Why aren't some concerned about putting a turbo on a high compression motor?

[dave77]

So here is something interesting, assuming it's correct from wikipedia. Notice how when subaru made the FA20 turbo engine they lowered the compression to 10.6:1.

http://en.wikipedia.org/wiki/List_of...baru_FA_engine

Subaru FA engine[edit]
(Japanese: Subaru FA engine) The FA was developed from the FB engine, however, efforts to reduce weight while maintaining durability were the main goals of the FA engine. While the FA and FB engine share a common platform, the FA shares very little in dedicated parts with the FB engine, with a different block, head, connecting rods, and pistons. The FA also features direct injection (from Toyota) and Subaru AVCS variable valve timing system. It is used in the Subaru BRZ, and is identified by a Toyota engine family code known as the 4U-GSE, which is installed in the Toyota 86 and the Scion FR-S.[6] According to Subaru, 0W-20 oil is recommended.

Bore: 86 mm
Stroke: 86 mm
Displacement: 1,998 cc
Compression Ratio: 12.5:1
Power: 200 PS (147 kW; 197 hp) at 7,000 RPM
Torque: 20.9 kg·m (205 N·m; 151 lb·ft) at 6,400-6,600 RPM

A version with direct fuel injection and twin-scroll turbocharger was introduced in 2012 to the Japanese market for the Legacy GT DIT (direct injection turbo) sedan, and the Legacy GT DIT Touring Wagon.
Bore: 86 mm
Stroke: 86 mm
Displacement: 1,998 cc
Compression Ratio: 10.6:1
Power: 300 PS (221 kW; 296 hp) at 5,600 RPM
Torque: 40.8 kg·m (400 N·m; 295 lb·ft) at 2,000-4,800 RPM

[Poodles]

E85 isn't a consistent fuel, so unless you have a flexfuel sensor, it's a roll of the dice.


Everyone has already mentioned direct injection, but there's variable valve timing (on both intake and exhaust) and the computers used to run engines these days are very VERY good. Not to mention combustion chamber design, metallurgy, etc...

[diss7]

Fwiw, e85 is consistent, just not in the US.

[Mars2]

Vishnu has also proofed that our ECU can adapt to medium variation of Ethanol content. Just don't floor it going off the gas station.

[PStaff716]

When asking my mechanic about boosting, he expressed concern with anything more than 6psi with the stock internals/CR.

A swap of the rods and pistons, as someone else mentioned, was his biggest suggestion.


But then I see guys running like 14-20psi on the stock block and they're making over double the power, shit @lexusb3 is making triple the stock power at the wheels and nothing has gone kaboom yet. I'm hoping these engines prove to hold strong even at 10+psi of boost

[slicktop]

@Fabron757 makes 471whp on the stock block at 16psi for almost a year. Daily driven.

Get a good builder and even better tuner.

[carbonBLUE]

Originally Posted by dave77

I see people post about getting a turbo or thinking about it, on the stock FA20 engine. But with the high compression of 12.5:1, I don't think it's a good idea. I'm not an expert at all on engines, but this is one of the more common sense things about cars. It just adds pressure to an engine with already high pressure.

there are a good deal of people running 400 whp on the stock block since 2012, if it were actually a problem, they would have all blown up by now lol...

engines are built with more precision these days, with better materials and more powerful computers running them.

there's an eco car that's turbo'd with a 13.5:1 compression ratio from the factory, forgot which one it was though.

[ecko04]

Originally Posted by PStaff716

When asking my mechanic about boosting, he expressed concern with anything more than 6psi with the stock internals/CR.

A swap of the rods and pistons, as someone else mentioned, was his biggest suggestion.

But then I see guys running like 14-20psi on the stock block and they're making over double the power, shit @lexusb3 is making triple the stock power at the wheels and nothing has gone kaboom yet. I'm hoping these engines prove to hold strong even at 10+psi of boost

Don't listen to your mechanic ever again if he told you 6psi max. All FI isn't the same.

6psi with an Innovate is not 6psi with a Vortech is not 6psi with Kraftwerks. 6psi with a T3/T4 60 trim is not with a 57 trim is not with a 50 trim is not with a GT3076R.

The guys pushing your stated 14-20psi are not doing so on pump gas.

[Ny Brz]

It also depends on your driving style, if you travel 60-70 miles a day DD and beat the piss out of your car then yeah I could see the motor going sooner than later as opposed to driving ever so often or 5 -10 miles a day. Sometimes it's just a roles of the dice and ish happens, just make sure you maintain your car and try to make sure you are running the correct tune.

[OjiGeorge]

Originally Posted by dave77

So I guess the consensus argument for turbo is 1) use E85 gas and 2) direct injection helps cool things.

Don't forget WMI. It seems to be underused on this platform with FI.

[lexusb3]

Originally Posted by ecko04

Don't listen to your mechanic ever again if he told you 6psi max. All FI isn't the same.

6psi with an Innovate is not 6psi with a Vortech is not 6psi with Kraftwerks. 6psi with a T3/T4 60 trim is not with a 57 trim is not with a 50 trim is not with a GT3076R.

The guys pushing your stated 14-20psi are not doing so on pump gas.

All done one e85 for me. If I were to use pump gas on high boost I might as we'll get a new car lol.

[lexusb3]

IMHO that recommended 0-20w oil is water I don't think anyone boosting is using that? Correct me if I'm wrong.

[ecko04]

Originally Posted by lexusb3

IMHO that recommended 0-20w oil is water I don't think anyone boosting is using that? Correct me if I'm wrong.

I am. Eneos Sustina 0w-20. Using it since my first oil change, nothing else has gone in it.

[ecko04]

Originally Posted by OjiGeorge

Don't forget WMI. It seems to be underused on this platform with FI.

Agreed but some vendors in particular @ptuning @Mrc@ptuning have tested it with their systems and tuned for it pretty extensively and offer it as an add-on.