PORTING (making sense of it all)

[PGiljevic]

Why don\'t a lot of turbo cars run lower compe rotors then? Are their not that many around or is it that the fd rotors are good even at 9.0-1 compression?

Cause its an engineering fact that is COSTS you power, rather than improves it especially if you are not limited by fuel type you use.

My personal example of changing out 9.0:1 to 7.8:1 rotors cost almost 10bhp in NA terms on the same set up tuned to MBT but the change did allow the owner to sleep at night knowing his engine was more safe running pump fuel, and it was easy to gain the power lost by a small boost increase :Talking1 and ultimate power can be improved by BIG BOOST INCREASES, just like was done in the 1000bhp F1 turbo era and is the aim of this thread! power is proportional to boost increase and you only trim the compression ratio if you are exceeding the limits of the fuel you are using. A good way to know if you are at those limits is work back to your almost ideal NA power level if you are using too much excess fuel ratio or too much spark retard then you NA power level will be down allot .............. its pretty simple that is why I like this method of analysis.

That answers your question WHY? don\'t more people run low compression rotors or pistons, the answer WHY? is it costs power if you are NOT fuel/detonation limited, that is a proven fact

[PGiljevic]

To make it clear for layman as well, that NA power (equivalence) is seen all the way up through the boost curve, so a power loss at NA level is seen at say 21psi So in summary you need a couple more psi boost pressure to pick up the power you lost by lowering the compression ratio

If you want/have dreams of running BIG BOOST PRESSURES you will need to look at lower compression ratio\'s OR just like the Air Racers well know, use 130+octane fuel! + WM50 (water injection) to keep here all going (or use methanol as the main fuel supply! *easy way out*)

[Grant Monkhouse]

I understand what Carl is saying and also what you are saying Peter. From your example the f1 teams increased comp ratio but lowered boost as they progressed. To achieve the same power outputs ish?? Surely there must be a point at which increasing comp ratio is not good in turbo form anyway. In NA forms 13-1 with race fuel can achieve great power, on v8 anyway:D

I think when Carl means volume he is referring to boost as what you have described, different people have different ways of explaining things.

I think you would both agree on having a lower comp ratio gives tha piece of mind if you are stuck with certain fuels and gain the post HP back with that little but more boost.

[matt p]

That\'s all the old ford nuts over here were doing for years, drop the compression on the pistons and wack the boost up till either the heads lift off the blocks or it explodes.

Trying to make sense of your first posts so I can very roughly guess what I\'ll achieve on my setup.

[Grant Monkhouse]

You need to know your NA HP to work it out Matt. If you have figures from a similar setup as you then you should know what your going to get:)

[matt p]

Unfortunatley I don\'t dude other than it will do 500rwhp minimum at 1bar boost dude. My sister car is still having work done at the mo, all be it mine has a couple of different things though.

[PGiljevic]

The compression ratio is a means to an end.
*If fuel is a limit you need lower compression. (fuel economy eats penis! and power just licks the bag a bit).
*If you are forced to run an arbitrary boost limit (like F1 did in stages) to then make up the power you must INCREASE the compression ratio. (fuel economy massively improves, and power picks up too)
*To run high compression ratio\'s especially at higher boost pressures (I think what Hay is saying? gives power *I hope that is what he was trying to say*) to get the increases in power you want, then you need more and more exotic fuel, high levels of tetra ethyl lead or Methyl Benzene majority based OR Methanol........

That sums up that! now back to PORTING!!!!

[Grant Monkhouse]

Unfortunatley I don\'t dude other than it will do 500rwhp minimum at 1bar boost dude. My sister car is still having work done at the mo, all be it mine has a couple of different things though.

That much at 1 bar? What porting?

[matt p]

One of Powergains half bridge ported engines Grant.

[PGiljevic]

That much at 1 bar? What porting?

quick maths here.

say ~600bhp 2 bar absolute means 300bhp NA!
so needs bridge port and custom inlet manifold and BIG REVS to achieve that goal

Hence the benefit of this thread, you can work it all out pretty quick. :Typing
(this is where the list of proven cars on the first page with normal revs and set ups can be your guide to what is achievable)

[matt p]

There won\'t be a custom inlet, was advised by various people that the custom inlets won\'t be needed as my Cosmo intakes will be good enough for when the boost gets turned up.

Also that won\'t be happening until a water injection system is fitted and more mods to the fuel system.

[Grant Monkhouse]

Only half bridge? Are you using Cosmo ports too? They\'re all big ones

[matt p]

That\'s the ones dude, they came of Marc\'s drag setup. Need a little modification and bit of tidying on the elbow but I\'ve sorted that already

[Carl]

^That is a common mistake most mechanics make.QUOTE]

I am sorry Peter but you are wrong. It is a common misconception that people fall into the trap of especially on turbo engines due to swept volume being the same but potential on turbo engines volume increases.
When the compression is lower the actual chamber volume increases but the swept volume does not due to the combustion chamber still displacing in one steady revolution the same amount.
Think of a piston engine for example, a low comp piston will be physically lower in the cylinder at TDC which means that it will correspondingly be lower at BDC(Meaning same swept volume), but the point is that when at BDC the amount of volume is greater than a high comp piston in the same engine, the only difference is that because the engine runs lower compression it makes less power in N/A form,but as soon as you a strap a turbo on you have a variable compression ratio once above 0 bar N/A and thats where it becomes exciting cos by running higher boost you effectively can make more power by getting more charge mixture into the chamber. Boost level determines whether this is succsessful or not in contrast to higher compression rotors.

[Carl]

quick maths here.

say ~600bhp 2 bar absolute means 300bhp NA!
so needs bridge port and custom inlet manifold and BIG REVS to achieve that goal

Hence the benefit of this thread, you can work it all out pretty quick. :Typing
(this is where the list of proven cars on the first page with normal revs and set ups can be your guide to what is achievable)

Doesnt work in the real world though.
You would be lucky to get 250hp in N/A form for that.
Also you need to approx about 1.2 bar to get what N/A would be taking into account that the turbo heats up the air which reduces the actual volume of air.