PORTING (making sense of it all)

[HaywardRotary]

A real life engine was the Renault F1 turbo engine seen here
http://www.gurneyflap.com/renaultef15.html
Notice that in qualifying they ran lower compression at 7.0 to 1 and were able to run higher boost and make more power than the race engine which ran 7.5 to 1 compression with lower boost.
Why did they do that? Cos it worked for ALOT more power,albeit at the expense of reliablity.

[HaywardRotary]

Normal set ups like people would run here, 9.0:1 rotors V\'s 8.5:1 S4 rotors or modified S4 rotors you will always see a power drop when reducing the comp ratio. *remember variables held same so you can ascribe the loss in power to reduced engine compression)

To justify the lower compression you really need to using a very knock limited set up (very poor quality fuel) no water injection etc.

Which is covered in the "tuning caveat I mention in the first few posts :cheers

Running lower compression enables much higher boost levels for everything else being the same Peter. The only way to make alot more power is for more ignitable mixture to get into the engine, this can only come with alot more CFM which means boost. If you are running everything else the same then that can only come from lower compression which certainly has the added advantage of allowing alot more workable volume.

[PGiljevic]

Carl this is why when F1 got reduced to 2.5bar absolute (~21psi boost) they all went to 9.0:1 compression ratio\'s from the earlier ~7.4:1 on 4 bar absolute maximum limit.
When fuel was limited they started out on 6.5:1 running AVGAS doctored. All on allot lower power at same boost levels.

If you want a good book to read up on the subject I suggest you look for
The 1000 BHP Grand Prix cars (A Foulis motoring book) (Hardcover)

                          by Ian Bamsey

[cona2k]

A real life engine was the Renault F1 turbo engine seen here
http://www.gurneyflap.com/renaultef15.html
Notice that in qualifying they ran lower compression at 7.0 to 1 and were able to run higher boost and make more power than the race engine which ran 7.5 to 1 compression with lower boost.
Why did they do hat? Cos it worked for ALOT more power.

I think this works. Only one way to find out I guess

[PGiljevic]

Running lower compression enables much higher boost levels for everything else being the same Peter. The only way to make alot more power is for more ignitable mixture to get into the engine, this can only come with alot more CFM which means boost. If you are running everything else the same then that can only come from lower compression which certainly has the added advantage of allowing alot more workable volume.

No you are totally wrong. There is NO increase in "workable volume" < this is called the Displacement of the engine and it does NOT change with compression ratio

[HaywardRotary]

In this link  http://www.gurneyflap.com/zakspeedengine.html
You can see that when boost levels were compulsory reduced for F1 engines manufacturers upped the compression the compensate for the power drop.

[HaywardRotary]

We will just have to agree to disagree Peter.:Thumbs-up

[Erdin]

This is a good thread however I think allot of people without the engineering background will struggle. Best thing is to keep it all in simple English so everyone can understand.  :driving

[HaywardRotary]

No you are totally wrong. There is NO increase in "workable volume" < this is called the Displacement of the engine and it does NOT change with compression ratio

BTW i have said and agreed with that all along, but you are not taking into account boost level. That is the fundamental difference.

[Grant Monkhouse]

Erm? By reading both your information I think I can say that you are both talking about the exact same thing. Different explanations.

You both agree that comp went up in the turbo motors when the boost went down to compensate for power loss. Higher comp, less boost equals roughly the same out put. Buuuuut as technology advances and mapping skills advance I bet they made more power from less boost and higher comp?!

[PGiljevic]

We will just have to agree to disagree Peter.:Thumbs-up

That is o.k. :yes
Best thing I say to you is when you have a chance build a 13B and run it on whatever fuel you want use 3 bar absolute boost and simply change out the rotors (use race fuel or pump with WI) and then you will see the difference in power the lower compression gives on the same boost, it will always be lower.
Good luck getting someone to run more than 30psi gauge pressure in a road car set up to make full use of the lower compression ratio benefits it will give.

:burnout

The question then becomes is it needed and at what point? that is a discussion for another thread :Thumbs-up

[HaywardRotary]

Let me put it this way, a 1000cc engine displaces 1000cc at atmospheric, but at slightly over 1 bar boost taking into account that the inlet charge is slightly heated the engine now is taking in the equivalent of a 2 liter N/A engine in its capacity, this is where I am saying that the volume increases, but with high compression you reach a limit much earlier for what the engine can injest due to the onset of too much heat all other things being equal.
Lower compression allows more inlet charge to go into that engine than higher compression as I said UNDER BOOST, hence making more power.

[Erdin]

Erm? By reading both your information I think I can say that you are both talking about the exact same thing. Different explanations.

You both agree that comp went up in the turbo motors when the boost went down to compensate for power loss. Higher comp, less boost equals roughly the same out put. Buuuuut as technology advances and mapping skills advance I bet they made more power from less boost and higher comp?!

yep i can agree with this. some good stuff from two experienced individuals, good work guys:mmmm

[PGiljevic]

yep i can agree with this. some good stuff from two experienced individuals, good work guys:mmmm

And not one swear word or derogatory comment posted :Ladys-man

[HaywardRotary]

Erm? By reading both your information I think I can say that you are both talking about the exact same thing. Different explanations.

You both agree that comp went up in the turbo motors when the boost went down to compensate for power loss. Higher comp, less boost equals roughly the same out put. Buuuuut as technology advances and mapping skills advance I bet they made more power from less boost and higher comp?!

No where near the same output Grant,and that is my point, these engines were running in each form the same capacity,but when the boost level was limited to a much lower amount no amount of upping the compression ratio brought the power level up to what it had been and in F1 they would have ran as high a compression ratio a they could if it had worked better for them.

In our engines we too run into limits but not for boost level with the exception of when the engine dets which is in part caused by boost level and compression ratio.