head work any point

[jwhoss76]

I had to bring this up again. I'll accept what you guys are saying as true. I tried to share this info with a friend and he thinks you're all nuts. I even gave him the HTMLs posted here and he still came to the conclusion that this only applies at extremely high flow rates, ie 2000 mph. I've read the articles several times and am still at a loss to his reaction. Any help? Or is he a lost cause, this is the same guy who tried to tell me that porting the head was great but only for racing.

 

[Thad]

DG 76,

Never try to teach a pig to whistle, it is an impossible task and it tends to agreviate the pig! :roll:

This has been an interesting and enjoyable thread

 

[jwhoss76]

Good advice. Thanks again to all for the insight

 

[J.R.]

1) Well, to throw another parameter into the mix here, what about head porting & mods on a mildly-boosted(9 psi) turbo'd & intercooled EFI 300" truck-torque motor with Isky Turbocycle cam (goal is a torque mule from 800-3200rpm)?

2) Obviously fluid flow dynamics principles still apply, but practically speaking, what differences in power, fuel efficiency or emissions would porting, polishing, or bigger valves make for that engine(mine), if it never sees above 4000rpm?

3) Guess the subject of intake runner lengths beg the same type question: does the beneficial 'ram' effect of a long runner at low rpm even occur for a boosted engine in just plain ol' work and highway use? (Under load this engine/turbo combination is supposed to start making boost just above idle, and reach 9psi by about 2400rpm. Spinning a built C6 with 'Lo-stall', RV-style, torque convertor.) Long runners still best? Short just as good?

Looking for answers before I start cutting or welding! Thanks.

J.R.

 

[Anlushac11]

8)

I have a book on turbocharging and it says that you dont need to port and polish a head for more power since the turbo will push the air/fuel mix through. To an extent that is true.

BUT..I dont agree with that thinking 100%.

WARNING: The numbers quoted are for use as examples and are in no way to be connected with any performance figures.

In cases where turbos were put on a stock headed motor you may make say, 300hp with 10lbs boost but you get pressure diffrences wherever a bottleneck is.

You throw a ported and polished head on and suddenly your making 350hp with 6lbs boost. The turbo doesnt have to work as hard building pressure to overcome a bottleneck and pressure equalizes til you hit another bottleneck.

as with any ported head, low lift and low rpm flow will affect how much power the turbo can add to the engine at low rpms. I have seen cases where a good ported and polished head and a low restriction intake and exhaust system have caused the turbo to start spinning up and making boost as low as 1500-1800 rpm where before it didnt start spinning up and making boost til around 2300-2500rpm. Its because the system didnt need to work as hard to get air through to spin the turbo,ergo the turbo wasnt fighting to push air through the system.

 

[Anonymous]

Outstanding post, Anlushac11.

Read and heed, turbo lovers!

 

[J.R.]

Yeah, thanks. That makes sense to me too. Any insights on the intake runners? For a turbo'd EFI engine, would the factory upper intake manifold's long runners have a helpful 'ram' effect, providing smoother flow into the intake ports as they do on the stocker. Or would they just be areas for more heat absorption by the pressurized & intercooled intake air? TIA.

J.R.

 

[Anonymous]

It may seem counterintuitive, J.R., but the diameter of a "tuned pipe", which what your intake runner is, has little influence on the 'ram' effect, except at very small and very large diameters. The length is "everything", for all intents and purposes. Porting your intake runners might allow the engine to make more boost at a lower RPM (by increasing flow efficiency - technically "volumetric efficiency"), but it won't affect the RPM at which the engine makes max torque or hp. I wouldn't try anything beyond mild port matching...it's real easy to screw it up if you start hogging it out...

 

[StrangeRanger]

I'm not sure the rules are the same on a boosted engine. The negative pressure wave that gives the ram tuning effect may just get buried under all that excess pressure, so length may be a lot less important.

The whole business of diameter may change too. In an N/A engine the idea is to keep the cross sectional area and thus the velocity constant throughout the length of the inlet tract. By matching this to the engine's other characteristics performance can be optimized throughout a fairly wide range. When you boost it though, what you're really trying to acheive is mass flow so the larger the areas and the smoother the flow paths, the better.

I'm sure that's an oversimplification, that there's balancing act of some sort going on with a blower just like there is on an N/A engine. I'm just not sure what the tradeoffs are.

 

[J.R.]

The engine speed for torque peak on this specific engine is just fine: 1650rpm, with a fairly flat curve from 1200-2800. The concern is not to mess up the benefit the long inlet tract gives the engine (before the turbo reaches full boost) between 800 and 1400rpm, while still maximizing torque & power available in the 2400 to 4000rpm range. Obviously from 4000rpm on up the long upper intake runners probably hurt a stock 300' I6's ability to draw as much air as possible at high RPMs, but that's not where most 'working' 300s spend much time.

This truck has gears that should allow it to stay near the peak of the torque curve at almost any legal speed. Just want that curve to be as strong, flat, and wide as possible, assuming that will also have a beneficial effect on fuel efficiency. Third gear on the C6, with both overdrives engaged, will put that 1650rpm torque peak right @ 60mph. Having a very flat curve should mean that the RPM range at which the engine will get its best fuel efficiency is also a wider spread.

Realistically, most road vehicles start requiring much greater amounts of power [and, therefore, fuel] to maintain steady-state cruising on level ground, at about 55mph; this due to aerodynamic drag, rather than rolling resistance of the tires, taking over as the primary power drain. Our trucks & SUVs are, aerodynamically, typically much worse than average cars, so that crossover point may be quite a bit lower than 55mph! Again the benefit of a wider, flatter 'high' torque range come into play.

Look at all the Ford engines that have 'variable length' inlet tracts. The little 4.2L V6 has a very wide range of 'high' [yeah, it's a relative thing]torque availability, for a small "V" engine. A lot of that's due to the dual inlet tracts. [The new Audi V8 40-valve RS-6 gas engine has 3 separate intake tracts per cylinder & puts out 450hp, and the 419lb/ft. torque is availabe from 1950 to6700rpm, all from only 4.2 liters. Their V8 diesel has only 32valves, producing only 274hp with 481 lb/ft; that from 4.0 liters; wouldn't that kick a 4.0L Ranger down the road!]

Don't know if multiple intake tracts was ever tried with our 300" I6, but the physics are the same. For Ford Motor Co. to have developed an aluminum crossflow head for the 300'/4.9L, with dual intake tracts(one a little longer than our EFI engines' intakes & one about half as long) would have been relatively simple or at least "do-able", and the results could have been staggering, not to say "embarassing" to the 4.6LSOHC V8 afficianados. For an individual to develop a dual length intake system, and for a non-crossflow head, seems like a huge undertaking. That, and I still can't get a fix on whether it even matters or not on a turbo'd engine. Any suggestions on where to look for this info are definitely welcome. For now the Sawzall isn't plugged in! TIA

J.R.

 

[Anonymous]

The scavenge effect of a tuned port intake never goes away no matter what the input and output pressures are. It can have the tendency to shift the natural frequency slightly, however. The natural frequency of an intake runner is determined predominantly by it's geometry and secondarily by the characteristic changes in it's fluid (air/fuel mixture).

Any intake port is going to have a set natural frequency at a set barometric pressure based upon it's geometry. The idea with a tuned port intake is to have all the intake runners of equal length such that they all hit their natural frequency at the same time. This creates a small rpm band where an intake essentially supercharges itself using the pressure pulses from the intake plenum provided by the other intake runners.

Now if you supercharge this intake, you are not changeing the geometry, so this same scavenge effect will occurr at close to the same frequency. What you are essentially changeing is the intake barometric boundary pressure.

 

[Stubby]

Engines running boost do respond to porting. It will take less HP to turn a blower. A turbo or a blower will respond to improved quality and I think quality is what is most important unless you are making an all out effort on a race car. Quality comes cheap, quanity cost tons of money. Even when going for quanity you still have to maintain quality.

As far as turbulance goes it is a good thing when used in moderation. I don't have a degree to back this up just experience. Back in the 80s one of the big names in drag racing was boarding an airplane and noticed louvers on the wing. These wern't functional vents so he asked what they were for. He was informed they were vortex generators. On the wide part of the wing next to the fuselage the air tended to tumble over the back and create drag, (if a wing isn't creating lift it is only creating drag) by generating turbulance the air followed the contour and made the wing work better. A short time later a Funny Car showed up with vortex generators ( louvers ) He got better air flow over the car, mainly due to the air following the contours which allowed him to reduce the rear wing. More downforce less drag. It didn't take long and NHRA said NO!!!

The next big thing in aerodynamics other than small tires and nose that help you flip over backwards(landing gear from an airplane) was a film that does the same thing, only this time they borrowed it from a sail boat. It works on more of a microscopic level.

I think this is what an engine responds to. The roughness helps the a/f mix follow the contours, and the turbulance along the surface helps the quality. Imagine a collom of air and fuel traveling thru a tube with light turbulance around the perimiter, when it has to make a turn, the fuel wants to keep going straight. (enertia) When it reaches the boundry layer of turbulance it is helped around the contour by the turbulance.

You do not have to have a degree, or know exactly how or why it works to be able to use it. Just use good judgement and staw away from mores law and you will be fine. MORES LAW (if a little is good more is better) Which is not to say that you can't make it morebetter.

 

[80broncoman]

Back in the 80s one of the big names in drag racing was boarding an airplane and noticed louvers on the wing. These wern't functional vents so he asked what they were for. He was informed they were vortex generators. On the wide part of the wing next to the fuselage the air tended to tumble over the back and create drag, (if a wing isn't creating lift it is only creating drag) by generating turbulance the air followed the contour and made the wing work better. A short time later a Funny Car showed up with vortex generators ( louvers ) He got better air flow over the car, mainly due to the air following the contours which allowed him to reduce the rear wing. More downforce less drag. It didn't take long and NHRA said NO!!!

I remember this but i just cant remember who it was.

 

[Anonymous]

Well, you have to know WHERE the vertex generators (and other surface treatments) should be placed to have a useful effect. Just putting vortex generators anywhere on the car won't help, although racers do things like this, and then convince themselves there is a difference in performance from doing it. I can envision only a couple of spots on a dragster where vortex generators MIGHT be useful.

Interesting to see this discussion, as I was asking about this stuff last year. I wondered if dimpling the short-turn in an intake port would do anything for airflow. Got some indulgent chuckles out of Deano. Haven't tested the idea, but will do so on an old outboard racemotor, if I can finish all the stupid boring projects that take up my time.

 

[Stubby]

It was a funny car. The first place they showed up was the front of the hood. The second place they showed up was the timeslip. I would think if you had a setup to flow smoke and visualy watch the flow you could see the effects, good or bad.