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The Wife and the Car
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Discussion Starter · #1 ·
I noticed this on quite a few cars. We tuned.
Something happens between 4000-5000 RPM on most Honda vtec motors.

First I thought it was the Y7 manifold. But it was there with the Z6 and y8 and even the edelbrock manifold. We tried different intake lengths same issue.

Then I thought it was the exhaust. We tried all kinds of Exhausts it still remains.
So its not the Intake or the Exhaust.

We also tried different cams. Stage 1,2,3,x
Same issue.

Also tried porting mods.

I came to the conclusion that this was something to do with the mismatch between the small intake low lobe and the large Exhaust Cam which is designed to match the Vtec lobe vs the smaller low intake lobe.

What are your thoughts on this.

My key questions is do you see this bump on all Honda engines or only Vtec Engines. ?

Then I read somewhere a post by Dan where he said you can fix this bump my taking out timing. I on the other hand found that adding timing was the only way to sort it out.

Any thoughts ?
 

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Brokedick Millionaire
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40,797 Posts
tuning the VTEC switchover.

Toyota did something similar on the GTS motor.

Might be why my 4400 Z6 VTEC switch point tune by Blundell worked so go, he smoothed the dip out?

It is magic I swear!
 

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VTEC withdrawals
i "ride" yo momma
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my 4400 vtec i found works better as well
 

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The Wife and the Car
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Discussion Starter · #4 ·
found that the switch point on the stock cam is better at 5500
Then as you go stage 1,2,3 this point starts climbing till in some cases you dont enter vtec till 7000+ RPM.

Based on my Dyno tuning sessions.

My question remains.
1. Is this something only observed on Vtec's
2. Is the solution more timing or less. (more has worked for me).
 

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889 Posts


There is my dyno in all it's 109hp 97ftlbs torque glory on a Mustang dyno.

D16A6 75.5mm bore stock PM6 pistons
.030 taken off head/block total
Stock ZC cam
Slightly ported A6 non vtec head
Bisimoto Springs
Ebay chip as a "tune"
 

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()*#$(*$
93 Legend L Coupe.
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11,404 Posts
Ron-

You really like to do the opposite of everyone else. Nearly every Z6 needs the switchover point at about 4400, at least in stock-ish form. 5500 is, IMO, way too high, as you will fall out of VTEC on a gear change and I can't see it being a smooth transition between the high and low cam.

The Y8 switches the cams even lower than the Z6. I forget the exact figure, but it is definitely lower.

You keep posting these questions, but don't really give enough info for use to see what is going on. If you are able to, post the cal/bin/tune, corresponding dyno chart or at least a screen shot of your high/lo timing and fuel tables along with an exhaustive build list.
 

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found that the switch point on the stock cam is better at 5500
Then as you go stage 1,2,3 this point starts climbing till in some cases you dont enter vtec till 7000+ RPM.

Based on my Dyno tuning sessions.

My question remains.
1. Is this something only observed on Vtec's
2. Is the solution more timing or less. (more has worked for me).
5500K, on a stock cam, you nuts??

Matt is right, and right before the vtec swichover add some fuel to smooth things out.
 

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Brokedick Millionaire
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Ron-

You really like to do the opposite of everyone else. Nearly every Z6 needs the switchover point at about 4400, at least in stock-ish form. 5500 is, IMO, way too high, as you will fall out of VTEC on a gear change and I can't see it being a smooth transition between the high and low cam.

The Y8 switches the cams even lower than the Z6. I forget the exact figure, but it is definitely lower.

You keep posting these questions, but don't really give enough info for use to see what is going on. If you are able to, post the cal/bin/tune, corresponding dyno chart or at least a screen shot of your high/lo timing and fuel tables along with an exhaustive build list.
Matt, RDC has to be vague at times. I know I busted his balls on here when he started here but his competitors are on here as well.

I have to bite my tongue on certain racers gear changes for the same reason.

Y8 stock cam switchover is higher @ 5500 rpm IIRC due to the bigger primary lobes
 

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()*#$(*$
93 Legend L Coupe.
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I understand that, but asking vague questions publicly gets vague answers, which only confuse the issues.

You're right about VTEC on the Y8, too, Bone. I thought it was much lower than the 55-5600.
 

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I'm going to assume that you are only speaking of vtec engines. So is the bump/dip when vtec engages? I have seen a few graphs that look pretty smooth. The issue is its a science of the tuner. All competition aside have you talked to anyone else that tunes on your level or higher. Sometimes people come together for the greater good. And if that means make a better power band and keeping the surge down or at least smooth enough to control. This is a NA car you are talking about right? Think about the simple things before you start grinding the brain gears. Start at the beginning and think about engine design. Bigger intake valves vs smaller exhaust valves and then opening the intake valves more on an upper rpm. The scavenging effect. Remember the reason for vtec was for a fuel economic car that could have a little more power when pushed a little harder, but got great gas mileage when driving like that old guy that won't sell you that hatch you've been eye balling. I'm not claiming to know anything about anything, I'm just trying to help with the brain storming. I know sometimes it takes someone with less intelligence (that's me) about the subject to think in a different way to help figure something out. How about cam timing? Again I am only making suggestions, I don't tune on any level, but I understand this engine.

You asked.
 

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The Wife and the Car
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Discussion Starter · #12 · (Edited)
I dont see any reason for confusion.
First off I have tuned every possible cam combination there is for this engine from stock to wild. And when I say tuned it means the final dyno result has been a text book smooth curve. With a table top flat torque curve.

My comments on the Vtec switch over points are dead easy to back up. You do a run with low. You do a run with high. Where they cross over you set your point.
Its not rocket science. Nor do I need to speak to anybody about this.

What caught my eye was Beve telling a guy that he had an AEM Hump in his dyno curve. Between 4000-5000 RPM.

I noticed this on all my builds. And I also know how I fixed it. With more timing.
Then Dan also mentioned that the only way to remove this hump was drop timing.

I found this in direct contrdiction to my findings hence this post.

My conclusion after studying the wave dynamics of the engine. Is that this hump is not being caused by intake length or manifold or exhaust design. Its being caused by the Vtec Cam. i.e. the huge mismatch between the large exhaust and the small intake lobe.

I normally wont bring up a topic. Unless I see stuff which directly conflicts with what I have found to be true.

One simple fact that you guys are tending to over look is that our cars came with a D16y8 cam and head but the block is a D15. This changes the way in which you work your STA numbers. I cant find a simpler way of explaining this.

I keep this fact in mind when I read D16 posts. Consider it when you read mine. I run a 1.5 Engine. Think about it. Now you get why the switch over RPM is higher ?


If you have seen any of the dyno curves I have posted. There is never a dip anywhere. So its obvious that its not something Im having problems resolving. My only point was with the manner in which its being recommended to solve it. i.e. drop timing. Vs in every engine Ive tuned Iv had to increase timing here.
 

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Brokedick Millionaire
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rdc, blundar and me need to make a trip to you.

he didn't think "our" combo did so well until I mention to upped the base timing from 16 BTDC to around 22 BTDC.

Sorry I'm not on here as much as I wish to be to read entire threads.
 

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Ron-

I keep forgetting that you are running a 1.5L sometimes. That does make a difference in that with the shorter stroke, the way the engine builds pressure as related to crank rotation is different. The other issue is that the D15 has shorter rods, which decreases piston dwell time, so that can correlate to needing to advance the timing to arrive at MBT.

I don't know why you would want to tune out the "AEM Hump." More torque is more torque. It is usually in a good area for a stock-ish engine, too, since you would have the engine drop to that arear of the torque curve after shifting, which is a benefit, I think.

I have never "fixed" that at all. I would also lessen the ignition advance to reduce the torque, if needed. If you are looking at a mostly stock D15 you can go well past MBT by advancing the timing and not have any noticeable detonation since the chamber, especially if it is a Y8-headed chamber, but doing that is adding in a lot of stress on the rods and oil film. I would definitely try backing off a few degrees instead of adding in that much timing and see how the engine responds while driving.

I will completely disagree with you about the hump being a VTEC thing, as you can see it on non-VTEC engines' dyno charts, too. It IS resonance. You can easily prove it by adding or cutting off a few inches and re-dynoing the engine.

I would listen very carefully to what Dan (triple D) has to say about this stuff, too. He's got more practical hands on experience with engines on dynos than anyone I know (at least on this forum).
 

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Classic Man
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I dont remember ever saying to remove a hump to remove timing.

can you provide a reference please? or stop saying that.


Has my head swollen so much I assumed you were referring to me as "dan" I know there are millions of us! hahah
 

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I dont remember ever saying to remove a hump to remove timing.

can you provide a reference please? or stop saying that.


Has my head swollen so much I assumed you were referring to me as "dan" I know there are millions of us! hahah
Not me Dan either, from what I can remember...

Thanks for the shameless plug, Matt ;)

Like Matt said, it's either resonance or some sort of inertial tuning effect, but I don't know what. You can't tune out physics, so I wouldn't worry about it in that sense.
 

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He is finished taking about this.
"It's not rocket science, nor do I need to talk to anyone about this"

Well... on to the next one.

You asked.
 

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The Wife and the Car
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Discussion Starter · #19 ·
sorry danz I sometimes make mistakes when remembering who said what.
But I take anything guys like you Beve, bone, DDD say very seriously. Because I know you guys have way more experience than me with these engines.

In the two bike world. We call these things flat spots. And they are a bitch to tune out. Bike or car.
 

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Dips are inevitable with tuned length inlets and/or exhausts. Your only available option is to move them around.

I think it is bad form to smooth them out by reducing torque either side. It is much better to get more total area under the used part of the power curve. Pulling timing will only make the dip disappear by reducing torque either side of the dip to "blend" it in.

Obviously if power is dropping off with the small cam, and has not yet come on with the big cam, you will get a cam induced dip at the switch over. The only fix I can see for that which increases total area under the curve is to make the small cam bigger.
 
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