Turbo Blanket

[Rocklobster]

Hi all

I've always thought the underbonnet temperature is excessive on an Elan. Has anyone ever removed the turbo heatshield and replaced it with a turbo blanket (or fitted additional insulation beneath the heat shield)? Any info or thoughts welcome, just refrain from the dickhead references.

[chrisP]

I have lagged the exhaust from turbo exit to the point where the exhaust passes the subframe, it does help with the heat to some extent, but i have no metrics for you. Ceramic coating may be the way forward

Chris

[Giniw]

I've always thought the underbonnet temperature is excessive on an Elan.

Hi,
Based on what data?

[Rocklobster]

Based on nothing more than the heatwave when the bonnet is lifted and compared to every other car I've ever owned.

Just to move things on though and following Chris's post above, there's very little room to fit a turbo blanket due to the internal wastegate, however, I have wrapped the turbo and downpipe (because I was bored after 3 months of furlough) and now the heatshield, the underside of the bonnet and the compressor turbine backplate are all notably cooler (having been measured with I/R pyrometer). This would indicate that the insulation is reducing the amount of heat transfer from the exhaust gasses into the turbine housing and into the engine bay.

Just for good measure, I've also extended the exhaust wrap past the subframe as I was concerned about the heat that the jackshaft bearing was exposed to.

[Rusty Wishbone]

Can't the turbo overheat? If so, you are probably going to damage the bearings by lagging it.

[Rocklobster]

There's a lot of information and a lot of varied theories about overheating the turbo. As it's both oil and water cooled, I don't believe there's any danger as turbo's run much higher boost pressures and temperatures on other cars.

If you take a look at the cross section of the turbo, you'll see there is a heat shield and the water jacket between the exhaust turbine housing and the bearings. If you lag the exhaust housing, you also massively reduce the radiant heat. Most of the retained heat will then be transported out to atmosphere in the exhaust gas. The theory is that due to this retained heat (in the exhaust gas), the exhaust gas doesn't contract as much due to cooling and so the turbine works more efficiently and spools faster.

If I'm wrong and I cook my turbo, I'll be sure to post the pics to amuse you.

[cliff]

I had my Piper down pipe ceramic coated by Camcoat, I cannot say how much difference it makes. I also had the upper heatshield done but have since had it powder coated to match other parts.

I wouldn´t say that the engine bay gets excessively hot even though I have no lower heatshields fitted.

CIMG1226.jpg

[Giniw]

Based on nothing more than the heatwave when the bonnet is lifted and compared to every other car I've ever owned.

OK, strange, as I don't think there's such a massive heatwave in mine.
If yours is confirmed to be really hotter than normal you might need to check why it is ... and if it's like any other Elan, I would have suggested to do nothing at all

[Rocklobster]

The downpipe looks tidy having been ceramic coated Cliff. I see it was a few years ago, but do you remember how much it cost for reference?

Just for the record, I'm not concerned about the car running hotter than it should, I'm probably just being a bit overzealous about having a very hot turbo a few inches away from the bonnet of a plastic car. Clearly, it doesn't cause any problems, as they would have come to light before now on a 30 year old car.

[Fetnas]

I'm going to throw my 2 cents in on this one.

My dad was involved in the heat soak testing of the early prototype cars in Death Valley Arizona, I think he was driving in about 50 degree C heat at times. He would have had data loggers set up monitoring under bonnet temperatures and themal ink heat stickers in strategic locations. He would often bring test Holdens home as part of the AC system assessment with thermocouples all over the cabin and engine bay for data logging. He was a research and development engineer at General Motors at the time working on engine cooling and AC systems.

When I upgraded the radiator on my elan, he commented that the engine cooling was already pretty good on the car and that the factory rad was quite large compared to the power output of the V6 and V8 engines he had been working with at the same time. He wasn't involved in the design of the elan, but I think he was sent to Norfolk once prior to the Arizona testing, probably to set up some of the test equipment before the cars were shipped.

So from what he's told me, the under bonnet temp shouldn't be unreasonable. Perhaps the lower thermal conductivity of the fiberglass holds onto the heat better when the car has stopped and there's no longer any airflow. That said, using modern techniques to reduce the temperature further can't be a bad thing.

[steve matthews]

Temperatures after a heavy run stock heat shield ranged from 800 to 850 Deg. as measured on the heat shield and surrounding. We sent
Turbo off to be ceramic coated (Swain Tech) out of New York USA rumor has it this is what they used on the space shuttle. After heavy run
NO heat shield just Turbo temp 400 to 450 deg. Both runs during 85 Deg. days.

Hope this helps. The turbo also looks much better without that shield.

These # are in fahrenheit.

[Rocklobster]

Interesting info from Fetnas, thanks.

I agree with your thoughts. The cars cooling system has always coped well and I never have any concerns about it running hot, my thoughts were only that the engine bay seems to be quite hot when I open the bonnet. I think it's a combination of several factors; heatsoak from quite a lot of "stuff" in a relatively small engine bay, the turbo being at the front and nearest to you when you pop the bonnet, and as you note, the poor thermal conductivity of the fibreglass shell. All adds up...

And Steve, serious numbers, I presume from the U.S. they're Fahrenheit or we're in a lot of trouble. Ceramic coating makes more difference than I thought it would. That'll have to be a project at some time.

[Rocklobster]

To close this out and for info if anyone's ever considering a turbo blanket:

I bought a cheap ebay turbo blanket to see if/how it fitted and if it would make any difference to the engine bay temps. And the answer is, they don't fit due to the integral wastegate housing, so don't bother.

However, I did partly wrap the exhaust manifold, the hot side of the turbo and the downpipe with an unexpected result (that some might think I imagined). It's not made a great deal of difference to the under bonnet temp as over a period of time, heat soak comes in to play and everything gets hot anyway, it just takes a bit longer than it did. What I have noticed though (immediately) is that maximum boost (0.9 bar - Everest chip fitted) is achieved much easier. Prior to wrapping, I would rarely see the boost gauge go much beyond the 3/4 mark, but it's straight past it now with no other changes having been made. That might also indicate slight turbo wear & tear though...

My thoughts are that retaining the heat inside the turbo does improve its efficiency, ask any thermodynamicist about that. That doesn't mean peak power is increased because that's limited by the wastegate limiting the boost and by fuel cut-off to protect the engine via software. It might mean at best that the turbo spools up at slightly lower revs, moving the power curve slightly down the rev range, but any mid range gain would be so small as to probably be imperceptible.

Basically, there may be no gain. I believe there is an improvement in the pumping efficiency of the turbo, but I don't think you'd actually feel the difference on the road. Personally, I like the idea of a more efficient turbo and I'll go down the route of ceramic coating the turbo housing (hot side) and the down pipe. A job for the future.