92 Civic VX stumbling/hesitation

[VXonFumes]

TheHolyCow: thank you for your post. I haven't had the civic on the road long enough and with enough consistency in conditions to read too much into anything yet. I have no long term averages.

As for the back-pressure/torque thing, if I'm permitted to speak on it quickly (not sure if considered off topic), my experience, for what that's worth, is that longer, skinnier, more restrictive intake tracts and exhaust tracts produce more usable low-rpm torque. It definately squelches upper rpm breathing like breathing through a straw would do for us, but for low rpm's it helps. I don't know how exhaust gas velocity would have anything to do with it.

For example, for years Yamaha has had their patented "EXUP" exhaust power valves that would stay closed or close to closed at low rpm's for a significant boost in low rpm torque. They advertised it that way too, and it worked. As rpm's opened up, the valve did too, and suddenly it could breath better for more upper rpm horsepower production. And in the last several years they did the same thing with the intact tract. Ingeniously, they lengthen the intact port/mouth in front of the intake for slightly more restriction at low rpm's and increased torque. As the rpm's ramp up, the bell opening actually shortened via servo's or some other mechanical setup, and high rpm breathing and horsepower increased.

I also have a 1990 honda prelude 4WS, and ingeniously Honda already way back then had a valve somewhere in the intake track that would partially close at low rpm's for increased restriction and increased torque in lower rpm range. It would open up at upper RPM's for better breathability and more horsepower. They did that b/c that was before V-Tec was introduced and those engines were biased towards high rpm running and horsepower, so they needed a boost down low. It is a pretty torquey 2.1 liter engine actually, considering it's age and lack of v-tec.

I've also had a descent amount of experience with those short stacked, cold air intakes. Sure they help for horsepower production screaming around a track, but low rpm torque and everyday drivability (and mileage) usually suffers as well. (this is assuming nothing else was changed with it...some will completely tune and mod their cars into something different and argue with me, but they're comparing apples to oranges.) Same with low resistance, wide diameter exhaust pipes and catback systems...low rpm torque is reduced while upper rpm horsepower increases. That's just my experience working on quite a few cars over the years. I'm sure others have had different results, or at least want to believe they did!

I can't fully explain it: I think it's a lot more complicated than most people think. Many think you can just slap on a fat pipe somewhere or short intake and instant gains. That's not true...there's give and take everywhere. These are tuned systems, with acoustic resonancing and more all playing a part, including the length and diameter and "restrictiveness" of intake and exhaust tracts playing an integral part. Since small displacement cars by default don't normally have a lot of torque, losing more of it via mods or exhaust leaks, etc, can hurt them badly in terms of everyday drivability and mileage.

Sorry if I rambled too much, and hope this info is useful to someone.

John

[VXonFumes]

@ add|ct:

re. a possible coolant intrusion near a faulty intake manifold gasket, there is definately potential for ingress there. There's a little port hole and rubber gasket built into most paper intake manifold gaskets at that point too, on most four cylinder honda's anyways (that's what I'm familiar with).

I was going to suggest oil analysis as a valuable too, then read you have been doing that some. That was wise. I do oil analysis for customers on a semi-regular basis and it's a super tool, depending on who does it (some analysis are more thorough). If you have already been alerted there is even a small amount of coolant in the oil (usually showing up as Sodium and/or Potassium for most standard coolant types) then do not take chances with that! It will only get worse too over time. Standard, Ethlyn Glycol coolants are very very hard, caustic even, on engine innards, and promptly destroy the lubricity of the oil, especially cheaper petroleum oils, and do other bad stuff chemically too, and lead to engine damage and blown engines in short order if allowed to keep going. Propylene Glycol is not as harsh on an engine if there is ever contamination, but regardless, any coolant in your oil is a bad sign.

You really should not take chances with it: I'd change the intake manifold gasket asap, they're not that expensive, and then change the oil asap and keep taps with analysis, or at least open the rad cap and overflow periodically and check to see that you don't have grey sludge crap in there, and the same thing on your oil dipstick. Those are signs that a lot of ingress has already happened and major financial emergency is coming your way if left untreated.

Hope this helps bro!

John

[theholycow]

VXonFumes, usually the people who think backpressure=torque are the same people who think you can just slap on a fat pipe somewhere or short intake and instant gains, having bought into plenty of marketing without doing much thinking. I'm glad to see that you're not such a person. You've put plenty of thought into it for sure.

However, I remain unconvinced. You've described a correlation, not the "why" or "how". The same narrow pipes correlate with velocity as well as they correlate with pressure. Here's some threads to help explain...

A thread where I asked about it:
http://www.gassavers.org/f5/pumping-...html#post99944

A post from when I remembered a lot more about the issue than I currently do, having put some study into it at that time:
http://www.gassavers.org/f7/actual-v...tml#post127859

A thread where someone actually tested by choking his tailpipe:
http://www.gassavers.org/f6/tail-pip...test-5668.html
(Perhaps not fully relevant when mounted at the tailpipe, depending on how the science may work, but containing useful discussion.)

I don't know what's up with Yamaha's EXUP exhaust throttle or your Prelude's pre-throttle throttle. I imagine they were more complete systems than a mere throttle added to a pipe, and they may have been more about emissions than anything else - usually that kind of gizmo is (regardless of how it's marketed). That's just a guess, though. If torque and fuel economy gains were available by adding more throttles to intake and exhaust then I imagine we'd see plenty of that...it's exactly the sort of thing manufacturers seem to like.

Bringing it back down to street level, where a hobbyist is attempting to save fuel, a lot of this stuff is merely theoretical. It rarely pays to invest in such modifications if you're trying to save money, though if you're willing to spend more money overall to save fuel for other reasons (political, competition, technology development, etc) then it might be more worthwhile.

Bringing it even further back to what's relevant to us, I imagine that if your exhaust leak reduced torque, it was probably either because the leak had an effect on your O2 sensor or the turbulence caused by the leak increased backpressure while reducing EGV. I think that same turbulence may be part of why my 1980 Buick feels more powerful after finally getting my exhaust manifold leak fixed.

[VXonFumes]

@ Holycow. thanks for your post...I'll look at those links one of these days. I'm sure I'll learn more. I listed my experiences with these things installed on my honda's over the years, and other's vehicles, just for people's interest. They were always four cylinder Honda's ("normal" and Si civics, Accord engines, etc.) and the results were *always* consistent, for what it's worth. I even remember in college many moons ago a roomate had a tiny little firefly and popped a good leak somewhere in the middle of his exhaust and his mileage just tanked as soon as that happened! I should qualify what I said earlier too: obviously there are limits to this. Making a car breath through a straw would not increase torque even more: it would kill the engine. Etc.

You're right, I am pointing out, at least in my experiences, correlations. I've already admitted I can't explain the *how.* Some might even say it's just anecdotal. I believe these consistent observations demonstrate causation, but others don't have to believe that and that's fine. But I don't know...I think maybe your buick's increase in power after fixing an exhaust leak is exactly what I'm talking about there.

But it's not just my own thinking/experiences here. My thoughts were also largely moulded by these company's own statements, and they have the engineers working for them. For Yamaha's EXUP and my 3rd gen prelude, I know for certain from years ago those valves, and that's all they were in essence: butterfly type valves that blocked off exhaust/air flow at low rpm's, were specifically made to increase restriction at low rpm's to the end result that low rpm torque was boosted.

Yamaha's and Honda's own literature stated the purpose of these valves in this way, and this is how they marketed them, so now it's these companies claims you are not convinced of as well. It doesn't help my case that I can't show you from where anymore...the prelude info in particular was more obscure and hard to find...it's 23 years old now almost. I think it was mentioned in an original online Honda brochure from somewhere. But I guess you won't believe me unless I can produce it. I'll do some digging if I get some time, but no guarantees I'll find it. Would be good if I could...it's in the corners of my memory and I would like to refresh it too.

I don't know why other manufacturer's didn't follow suit with these valves. Perhaps they were patented and after the 10 year patent period things had changed sufficiently with engine design they moved on? ON the other hand sometimes good designs are not followed up on and we scratch our heads. Back in 2006 Honda (and GM too I think) was working on HCCI (Homogenous Charge Compression Ignition) engines and the they showed great promise, but apparently they couldn't quite make them work smooth at upper rpm's...what a shame! I'll tell you, what I wouldn't give to be able to sit down and have a long talk with the head engineer at Honda who oversaw the VX project! Anyways, I'm rambling, thanks for your input I'll look into that stuff one of these days.

Cordially,
John

[theholycow]

I completely understand where you're coming from. I too have experiences that differ from what people tell me, and I have to believe my own experience. In short, you can't argue with results! (And why would you want to? Getting results is what we're trying for, isn't it?)

I've learned to be skeptical about what the manufacturers say. Apart from intentionally misleading us, there's always issues with needing (or thinking they need) to dumb it down for release, even releasing to technical audiences, and of course just the fact that everything released filters through a series of lawyers and marketers before we get to see it.

Patents in the US are good for 17 to 20 years (depending mainly on when it was filed). Manufacturers do a lot of weird stuff with not developing patents, not using technology that's already been developed, etc. Sometimes I look at something and say "there's absolutely no reason they'd ignore such easy gains" (like if an exhaust or intake was so narrow and restrictive that fuel economy suffered, despite the potential CAFE fines, unmarketability of the associated power loss, and maturity/low cost of the technology), but sometimes it's undeniable that they've got some other design compromise in mind (a car lacking a decent highway gear, wastefully buzzing along at 1000rpm more than it needs to, like the 2008 VW Rabbit I had - that transmission was made for their larger European market who doesn't want to be bothered with downshifting and has a smaller engine).

I wonder if the HCCI concept has been rendered obsolete by the introduction of gasoline direct injection, which seems to offer many of the same advantages and is actually in many new cars now.

[VXonFumes]

I have a 13 page paper from SAE International, published April 2011, where they have a test rig HCCI engine and all sorts of good data to go with it if you want it. Delphi made the engine I believe. Summary is: a lot of progress has been made already, it shows good promise for fuel savings even now over what's currently available, but much more work needs to be done to make it practical & viable to mass produce. :/ I'm sure there are lots of control related issues for such a finely tuned system.

Google this (without quotes here): SAE Int. Gas Direct Injection Compression Ignition Engine by Delphi.pdf My pdf and others will appear. You might find it interesting.

[add|ct]

@VXonFumes, thanks for the reply. Yes, I've gotten oil analysis a few times. I'm hoping it's the IM and not the head gasket. Raining today, I'm gonna pull the plug for #4 my next off day and try to inspect the plug and shine a light onto the cylinder itself. I already have parts. May just pull the IM back and replace the gasket anyway since it can be done with a HG job anyway.

[VXonFumes]

If it were my car I'd change the intake manifold gasket right away...you don't need to pull the head to do it, just the eight or so nuts holding it on. (I'm sure you know that). Maybe drain a little bit of coolant into a clean container first as some will dribble out of the port otherwise. It's a fairly easy, fairly cheap piece of insurance. If it turns out to be the head gasket after that, well, that sucks eh? But at least you will have elimintated this variable and it feels good knowing you didn't pull the whole head when it *could* have been something simpler afterall.

[add|ct]

Originally Posted by VXonFumes

If it were my car I'd change the intake manifold gasket right away...you don't need to pull the head to do it, just the eight or so nuts holding it on. (I'm sure you know that). Maybe drain a little bit of coolant into a clean container first as some will dribble out of the port otherwise. It's a fairly easy, fairly cheap piece of insurance. If it turns out to be the head gasket after that, well, that sucks eh? But at least you will have elimintated this variable and it feels good knowing you didn't pull the whole head when it *could* have been something simpler afterall.

I'm going this very route. I have noticed what appears to be a coolant leak; albeit slow, externally from somewhere under the thermostat house/head/block/IM at that #4 runner area. Before, I thought it might be the breather box the PCV valve seats into, but this leak is a little higher up; I can't tell the exact source, all along the right side of the the location of the breather box.

Here's a pic, zoom in. See the end of the slime-like leak on the right?

http://img23.imageshack.us/img23/2729/1004077e.jpg

It comes from up higher.

Also, it appears at some point the PO had the thermostat housing opened and there is RTV sealant around where the thermostat goes, instead of just the rubber gasket.

[sebass]

bcfromfl what did it turn out to be for you and others that had that issue here. I also have occasional and slight hesitation but only happens when i'm on high gear and low rpms but i talked to my bud that has similar driving habits and that does not happen on his VX. I did already ran few times fuel system cleaner but that didn't help.