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Old 08-29-2003, 11:20 AM   #1
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Default Are DOHC engines powerful?

I had some members last night talking about the GXP will be slow due to the fact that its Dual Overhead Cam doesn't have muscle. With 285hp and 290ish torque, I thought it could do something. Does anyone think differently?
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Old 08-29-2003, 11:22 AM   #2
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My Aurora is DOHC, I guess I will find out how slow it is. I drove my 89 for over a year and it was peppy (good ol pushrod) I also drove the 97 SSEi and it hauled. But the DOHC Northstars that is in the Aurora, most Caddys and the GXP is no slouch.
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Old 08-29-2003, 11:32 AM   #3
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From what I hear, the overhead cam designs are more efficient at high RPM'*, and the pushrod designs are good for power on the low end.
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Old 08-29-2003, 11:36 AM   #4
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Excuse me for my ignorance, but what is "low end"?
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Old 08-29-2003, 11:41 AM   #5
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Basically, a lot of DOHC, multi-valve motors like to make their power up in the higher RPM range. However, this isn't always true... the midrange is probably a better description. OHV motors such as the 3800 like to make their power down low, and are lacking a bit up high. They're better off the line, but once you get oh, say, past 4 grand RPM, a DOHC motor has it beat.

This does not, however, mean that a DOHC motor that makes power up higher has no power at all down low. Variable valve timing (ie, VTEC or VVT-i) does not always give you top end power. In mainstream cars, the variable valve timing is tuned to give more power across the whole rev range. That'* the difference between Honda'* SOHC VTEC and DOHC VTEC. SOHC VTEC= power across the whole rev range for streetability (ie, Accord V6, Oddysey), DOHC VTEC = pure top end power (ie, 2000 Civic Si/SiR, S2000). The new i-VTEC gives you top end power with added low end as well.

Whether what car is faster than what is debatable. It all comes down to weight and gear ratios.

Example, the Toyota Camry'* 8.0 0-60 run doesn't seem special, but even though it'* a DOHC motor, it has a lot of oomph down low, as well as up top. The Impala LS with the 3800 gets to 60 in 7.7, according to Motor Trend (whose numbers seem to be always a few tenths faster than other magazines ), has all its power down low and some in the midrange. Up high, it'* drivable, but not as good as other cammers.

Although you probably would feel more power in a vehicle with torque down low - but not necessarily be faster... thanks to good off-the-line, yet poorer high end acceleration.

edit: low end = low RPM power.
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Old 08-29-2003, 11:52 AM   #6
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So in other words, if I don't floor the car, I get more power. Like on the expressway for instance, I am inoverdrive passed 55mph, THe rpm'* are at 1900, I push the accelorator a little and the rpm'* move to 2000 and the car is at 65 or 70mph and I haven't floored it. THats low end?
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Old 08-29-2003, 12:37 PM   #7
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all i know is that their harder to work on from what i hear. the mid 90s monte carlo z34 were 3.4 dohc 4 cams
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Old 08-29-2003, 01:45 PM   #8
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DOHC have many more valves, so more fuel and air can go in. They are generally made to rev higher as well. You can squeeze more HP out of an engine with the same displacement as a OHV car, but they generally are lacking in torque. Yes they are generally harder to work on, and such. I like to think that OHV, both of the ones i normally drive 3800 series I, and a 350 V8 in a 98 yukon, have a very flat, and powerful power band, especially for the torque. I don't think they slouch above 4k personally, I've heard you never have less then 90% of the peak TQ in a 3800? Anywho i like muscle cars, and OHV engines, not cars with a hot cam that kicks in at 4k RPM.
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Old 08-29-2003, 02:13 PM   #9
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Quote:
Originally Posted by L27Buick
all i know is that their harder to work on from what i hear. the mid 90s monte carlo z34 were 3.4 dohc 4 cams
oo, the good ol' DOHC 3.4. Possibly one of GM'* worst engines for reliability from what I hear... to add insult to injury, parts are madly expensive

Quote:
So in other words, if I don't floor the car, I get more power. Like on the expressway for instance, I am inoverdrive passed 55mph, THe rpm'* are at 1900, I push the accelorator a little and the rpm'* move to 2000 and the car is at 65 or 70mph and I haven't floored it. THats low end?
Your engine is in the low end, sure, but with the power you demand, you don't need all the power at that moment. Think of the power you need when merging or passing.

Not all DOHC engines are hard to work on, the RWD I6 in my '85 Toyota Cressida is pretty easy to work with... but then again, its an old motor... and has two valves per cylinder

But keep in mind, unless you've got like less than 100hp, your motor should be 99% enough for everyday driving... just, you might not like it
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Old 08-29-2003, 05:40 PM   #10
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Quote:
Originally Posted by jr's3800
And I do agree, the chevy 3.4 DOHC engine was junk....
There'* a fellow two houses down from me with an Olds Cutlass Supreme thingy coupe, $1000, 3.4 DOHC with a nasty noise - valve tap, noisy lifters, I dunno. Any takers? :P
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