wet around here. as much as i'd like to see how hard she goes, don't want to wrap her around a pole somewhere.
Welcome Tom Can't answer your question re: gearbox. The boost guage is calibrated in millimeters of mercury (mmHg) So maximum standard 9psi of boost is 465mmHg or 4.65mamamahoogs on the guage. The 14 on the guage you refer to is from a US car in psi. While we're on the subject of guages - it is not unusual for your oil pressure guage to read zero. It will be the crappy sender that's at fault not the guage. Cliff
Straight cut gears would mean a complete new gear box or ...>> all new gear box internals. The only one I know of is $9500 for the gear set. Your gearbox crunch options are: 1. Redline oil $100. 2. New stock syncros $1k+ 3. New stock gear box $3796 4. Race gearbox internals $10k+ 5. Other gearbox conversion $???? Staright cut gears are to make the gear box stronger and do nothing to help the syncros.
