well i went to the dyno again tonight and power was not as expected. i'll leave the numbers for later as i have a problem to diagnose. *suspense* i'll tell you this, they're lower then coreys. And not much higher than my last dyno numbers.
let me say this, the car feels strong and my statements about the night and day diff. with this header still stand.

well here is the symptom, the car hesitates in the low end.

........................................ _-
the graph looks like this _-_- , then when it hits vtec the power climbs normally all the way to 7400-7500. its the exact same way with tq.


The dyno operator said this is the culprit of the low(er) numbers, as accel. isn't smooth. he suspected it was an ignition problem, but timing is dead on. We adv. and ret. timing while on the dyno (set it at 14 deg.) there is no apparent misfire (except at idle). which ties into my current theory.

well here it is, i searched and found a thread related to a flat hp curve after vtec due to the iabs staying closed. my theory at this point is the iabs are constantly open causing the lack of low end performance. if this is related to a loose vacumm line then that would also explain the misfire (or lope) at idle.

ill post the graphs up tom. after they're emailed to me.

thanks in advance.

 

also can anyone tell me where this vacumm line is?

 

cant following your graph, but its HARD to draw a dyno

i believe the vacuum line is near the fuel rail, by the regulator.

 

that was a basic example of what the power curve looks like below vtec.

 

I can tell you this much, the IAB will not cause a studder in the low end. It'll remain consistantly a little low, but nothing that will cause any kind of spikes. But in any case the vacuum line is on the back of the plenum on the drivers side. It's a 1/8" nipple back there. You can check this by looking at your IAB's (drivers side of the manifold again) and look for a spring like assembly (you should be able to actuate it by your hand) and place a piece of tape on it while the car is off. Start up the car and it should close thus making your tape come off.

But I really doubt that was your culprit as you'd just have a very little bit more air going into your manifold. I had this setup for a while (had them completely removed) and while I lost low end, a dyno would just show a little loss in the low end.

When was the last time you replaced your ignition components, and what was your A/F ratio?

Edit: Here's what you're looking for... The nipple left of where #44 goes in is the vacuum line for the IAB box. The IAB's are actuated via #16.

 

I don't buy that...I run my secondaries open all the time and my graph is very smooth. Open IABs should not create a choppy graph.

If you want to e-mail the graph to me at jbycraft.hba2002@ivey.ca I can help you analyze it, I will keep the graph confidential of course.

 

that makes sense, i now remeber the threads posted about running them open all the time.

 

Well, the major problem that that I see is the loss of power on the low end. That makes me nervous.

I'm not saying this is the absolute case, but what you are describing is a car with a one of the cylinders low on compression. It has a studder in the bottom, it misses, has a lopey idle, awsome header, and not much power gain... and goes away when you get farther up in the RPM band.

Just for curiosity's sake, run a compression test.

This could also be the culprit of a wire breaking down, the cap being burned up etc... so don't go getting all excited and worried and ****...

let me sleep on it tonight and see if I can come up with something... usually I can find a better solution after I've had a nights rest with a problem under my pillow.

 

If you don't have an A/F readout my guess is a free flowing header running super lean, inducing knock, knock sensor kicks it at VTEC are and retards timing, then stops reading at high rpms so it smooths out.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TimeRacer &raquo;</TD></TR><TR><TD CLASS="quote">
When was the last time you replaced your ignition components, and what was your A/F ratio?

</TD></TR></TABLE>

i replaced the plugs in june, checked them after last weeks dyno they are good. the wires are new but i suspect the no.3 wire. I pulled them while at idle and it had some effect but not as much as the others. the air fuel is in the 13.0 to 14.0 range through the powerband.

however at first there was a slight bog around 1000 rpms while he was rowing through gears to 4th. i leaned it out on the narrow throtlle func of the vafc.

edit: i also did a visual insp. of the cap and rotor, they looked ok.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Lone Luder &raquo;</TD></TR><TR><TD CLASS="quote">
Just for curiosity's sake, run a compression test.

</TD></TR></TABLE>

did one last week, forgot to mention that.
4....3.....2.....1
212,210,210,210

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by satan_srv &raquo;</TD></TR><TR><TD CLASS="quote">If you don't have an A/F readout my guess is a free flowing header running super lean, inducing knock, knock sensor kicks it at VTEC are and retards timing, then stops reading at high rpms so it smooths out.</TD></TR></TABLE>

a/f ratio is dead on.

edit: here is the original thread where i gave my first impressions of the header. (for those that missed it)
https://honda-tech.com/zerothread?id=657068


Modified by 93preludevtec at 11:46 PM 12/3/2003


Modified by 93preludevtec at 11:47 PM 12/3/2003

 

Damn, Steve, that sux about the dyno numbers. When I rode in your car...I was very impressed how well it pulled throughout the rpm band. That was my first time riding in a VTEC Prelude.

Maybe next time you are in town...we can run our cars to see how they compare.

Anyways, hope you get your car troubles worked out and the numbers change for the better next time you dyno.

 

The header is broken. Send it to me, ill give you $20 for it. Much more then its worth

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by AndyD &raquo;</TD></TR><TR><TD CLASS="quote">Damn, Steve, that sux about the dyno numbers. When I rode in your car...I was very impressed how well it pulled throughout the rpm band. That was my first time riding in a VTEC Prelude.

Maybe next time you are in town...we can run our cars to see how they compare.

Anyways, hope you get your car troubles worked out and the numbers change for the better next time you dyno. </TD></TR></TABLE>

well i'm not as concerned about the numbers, the butt dyno likes it if both disagreed i might be feeling a little differently right now. i would definetly prefer a 200 whp showing but as i stated before there was a definite increase after the installation. BTW i'll be up there in dec. for christmas, i'll give you a call.

*shot in the dark*, could a failing auto tensioner have any bearing on the situation? i have a tapping that could be t-belt related? i also recently adjusted the valves, trying to fix the aformentioned tapping. just trying to throw some ideas out there.

 

a failing tensioner will give a flapping sound on and off the gas from the timing belt. It will also cause the cam timing to be retarded once the belt gets some slack in it and it'll run poorly throughout the lower rpms, and "seem" to clear up in the higher rpms... but that can be very misleading. You should lose power off the top end too.

The miss at idle is what has me stumped. Usually a vacuum leak will cause the idle to jump up and down, but not a miss or stutter. But, there are exceptions to every rule. Welcome to owning a Prelude VTEC.

 

I would take a quick look at your intake manifold and make 100% sure that everything is snug. My GSR swapped EG (rest in peace, go to hell thieves) friend of mine had irratic idle and obvious stop and go acceleration problems until we sealed his skunk IM holes properly. Worth a look unless your shop has done it already. Good luck!

 

Check your ignitor.. It sounds like an ignition problem to me. Also check your fuel components and make sure everything is good there. Fuel filter and such..

 

Ive heard of a choppy dyno graph before from a loose and flapping timing belt.If thats the case,might wanna try the h23 tensioner.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 93preludevtec &raquo;</TD></TR><TR><TD CLASS="quote">

a/f ratio is dead on. </TD></TR></TABLE>
Dead on what? Would be nice to at least see an a/f curve.

 

yeah i agree as 14:1 didn't make any power on my motor, curves would help

 

ive seen instances of loose tensioners causing the knock sensor over compensate and reducing timming .....if you have the flaping noise then that would be the best place to start....weather or not its affecting power..it could do alot of damage but

do you ever get a studder when crusing at 3000 or so rpm.....or any where in that range

 

just post the graph, we're all intelligent enough to not blame the header.

just don't put any thing about the header on the image, so incase it starts flying around the internet, the story won't get twisted.

FWIW, I'd consider the knock sensor, ignition coil, and the igniter. I had problems like you describe, and that seemed to fix it.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Greyout &raquo;</TD></TR><TR><TD CLASS="quote">just post the graph, we're all intelligent enough to not blame the header.

just don't put any thing about the header on the image, so incase it starts flying around the internet, the story won't get twisted.

</TD></TR></TABLE>

i will post the graph once wayne (dyno owner) emails them to me. Should be around 6 pm tonight. I spoke to dave about the previous showing on the dyno and i don't think anyone would mistake the problems for a lack of performance from the header.

one question i have is will the hesitation in the low end cause lower peak numbers. it seems logical to me, just want someone to verify that.

well i may have solved the hesitation problem, i leaned the lower vtec settings (lvt)on the vafc and it feels as it should, constant pull from 2000 rpms through vtec.

heres what ocurred when i tuned it (on the dyno), first run the lower end was smooth and the higher rpms were choppy but didnt surge. the lvt setting were unchanged, while from 5000 on were 5k+1, 55k+2, 6k+3, 7k+3.

after the first run wayne had me add +3 from 3k to 5k, and remove 5 from 55k to 7k. well then the low end showed the hesitation/surge and the high end smoothed out. we did two more runs adjusting HVT settings and kinda forgot the change in the lvt settings. we chalked the lower rpm surge up to an ignition problem, and started sampling from 4k on up. i just lowered vtec to 44k and tuned, adjusted timing, etc.

on a side note to better describe the sit., wayne had a few customers in the shop while we were tuning. he would run it, tell me the changes and i would enter them, while he went to speak with the other customers. also the buttons on my used vafc stick, so making adj. had me a bit frustrated. which complicated the sit. a bit more.

well it dawned on me today and i went back and leaned out the lvt settings. 2k through 5k. the lower rpm hesitation/surge seems to have went away. i'm going to talk to wayne tonight and see if he can fit me in for a few runs, anyway, i'll know by about 6 tonight what the plans are. oh and for whoever asked the air fuel ratio is about 13.0 to 13.5, aside from the 2k to 4k which wasn't plotted. i will also have the other/all plots sent so they can be posted.

cliffs: will the lower hesitation/surge cause a lower peak hp/tq figure?
and hindsight is always 20/20.





Modified by 93preludevtec at 6:30 PM 12/4/2003

 

so how muc hp did you gain and what is your setup