STiLtd683's SVX build: Opinions and advice wanted

[icingdeath88]

If you want to stay N/A, then how bout going 11:1 CR? If you're already going to have pistons made, may as well go in one direction or the other. Also, if you have any ideas for changing valve sizes, make a final decision before ordering pistons, since the pistons have cutouts that you will have to worry about having clearance for the valves to maintain non-interference. If 11:1 seems like it might be too much, maybe in-between would also work (10.5 or .6 perhaps). CP will make any compression you want, and can alter the valve cutouts for +1 or 2mm valves for example.

The stock CR is in an awkward spot. It's not low enough that it's very turbo-friendly, but it's not high enough by today's standards that it makes a lot of power for it's size. You will find some that disagree about both those statements, but it is what it is.

[SURTEESS]

Sorry just thought I would add my 2 pennies worth - rather than forking out for pistons etc why not just get thicker head gasket made to lower the compression in a turbo model.

I did that with a 1987 Honda Civic 1300cc (1mm spacer) with 20Lb boost & water injection into a 2" SU carb = 225km/h + still returned 32-35mpg (UK size gallon).

The only issue was the torque steer - due to different length drive shafts.

It was a fun car to drive (with NO noticeable additions from the outside). All skirts etc were from show room - my first & only brand new car, that 6 months later was turned into a wolf in sheep's clothing!.

I fabricated everything myself from the inlet plenum to the waste-gate piping.

Only needed 1 rebuild in 12 years after doing 215,000km. Photos are taken just before it was sold (Hence 1 OF 1 plate was removed & currently on the SVX).

The only book that I used was a Haynes book on Turbo-charging Techniques & Ideas.

[icingdeath88]

Originally Posted by SURTEESS

Sorry just thought I would add my 2 pennies worth - rather than forking out for pistons etc why not just get thicker head gasket made to lower the compression in a turbo model.

I did that with a 1987 Honda Civic 1300cc (1mm spacer) with 20Lb boost & water injection into a 2" SU carb = 225km/h + still returned 32-35mpg (UK size gallon).

The only issue was the torque steer - due to different length drive shafts.

It was a fun car to drive (with NO noticeable additions from the outside). All skirts etc were from show room - my first & only brand new car, that 6 months later was turned into a wolf in sheep's clothing!.

I fabricated everything myself from the inlet plenum to the waste-gate piping.

Only needed 1 rebuild in 12 years after doing 215,000km. Photos are taken just before it was sold (Hence 1 OF 1 plate was removed & currently on the SVX).

The only book that I used was a Haynes book on Turbo-charging Techniques & Ideas.

He already said he wasn't interested in FI.

Also, a while back, I did the math on this. Post number 8 is my favorite post I've ever posted.

http://www.subaru-svx.net/forum/showthread.php?t=58062

Edit: TL;DR: Thickest headgasket cometic makes, which is just short of 2mm, will only lower the CR to 9.8:1. Still not usefully low.

[STiLtd683]

Sorry for the delay in replying. Ice, your my hero. I'm looking into the 11:1 pistons right now and it's likely I'll go that route. I'm planning on a full port and polish job but I don't know if I'll be increasing valve size. Do you think I would need too?

[icingdeath88]

Originally Posted by STiLtd683

Ice, your my hero.

Originally Posted by STiLtd683

I'm looking into the 11:1 pistons right now and it's likely I'll go that route. I'm planning on a full port and polish job but I don't know if I'll be increasing valve size. Do you think I would need too?

While I don't think it would be very worthwhile for my build, it might be for yours because you're planning to bore it out. I don't know how that factors into it all. It would increase the cost a good bit though.

You should read these threads: http://www.subaru-svx.net/forum/showthread.php?t=52222

http://www.subaru-svx.net/forum/showthread.php?t=50837

There are a lot of pictures, discussion, and useful background info in both. It doesn't seem like either used oversized valves.

If I were you, I'd keep the stock size valves, just to keep make sure the engine stays non-interference. That is a high priority for me. It scares me to spend thousands of dollars on an engine only for it to fail because a timing belt breaks. Not that it's not doable, I'd just rather keep it simple.

Maybe someone else with more experience can weigh in. I know Harvey's (oab_au) done some computer modeling or something in the past.

Edit: Found some more related info, although you probably have seen it before. See post # 35 especially: http://www.svxworldforums.com/view_t...94&forum_id=13

I had considered doing the stroker crank thing as well, but it seems ill-matched with FI, and not very cost-effective.

[STiLtd683]

I'm reading through those threads now. And I completely agree with staying non interference. I'm not dropping 1k on pistons alone just to see them get dented if I make a mistake or the belt breaks. And I seriously considered following NeedForSpeed, but I decided it's outside my budget and I likely wouldn't remain street legal. Slightly oversized pistons and increased compression ratio seems to be the best route for what I have in mind.

[oab_au]

Originally Posted by STiLtd683

I'm reading through those threads now. And I completely agree with staying non interference. I'm not dropping 1k on pistons alone just to see them get dented if I make a mistake or the belt breaks. And I seriously considered following NeedForSpeed, but I decided it's outside my budget and I likely wouldn't remain street legal. Slightly oversized pistons and increased compression ratio seems to be the best route for what I have in mind.

It is not easy to add power to the engine, but it is very easy to kill the power that it already has.
The IRIS inlet system is responsible for the wide, strong, torque that has two peaks in the torque curve. This is where the wide torque curve that starts at 2500 and goes right up the peak rpms is produced.
The first is due to the Inertia system that produces a higher pressure in the inlet manifold of about 5/7 psi, that starts about 2500 peaks at 3500, then drops to 4200 where the inlet systems changes to the resonate system, that uses 'sound wave pressure', to increase the cylinder filling to a torque peak at 4800/5000.

This all relies on the exhaust staying the same, from the second cat forward, for the Resonate system to work and the cam timing for the Inertia system to work.

If you are staying NA then a higher comp, and the original cams with a higher lift, are about the only things that will increase the power, without killing the power it already has.
We did a cam years ago that increased the inlet lift to 8 mm that worked well. As 8.75/mm is as much as you can get with the standard springs and lifters. To go higher like to 10 mm you would need to do solid lifters, but it would spread the torque a lot wider.

Harvey.

[STiLtd683]

Well, after much deliberation I decided to put this project on hold. Every time I look at a link my budget goes that much higher and I think I should wait til I'm done with school to attempt a build such as this.

On the bright side, I'm going to pick up a complete engine and toss that in so I can at least daily drive the thing.