Vibrations and no low end
Vibrations and no low end
Vibrations still in engine noticably at 1800-2400 range , slight at idle. annoying at 70mph. 80 mph fine..i know i have a lota work ( mechanically )to be done, just want to plan out $$$ vs needs. from stop no hole shots ( are these cars suppose to have as much power on the low end as at higher speeds?) around 45mph power starts Vibrations start - 80 mph hold on your pressed into the seat. bought car used 260k miles no known history looks like someone put $$ into it transmission mount and engine mounts good . After reading many threads I'm thinking knock sensors.. am I on the right track? Where can i get service manuals/cd's without going to dealers.. Jd.
jd:I had a similar vibration problem. Dominate at 2250 rpm even in park. Bad at 70 mph, gone at 80 mph although none at idle. Problem traced to the driveshaft and a bad transmission mount. All of this at 90K miles. Be sure to take a close at the transmission mount. mine was only broken on one side. You couldn't really see the break until it was removed.
W. Long96 Q45
W. Long96 Q45
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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 power cylinder engines suffer from too much valve area in the low rpm range.......why the redlines are 6900 rpm.......they are just barely functioning below 2,000 rpm and max aid flow per revolution doesn't occur until 4,000 rpm.
The extra displacement [4.5 liters] and gear multiplication makes the low rpm functional.Unfotunately the 9.85 gear multiplication means nothing much happens till 25 mph [133.3 x 25= 3,333 rpm in 1st gear].
More modern designs [5 speeds] use a higher 1st gear to allow the engine to rev faster [get to 3333 rpm faster]. Instead of 9.85 they use 12.5-13.5 total gear multiplication.
Besides the 30% more torque multiplication they get on cam at 18-20 mph.
Domestic V8 [2 valves per cylinder] have a low speed advantage but are less efficient at high rpms thus the tendency to go for more displacement.
Highway mpg is all about optimizing air flow at cruise rpm, a big US V8 may make the same torque at 1700 rpm as a smaller 32 valve V8 at 2,000 or 2,200 rpm but the smaller V8 uses less fuel at idle or in stopped traffic.
The extra displacement [4.5 liters] and gear multiplication makes the low rpm functional.Unfotunately the 9.85 gear multiplication means nothing much happens till 25 mph [133.3 x 25= 3,333 rpm in 1st gear].
More modern designs [5 speeds] use a higher 1st gear to allow the engine to rev faster [get to 3333 rpm faster]. Instead of 9.85 they use 12.5-13.5 total gear multiplication.
Besides the 30% more torque multiplication they get on cam at 18-20 mph.
Domestic V8 [2 valves per cylinder] have a low speed advantage but are less efficient at high rpms thus the tendency to go for more displacement.
Highway mpg is all about optimizing air flow at cruise rpm, a big US V8 may make the same torque at 1700 rpm as a smaller 32 valve V8 at 2,000 or 2,200 rpm but the smaller V8 uses less fuel at idle or in stopped traffic.