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Speculation: Why do boltons give very little gain?
Ok, by now, the d17's have been out long enough for people to find out that bolt ons (namely intakes, headers, and exhausts) give very little gain. This does not hold true with previous motors (ie. the bisimotor header for a d16z6 dyno'ed an 8whp gain over stock, with no other added mods).
I've been reading many threads and why "power" mods add no power leaves my mind open to speculation. After a brief moment or two, I've come up with a few reasons ...
1 - Honda has already maxed out the power for the d17 motor. This does seem to be the case, since it does come 'optimized from the factory' .. as I read that somewhere. Optimized from that factory with keeping legalization (ie. sound muffling, etc) in mind.
2 - the boltons that are being added already beyond the point of giving much more power (ie. engine already takes in the needed amount of air, etc).
(I personally think the cam is already maxing out the air)
I suppose 1 ties in with 2 though ...
Solutions?
the two easiest solutions ... turbo, swap, n2o. Other solutions ...
1 - get a custom cam. If the engine is already intaking enough air, then a cam would have the valves open either wider or longer ... either way, having the engine consume more usable air. Higher lift would mean solution 3 would be needed
2 - upgrading valves. bigger valves, more air. ties in with solution 1.
3 - upgraded valve springs. I don't know how much the stock valve springs can handle as far as lift is concerned ... but upgrading valve springs would be good ... and as compression is greater, along with higher/longer lifting cams, revving higher would also come in handy. (*cough cough hondata's k-pro cough*)
These are the only things that I can think of that would be related to non-responsive mods ... of course the next few things would also help, but I wouldn't think they would make mods more responsive...
1. upgraded fuel system. for more air, more fuel.
2. tuning - more air, more fuel, more discrepancies between optimal fuel/air timing.
3. boring the block - allows more air, more fuel.
4. port and polish head - allows more air. best if used with a cam and/or valves that takes advantage of the extra air that is coming in.
5. port and polish intake manifold. more air. Our current plastic design seems to help for torque ... but a d16y8 intake manifold conversion (already been done) and perhaps a (ported) skunk2 d16y8 IM would be more practical for higher horsepower applications.
6. ported throttle body. more air.
someone should build a full n/a d17 ... bored block, stroked, everything. That would be nice. ;P
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Last edited by aznboysrfr; 11-02-2004 at 05:31 PM.
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doesn't the ecu compensate for boltons? I don't think a true N/A project could begin until Hondata comes out with that new ecu. I don't really know though.
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Bored throttle body (even only a few inches)--this will cause huge low end loss and almost cause the car to stall when accelerating from a stop.
port/polish head--great for turbo, relatively no effect for NA even with oversized valves (which I also have). I really think you need a new cam to take advantage of any kind of head work.
It does seem like Honda did a fairly good jub of matching everything to the engine. This is why adding boltons to open up air flow almost always causes power loss. In the older hondas, the intake flow was not maxed out, which is why an intake really did give 10whp by itself instead of 1-2whp on our cars.
Tuning is so good from the factory, additional modification with vafc or other tool yields maybe 5whp average.
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Bored throttle body (even only a few inches)--this will cause huge low end loss and almost cause the car to stall when accelerating from a stop.
port/polish head--great for turbo, relatively no effect for NA even with oversized valves (which I also have). I really think you need a new cam to take advantage of any kind of head work.
It does seem like Honda did a fairly good jub of matching everything to the engine. This is why adding boltons to open up air flow almost always causes power loss. In the older hondas, the intake flow was not maxed out, which is why an intake really did give 10whp by itself instead of 1-2whp on our cars.
Tuning is so good from the factory, additional modification with vafc or other tool yields maybe 5whp average.
all good points .... except that I mentioned that the last 6 points wouldn't make the car more responsive ...
boring the tb a few inches? ... mm? ;P ... in most cases, it helps when your motor is in need of more air (ie. fully built setup) ...
PnP is what I listed under the "non-responsive" mod solution ...
clarification: the 2nd set of solutions are things that would make all the other boltons more responsive ... the 3rd set are things that would further add to the 2nd set
gearbox: as far as your last paragraph goes ... that's the main point I was trying to imply ... also noted in the bit about the bisimoto header ;P
Oh I see. Yeah I meant mm instead of inches. So our cars are pretty hopeless looks like as far as staying NA. I'm waiting for someone to make a more aggressive cam for our cars (not regrind).
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So wait, if our engines are already pretty tuned from the factory, and they still make the same HP as previous generation Civics (at least the EX does), then wtf?
6th gen EX = 127 hp (poorly tuned, bolt-ons give decent increase)
7th gen EX = 127 hp (well tuned, bolt-ons give pretty much nothing)
Why doesn't that seem right? It sounds like if the 6th gen engine was less tuned from the factory and it made the same amount of power that it was a better engine. Make sense? Like, in order to squeeze out equal performance from this one, they had to tune it better.
Ok, so the 7th gen engine has a little more torque than the 6th gen, but still. They're pretty much the same.
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well, the idea of my post was to motivate d17 people to not think so poorly of their engine. with an upgraded cam, I think the engine would pull very nicely since the engine is already pretty much maxed out on its air intake
What is it about this engine that is causing the lack of response to n.a. mods? It just to me seems that every attempt from Gude to DH racing has been poor results when aiming for n.a.. What is holding the d17 back that isn't holding back the d16. Stock for stock a d17 car is faster then a d16 car with drivers of the same ability. My speculation is that a n.a. setup on a d17 should be greater then a n.a. setup on a d16 car because of the similar engine characteristics and the greater displacement for the d17. Maybe the answer is fundamental, maybe by comparing the difference between the d17 and d16 we can resolve this issue. ie. d17 ecu vs. d16 ecu, d16 cam vs. d17 cam, return vs. returnless, etcetera. It is less likely to be one thing that is holding the d17 back but the entire system.
I don't really know though. 
