running above 1bar

[richard cash]

I have had lots of advice on this but most is contradictory and im just getting confused. I spoke to reworx when i had my car mapped about boost levels and they said that 1bar of boost is the "safe" limit for the rotary. They got technical and started going on about the differences between compression and effective compression and said that above a bar it starts getting risky. What they said made sense, and was backed up by evidence that people tend to stick to around a bar on here. Ive seen a few people go to 1.2bar and a handful try out 1.4 but nothing much more.

yet over at //www.rx7club.com i was broswing and have seen loads of people well over 1bar of boost, some even at 2.5bar on GT42R\'s!!! How can they get away with this and what are peoples opinions on boost levels.

Can the rotary squeze out more boost on a certain turbo to acheive higher power figures or should it be a case of if the engine cant reach the required levels then a bigger turbo should be used at the same boost.

[BlitzBoy]

1 Bar is safe for Pump fuel, if you want to run more boost then that then you have have to use certain methods to control det

[Grizzly]

Hang on but is\'nt 1 bar diffrent on say Stock twins to a Kia??

Isn\'t it 1 bar on stock twins?

I was led to belive that its the Compression ratio of the engine, it gets more unstable/Prone to Uneven burn the more Boost you run?? Also the twin Turbo\'s efficancy is somthing like 11psi so the power per psi drops off towards 1 bar? o and theres the fact the Twins don\'t have 360 bearing so they will blow oil past the seals before long at that boost?

As for Singles, i thought they could run as much boost as the Fuel system/Map will let them?

[BlitzBoy]

1 bar is about the limit for stock twins anymore boost and it just heats the air the too much to give u any extra power. medium to big Singles I found are good for  1.2 Bar on good pump fuel, anything more then that then either run WI or some form of race gas

[G@NDY]

I agree with Blitzy:yes . Mine is mapped at 1.2 high boost setting and reaching a safe 85% injector duty with 1680 secondaries and around 25-30 knock, running pump fuel. Anything above the 1.2 and you would need water:Santa

[Grizzly]

So if you ran 4x1600cc\'s 2x040\'s and big bore lines etc, Inhition amps etc basicly the lot you could\'nt run say 2 bar without water and race gas?

[maximtaylor]

Wind the boost up to 2 bar you\'ll end up with a pile of melted turbo parts on your engine tray and/or blown out of your bonnet.

Each turbo has a different efficiency range, which you can determine by some understanding of the compressor maps for them.

Most of the mid size single turbos for an FD start struggling much past 1.2 bar. The mid to big ones not much further beyond this. To run serious boost you need a serious turbo. And for 2 bar you\'ll need considerably bigger than T51, T78 size.

The side effect is of course you\'ll get not much boost until your engine is really wound up to over 5k revs.

[richard cash]

i dont think this is an issue with the twins, as when i spoke to reworx about it we was talking in the context of my car (GT40 single)

i ended up going to 1.0 bar. This produces 380rwhp, 70-75% injector duty cycle and 8-11 on the knock sensor at all times. But now my car has to be rebuilt i was thinking of getting it increased to 1.2bar. I also have water injection and 850x4 injectors in fuel system and 680x2 near the TB controlled via HKS aditional injector controller

[richard cash]

max, to get the compressor maps do you have to go the the turbo manufacturer or can you see this from the RR

[maximtaylor]

Hunt around and you can find them on the web - trying to translate them into something which you or i would understand is another matter!

[AdrianE]

Isn\'t the case that if you run 1bar on one turbo setup (eg. stock twins) then the \'ammount\' of air forced into the engine (in lbs/min) is different to what you would get on another turbo setup (eg. GT40R)? And this difference is not just due to the temperature of the air being forced in?

The bigger turbo will supply much more air (eg. 50lbs/min) at a pressure of 1 bar than the smaller turbo setup (eg. stock twins at 1 bar supply air at 25lbs/min). If you look at the compressor maps for 2 different turbos (eg.GT40R - http://www.atpturbo.com/root/maps/gt40r.htm and GT42 http://www.atpturbo.com/root/maps/gt42.htm) you can see that for a given boost pressure (eg. 1.4bar) the ammount of air forced into the engine (lbs/min) is different! If this is true then the old adage about the 13B engine being "safe to 1bar" is misleading (or even just plain wrong!) because it depends on the turbo (and its associated flow in lbs/min) that you\'re using.

I was told that running >1bar on the 13B (on singles or twins) would have the effect of blowing/forcing the rotor housings apart (and rotating them slightly as well). That\'s why engine builders use dowelling to stop this happening. But 1 bar for what turbo? Surely the safe maximum for a non-dowelled 13B  should be measured as how much air you can force into the engine (for a given air intake temp) without producing this nasty rotor housing effect. I\'m no expert on this but, am I right about this?

Adrian

[stuart wizy]

the volume of air pumped into the engine is in cfm (cubic feet per minute).
use a bigger turbo and it will flow more volume of air at lower boost,  
(psi )doesnt really mean a lot, its how much volume of air is pumped in that counts for big power.
getting back to using twins, ive found they get really really hot when used on track above 12psi and your under bonnet temp will rocket when used at full boost for long periods of time, also you can cool your inlet temps down with big intercoolers chargecoolers etc but you cant cool down the water coming out of the small twin turbos when they are glowing cherry red at 1 bar,
My twin setup was running at 12psi with big ic and ally rad and i couldnt do more than 4 laps round a track without water temp going over 100deg.
The problem is the heat cant get away from the twin turbo pack because theres no room down there for the air to move around.

[AdrianE]

OK Stu thanks for that reply. Air flow in cfm (for a given air temp) should be equivalent to lbs/min that you see on the turbo compressor maps.

If you have a large IC and a radiator that is fed air coming from the IC, then in this hot weather (>30degC) you will get high water temps. I had the same setup (and was getting >105deC) but now I\'ve installed a V-mount IC/rad the water temp stays around 70degC when cruising and hits 85degC after a good run on boost.

[monkey-fd3s]

So if you had a ported / dowelled engine then it could take more boost than the 1 bar because the dowelling would increase the threashold at which the boost pressure pushes the housings apart?

and also

If you were running water injection you would be able to (take the risk) of running higher boost with some water/methanol mix?

So lets say you had a ported, dowelled motor with a decent sized (lets say HKS T04Z/.96 AR) turbo and IC setup you\'d be able to run 1.2 bar ok?

Cheers
Dave

[richard cash]

that seems like way more than some peoples specs on here that are running 1.2bar