Question for the Turbo Guys...

[ProTouring442]

Normally, when building an engine for power, I understand that you should run low compression on a turbo engine, but low compression makes for an inefficient engine, thus eliminating some of the benefit of a turbocharged small displacement engine. Ford's new Ecoboost engines run much higher compression ratios, and I am guessing that this is to increase the efficiency.

I have a 1988 Thunderbird Turbo Coupe with a 2.3, stock 8.0:1 compression, and a stock IHIRHB-52 turbocharger. Would it not be smart to boost compression, say to 9.5:1, then counter with a slightly bigger cam, thus reducing cylinder pressures likely to lead to detonation? Coupled with the stock IHI turbo set to 15 or 18 psi, this should increase power and economy. Heat reflective coatings on the piston top, the combustion chamber, and the valve faces would go a great distance towards capturing lost energy, and thus efficiency, and would have the further benefit of decreasing the likelihood of detonation. A larger intercooler or methanol injection might be needed under full boost to counter boost induced detonation I would think, but I cannot think of any other reason as to why you wouldn't want to build an engine like this.

No, it would not be the best all-out power engine, but for a street driven vehicle, can anyone tell me why I am wrong in my assumptions?

Shiny Side Up!
Bill

[redhead]

I am not familiar with your stock turbos effeciency range or the bottom end strength of the ford 2.3 so my comments are based on my experience building and tuning other 4 cylinder turbo combos.
first off an increase in cr from 8.0 to 9.5 is drastic. typical cr bumps on a well prepared block and rotating assembly for street use is less then 1.0.
second, by adding a 'bigger cam' I assume you are planning to drop cylinder pressure through increased overlap. one aspect is that overlap in a turbo application has a much more dynamic effect as boost increases. in my experience aftermarket turbo cam for the street do not produce returns similar to na applicaitons. the major considerations here is boost lag and low end power loss. ultimately your plan also works against itself. your adding compression only to leak it away. this combination would really hurt fuel economy too.
again I'm not versed on the stock t-bird turbo but in general stock turbo are only good to maybe 12psi. after that their effeciency drops and the heat introduced is counter productive. consider getting the head to flow, open the exhaust, bump the turbo size and increase compression only moderately like 0.5.

[6'9"Witha69]

I am not familiar with your stock turbos effeciency range or the bottom end strength of the ford 2.3 so my comments are based on my experience building and tuning other 4 cylinder turbo combos.
first off an increase in cr from 8.0 to 9.5 is drastic. typical cr bumps on a well prepared block and rotating assembly for street use is less then 1.0.
second, by adding a 'bigger cam' I assume you are planning to drop cylinder pressure through increased overlap. one aspect is that overlap in a turbo application has a much more dynamic effect as boost increases. in my experience aftermarket turbo cam for the street do not produce returns similar to na applicaitons. the major considerations here is boost lag and low end power loss. ultimately your plan also works against itself. your adding compression only to leak it away. this combination would really hurt fuel economy too.
again I'm not versed on the stock t-bird turbo but in general stock turbo are only good to maybe 12psi. after that their effeciency drops and the heat introduced is counter productive. consider getting the head to flow, open the exhaust, bump the turbo size and increase compression only moderately like 0.5.
Just an FYI, the turbo on GM LNF (2.0 Ecotec) engines can go 20 psi efficiently.

[ProTouring442]

I am not familiar with your stock turbos effeciency range or the bottom end strength of the ford 2.3 so my comments are based on my experience building and tuning other 4 cylinder turbo combos.
first off an increase in cr from 8.0 to 9.5 is drastic. typical cr bumps on a well prepared block and rotating assembly for street use is less then 1.0.
second, by adding a 'bigger cam' I assume you are planning to drop cylinder pressure through increased overlap. one aspect is that overlap in a turbo application has a much more dynamic effect as boost increases. in my experience aftermarket turbo cam for the street do not produce returns similar to na applicaitons. the major considerations here is boost lag and low end power loss. ultimately your plan also works against itself. your adding compression only to leak it away. this combination would really hurt fuel economy too.
again I'm not versed on the stock t-bird turbo but in general stock turbo are only good to maybe 12psi. after that their effeciency drops and the heat introduced is counter productive. consider getting the head to flow, open the exhaust, bump the turbo size and increase compression only moderately like 0.5.

thinking more, I don't think I would go for too much more overlap, but rather just a good turbo cam...

Many new turbo motors are running 9.5 or higher, and I can't help but think that a lot of that is because they are looking to increase mileage. As an example, the BMW 7 series twin turbo runs 10.0:1

The IHI, as far as I know, remains reasonably efficient up to 18psi.

Shiny Side Up!
Bill

[WS6]

What are the boost levels of these modern engines though, Bill? I've put superchargers on 10.5 and 10.75:1 engines that run 93 octane and are street driven regularly. Boost is only 5-7 psi though. That's all you get from Magnachargers and ProChargers with their stock applications. Boost is boost regardless of it's from a turbo or supercharger.

More than likely, what you'll want to do to achieve your efficiency goal is lower boost and raise compression. However, given the small displacement of your engine, this may backfire severely as the engine doesn't make good power when not boosted.

[ProTouring442]

What are the boost levels of these modern engines though, Bill? I've put superchargers on 10.5 and 10.75:1 engines that run 93 octane and are street driven regularly. Boost is only 5-7 psi though. That's all you get from Magnachargers and ProChargers with their stock applications. Boost is boost regardless of it's from a turbo or supercharger.

More than likely, what you'll want to do to achieve your efficiency goal is lower boost and raise compression. However, given the small displacement of your engine, this may backfire severely as the engine doesn't make good power when not boosted.

True, but I would think that the bump in compression should give it a nice boost in power. It's just physics really, and as long as you can keep detonation in check, it should give more power.

Shiny Side Up!
Bill