GTR Forum banner

61 - 80 of 108 Posts

·
Registered
Joined
·
8,540 Posts
What has boost got to do with trap speed Dan?
Surely over a given distance, a car producing more boost (and I shall generalise by assuming that more boost=more power) will accelerate faster therefore at the end of said fixed distance, the terminal will be higher than a car with less boost (power).


Just my comprehension of it and more than happy to be corrected!!



TT
 

·
Following EJH#25
Joined
·
6,824 Posts
Surely over a given distance, a car producing more boost (and I shall generalise by assuming that more boost=more power) will accelerate faster therefore at the end of said fixed distance, the terminal will be higher than a car with less boost (power).

Just my comprehension of it and more than happy to be corrected!!
The thread is about power vs boost pressure - there's more factors to terminal speed vs boost pressure as far as I'm aware.

What type of Fuel inc additives is used, size of turbo and whether nitrous was used all have a bearing, not just the boost pressure; that also doesn't cover the vehicle weight and that of the driver - but like you, I'm happy to be corrected too!!

I just thought comparing boost pressure to terminal speed isn't a good comparison.
 

·
Following EJH#25
Joined
·
6,824 Posts
I always understood it as efficiency changes with load, therefore the engine is most efficient at WOT.
 

·
Registered
Joined
·
212 Posts
Engines are most efficient at WOT, yep. Efficiency is largely dependent on your compression ratio, taking into account your VE to get your dynamic compression ratio - the more pressure you can make in the cylinder at ignition (with a close to stoich mix) will give you the highest PCP->bmep.

More pressure in inlet does not equal more pressure in cylinder though. And more boost doesn't even equal more air mass in inlet, because it depends on your turbo and intercooling.

So boost, probably not that good an indicator of power. I find torque to be a good indicator of power personally :chuckle:
 

·
Registered
Joined
·
2,303 Posts
Discussion Starter #69
I really can't see the point of this thread.
What are you trying to understand Dan?

Because I don't understand how some people can have so much power on so little boost and others on bigger turbos need to run lots of boost to make slightly more power.

Trying to get a understanding
 

·
Skyline Section Manager
Joined
·
11,872 Posts
Because I don't understand how some people can have so much power on so little boost and others on bigger turbos need to run lots of boost to make slightly more power.

Trying to get a understanding
There are a number of books available that will assist in your understanding for forced induction.

A good one is 'forces induction performance tuning' by A. Graham Bell.

Try here

Get books, read, learn off line. There is a ton of really good info out there.

Soo many people go on about 'spec this' and spec that'. Well, its mostly bollox but the people withthe greatest understanding get the better results with the parts they have bought because they know who they compliment each other. Remember, most things on an RB engine are a compromise. E.g. non variable cam timing, no variable vain turbos, no variable inlet runner length.
 

·
Registered
Joined
·
212 Posts
Because I don't understand how some people can have so much power on so little boost and others on bigger turbos need to run lots of boost to make slightly more power.

Trying to get a understanding
Well that's what I was saying... Boost is NOT how much air is being consumed, it's how much pressure is being created outside the engine. Maybe you've got one 90mm TB? :runaway:
 

·
Registered
Joined
·
2,303 Posts
Discussion Starter #73 (Edited)
Well that's what I was saying... Boost is NOT how much air is being consumed, it's how much pressure is being created outside the engine. Maybe you've got one 90mm TB? :runaway:

Shows what you no as map sensors have to be after throttle body lol

I also have fairly small lift cams beeing 10.06 meaning it will need more pressure to get the same amount in cylinders
 

·
Skyline Section Manager
Joined
·
11,872 Posts
Shows what you no as map sensors have to be after throttle body lol

I also have fairly small lift cams beeing 10.06 meaning it will need more pressure to get the same amount in cylinders
Tath is quite right. Your mass air pressure sensor is out side the engine. E.g. not in the combustion chamber. So, its measuring the pressure of the air waiting to enter the engine.
 

·
Registered
Joined
·
2,503 Posts
Boost is a measure of an engines restriction, it is not a measure of an engines overall efficiency.

Most big turbo engines produce more power for an equivalent boost pressure to a smaller turbo engine.

A smaller turbo'd engined is likely to be a torquier and more pleasant car to drive.

A larger turbo'd engine needs more rev's to achieve the same power as the smaller turbo'd engine.

BorgWarner EFR turbos appear to have re-written the book on turbo efficiency.

Engines need to be built so that all components including compression ratio, squish, port sizes, valve lift and valve timing are optimised for the turbo you are running.

Individual throttle bodies versus single throttle body is usually a driveability versus power option, however smaller volume plenums make this less of a certainty.

Yawn!!!!!
 

·
Registered
Joined
·
212 Posts
Shows what you no as map sensors have to be after throttle body lol

I also have fairly small lift cams beeing 10.06 meaning it will need more pressure to get the same amount in cylinders
No it shows that you seem to think your throttle body is inside your engine :confused:

Seriously, read the book that was recommended.
 

·
Registered
Joined
·
2,303 Posts
Discussion Starter #77
No it shows that you seem to think your throttle body is inside your engine :confused:

Seriously, read the book that was recommended.

No I don't were talking boost pressure not cylinder pressures. My boost pressure is read after my throttle body in exactly the same way it was when I had multi tbs
 

·
Registered
Joined
·
212 Posts
What? The thread is power vs boost pressure.

Boost pressure is not a reliable indicator of power, because it is not the mass of air being consumed by the engine, it's the pressure created outside the engine.

Cylinder pressure is a more reliable indicator of power, because it is related to the volumetric efficiency and actual air consumption of the engine.

Which bit are you struggling with?
 

·
Registered
Joined
·
2,303 Posts
Discussion Starter #79
What? The thread is power vs boost pressure.

Boost pressure is not a reliable indicator of power, because it is not the mass of air being consumed by the engine, it's the pressure created outside the engine.

Cylinder pressure is a more reliable indicator of power, because it is related to the volumetric efficiency and actual air consumption of the engine.

Which bit are you struggling with?

None of that and I agree, although I don't understand how matts engine can produce 1300 bhp at 1.7 bar with multi tbs on a gtx45 turbo then the likes of top speed from Ukraine need 3 bar on a gtx55 to produce 1400?

Same goes for rips have they ever seen that sort of hp at that boost I don't think so?? Matts engine must be the most efficient rb ever built then? In fact it's showing its more efficient than a r35 engine isn't it?

Or do I have it wrong again...
 

·
Following EJH#25
Joined
·
6,824 Posts
I don't understand how matts engine can produce 1300 bhp at 1.7 bar with multi tbs on a gtx45 turbo then the likes of top speed from Ukraine need 3 bar on a gtx55 to produce 1400?
You're misquoting Dan, mine made 1119bhp at 1.7Bar on Race Fuel.
 
61 - 80 of 108 Posts
Top