Turbo sizing calculators ?

[30psi 4agte]

I thought id start this thread not that we dont already have numerous threads on this issue but more directly aimed at the exhaust A/R sizing of a turbo in relation to engine size and boost being run.?

Understand???

What im geting at is: Is there a way to calculate the back pressure of an engine if you know the capacity/ boost being run and the turbo exhaust A/R ?

Or is there a way to calculate if you can go smaller on the turbo exhaust housing without creating excessivley high back pressure ?and loosing substantial hp.Or is this just a trial and error thing.

This isnt the easiest thing i have had to describe so hope you can understand me.

Basicly i want to know if i can drop from a .82 to a .63 housing on my GT3540 without loosing too much up top.
However if you have seen my thread in members rides you will notice that the power isnt dropping off even at 8500 rpm. I would like to contain the max power around this rpm ,so mabe dropping down will help.

Running an 44mm external gate should allow me to drop the housing size and still vent enough exhaust gas to keep back pressure to a minimum..... ????????????


Any opinions welcomed !

[Cameron_Datto]

Here is a link to a .73 A/r , but it`s made for a smaller turbo than yours . just a thought http://www.avoturboworld.com/pdf/gts...st_housing.pdf

[oldeskewltoy]

Turbonetics is one of the best turbo companies out there....... not sure if the info you want is on here... but there is substantial turbo info

http://www.turboneticsinc.com/techdata.htm

[mic*]

What is the point of this? To pick up enough power in the lower ranges to justify the top end loss? Given such a big turbo for a 4A, lower A/R should be ok???

Changing to a lower A/R to improve turbo response will always be a trade off against top end AFAIK. To explain myself, if the nozzle area is reduced to increase exhaust velocity for quick spool, the expense is higher TIP (turbine inlet pressure). Since that will adversely affect TIP/MIP (manifold inlet pressure) ratio, the same boost will equal less power, due to greater reversion. This is regardless of your wastegate size as it will be closed until set boost is achieved.

[30psi 4agte]

I guess i want to know if you can calculate the loss up top if any and the pressure difference.

I know in most situations you will gain bottom end and loose top end.

I was reading about a sr 20 drag car which was running the same turbo with the 1.06 housing. (which is quite large for a 2ltr)They did a back to back test on the dyno of the .82and the 1.06 housings. The exhaust manifold pressure only showed a 1 psi difference between the two .

the 1.06 was 25 psi
the .82 was 24 psi

Now the response of the turbo was greatly improved and hence their
times dropped.
what im getting at is bcause of the size of the turbo switching to the .63 housing may have only positive effects as it is so big.

At the moment my turbo response is vey linear. Which is same as the guy with the sr 20 was describing when he was using the 1.06 housing.

[30psi 4agte]

Turbonetics is one of the best turbo companies out there....... not sure if the info you want is on here... but there is substantial turbo info

http://www.turboneticsinc.com/techdata.htm

Yeah there is a guide on there that has some of the info on there. It says for a 1.5L to make 700hp you will need the T72 with a .58 rear.
So the .63 on a 1600 should be sweet!
Cheers mate + rep

That turbo matrix is an excellent guide! Now if i can just find one for the garrett range

[chris davey]

On this topic,

I was thinking about boost thresholds with different turbos. I have plotted some compressor maps for my 1jz. However, to determine the boost threshold is a bit of a guessing game.

What I was wondering is, by looking at the turbine flow maps like this one



Could you assume that say if the max flow is 27lbs on one turbo and you know what boost threshold that has then another turbo with a different size exhaust wheel but the same 27lbs would have similar boost threshold. If the second turbo has a larger compressor wheel then it will be a little later because more inertia is required to spin it but would this be a good guesstimate?