.50 And .70 Comp Cover

[Ralph Wiggum]

Good read Ben.. You have pretty much talked me out of going to to a .7 comp cover. I love the low down push and dont want to loose that...

[Geeseman]

Interesting results. I have the same turbo modification however I still drive with the .7 compressor cover. Last run it made 363rwkw@ 17.5psi with 300rwkw just over 3000rpm. Car could run more timing (although it wasn't fully messed with at this stage to get more power), and it seemed slightly down on power in low rpm but only slighly so. Top end power was certainly stronger.

The autotech stage IV kit uses an almost identical setup (.7cover with 66compressor wheel in a 800hp turbo, although external gated) and it certainly kicks of hard at low rpm.

Edited 03/02/07 01:56 AM by Geeseman

[xrdreaming]

I would have to agree that the .70 comp cover does lose some of the low down grunt. I am running about a 360rwkw at 15psi map at the moment. The push in the seat below about 3500rpm is not as great as with the standard comp cover.

It is true though that instead of tyre smoking fun it grips the road and the feeling up around 6500rpm in any gear is quite fun although useless on the street unless you want your car impounded.

[F6 UTE]

  Geeseman said:

Interesting results.  I have the same turbo modification however I still drive with the .7 compressor cover. Last run it made 363rwkw@ 17.5psi with 300rwkw just over 3000rpm. Car could run more timing (although it wasn't fully messed with at this stage to get more power), and it seemed slightly down on power in low rpm but only slighly so. Top end power was certainly stronger.

The autotech stage IV kit uses an almost identical setup (.7cover with 66compressor wheel in a 800hp turbo, although external gated) and it certainly kicks of hard at low rpm.

←

Are you running a stock turbo with a .70 as I was?

When you say " It seemed slightly down on power " Did you get it dynoed, or seat of the pants?? Mine always 'seemed' slightly down, but it never 'felt' 55rwkw down, untill you go back to the original setup.. The gained top end muffles the lack of low down ( as a seat of the pants feeling )..

The Autotech combo with manifold would be like apples and bananas, too much has changed to compare one factor, and I still run the 61mm wheel.

I still do not have a high flowing exhaust setup, but regardless all my comparisons are with the same setup ( eventually )

My peak HP would always be higher with a good quality exhaust..

[Geeseman]

Im running 66mm wheel in mine. The lag is more notable now, however it isn't a big difference over the stock turbo.

The autotech stage 4 is essentially the same as it has .7 housing and 66 compressor wheel although it does have an external gate and different exhaust manifold which would aid in spooling of the turbo.

Do you run an external boost controller? Id recommend this as it will help in controlling the boost down low.

[xlnt6]

Hi Ben,

I'm a bit perplexed by the outcome of your results, as I would not have though it would make such a dramatic change. Given you have the 61mm wheel and you changed just the comp cover from 0.7 to 0.5 I would have thought the following should occur:

1. Initial boost will spike higher as the same flow is now trying to go thru a smaller discharge area, ie so pressure increases. This means the turbo will "boost" quicker at low RPM and the higher relative boost will result in more average power in the lower RPM range. Also as the gas flow is quicker it may help improve low down torque. At low RPM glas flow is much less than peak, so comp cover flow limitations and exhaust gas flow restrictions are not coming into play.

2. At higher RPM and peak boost, the reduced flow capability of the comp cover will come into play, but so will exhaust flow restrictions and any flow restrictions due to cam/valve duration, etc. But since the exhaust and engine parameters are constant, the change will relate directly to the flow capability of the comp cover, ie you should see slightly more power.

This is supported by the garrett website:

"Compressor A/R - Compressor performance is comparatively insensitive to changes in A/R. Larger A/R housings are sometimes used to optimize performance of low boost applications, and smaller A/R are used for high boost applications. However, as this influence of A/R on compressor performance is minor, there are not A/R options available for compressor housings."

So your result tend to make sense, but it should not be that dramatic. I suspect it may have something to do with the tune. As the engine is operating at a different manifold pressure at the same RPM, it using a different set of fuel/timing map parameters so it could be dramatically different in timing (ie 5 degrees ?? for example). So you may think it is all the same but that difference is influencing the result.

Anyway one thing is for sure, you can never tell what the end result is until you try it, and I'm glad you willing to tell us your findings. Keep up the work !!!

Cheers

Robin.

[SCRIBR]

I dont wana sound like an idiot (too late) but what is this comp cover you speak of?

and wat is the .7 & .5?

[Ralph Wiggum]

  SCRIBR said:

I dont wana sound like an idiot (too late) but what is this comp cover you speak of?

and wat is the .7 & .5? 

←

http://www.turbobygarrett.com/turbobygarre...ech_center.html

Read the turbotech 101,102 and 103 sections and you'l be full bottle....

Luke

[SCRIBR]

WOW!

thanks alot!

101-103 read

now I can but my nose into every convo!

[F6 UTE]

  xlnt6 said:

Hi Ben,

I'm a bit perplexed by the outcome of your results, as I would not have though it would make such a dramatic change. Given you have the 61mm wheel and you changed just the comp cover from 0.7 to 0.5 I would have thought the following should occur:

1. Initial boost will spike higher as the same flow is now trying to go thru a smaller discharge area, ie so pressure increases. This means the turbo will "boost" quicker at low RPM and the higher relative boost will result in more average power in the lower RPM range. Also as the gas flow is quicker it may help improve low down torque. At low RPM glas flow is much less than peak, so comp cover flow limitations and exhaust gas flow restrictions are not coming into play.

2. At higher RPM and peak boost, the reduced flow capability of the comp cover will come into play, but so will exhaust flow restrictions and any flow restrictions due to cam/valve duration, etc. But since the exhaust and engine parameters are constant, the change will relate directly to the flow capability of the comp cover, ie you should see slightly more power.

This is supported by the garrett website:

"Compressor A/R - Compressor performance is comparatively insensitive to changes in A/R. Larger A/R housings are sometimes used to optimize performance of low boost applications, and smaller A/R are used for high boost applications. However, as this influence of A/R on compressor performance is minor, there are not A/R options available for compressor housings."

So your result tend to make sense, but it should not be that dramatic. I suspect it may have something to do with the tune. As the engine is operating at a different manifold pressure at the same RPM, it using a different set of fuel/timing map parameters so it could be dramatically different in timing (ie 5 degrees ?? for example). So you may think it is all the same but that difference is influencing the result.

Anyway one thing is for sure, you can never tell what the end result is until you try it, and I'm glad you willing to tell us your findings. Keep up the work !!!

Cheers

Robin.

←

I know what you are saying, but I can only assume the 61mm wheel is not suited to the .70?

I know Garret mention the difference is marginal, but simply, we couldn't possibly get the .70 to boost low down.. Irrespective of timing ( .70 used alot ). On the other side of the coin, we could manage boost in the higher revs with ease, unlike the .50.. ( flow properties I would assume.. )

The .50, with more boost, used the same timing and didn't det at any stage.. Simon may be able to chime in on my table setup, as I have nfi where it's sitting.

The .70 tune was optimised with the plenum, the .50 used that tune and probably could use some more work, and hence change the result again..