Why do our turbos hold less to redline?

smh0101 · Post by **smh0101** » Mon Mar 16, 2009 12:17 am

So, my vf10 boosts to 16lbs great... But the boost falls flat on its face to about 10-12lbs at redline.

I've read a lot about the vf10s, vf11s, vf8s, etc doing this...

My question... How come?

And... Is there any way to overcome that?

I read something about it having to do with how the wastegate gets blown open by exhaust gases and not going though the actual turbine... Is this fairly accurate, or just bs?

thanks!!

green91 · Post by **green91** » Mon Mar 16, 2009 12:38 am

Low CFM output. The small compressors simply can't meet the engine's air consumption at those speeds. Upgrading to a larger turbo is pretty much the only solution.

asc_up · Post by **asc_up** » Mon Mar 16, 2009 12:38 am

I definitely have the same problem right now, although I'm positive that it's because I have the stock 22T heads still. My friends JDM WRX swap had the same turbo except with EJ20K heads and it held 18 PSI all the way to redline.

If you've already upgraded your heads, then I would look at the wastegate as being the source of your problems. They do make upgraded wastegates for the VF series turbos, that way they can hold boost all the way to redline.

I'm actually buying one of these with my next paycheck:

http://www.avoturboworld.com/avoshop/pr ... cts_id=123

dscoobydoo · Post by **dscoobydoo** » Mon Mar 16, 2009 2:31 am

The reason the turbos only go so high, is the CFM numbers. The VF-10/8/11/12 were meant for quick spool, which means low numbers:low RPM full power, low power output and low boost psi limits.

Look at the 18/20G turbos in comparison: they don't come on full till about 3500 rpms but they push all the way to 22 psi.

The 22t heads are low flowing because it improves the low end power and tq. When I swap to the K heads, I expect more top end, but I expect to lose some low end power in return.

93forestpearl · Post by **93forestpearl** » Mon Mar 16, 2009 3:28 am

With higher flowing heads, you will maintain even less boost to redline. Less restriction in your heads will put you closer to the choke flow line on your compressor map at a lower pressure ratio (boost). The compressor can only move a finite amount of air, so you will reach that threshold sooner than with 22T heads.

Changing your wastegate actuator will not get around the simple fact of your compressor being too small for what you are asking of it. Sure, it will be "easier" to maintain a higher target boost level due to your boost control solenoid having to work less, but it is false economy.

Also, the small turbine and housing become a restriction as overall flow increases. For instance, change the compressor wheel and housing while still having the tiny exhaust side of the turbo, you'll still have trouble up top, and the turbo will likely surge very easily. This is why "matched" turbos are so important. The wheels and housings complement each other so you have the right spool-up and proper flow dynamics under high load and airflow.

What does this all mean? If you want more boost at redline, you need a larger turbo, and all of the related components to make it work.

This is a recent conversation with a DSM "tuner."

"So what is done to this thing?"

"Intake, exhaust, MBC, etc ....etc......21psi"

"What turbo?"

"13b"

"LOL"

smh0101 · Post by **smh0101** » Mon Mar 16, 2009 4:35 am

Wow, for some reason I just hadnt thought of the compressor being able to keep up with the engines needs. Huh.

So... I think a vf30 should hold quite a bit to redline eh?

Any idea how much to redline?

douglas vincent · Post by **douglas vincent** » Mon Mar 16, 2009 6:38 am

PP6 first!

93forestpearl · Post by **93forestpearl** » Mon Mar 16, 2009 6:54 am

Yeah, there are a multitude of turbos that can satisfy your needs. But the big question is, can you control it? A PP6 or MAF Translator Pro can make that happen to some extent. There are other things to think about too, but one thing at a time. A little time with a welder can make any turbo be plumbed in your car, but it is the peripherals that get nasty.

smh0101 · Post by **smh0101** » Mon Mar 16, 2009 3:08 pm

douglas vincent wrote:PP6 first!

haha, I know Doug, I'm not doing ANYTHING until I get one. Its the top of the list right now.

tturnpaw · Post by **tturnpaw** » Wed Mar 18, 2009 6:24 am

It's actually a combination of the exhaust trim being extremely small and camshafts. The ej22t was designed for midrange power. So matching a decently sized trim of around .70 with a decent amount of duration in the camshafts will power till redline. It's that simple no other way to put it. The smaller the trim the faster the spool but you will sacrifice top end power, and the turbos capability for high boost. The key is to find that happy point in which it's smooth spooling and top end power. Instead of piecing it together find your goals and match the parts to them starting with management, turbo, then engine internals.

93forestpearl · Post by **93forestpearl** » Wed Mar 18, 2009 6:41 am

You cannot get around the simple fact of a compressor being too small to flow a given amount of air. Trimming a turbine wheel reduces it's efficiency, and is not an ideal way of raising a turbo's efficiency at higher pressure ratios. Cams are not a major player in a turbo's airflow capability.

tturnpaw · Post by **tturnpaw** » Wed Mar 18, 2009 6:44 am

Didn't say it was efficient. It's a hair dryer at that point. I've seen 40psi on a 16g on a 2.5l myself. Of course with a little meth and nitrous it was safe.

93forestpearl · Post by **93forestpearl** » Wed Mar 18, 2009 6:56 am

Touche. I guess I like to lean towards ideal solutions versus the cheap ones, but anything can be done with proper precautions. Like Innovative running a 35R on a 22T with no intercooler and a ton of meth, roasting four tires at speed.

tturnpaw · Post by **tturnpaw** » Wed Mar 18, 2009 10:26 am

Exactly. I wouldn't suggest it, and technically when you play with the numbers it isn't feasible, but I've seen it happen. I myself like to keep meth and nitrous as a safety not require it.

But again with numbers involved changing the camshaft may not change port cfm or head flow, but it will change velocity and valve overlap counts as head flow. So if the cams are holding a turbo from redline, more duration will actually improve the flow of the heads and port velocity thus spinning a turbo with more torque (yes torque) and velocity. It's not good for a turbo but it definately is possible.

Point in fact my tw hit 25+psi the other day and ripped till fuel cut caught up.

93forestpearl · Post by **93forestpearl** » Wed Mar 18, 2009 6:42 pm

Still, comrpessors can only move a finite amount of air, whether you look at it in CFM or lb/min. At some point the compressor will choke.

BXSS · Post by **BXSS** » Tue Mar 31, 2009 6:29 pm

tturnpaw wrote:It's actually a combination of the exhaust trim being extremely small and camshafts. The ej22t was designed for midrange power. So matching a decently sized trim of around .70 with a decent amount of duration in the camshafts will power till redline. It's that simple no other way to put it. The smaller the trim the faster the spool but you will sacrifice top end power, and the turbos capability for high boost. The key is to find that happy point in which it's smooth spooling and top end power. Instead of piecing it together find your goals and match the parts to them starting with management, turbo, then engine internals.

I was just giving this a read & thought - HMMMM if he means Turbine AR alot less will hold boost until redline.

A TD05-16G with 7cm e-housing is supposed to have a turbine AR of just about .48 & those will hold 20PSI to Redline.

tturnpaw · Post by **tturnpaw** » Tue Mar 31, 2009 7:14 pm

Too little exhaust trim or a/r will create faster spooling but sacrificing top end power. Even to an extent of falling off boost at 20psi.

Too large of a/r will hit like a rock when boost comes on, is hard to tune, and has late spooling enough to miss a powerband.

You want to find a happy medium for the goals you want. It can even be more precise than that by using cfm calculations as already said, not only from the turbo but the engines output per flow @ rpm. You can also find an engines powerband that way.

20psi is not a lot in the world of turbos. It's a common misconception. Most tuned racecars are in the 30psi range. I can also think of a drag supra running 48psi on a 42r.

BXSS · Post by **BXSS** » Tue Mar 31, 2009 8:10 pm

Your right 20psi is not much especially on a small turbo/low CFM turbo.

We run GT45R's @ around 35PSI on our 2 KP61 Starlet Rotary drag cars & even that is low.
We have not tuned the 1980 2JZ Powered Toyota Corolla yet but I think boost will be relatively low on that car it also has a GT42R, big t-body, big plenum intake, back 1/2 chassis, powerglide with trans brake, blah, blah, blah....

Our fellow Rotary / 4CYL Drag guys will run upwards of 58PSI on their cars some of which are still carb'd.
A friend of ours with a Old Toyota 1.8l 3TC powered Datsun 1200 has run 8.50's on a turbo pushing 58psi through WEBERs!

I believe some of the guys from PR are running 70+psi of boost which is how they get 1308cc cars to run 6.9's in the 1/4 mile.

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Why do our turbos hold less to redline?

Why do our turbos hold less to redline?