boon

Hi

A mate of mine was unhappy with the way the turbo was spooling up on his MR2 turbo (reaching 1 bar at about 5000 RPM). He took off the exhaust manifold and found massive discrepancy between the manifold and the head. See pic.



He's about to get new manifold made but wanted another opinon that this is going to cause his spool-up problems.

Turbo is a Precission SC61.

Cheers as always,
Boon

Rs1

iTrader: (1)

Well it sure as shit aint gonna help. Surly it the wrong manifold for the head or vice versa(provding that the head ports match the gasket)

boon

lol Yeh, the head and the gasket match perfect.

Alps Pacino

Theres a bloke on snowdon road Enigma performance that might be able to help, i went down there to see about a few bits for me car, he had a few mr2 tubs in there expecting big power out of them i think

slipslide

that was probaly the reason of slow spool then

boon

Cheers Alps, i'll tell him to give them a shout.

Common sense tells me it's got to be contributing to the slow spool up if not the sole cause.

Stavros

Surely that gasket aint right, can be a bit away, but that takes the piss!

That turbos pretty big tho, about GT35R size, so wouldnt spool super quick anyhow.

Lairy cams fuck it right up too, and i know how jap car owners love them so much.

Anonymous

It will have a negative effect if you have an obstruction like that, you get all sorts of air stalling issues as it tries to get past a restriction, but i bet that it has FAR less effect than he is thinking it does!

boon

Thanks for the replies guys.

The gasket is right mate - well it matches the head perfectly. It's the manifold that is different.

Showing my lack of knowledge here, but is it the volume of air that causes the turbo to spin up rather than the pressure? With that restriction, I imagine there will be less volume but at a higher pressure (imagine partially blocking the end of a hose pipe with your thumb).

Either way, it must be true that the car will never release it's full potential with this setup...right?

Anonymous

The two are interlink, the pressure is a measure of how much air is passing out of the head versus how much is making it through the turbo effectively.

If you have a restriction on the manifold like this, its going to effect it, because there wont be as much flow into the turbo as easily, but its really not going to be a huge effect.

HOWEVER at really high rpm when running full boost, this restriction will be strangling the power of the engine.

So its more the peak power than the spool up that it will effect most of all.

paul16v

That would be Pete one of my oldest mates, he is expecting some big power from his rx7 this year aswell

Anonymous

if your mate hasnt got a turbo yet for his big power rx7, pm me.

ive got a gt42r that would be ideal for a 700bhp+ rex

xrsi

iTrader: (1)

WRONG - a pressure is a force, the pressure is the force being exerted on the surroundings.

The flow rate of the air is the amount of air pasing through a known section in a given amount of time.

yes it is, why do you think that ports are matched, its not to make them look pretty and to make the head or manifold weigh less if there is a restriction it creates turbulant flow and also with a flow of fluid through a pipe (air is classed as a fluid when dealing with flowrate, and the ports cna be modeled as a pipe) the boundary layer always moves slower than the rest creating a none liner flow throughout the section, where the bit that is in the boundary layer hits the sudden restriction it effectivly stops and the layer that was quicker moving will instantly slow down due to sudden increase in friction slowing down the flow rate no end!

the spoling of the turbo relies on the flow rate of the air, slow flow rate into the exhaust housing will mean slow spooling of the turbo, this will then effect the power output of the engine due to efficency and the compression of the charge air going into the cylinder.....

but anyways, that is a shocking match! you sure the thing is actualy for an mr2?

Anonymous

How is it wrong?
As i said, pressure is amount of flow out of the head, minus amount of flow through the turbo, thats just common sense, if more air is getting into the manifold than getting out then the pressure will increase.
The pressure then in turn effects the flow in both directions too, its very obvious that the amount of air flowing through each section is going to effect the pressure.

I cant even begin to imagine how you can be confused over that and think there is no relation between the two at all?


Absolutely true in every respect, EXCEPT the bit at the end where you say it slows the flow "no end", thats not true at all, it slows the flow by a very finite amount, and this is my point i was making from the beginning, altohugh it will effect it, it wont do so enough to single handedly stop the turbo coming on boost for an extra thousand rpm.

What you are saying is correct qualatitively, but you are exagerating the effect quantatively

Indeed, but it will effect it more at high rpm, like i said in the first place, as at high rpm you have an ever diminishing exhaust stroke timebase during which to evacuate the cylinders.

xrsi

iTrader: (1)

the standard definition of a pressure is a force being exerted over a standard unit area of surface.

you agreed that the boundary layer through a section is considered to be experiancing a huge level of friction opposing the flow, this causes the boundary layer to be at almost standstill..... Where this layer hits a sudden restriction or blockage it is in effect becoming stationary and the layer that was slightly above the boundary layer is now suddenly experiancing all of the friction that the boundary layer was experiancing and slows right down! so the whole flow rate decreases drematically when the sudden blockage is hit! so does effect it 'no end' was just putting it in more simple terms! if the restriction was a venturi as found in rally car restrictors then the flow rate would increase, this is why they use venturis and not a suden flat edge!
yes there will be a slight pressure increase where the air is being slowed down as the air is trying to be forced through but flow rate and pressure are not the same as how you tried to describe them. If more air is getting into the manifold than getting out, soon as the pressure evens after the exhaust valve opens the air will slow right down anyways..... also after the resriction the port will open right up again resulting in a big pressure drop so slow the gasses down also resulting in a longer spool up time due to the slower flow rate.