Installed a head shim now only 6 lbs boost.

[Rx1M5]

OK here's what we have. It is a Bender rear mount GT25 stage II on an Rx1,

The sled has always been run on 50/50 race/premium fuel and then we decided to put in a head shim to save some $ on fuel. Pre 80 thou head shim the sled made 10-11 lbs consistently. The sled used to have a high low 6/12 switch which has been removed and replaced with a straight piece of tubing from the vaccum pot to the turbo compressor housing.

As a temporary measure a reverse kit was installed with 21/39 gearing where it used to have 21/42. The sled will have 19 39 gearing when the new top gear gets installed but for now it's got the tall gears in it. Currrently the sled is only pulling just over 10k rpm and about 9600 in deep snow. Even being pulled down by the gearing change the motor should still make boost, right?

Here's the problem, the sled now only makes 5-6 lbs of boost. We shortened the rod on the turbo which actually seemed to make less boost if that's possible. The rod is maxed out and there is about 3/16 of an inch of preload on it in relation to the pin on the wastegate.We removed the entire exhaust system and checked for leaks. The only thing I saw was a small flat spot in one of the exhaust manifold gaskets around 1 cylinder but no real sign of any leaks.

The hoses with the oil restrictor were swapped out and the oil restrictor is not back in there so the sled is using a bit of oil.

There don't appear to be any leaks on the compressor side of the system.
Prior to the head shim the thing was pretty reliable and consistent.


What have we over looked of forgotten?

Thx Rx1M5

 

[Blue shadow]

First check your compression on all four clys,if ok remove the hose from the waste gate and run full boost with race fuel and it will go to 15 psi .If that don t do then you have a leak in your exhaust .GT25 54 will go to 15 psi max,gt 25 60 will go to 22 psi max,hope this helps.

 

[Blue shadow]

Also by putting a head shim in you change the timing so you have to slot the timing gears to put it back in the stock position.

 

[mulot30th]

OK here's what we have. It is a Bender rear mount GT25 stage II on an Rx1,

The sled has always been run on 50/50 race/premium fuel and then we decided to put in a head shim to save some $ on fuel. Pre 80 thou head shim the sled made 10-11 lbs consistently. The sled used to have a high low 6/12 switch which has been removed and replaced with a straight piece of tubing from the vaccum pot to the turbo compressor housing.

As a temporary measure a reverse kit was installed with 21/39 gearing where it used to have 21/42. The sled will have 19 39 gearing when the new top gear gets installed but for now it's got the tall gears in it. Currrently the sled is only pulling just over 10k rpm and about 9600 in deep snow. Even being pulled down by the gearing change the motor should still make boost, right?

Here's the problem, the sled now only makes 5-6 lbs of boost. We shortened the rod on the turbo which actually seemed to make less boost if that's possible. The rod is maxed out and there is about 3/16 of an inch of preload on it in relation to the pin on the wastegate.We removed the entire exhaust system and checked for leaks. The only thing I saw was a small flat spot in one of the exhaust manifold gaskets around 1 cylinder but no real sign of any leaks.

The hoses with the oil restrictor were swapped out and the oil restrictor is not back in there so the sled is using a bit of oil.

There don't appear to be any leaks on the compressor side of the system.
Prior to the head shim the thing was pretty reliable and consistent.


What have we over looked of forgotten?

Thx Rx1M5

By doing this, its the same as being on your 'low' setting on your hi/low switch... since you don't bypass any pressure....

 

[givemeaboost]

Just like Molot turbo says. When you bypassed the switch and went directly to the wastegate actuator you are only going to get whatever it is set at for boost. I'm not sure how Bender's boost switch works but is most likely the way most controllers are and take a certain amount of boost pressure to overtake the spring pressure to then let the air out and open the wastegate.

 

[lakercr]

Absolutely, if you removed the high-low switch as part of doing the head shim you will only get the boost level you had on the low setting now. Bender's high/low is just a simple air bleed on a toggle switch.

You aren't bleeding any of the pressure to the wastegate actuator anymore.

 

[Rx1M5]

I guess I forgot to mention that I cranked the rod in as far as it will go so in my understanding this should be at the max boost possible or am I missing something here?

I also forgot to mention we slotted the cam gear. we opened up the valve cover and rechecked to make sure we didn't screw it up. I'm pretty confident the valve timing is dead nuts as I've done 4 now and I know what I'm looking for.

OK another question here and I should probably know this: Does the waste gate actuator work on pressure or vaccuum created by a venturi effect from the compressor? I thought pressure.

Maybe I'm just havin a giant brain fart. So far 2008 hasn't gotten off to a great start.

Rx1M5

 

[lakercr]

I guess I forgot to mention that I cranked the rod in as far as it will go so in my understanding this should be at the max boost possible or am I missing something here?

I also forgot to mention we slotted the cam gear. we opened up the valve cover and rechecked to make sure we didn't screw it up. I'm pretty confident the valve timing is dead nuts as I've done 4 now and I know what I'm looking for.

OK another question here and I should probably know this: Does the waste gate actuator work on pressure or vaccuum created by a venturi effect from the compressor? I thought pressure.

Maybe I'm just havin a giant brain fart. So far 2008 hasn't gotten off to a great start.

Rx1M5

Actuator works on pressure.

I don't think I have a clear understanding of your set-up. In your most recent post you say the rod is cranked all the way in, but in your first post you say that there is about 3/16 from the rod to the pin? Are both of these correct?

3/16 pre-load would be consistent with the boost you are seeing. This is a generalization, but you should be more in the range of 1/4 - 3/8" for the boost you are looking for...

 

[Rx1M5]

When I said "cranked all the way" in I meant the rod has no more travel left in it and it moves the pin on the wategate lever over about 3/16" from the hole on the actuator rod, so we have to pull the rod out of the pot 3/16" to put it back onto the pin.

When I did my own turbo also a GT2554 with a headshim I had to mod the rod but I thought I had about the same preload and I get 12 lbs. By installing the headshim on the Bender sled we obviously have lowered the compression but will that also slow the exhaust gas velocity? Is that why it's changed so much from the stock compression race fuel combo.

So you think we need to be in the 3/8" range for preload. We also checked the compressor side and found nothing and besides you would think the compressor could compensate for a small leak if one existed.

Rx1M5

 

[Rx1M5]

Absolutely, if you removed the high-low switch as part of doing the head shim you will only get the boost level you had on the low setting now. Bender's high/low is just a simple air bleed on a toggle switch.

You aren't bleeding any of the pressure to the wastegate actuator anymore.

Just reread this one this makes sense now. We will reinstall the switch and try it again.

Rx1M5

 

[Skydog]

You must put this on!!

YOU NEED THIS BAD!!!

http://www.ty4stroke.com/viewtopic.php?t=52436

 

[Rx1M5]

BINGO We have a winner.

Re-installed the high/low switch and the boost is back in fact after cranking up the rod we will have to turn it down as it makes like 15 lbs at 7000 rpm.

Thanks guys sometimes the obvious isn't always obvious to the idiot looking at the problem (me).

Rx1M5

 

[givemeaboost]

Don't be so hard on yourself there Paul. Brainfart maybe, but never an idiot!