Hi, I know it might sound stupid but may I ask why the car is not boosting when you wot it on rev in when it's in neutral ?

Also, can I tune the AFR meter while in neutral or does the car need to run ?

Thanks

 

You dont create enough load on the engine to 'boost in neutral'


also, no you cant tune the afr while its in neutral for the same reason, and by the way, uh how do you expect to tune your car?

 

Thanks, but can you define more specifically ''load on the engine''

Cheers

 

When your car is spinning the wheels WITH the weight don't u think it'll work harder than just reving your engine? Basically you can think of that as the "load" on the engine.

 

THink of it like this. Do you breath harder jogging in place or when your actually jogging?........Of course, jogging. You motor is the same way. Just reving your not putting the car under any "load".

 

mine doesn't either.

 

Really? I can hit full boost faster in neutral then when i'm actually driving.I think full boost hits about 1,600rpm in neutral and about 3,300rpm in gear....you need to fix that.....it makes tuning easy...

 

its all about compression and the size of the turbo....smaller turbos can spool in neutral, where larger ones don't...like-wise with compression, the higher your compression, more exhaust pressure is produced and the turbo spools at lower rpms,,,

 

i want to know how exhaust restriction affects this ability to spool in neutral. i dont really understand whats going on. why some people can spool and some cant with similar setups.

i know its doesnt matter but maybe spooling in neutral indicates exhaust restriction or some general rule of thumb we could come up with to understand the phenomenon.

 

not exhaust restriction...exhaust pressure..meaning more air is leaving the combustion chamber. Higher compression means more air being flowed in out of the cylinders, so you'll get higher exhaust pressure (or more air in the ex manifold) which in turn, spools the turbo sooner. So one way to spool quicker (although I don't think many will recommend this) is to raise your compression.

What was done with my engine (thanks to JDM_DOHC_SIR) was to wrap the ex. manifold with thermal wrap. This insulates the heat in the ex. manifold and raises exhaust pressure a bit (because heated air expands)...hence I am able to spool a bit quicker.

Larger exhaust piping helps too...golden rule, more air= more power...this applies to air leaving you engine too.

Final thing is to just get a smaller turbo. you'll lose top end, but you'll spool right off the line.


[Modified by MiraiZ, 2:46 AM 2/15/2003]

 

Actually, exhaust wrap helps produce power by making the Delta(T) as large as possible across the exhaust turbine. Mass flow across turbine is also a factor in power production, so yes, higher compression(more energetic combustion) will aid in 'spooling up' quicker.

BTW - Don't ever wrap your downpipe with exhaust wrap - it actually hinders power by reducing the Delta(T).

 

ohhh kay well none of this really applies to understanding why similar cars boost in neutral. but its all good info. i want to know what the delta is here.

 

the wheel doesnt run off exhaust.


it runs off unburnt fuel gases expanding in the turbine, correct me if im wrong but i know for a fact it doesn't work off of pure exhaust.


[Modified by bretx0r, 6:48 PM 2/14/2003]

 

don't think so...I think you're getting this confused with the misfiring system.

 

Can someone verify this statement? I always thought you'd compromise. spool up would be a bit slower while you would gain horsepower by getting larger exhaust piping? Right??

 

you will benifit by faster spool-up and more power, the only compromise is the added noise

 

I'm not an expert on this, but from what I understand boost is built because of a difference in pressure between the exhaust manifold and the exhaust system. so the higher the pressure differential, the fast you will build boost pressure i.e. large piping, low pressure exhaust will provide faster spool than a small restrictive exhaust. Unfortunately I do not understand why some cars boost in nuetral and some do not.

 

This is wrong, and here is your proof. When people get adjustable cam gears, they use them to "dial out" the overlap in the cam. Without any overlap, you don't get any unburnt fuel in the exhuat flow.

Also, a turbo DOES use just exhaust gas. I think what you are thinking of is the fact that the turbo uses the energy of the expanding gases to get the power to spool. That is why it is important to keep your exhaust manifold fairly short and small (to a point of cousre, this kind of goes against using equal length tubes, but there is a middle ground) so the exhaust gases stay as hot as possible from the exhaust valves to the turbine. That is why people use header wrap and jet hot coating. You want to keep a consistent temperature in the exhaust manifold so when the gases enter the larger area of the turbine, they will expand as much as possible. That is what you are talking about

 

Actually, if you get too big of an exhaust, yo can create back pressure and we all know what that does.

 

Well WTF? I've heard many times on this board that if you have a bigger exhaust, your spool up time will take longer, but when you hit full boost you will be making more power. I think there are exceptions maybe?

Some guy on here had an example about blowing air through a straw, and it stood behind what i'm trying to say. If that guy is out there, show your face now!

I'm probably wrong, because I'm no turbo expert, but i swear i've seen many people agree with that statement...

Anyone know whats the deal??

 

You're thinkin about the housing size of the turbo (AR) ,,,that's totally different from exhaust size....it goes back to what I said earlier...smaller turbos spool faster...bigger ones yield more top end power

 

ah, i give up
Peace

 

no wait, i dont give up
Check this link...a bunch of more indecisive statements in my opinion...
https://honda-tech.com/zerothread?id=413072

 

turbos get most of their energy from the heat in the exhaust gas. Unburnt fuel in the exhaust gas CAN be ignited if the a/f ratio ratio is within the igniting limits of gas, and if the turbo is hot enough.

 

Again. we're talking misfiring here, which most turbo setups don't have...as you said, igniting unburt fuel causes the turbo to spool quickly out of turns etc...


turbo housing and exhaust are two different things. when people mention 3" exhaust pipes being the best for a lot of power, they're usually referring to the downpipe back to the canister. This usually affects mid to top end power.

When the refer to AR or turbo housing size or spooling, this usually refers to how quickly the turbo can spool to produce lowend (off the line power)...

Unless you have high compression (like 10:1+) you probably won't see the turbo spool at idle with bigger turbos, but you will definatly see better mid and high range power.

Conversely, if you have a smaller turbo like an HKS gt25 or something like that, you'll probably be able to spool these things at any compression. They are made for instantaneously power off the line, but they reach their terminal velosity at about 6000rpms on a Honda.


[Modified by MiraiZ, 1:38 PM 2/15/2003]