Intercooler bypass valve

[Piwoslaw]

I read on the Peugeot forum that a newer version of my turbodiesel engine has a valve which allows the IC to be bypassed. This helps the engine warm up faster and is supposed to allow better EGR operation.

Has anyone seen this in action? Any comments?

[DonR]

I am envisioning two exhaust cutouts working together to divert air through a secondary tube around the intercooler. It certainly would get warmer air into the engine. No idea about the EGR valve operation.

Don

[JasonG]

That would make sense. Diesels don't like cold air.
Years ago I found some big trucks with intake air heaters, don't know if ny still have them though.

[dremd]

Interesting
Subscribed:
Could go with the simpler block off, but wouldn't be as effective.

[tasdrouille]

Originally Posted by Piwoslaw

I read on the Peugeot forum that a newer version of my turbodiesel engine has a valve which allows the IC to be bypassed. This helps the engine warm up faster and is supposed to allow better EGR operation.

Has anyone seen this in action? Any comments?

It makes senses. I'm not ready to say higher higher intake air temps makes for a faster warm up since Daox's experiment. But it sure can't be bad.

An IC is a restriction, so when you don't need it, i.e. when it's cold out or when you are at very low loads pushing 1-2 psi, it should be a good idea to bypass it.

I don't see how it allows better EGR operation though, because the IC is located before the turbo which is located before the EGR valve in short route cooled EGR, which is most commonly found in passenger cars. Maybe when it's really cold out, because the cooled EGR is never cooled below the dew point to prevent gunking of the intake manifold and cylinder head from condensation in exhaust gasses and EGR soot mixing. So when the ambiant air is really cold, maybe it could get the mix to condensate. But that should not be much of a problem with newer particulate filters.

There surely is ans SAE paper somewhere discussing the details of IC bypass systems.

[Piwoslaw]

Googling found this page:
AutoAnything.com - Intercooler By-Pass Valve
It appears to be offered in a few Audi and Saab models.
Replacement vavle costs $65. I'd love to toy with one of those...

[smokeyj]

I have a TDI and muse occasionally about the intercooler. The idea behind the intercooler is to cool the charge and make the air more dense so you can stuff more fuel into the chamber without smoke.

The intercooler helps make more power.

But heat rejection represents some kind of energy lost no?

If I don't want to make more power it would seem that removing the intercooler would be a way to go.

[Piwoslaw]

I looked for more about the Saab bypass valve and found this:
High Performance Bosch turbo bypass valve

From what I understand, this is not an intercooler bypass valve, but a blowoff valve. A blowoff valve relieves the high pressure ahead of the turbo when the engine suddenly goes from high to low rpm. Usually it releases the air into the engine bay, maybe in this case it bypasses the turbo and continues along the intake towards the engine, possibly bypassing the intercooler also. Either way, it does not bypass only the IC, and it is actuated by pressure difference only, so it is no longer of any interest to me.

When it gets warm enough to spend some time outside (the lastest forecast says no chance within the next 2 weeks), I will try to manually bypass the IC and see how the engine handles. Then I'll start thinking about actually constructing something.

I read that the main difference between the 90HP and 110HP versions of the HDi engine (both with the same displacement) is the lack of intercooler on the weaker one. Someone published a test (I think I posted it here somewhere, but can't find it now) in which they slapped an IC onto the 90HP HDi and saw a gain of about 10HP. The other 10HP apperently comes from remapping the ECU to sqeeze more out of the engine once the intercooler is in place. This makes me wonder if bypassing the IC will noticeably reduce performance. On the other hand, as you guys noted, the IC counts only when near full load. Maybe by the end of summer I'll finally get a ScanGuage and see if there is a difference with and without IC.

[vtec-e]

This was talked about here before and afterwards i tried a partial and full IC block. Made my mileage worse, according to my SGII. But i wouldn't be averse to doing it again if there was a different/better way of doing it.

ollie

[mikeross]

Originally Posted by DonR

I am envisioning two exhaust cutouts working together to divert air through a secondary tube around the intercooler. It certainly would get warmer air into the engine. No idea about the EGR valve operation.
Don

Nice thinking.. I think the warmer the air that goes into the engine, the more fuel efficient it would be and lesser heat loss.