Lets talk turbos

[eHoward]

Lets talk turbos.

I figured we could get some good tech talk going here since we really have some of the best from the other forum and we’re starting to get a pretty good signal to noise ratio. I’m not presenting anything here as gospel. If I’m wrong, I’d like to find out sooner then later so call me on it!

I ran some basic turbo calculations.

I used the formula CFM = (displacement*max RPM* 0.5 * efficiency)/12^3

The 0.5 is because the engines are 4 strokes. The 12^3 is to convert cubic inches to cubic feet.

I am using an efficiency number of .9 for the 4 valve heads and a number of .85 for the 2 valves.

The most interesting thing I saw was that the GM 60 degree 2.8 is flowing more on paper then the Honda B16 at its redline. Shaun and I are thinking it might have to do with a pushrod engine losing efficiency at redline while the vtec motor might be coming into its own. The static number of .85 or .90 really might not be most accurate way to do these simulations.

My turbo results can be found here: http://www.howard.saturnet.net/turboInf ... rkbook.htm

The actual excel spreadsheet is here:
http://www.howard.saturnet.net/turboInf ... rkbook.xls

I included some Honda engines cause I'm probably going to build a turbo Honda, but also because there's tons of dyno runs available with just about every turbo so I can easily compare theoretical information to real hard numbers.

[eHoward]

I know the T3s are very popular on Old Europe despite warnings from Shaun and myself that they are bad news on a 2.8. So that was the first thing I ploted:



What those dots at the end of the line are are where the turbo would end up at redline. If it goes off the map, that means you're blowing really hot air. As far as I know, the super 60 is the largest T3 turbo one can buy. After looking at that result, I decided it would be a waste of time to plot smaller T3 turbos.

The following is a T4 compressor.



Note that the engine would not fall off the right side of the map if using this compressor. What does this mean? You won't be pushing 400F degree air into your engine.

For the next one, I decided to go a little big:



I still think the 60-1 is bigger then a 2.8 wants.



We'll start looking at other engines and then turbine selection later.

[stimpy]

Math is hard. Got crayons?

[The Dark Side of Will]

Lets talk turbos.

I used the formula CFM = (displacement*max RPM* 0.5 * efficiency)/12^3

The 0.5 is because the engines are 4 strokes. The 12^3 is to convert cubic inches to cubic feet.

I am using an efficiency number of .9 for the 4 valve heads and a number of .85 for the 2 valves.

The most interesting thing I saw was that the GM 60 degree 2.8 is flowing more on paper then the Honda B16 at its redline. Shaun and I are thinking it might have to do with a pushrod engine losing efficiency at redline while the vtec motor might be coming into its own. The static number of .85 or .90 really might not be most accurate way to do these simulations.

Regarding Volumetric Efficiency...
In a naturally aspirated engine of streetable compression (10:1 or so), approximately 85 ftlbs/litre is 100% VE. That's a rule of thumb I've come up with from various things I've seen here and there.

So the tractor engine makes 275 ftlbs from 4.9 litres... that's 56 ftlbs/litre. 56/85 = 66%. So the tractor engine pulls 66% VE at peak torque.

The 2.8 makes approximately 60 ftlbs/litre (175 ftlbs/173 cid). 60/85 = 70% VE at peak torque... so yes, 0.85 is a bit high...

[eHoward]

So Will, would you throw .70 into the spreadsheet instead of .85 for the 2.8s and pushrod 3.4s?

[eHoward]

Thinking out loud here. . .

The B16 makes 111 ftlbs of torque with 1.6L. Your method would put it at .81. I'm not sold yet.

[The Dark Side of Will]

Why not? do you think that's too low? Remember that you're talking about an emissions compliant engine and that the design is 8-10 years old (don't know exactly when the B16 came out)

The F20C1 makes 75 ftlbs/litre and should be about 88% VE.
Toyota's 2ZZ-GE also makes 75 ftlbs/litre
The current M3 engine (S32?) makes 275 or so ftlbs out of 3.2 litres for an honest 100% VE, which is pretty darned amazing (as is the replacement rate of these engines).

Remember, this is a rule of thumb, not a hard and fast calculation.

[The Dark Side of Will]

Yes, I think 0.7 is more realistic for the pushrod V6's

[eHoward]

Mainly because Corky is calling the ford small block .85 and I dont think the 2.8 design is that much worse. Now, I have no clue where Corky pulled numbers from.

I agree that it is a rule of thumb, but want to get these numbers as true to life as possible.

Why not? do you think that's too low?

. ..

Remember, this is a rule of thumb, not a hard and fast calculation.

[Shaun41178(2)]

hmmm yea I dont' know how corky came up with those numbers

Maybe it has something to do with the engine on teh turbo being at those Ve's? and predicting in advance so one can choose a proper sized turbo. No clue.

Either way I am sure he got his equation from somewhere so it totally shouldnt' be discredited.

I also think calculating Ve is anybodys guess. I guess you could say 85lb/ft-liter is 100% Ve but is there any real way of knowing this?

either way I think it still shows any T3 is too small for a 2.8 pushrod. the T3's are supposedly good till what 300 hp so its claimed? However I am sure thats at extreme heat and a large intercooler necessary to achieve that. With our small engine bays with no good place for an intercooler, I am going to side on the larger side for a turbo application. Not because I got a cheap turbo from a junkyard. Its not about boost. Its about CFM. I will take a larger turbo that can push just as much cfm at a lower comp speed then a smaller one that needs to spin 30% faster to push the same amount of cfm. This is just extra heating.

T4 all the way.

[eHoward]

I also have a copy of the Hugh MacInnes book which was written about ten years before the Corky Bell book. It lists VE in its example at 80%. No explanation there either.

Ray Halls website has the following for VE:

VE: Engine Volumetric Efficiency in percent. VE changes with engine RPM, a engine at wide open throttle at 3000rpm could have a VE of 90% and at 6000 rpm 60%. This is a rough guide. At maximum RPM modified engines may have a better VE, e.g.: average overhead valve engines 45% to 75%, overhead cam twin valve 65% to 80%, four valves per cylinder 85% to 95%. On some modified engines 100% to 110% VE.

http://www.turbofast.com.au/turbomap.html

[The Dark Side of Will]

Torque is a direct result of combusting mixture with an engine's cylinders. In a given engine, torque is directly proportional to VE. An engine will pull peak VE at peak torque RPM. If torque is 75% of peak at a certain RPM, then the VE at that RPM is 75% of the VE at peak torque RPM.
IOW, you can extrapolate a relative picture of the engine's VE curve from its torque curve.

The biggest thing that affects VE/torque relationship is compression ratio. The higher the compression ratio, the higher the torque-integral per firing event, and--more fundamentally--the more energy pulled out of the combustion by the engine. Another way of saying that high compression engines make more torque than low compression engines... duh.

A more insidious factor affecting VE/torque is rod ratio. The compression ratio raises or lowers the torqeu curve as a whole, while the rod ratio can change the shape of the cuve, albeit to a lesser extent than compression ratio. With longer rods, high RPM VE is worth more in the torque curve, while with shorter rods, high compression affects torque at low and medium RPM more.

Anyway, since compression ratio is the biggest factor affecting VE vs. torque, that's what we have to watch out for when comparing different engines.
My estimate of 85 ftlbs/litre being 100% VE is for engines of streetable compression, typically about 10:1. Some of the engines mentioned further up in this thread have higher compression, on the order of 11:1 or higher. This will throw off the relationship of VE to torque as the engine will make more torque from the same VE.
Since the 2.8 has less than 10:1 compression, it does less with the same air and the my estimate would tend to underestimate its VE by a few to several percent.

I think it's a pretty good estimate, and it's fine for looking at turbo maps, because the engine's VE at the RPM point in question can be estimated, rather than using a blanket VE guess for every calculation involving that engine.

[Shaun41178(2)]

just for arguemnts sake maybe replot them with .70 VE see what happens.

[eHoward]

I will update the above charts soon to have both 85% and 70% VEs and start adding other motors.

For now, here is some inspiration:


Honda B16 with 2 bar of boost from a T67.

[donk_316]

Honda B16 with 2 bar of boost from a T67.

Dood!

theres gotta be more than a 1.6L and a turbo for those kinda numbers...

...I just cant wrap my head around that... my 3.4L with a T4 MIGHT see 400hp.


Is really that easy? Just matching the map to the motor?

Do mine next! T4 60-1 hifi on a 3.4L!

[The Dark Side of Will]

Notice the graph extends to 10,500 RPM and it's running 2 bar (30 psi)...

Not exactly a stock B16...

[eHoward]

Its not stock but assembling a honda engine ist exactly rocket science.

I would recommend the SC61 over the 60dash1. I will plot both though.

Honda B16 with 2 bar of boost from a T67.

Dood!

theres gotta be more than a 1.6L and a turbo for those kinda numbers...

...I just cant wrap my head around that... my 3.4L with a T4 MIGHT see 400hp.


Is really that easy? Just matching the map to the motor?

Do mine next! T4 60-1 hifi on a 3.4L!

[eHoward]

i updated teh T3 super60 map and plotted another T4, both with the 2.8 and 6k redline.

note: even with the pessimistic VE, the T3 compressor still falls off the map at redline.





I will do some 3.4 plots next. This is nothing special. With the formulas I provided or excel spreadsheet, anyone can do these.

[Shaun41178(2)]

I was looking through some maps and I guess there is a "super 57" and a "super 60"

Kind of makes me wonder about these. Maps are provided for them, so I guess the wheel exists but I see no place to buy them. They also dotn' seem to be much better at all then a standard 50 or 60 trim. If they cost more its not worth it in my opinion.

I still like the 60 trim. Doesnt' matter what the VE is between .70 and .85 it still pretty darn efficient.

However I will prob go with a junkyard t3 since they are cheap and work perfectly!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!uno And cheap!

[Shaun41178(2)]

that 50 trim looks pretty darn good too I must say