Smart CDI Intercooler. yes or no?

[touchwoodsden]

Lots of Smart CDI installations (including Eva Trak) dispense with the intercooler.

I was hoping to get away without it on my K100 Smart CDI.

Doesnt an intercooler increase turbo lag as the compressed inlet air has more space to fill before it is forced into the engine?

Does anyone have thoughts or suggestions on this?

Cheers all
JM

[mark_in_manchester]

Well...a plenum is pretty usual, to smooth out the pressure pulses which result from the turbo reacting to the pressure pulses in the exhaust gas stream which are driving it. Having said that, given a multi-cylinder engine and the fact that the turbo spins at high speed (meaning its rotational inertia should be huge, light-weight as it is) I would be surprised if it makes much difference. On the charade diesel I use, the plenum is a cast thing which is a hassle to get rid of, so it stays on. I think a plenum volume equivalent to swept cylinder volume is normally a recommended rule of thumb?

By the way, I think in one of your posts you make reference to my bike (at an MZ rally) starting you off on this time-consuming journey of expense, dashed hopes and broken dreams. I hope you're not planning to sue me...I don't have much worth money but you could take my bike (which does not run at the moment - see time-consuming journey of expense, dashed hopes and broken dreams)

Oh...and I don't notice a turbo 'lag' - acceleration is not swift but is kind of slowly and surprisingly relentless to about 90 mph, in a kind of 'can the worn-out rubber coupling in the drive train near my right ankle handle this torque or is it about to come apart and take my foot off' kind of way.

cheers
Mark

[touchwoodsden]

Good evening Mark.
Yes, I think you came to Carrog didn't you? It was a couple of years ago. The rally is still there every year last weekend of June (10th year I think this year) and you are most welcome. You probably remember I am the national chairman of the club.

I must admit that your bike was one that got me on this rocky road!
The Smart CD I does have a plenum which is actually made of plastic but I'm not going so far as to remove it.

[UAofE]

I was hoping to get away without it on my K100 Smart CDI.

There are two sides to this.
1: The engine was designed with an intercooler. Meaning it may need it to keep combustion temperatures within safe limits.
2: The engine in a bike is much less stressed than in a Smart. So it may not need one to keep combustion temperatures within safe limits.

Doesnt an intercooler increase turbo lag as the compressed inlet air has more space to fill before it is forced into the engine?

No. The time it takes to pressurize the volume is a fraction of a second.

[BertTrack]

From experience with my Track:

When the pressure is limited to about 1.5 barg i never had error come up warning about inlet temperature being too high.

When they pulled the pressure up to about 2 bars i did have warnings in the ECU log.

[touchwoodsden]

From experience with my Track:

When the pressure is limited to about 1.5 barg i never had error come up warning about inlet temperature being too high.

When they pulled the pressure up to about 2 bars i did have warnings in the ECU log.

Thanks for that Bert. I will get a boost gauge.

[mark_in_manchester]

FWIW, I only get 10psi boost before the waste gate opens. I guess I could do something about that, if and when I get the bike back together, but cylinder heads on charade engines are fragile at the best of times.

[Bert in Weesp]

I used to drive a Charade TD in my car, built a intercooler on it just for the fun of it cause for my driving stile it was absolutely useless, drive like a Granny.
Only the extra volume that went into the inlet system caused the car to respond a bit quicker, at that time the intercooler was in place under the hood but still no airflow over it.
At motorway 65 miles per hour boost pressure was never above 0.2 bar, only when driving faster it went to 0.7.
Adding a little 2kgf spring to the turbo made it drive like a little rocket for about 7 days after which I had to replace headgasket........

[touchwoodsden]

...snip....made it drive like a little rocket for about 7 days after which I had to replace headgasket........

[Bert in Weesp]

I drove total 390.000 km with mine, minor cracks between valve seatings but they did not cause a problem.
Maybe there's some play on the waste gate control lever, adding a light spring to the waste gate lever till it reaches 0.7 bar is quite easy.
And warm her up slowly when driving.

[mark_in_manchester]

Thanks for these thoughts, Bert.

Elsewhere on the forum you may have seen this week my spare engine turns out to be runner Now I can see what has gone wrong with the other engine / water pressurisation - your confidence that those small cracks don't matter is helpful, because even if the head on engine one is very f*cked, I have a spare one which probably is described fairly by 'small cracks between valve seats'.

To come back on topic for this board - engine two had no turbo on it (although it had turbo-style injector pump and manifolds), so I had fun making one up from a pile of bits in my spares box. It felt a little stiff, but spins up OK - maybe bearings are tight when cold, given these things run hot and one has to ensure engine oil stays away from the intake side . I've not had the bearing / labyrinth seal (?) apart yet (I have more incomplete bits in the box) - it would be interesting to see how it is done.