If you had a 400HP engine........

[Huskymaniac]

One last question before I post my conclusions. What is the "no kidding" top speed of the stock SVX? I have seen 143MPH posted at several locations. However, peak HP occurs at an RPM that corresponds to 158MPH and I have also seen several people claim that they got their SVXs up to the 150s. What wasn't clear was whether or not they had a manual transmission and/or performance modifications. Does anyone have a definitive answer to this question?

[XT6Wagon]

92 is supposedly limited to 155mph. Later years tested much lower in top speed, but I'm not sure why.

Low frontal area and CD make some huge strides for the lack of power.

[STeeL25T]

I'm looking to make that kind of power out of my built motor, and the trans I chose was a 2005 WRX 5 speed with the 1-4 gears, main shaft, and synchros swapped to those of the Legacy GT. I didn't go with a 6 speed mainly because of cost and because I bought my car already set up and converted for a 5 speed so I had the parts already to just bolt it in.

Theory is that LGT gear are the same as earlier JDM STI non RA gears. Exactly the same ratio and thickness, at least.

[Huskymaniac]

Originally Posted by XT6Wagon

92 is supposedly limited to 155mph. Later years tested much lower in top speed, but I'm not sure why.

Low frontal area and CD make some huge strides for the lack of power.

Yeah but those were based on claims people made, as far as I can tell. I would like to hear from someone that actually has achieved those speeds in a stock SVX. Or perhaps an official claim from Subaru that it was the top speed of the stock SVX.

[Conn SVX]

The old Brochures clam 146 MPH I read where the newer ones 1994 and up had a speed limiter . Anyone know if that was engine or transmission .

[icingdeath88]

Originally Posted by Conn SVX

The old Brochures clam 146 MPH I read where the newer ones 1994 and up had a speed limiter . Anyone know if that was engine or transmission .

No USDM SVX ever had a speed limiter. Although at least some of the Japanese ones did.

I remember reading that there was a guy in Germany that got his into the 170s on the autobahn. But I don't know if that was stock or not, and there's no way to know for sure if it actually happened.

[XT6Wagon]

Originally Posted by Huskymaniac

Yeah but those were based on claims people made, as far as I can tell. I would like to hear from someone that actually has achieved those speeds in a stock SVX. Or perhaps an official claim from Subaru that it was the top speed of the stock SVX.

Thats what the magazines posted, Dunno if it was just repeating subarus stats or tested but they list at 155mph for 92, and far lower for later years.

I can believe a 92 SVX in proper shape could do 155. Good tires, well balanced unbent rims, engine in proper shape, good highoctane fuel, etc.

My 94 SHO with roughly the same power could get upto just over 140mph. This is with a larger frontal area, higher CD, and worse gearing.

I wonder though if top speed is best found with the torque converter locked or unlocked.

[Huskymaniac]

OK, here's the deal. I was intrigued by the engine that EFI Logics modified and is now selling. It is normally aspirated and produces approximately 416HP at 6650 RPM and 420HP at 8100 RPM. The power curve is very flat from about 6400 RPM to 8100 RPM. The stock redline is around 7000 so I don't know how comfortable I would be running it out past 8000 even considering the upgraded interiors.

I decided to use the 143 MPH number as the reference point for the stock car. After looking at the stock power curve, I estimated the power to be about 215HP at 4890 RPM where one would see 143 MPH. That's the reference point.

The power curve for the EFI engine can be seen in the attached file. This was measured with the engine in an Impreza with a manual tranny so I scaled these using an assumed tranny efficiency of 76% to get the engine numbers.

The attached spreadsheet shows estimates for the top speed that can be achieved in the SVX, with this engine, for both an automatic and manual transmission. I used 66% for the assumed efficiency for the automatic transmission. I calculated what the optimal final drive ratios would be for each type of tranny (Max Speed RPM = Max HP RPM) and then selected the closest ratio among the trannys I have heard discussed on this forum. Then I calculated what the actual RPMs would be at the calculated top speeds for each tranny type. You can see that the RPMs end up a little higher than the RPM at which the first peak in the HP curve occurs but it is within the flat region of the curve so the impact on top speed is minimal. These RPM values are also right around stock redline so that is convenient.

The conclusion is that this engine in an SVX with an automatic tranny can reach approximately 178 MPH and it could reach 187 MPH with a manual tranny.

[Cam]

Tony, I believe you have just proved that you are constantly bored throughout your everyday life .

In all seriousness though, are you purchasing that engine?

[icingdeath88]

Originally Posted by Huskymaniac

OK, here's the deal. I was intrigued by the engine that EFI Logics modified and is now selling.

Still for sale? I thought it would be sold by now. Anyway, my understanding is that it would be far from a drop-in swap into an SVX.

I'm honestly not all that interested in top speed. You just can't go that fast under anything resembling normal circumstances.

[Cam]

Double post...the phone strikes again

[kwren]

Originally Posted by Cam

Tony, I believe you have just proved that you are constantly bored throughout your everyday life .

CAM, I picked up on that months ago!

In all seriousness though, are you purchasing that engine?

Keith

[LetItSnow]

I'm still trying to sort out what you're trying to do! Is this supposed to be streetable? Pump gas or race gas? Only to set a known top speed? A term paper? Drunken math experiment?

Start backwards. Sort a power to speed requirement curve. <Here> is some handy info, and a wicked Caprice to boot. Frontal area and drag are on the web somewhere; I've found them before.

You're going to want to establish a maximum distance to achieve this speed, as well, unless you've got a ten mile long private straight to work with. This'll get some acceleration requirements defined for your gearing.

REMEMBER TO UPGRADE YOUR BRAKES.

[Huskymaniac]

Originally Posted by Cam

Tony, I believe you have just proved that you are constantly bored throughout your everyday life .

I am an engineer and Ferrari fan so I became intrigued as to how fast this car can go with an engine like that and how one would calculate such an estimate.

At least I am not sad enough to post a message about my birthday to solicit well wishes. (Not talking about you Cam)

In all seriousness though, are you purchasing that engine?

I have given it some thought. It would be fun to find a car with a 5 speed installed but with a dead engine and swap this engine into it to see what it can actually do. That would be one expensive SVX though and the wife might not think it fun.

[LetItSnow]

Originally Posted by Huskymaniac

It would be fun to find a car with a 5 speed installed but with a dead engine and swap this engine into it to see what it can actually do.

What about... a local car with a 5-speed installed but no engine?