Bad low end throttle response\
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elwesso
- Posts: 30810
- Joined: Sun Feb 23, 2003 4:52 pm
- Car: 94 Infiniti Q45t 5 spd
2007 BMW M Coupe
2007 Infiniti G35 S 6MT - Location: Indiana
- Contact:
Bad low end throttle response\
My Q runs pretty good, but the low end throttle response sucks. Ones it gets past about 3500 it takes off and is great, but I can BARELY even get the tires to squeal. I was thinking of replacing the spark plugs next weekend, and I want to know if there is anything else I can do while im in there! I know it is supposed to be better than this, and I have never even got it to spin the wheels or burn with TCS off.
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
4 valve per cylinder engines produce less low rpm torque than two valve engines because everything [air passages] are sized to work well at 6,000 rpm.
Kind of like a seesaw with the pivot point at 3,000 rpm...improve the top hurt the bottom.
274 cubic inches is a pretty small engine for a 4300 pound car yet by 2,000 rpm it has enough torque to run 60 mph on a level road with AC on.......pretty amazing if you ask me.
To improve [stay the same] city mpg [with extra weight of 94] the transmission gears in 1st and 2nd were reduced by 5% [on average] and the engine barely meets published numbers [due to emission redesign]. [90-93 typically exceeded published torque number by 5%]So a 94 is at a 10% total disadvantage compared to a 93.Some how the tweeked the tuning to still function at 2,000 rpm.
Short of changing the rear diff gear set to 4.083 [15.4% higher] not much one can do other than maintaining what you have to highest standards.
Modern 5 speed AT [M45] have a total gear multiplication in 1st of closer to 12-13 compared to your 94Q's 9.45.......this is 30-35% more rear tire spinning power for exactly the same engine output in 1st gear.
Anyway spinning the rear tires is counter productive in acceleration, what you want is 1% less that the tire spinning power.
Kind of like a seesaw with the pivot point at 3,000 rpm...improve the top hurt the bottom.
274 cubic inches is a pretty small engine for a 4300 pound car yet by 2,000 rpm it has enough torque to run 60 mph on a level road with AC on.......pretty amazing if you ask me.
To improve [stay the same] city mpg [with extra weight of 94] the transmission gears in 1st and 2nd were reduced by 5% [on average] and the engine barely meets published numbers [due to emission redesign]. [90-93 typically exceeded published torque number by 5%]So a 94 is at a 10% total disadvantage compared to a 93.Some how the tweeked the tuning to still function at 2,000 rpm.
Short of changing the rear diff gear set to 4.083 [15.4% higher] not much one can do other than maintaining what you have to highest standards.
Modern 5 speed AT [M45] have a total gear multiplication in 1st of closer to 12-13 compared to your 94Q's 9.45.......this is 30-35% more rear tire spinning power for exactly the same engine output in 1st gear.
Anyway spinning the rear tires is counter productive in acceleration, what you want is 1% less that the tire spinning power.
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elwesso
- Posts: 30810
- Joined: Sun Feb 23, 2003 4:52 pm
- Car: 94 Infiniti Q45t 5 spd
2007 BMW M Coupe
2007 Infiniti G35 S 6MT - Location: Indiana
- Contact:
How much different is the 4.08 rear end?
So what do you think my ulitmate problem is? I know my spark plugs havent been changed in at least 80k miles, so I would assume other things like a rail flush, differential gear lube change, brake and PS fluid hasnt been changed either. No work next weekend, so its tuneup time!
So what do you think my ulitmate problem is? I know my spark plugs havent been changed in at least 80k miles, so I would assume other things like a rail flush, differential gear lube change, brake and PS fluid hasnt been changed either. No work next weekend, so its tuneup time!
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Q45tech
- Moderator
- Posts: 14296
- Joined: Tue Apr 30, 2002 3:19 am
- Car: 1990 Q45 342,400 miles 22 years ownership with original engine
1995 G20t 5 speed 334,000 miles 16" 2002 wheels - 205/50/16 Sr20ve vvl
Changing the diff ratio is ALMOST like adding torque to the engine AT least in 1st gear...........a 15% extra multiplication will deliver at least 14.5% more pound feet at the tire road interface.
292 x 0.787=230 lb/ft x [total gear multiplication] @ 4,000 rpm divided by 2 [the power goes half to each tire].
The total gear multiplication 9.35 goes to about 10.8 and the rpm per 10 mph goes from 1267 to 1457 so max speed in 1st drops from 52 to 45 mph.......better but not ideal since 35 mph would be best for zero to 30 mph acceleration test.OR spinning rear tires at launch.
Problem is you cannot launch at 4,000 rpm where torque is maximized, since the torque convertor stalls at 2,200 rpm.
So if zero to 30 mph takes 3.8 seconds stock, a 4.083 diff might improve it by 0.1-0.2 seconds.
292 x 0.787=230 lb/ft x [total gear multiplication] @ 4,000 rpm divided by 2 [the power goes half to each tire].
The total gear multiplication 9.35 goes to about 10.8 and the rpm per 10 mph goes from 1267 to 1457 so max speed in 1st drops from 52 to 45 mph.......better but not ideal since 35 mph would be best for zero to 30 mph acceleration test.OR spinning rear tires at launch.
Problem is you cannot launch at 4,000 rpm where torque is maximized, since the torque convertor stalls at 2,200 rpm.
So if zero to 30 mph takes 3.8 seconds stock, a 4.083 diff might improve it by 0.1-0.2 seconds.
I don't think there is one listed in the manual...maybe 60k? Based more on the experience of shops/techs. Even then, I'll bet lifetime varies quite a bit. There is a procedure for checking it out of the car, but for an $8 part, once you remove it you may as well replace it rather than run a boiling water bath test.