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[Sideways]

Whilst I’m pulling everything apart on my 3.0 I noticed my inlet manifold was VERY dirty so I’m going to clean it up.

Whilst cleaning I saw how rough the casting is for the inlet manifold and the cast aluminium ducting beneath the manifold was. This lead me to think that polishing it could be some free horse power (minimal admittedly) however there seem to be 2 thoughts on this.

I have been told that rough casting can be beneficial as there is more surface area and greater turbulence to help the air/fuel mix better. However some say the cleanest route the air has to travel through will provide the most air, thus enabling to run richer.

Does anyone have any experience or knowledge of induction/fluid aerodynamics who could suggest the best method?

Secondly, as I’ve ditched my AC compressor (loads of stuff on sale on eBay if anyone is after anything, or just send me an e-mail (markduc916@hotmail.com)) I have more room and greater flow over the radiator. I might use this extra room to either have a direct cold air feed into the standard airbox or even move the rad down and align the multiram so it lies on its back side, rather than its bottom and have it going straight to the throttle bodies.

Would changing this induction from suction to pressurised air mess up much other than the mapping?

[Tezray]

Not sure about the mapping issues, but on the inlet a rough surface is definately beneficial imo. However i'm talking about the inlet manifold, not the plenum chamber. On the inlet manifold you need a certain amount of roughness to give the fuel particles something to 'cling' onto, thus suspending the fuel in the air and allowing it to mix well with the air. You may well increase the velocity of the air through the plenum chamber if you smooth the inside of it, but i wouldn't touch the inlet manifolds. I polished my exhaust manifolds and ports while the heads were off because obviously you want the gases to get out ASAP and the smoother the better.

How do you think it'd benefit the engine by having the multiram pipes lying on their back?

Mark, now my beast is back up and running i'll have to come over and have a look at what you're up to  

[Sideways]

No worries Terry,

The idea behind lying the multiram on it back is to allow the air to go straight from the grill (where the rad would normally be) into a filter, into the multiram then into the throttle bodies with no (or very minimal) bends and kinks.

[mar892ree]

The main induction ideal would be to try and cool down the incoming air, hot / warm air coming in to the intake of any combustion engine lowers efficiency

Mark

[EddieX]

In the days of carburators,(have I spelt that right? Hmm, stick to 'carbs.' in future.) a rough inlet manifold was needed to keep air turbulent and petrol droplets in suspension. It was found that with a pollished manifold and cold engine, so much petrol condensed on the manifold walls that the car became undrivable due to the weak mixture. However, with injection, the plenum and upper inlet tracts only carry fresh air, so a bit of a clean up would probably be OK.

What would be good for airflow, would be to match all the ports, ie. make the holes in the plenum the same size and shape as the top of the inlets thereby removing any edge or step. The bottom of the inlets should match the ports in the cylinder heads in the same way.
Depending on how bad things are as standard, you could see a 4 to 8 b.h.p. increase but only at high revs. and large throttle openings.

As for the 'ram air' idea I am not sure. It was a bad idea with carbs. because the carbs. got tuned on a rolling road with the car stationary but when in motion the 'ram air' effect varied the mixture. The amount of variation depended on speed, revs. and throttle position.
With injection measuring air mass and temperature in the intake ducting, it might work.

All the best with your project,       Eddie.

[Sideways]

The main induction ideal would be to try and cool down the incoming air, hot / warm air coming in to the intake of any combustion engine lowers efficiency

Mark

Is this not a trade off? If your inlet temp is really cold then it tends to condense on the walls. I know for turbo's this is less of a trade off as you need super cool air and don't have to worry so much about condensation, but not so sure on natural aspirated.

Something to ponder anyway.

[Tezray]

Cold air is denser than warm air, hence you get more air into the cylinders....More air=more fuel=more power!

Eddie good points, especially about matching the ports. When i rebuilt mine i noticed that the exhaust ports were actually very good, but the inlet ports had some rough edges and really weren't matched very well. Definately worth matching them, but i'd still keep the inlet manifold rough.

[omegaV6CD]

Whilst I’m pulling everything apart on my 3.0 I noticed my inlet manifold was VERY dirty so I’m going to clean it up.

Whilst cleaning I saw how rough the casting is for the inlet manifold and the cast aluminium ducting beneath the manifold was. This lead me to think that polishing it could be some free horse power (minimal admittedly) however there seem to be 2 thoughts on this.

I have been told that rough casting can be beneficial as there is more surface area and greater turbulence to help the air/fuel mix better. However some say the cleanest route the air has to travel through will provide the most air, thus enabling to run richer.

Does anyone have any experience or knowledge of induction/fluid aerodynamics who could suggest the best method?

Secondly, as I’ve ditched my AC compressor (loads of stuff on sale on eBay if anyone is after anything, or just send me an e-mail (markduc916@hotmail.com)) I have more room and greater flow over the radiator. I might use this extra room to either have a direct cold air feed into the standard airbox or even move the rad down and align the multiram so it lies on its back side, rather than its bottom and have it going straight to the throttle bodies.

Would changing this induction from suction to pressurised air mess up much other than the mapping?

The casting marks are there in the inlet manifold just because it costs a lot of money to VX to remove them so if you grind them off will only impprove minimally the engine performance. THere will be no issues with regards to turbulence and fuel mixture as the manifold in your case does't play primary role due to the fact that the injector is placed just before the intake port, so the roughness on the cylinder head and the tumble in the cylinder during suction is providing the primary turbulence.
If you are not concerened by low end toque then chuck the front multi ram assembly in a bin as it is not very air flow friendly  and use a high capacity resonator box between plenum and MAF+filterbox. Then also need to enlarge the TB. This with should give you a good top end improovement if combined with good remap.

[omegaV6CD]

Whilst I’m pulling everything apart on my 3.0 I noticed my inlet manifold was VERY dirty so I’m going to clean it up.

Whilst cleaning I saw how rough the casting is for the inlet manifold and the cast aluminium ducting beneath the manifold was. This lead me to think that polishing it could be some free horse power (minimal admittedly) however there seem to be 2 thoughts on this.

I have been told that rough casting can be beneficial as there is more surface area and greater turbulence to help the air/fuel mix better. However some say the cleanest route the air has to travel through will provide the most air, thus enabling to run richer.

Does anyone have any experience or knowledge of induction/fluid aerodynamics who could suggest the best method?

Secondly, as I’ve ditched my AC compressor (loads of stuff on sale on eBay if anyone is after anything, or just send me an e-mail (markduc916@hotmail.com)) I have more room and greater flow over the radiator. I might use this extra room to either have a direct cold air feed into the standard airbox or even move the rad down and align the multiram so it lies on its back side, rather than its bottom and have it going straight to the throttle bodies.

Would changing this induction from suction to pressurised air mess up much other than the mapping?

The casting marks are there in the inlet manifold just because it costs a lot of money to VX to remove them so if you grind them off will only impprove minimally the engine performance. THere will be no issues with regards to turbulence and fuel mixture as the manifold in your case does't play primary role due to the fact that the injector is placed just before the intake port, so the roughness on the cylinder head and the tumble in the cylinder during suction is providing the primary turbulence.
If you are not concerened by low end toque then chuck the front multi ram assembly in a bin as it is not very air flow friendly  and use a high capacity resonator box between plenum and MAF+filterbox. Then also need to enlarge the TB. This with should give you a good top end improovement if combined with good remap.

Sorry for the spelling mistakes everyone! i just noticed them

[Sideways]

Whilst I’m pulling everything apart on my 3.0 I noticed my inlet manifold was VERY dirty so I’m going to clean it up.

Whilst cleaning I saw how rough the casting is for the inlet manifold and the cast aluminium ducting beneath the manifold was. This lead me to think that polishing it could be some free horse power (minimal admittedly) however there seem to be 2 thoughts on this.

I have been told that rough casting can be beneficial as there is more surface area and greater turbulence to help the air/fuel mix better. However some say the cleanest route the air has to travel through will provide the most air, thus enabling to run richer.

Does anyone have any experience or knowledge of induction/fluid aerodynamics who could suggest the best method?

Secondly, as I’ve ditched my AC compressor (loads of stuff on sale on eBay if anyone is after anything, or just send me an e-mail (markduc916@hotmail.com)) I have more room and greater flow over the radiator. I might use this extra room to either have a direct cold air feed into the standard airbox or even move the rad down and align the multiram so it lies on its back side, rather than its bottom and have it going straight to the throttle bodies.

Would changing this induction from suction to pressurised air mess up much other than the mapping?

The casting marks are there in the inlet manifold just because it costs a lot of money to VX to remove them so if you grind them off will only impprove minimally the engine performance. THere will be no issues with regards to turbulence and fuel mixture as the manifold in your case does't play primary role due to the fact that the injector is placed just before the intake port, so the roughness on the cylinder head and the tumble in the cylinder during suction is providing the primary turbulence.
If you are not concerened by low end toque then chuck the front multi ram assembly in a bin as it is not very air flow friendly  and use a high capacity resonator box between plenum and MAF+filterbox. Then also need to enlarge the TB. This with should give you a good top end improovement if combined with good remap.

Sorry for the spelling mistakes everyone! i just noticed them

Thanks for that, it's really useful.

Couple of questions if I may.

What is a "high capacity resonator box", "MAF+filterbox" and "TB"?

Sorry if thats realy obvious but I'm obviously not up with the engine vernacular yet.

[omegaV6CD]

TB is throttle body MAF is mass air flow sensor and the resonator box is a box to fit between the MAF and TB if you remove the multi ram. Manzel  make one but it costs a fortune.

[stevief]

As for the 'ram air' idea I am not sure. It was a bad idea with carbs. because the carbs. got tuned on a rolling road with the car stationary but when in motion the 'ram air' effect varied the mixture. The amount of variation depended on speed, revs. and throttle position.
With injection measuring air mass and temperature in the intake ducting, it might work.

All the best with your project,       Eddie.

Ram air did work on carbs as used on quite a few American muscle cars in the 70s through bonnet ducts with great effect but the whole idea was to get as clean a run to the air box as possible to ensure that the engine always had enough air to work correctly. The theory was then transposed to suit production applications on later cars by feeding pipes through into the front of the radiator or down to a point close to the front valance in order to keep the maximum and coolest airflow to the engine.

It was identified in the 80s when injection realy hit the market that modifications to the air intake could yield increases in power and the trend of ducting pipe installations started in earnest. However the changes to the intake did not provide the full benefit because the air flow was metered to suit the engines requirements via the mapping and the set up on the airflow metering. Once the metering was adjusted the full benefit was achieved which is no different today I guess.

Steve