Intake runner diameter

[amichie]

I measured a few heads I have here
Mitsubishi 4g92 16 valve has 30mm dia valves and 45x28 oval runners 400mm long
Mazda 2 litre v6 24 valves 30mm dia valves and 42x28 runners 330mm long
Toyota 1800cc 4S 16 valve head 30 dia valves and 44x34 ports

Many thanks.

As far as I know the late model 4A-GE small port has 42 X 30 ports.

I've seen lots of pics online but not many actual measurements.

I must admit I dont have an accurate measure of the 7m ports yet. But I will have the manifold off shortly.

[andrew_mx83]

very keen to know how u go with the venturi's...have used them before on carby engines with much better bottom end response....would love to see how they go on efi and the 7m in particular.

i also must see one of these 16 valve rb25s you speak of

[amichie]

i also must see one of these 16 valve rb25s you speak of

Ooops.

That's not counting the other 8 valves.

I must have been using Cameron Smith's brain when I posted that up.

On another note. I have some more accurate measurments of the port and intake runner dimensions.

The oval shaped ports are approx 51mm X 32mm at the head and the ports at the plenum end of the manifold are between 44 and 45 mm and circular in shape.

[amichie]

Update.

I fitted my bodgy 36mm venturis yesterday and took it for a blast.

First thing I noticed was I had to retard the timing a couple of degrees due to a bit of pinging. After doing that I have a good improvement in the midrange and it still pulls strongly upto the 6100rpm gearshift point. The pinging may be due to better cylinder filling.



I will pull the venturis out again and do a better job of them but they will definitely be going back in.

[abently]

Sorry to burst your bubble but it would be pinging from even worse cylinder to cylinder flow distribution then Factory. The MAS can easily compensate for a reasonable increase in air intake... You really should setup the venturi's in the manifold on a flow bench or at least weld in bungs on each primary to fix each individual venturi's position in relation to the AFR results under dynamic conditions.

I hope you replicate your dyno butt experiences on an actual dyno back to back, for your own sake. Nothing is worse then thinking your on the right track only to find out your wrong months later after all the time and effort.

[Sam_Q]

poor port design may reduce effective port diameter, but the losses at the surfaces and corners...

the race thingy probably assumes the ports are a straight shot with ITB.

I totally agree, for example when the rules of thumb as mentioned by the said book is applied to the 16v 4age heads the figures give indication that the ports are just way too big for both heads. However in real world testing its been pretty much proven a small-port head cant flow enough to support power past a certain point. From what I understand the ports needs to purposefully over sized to compensate for air stagnation and turbulence as a result of the less ideal port shape and angle.

[amichie]

I hope you replicate your dyno butt experiences on an actual dyno back to back, for your own sake. Nothing is worse then thinking your on the right track only to find out your wrong months later after all the time and effort.

I will hook my PC dyno up again. That will atleast give me a relative measurement showing any improvement or otherwise.

I totally agree, for example when the rules of thumb as mentioned by the said book is applied to the 16v 4age heads the figures give indication that the ports are just way too big for both heads. However in real world testing its been pretty much proven a small-port head cant flow enough to support power past a certain point. From what I understand the ports needs to purposefully over sized to compensate for air stagnation and turbulence as a result of the less ideal port shape and angle.

I put the small port dimensions into the wallace racing calculator and the peak torque rpm was within 500rpm of actual. In my book this represents pretty good agreement.

[cambelt]

Are you doing all this thru your gas mixer??
Dave

[amichie]

Are you doing all this thru your gas mixer??
Dave

Yes and no. I have tried it both ways. I can whip my 225 out in about 30 seconds and turn the gas off at the tank for a quick test.

In both cases I got improved midrange on unleaded. I have still not done anythnig about my lack of gas supply due to the model J converter.

Here is a couple of pics of my new even more bodgy venturis. Made out of Aluminium tube and flared out by prerssing a socket inside using the vice. Then bashed on the tow ball until nicely rounded at the inlet and outlet. The inside diameter at the smallest point is set by the original tube 36mm.These fit snugly inside the intake runners at the plenum end.

[Sam_Q]

amichie: sounds interesting, in the four stroke performance book which I was refering to it gives a port diameter that is a percentage of the diamater, which they say by memory should be 0.83 to 0.87 which just happens to be way off the mark. So I am guessing theres heaps of tricky variables to use that racing calculator right?

[amichie]

amichie: sounds interesting, in the four stroke performance book which I was refering to it gives a port diameter that is a percentage of the diamater, which they say by memory should be 0.83 to 0.87 which just happens to be way off the mark. So I am guessing theres heaps of tricky variables to use that racing calculator right?

I'm not sure what you are saying here. Please rewrite your question.

[jeffro ra28]

I THINK that by making it ping with your venturies, you have actually reduced the efficiency of the engine and its ability to take spark advance. Maybe it FEELS better because it gives it a jaggered torque curve and when its over its reversion/spazz from your venturies it gives a bit more of a kick. Rather then a broad smooth powerband.

You cant make a silk purse out of a sours ear. By all means it is an interesting experiment. But to be half accurate wouldnt it be better to reduce the port diameter through its entire length? Throwing in sudden port restrictors wont be giving a true indication of the actaully theory your are trying to prove? Its basically worthless experiment unless you are able to reduce port diameter over the entire length, making it a smooth streamlined port runner.

Imagine that the dimensions of that port where all designed to work with each other. Then all of a sudden a single dimension is changed, throwing all other dimensions out of whack.

Edit: Sure, the book states this and that. But honestly how can the author of that book specify the points you have raised for "4 valve engines". There are a matrix of variables that confuse the matter worse. Id go with what toyota have come up with to start with . Perhaps make slight improvements here and there to the improve specific needs, such as peak horsepower, low end torque etc etc.

[amichie]

I THINK that by making it ping with your venturies, you have actually reduced the efficiency of the engine and its ability to take spark advance. Maybe it FEELS better because it gives it a jaggered torque curve and when its over its reversion/spazz from your venturies it gives a bit more of a kick. Rather then a broad smooth powerband.

You cant make a silk purse out of a sours ear. By all means it is an interesting experiment. But to be half accurate wouldnt it be better to reduce the port diameter through its entire length? Throwing in sudden port restrictors wont be giving a true indication of the actaully theory your are trying to prove? Its basically worthless experiment unless you are able to reduce port diameter over the entire length, making it a smooth streamlined port runner.

Imagine that the dimensions of that port where all designed to work with each other. Then all of a sudden a single dimension is changed, throwing all other dimensions out of whack.

Edit: Sure, the book states this and that. But honestly how can the author of that book specify the points you have raised for "4 valve engines". There are a matrix of variables that confuse the matter worse. Id go with what toyota have come up with to start with . Perhaps make slight improvements here and there to the improve specific needs, such as peak horsepower, low end torque etc etc.

Thanks for your 2 bobs worth.

Isn't spark advance and volumetric efficiency inversely related?

[Duk]

Thanks for your 2 bobs worth.

Isn't spark advance and volumetric efficiency inversely related?

I'm in agreeance
If you have made a breathing chacteristic change that results in detonation, I would call it an improvement that then needs the appopriate fuel (maybe some leaness) and ignition advance angle.

[Sam_Q]

amichie: I was referring to this book:

http://www.amazon.com/Four-Stroke-Pe.../dp/1859604358

just explaining how the port diameter formula in this book doesn't work for a 4age