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Old 11-03-2009, 01:36 PM   #81
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Ok so what do you do with the EGR when you have a FI engine?
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Old 11-03-2009, 01:41 PM   #82
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Generally, engines with dual overhead camshafts (DOHC) are higher performance engines, they produce more power, and can run at higher speeds. The biggest difference is that the DOHC has two camshafts, one thats controls the exhaust valves and the other that controls the intake. The SOHC just has one that regulates both. So the DOHC has better performance b/c of the two independent camshafts.
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Old 11-03-2009, 02:08 PM   #83
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Quote:
Originally Posted by natedawg9640 View Post
Generally, engines with dual overhead camshafts (DOHC) are higher performance engines, they produce more power, and can run at higher speeds. The biggest difference is that the DOHC has two camshafts, one thats controls the exhaust valves and the other that controls the intake. The SOHC just has one that regulates both. So the DOHC has better performance b/c of the two independent camshafts.

Though if you have a v-6 with overhead cams you have 4 camshafts
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Old 11-03-2009, 02:18 PM   #84
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So have having a DOHC helps with putting less stress on just one piece in the engine?

So people are buliding smaller engines and putting in bigger turbos and supers?
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Old 11-03-2009, 02:41 PM   #85
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just google something like "why is dohc better than sohc"
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Old 11-05-2009, 08:40 PM   #86
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pushrod > dohc
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Old 11-05-2009, 08:41 PM   #87
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Quote:
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pushrod > dohc

Why do you say this?
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Old 11-05-2009, 10:37 PM   #88
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simpler to maintain and work on. Less parts. Generally have timing chains rather than belts making them more durable.
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Old 11-06-2009, 03:08 PM   #89
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Quote:
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simpler to maintain and work on. Less parts. Generally have timing chains rather than belts making them more durable.

having a belt would you ever run into problems of it slipping with the extra power, or stretching faster?
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Old 11-06-2009, 04:31 PM   #90
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Actually a belt can have advantages.... Either way the extra power may cause faster wear/failure. Don't worry about it.

FYI - GM 4cyl uses a chain, not a belt (that's so japanese)
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Old 11-10-2009, 07:33 PM   #91
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i got a question. how bout turbos that are double finned. whats the diff on those?
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Old 11-10-2009, 10:48 PM   #92
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Quote:
Originally Posted by rida125 View Post
having a belt would you ever run into problems of it slipping with the extra power, or stretching faster?
Belts stretch and break after a while. On interference engines like ours that turns into bad juju very quickly.
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Old 11-10-2009, 11:18 PM   #93
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by the way rida, how did that "situation" turn out for ya?
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Old 11-11-2009, 09:53 AM   #94
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pistons vs. valves, unfortunately, one must lose....
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Old 11-11-2009, 09:59 AM   #95
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In my case when the keyway sheared off the timing gear both the pistons and valves lost. Bent all the exhaust valves and marked all the piston faces.

I was happy that it happened though. I got a new cam with ss valves and better springs out of the rebuild.
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Old 11-22-2009, 03:27 AM   #96
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you guys are killing me. I would have quit long before now.

And Chris, please stick to what you know, LOL.

Quote:
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a turbo uses exhaust gases to push its spool, thus having a lag on it, before it gives its full boost. Known as "turbo lag"
False. A turbo can be configured in the correct sizes to produce little to no lag. Some are even nearly into boost off-idle.
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a Supercharger is spun by the serp belt, giving instantaneous full load. No lag here. The downside is many trannys/engines cant handle the increased load of power, immediately. (w/o upgrading them)
Superchargers create boost incrementally by RPM's. Although boost is produced (minimally) off-idle, hence no lag.... full boost is usually achieved at redline unless using a centrifugal type, in most cases.
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Old 11-22-2009, 07:58 PM   #97
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you guys are killing me. I would have quit long before now.

And Chris, please stick to what you know, LOL.

False. A turbo can be configured in the correct sizes to produce little to no lag. Some are even nearly into boost off-idle.
Superchargers create boost incrementally by RPM's. Although boost is produced (minimally) off-idle, hence no lag.... full boost is usually achieved at redline unless using a centrifugal type, in most cases.


I'm going to have to disagree with some of this.....A centrifugal blower and a turbo have similar exponential boost rise characteristics. Both can be configured to have high boost at low rpm, with boost-limiting controls cutting the boost at upper rpm.

Near-full boost for a Roots or twin-screw is achieved amazingly quickly, but then it also levels off close to its maximum on up to redline (almost as if it had a boost controller in use). But still, the blower has to be size-matched to the engine to get that kick-ass performance we're looking for.

On my best 1/4 mile scans, from a 5% (that's low) throttle position and holding at 1500 rpm (65 MAP), full boost is seen after 1.02 seconds and 3600 rpm. It crosses into boost at 0.5 seconds. That's if I ease out the gas pedal just right. There is a slight increase of 1/2 -1 psi on up to redline, but it's essentially constant.

Now the main reason I take it to 1500 rpm is that I usually get a better reaction time and more consistent runs. Boost rise is just as quick from idle, but it's harder to time the launch.
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Old 11-22-2009, 09:46 PM   #98
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While that may be true on some of the newer setups, boost is achieved incrementally by RPM's on a supercharger, unless you're using one with a bypass valve where you can push maximum boost in the lower range because the boost levels are low.

I've been using older model S/C's on V8's during many of my earlier days, but that was pre-Vortec style, such as the original GMC, Weiand, etc, so my tech might be a little out dated on newer setups, but I usually don't mess with low-boost applications (below 15psi).
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Old 11-23-2009, 12:44 AM   #99
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Quote:
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While that may be true on some of the newer setups, boost is achieved incrementally by RPM's on a supercharger, unless you're using one with a bypass valve where you can push maximum boost in the lower range because the boost levels are low.

I've been using older model S/C's on V8's during many of my earlier days, but that was pre-Vortec style, such as the original GMC, Weiand, etc, so my tech might be a little out dated on newer setups, but I usually don't mess with low-boost applications (below 15psi).



What you are saying is true, but the increment of change between, say 3600 and 5600 rpm in my case is very small (about 11-13 lb at sea level) and I suspect if boost is lowered by using a smaller drive ratio, or absence of the bypass valve, that affects how large the increment of change is.

The bypass valve I'm talking about here is the type that opens under vacuum. It can also be adjusted and "tuned" to affect throttle response.

One thing I noticed when going to the 2.0 (and the 1.9) inch pulleys on the M62 was not only was the max boost level higher, but the time to reach near-maximum boost level decreased. I'm guessing that since it is now spinning faster at idle and in bypass mode, it has more momentum when the bypass closes and boost kicks in.

At this point, it is probably necessary to step up to an M90 to get all the potential out of this format, though there are still some technical advantages with the M62.
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Old 11-23-2009, 12:57 AM   #100
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At this point, it is probably necessary to step up to an M90 to get all the potential out of this format, though there are still some technical advantages with the M62.

I'm hoping you'll go for it with the M90, I'm anxious to see how hard that sucker will pound on that shit
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