What compression ratio should I be running on a turbo bug

[advinnie]

Hi all, just wondering what compression ratio i should be aiming for on my turbo 1600 bug?
I’ve just measured everything up and at the moment I’m running 8.5:1 witch I think is a little high?
I’m running 10 psi boost max
Cheers

[buguy]

Do you have an intercooler or water injection? What octane fuel will you be running?

[advinnie]

It’s a draw through set up so no intercooler, looking into water/meth injection at the moment.
I’m running 99 Ron fuel ( UK )

[risk]

I have done it a few different ways.. but I am running alcohol based E85 fuel:

low compression/high boost 7.8:1 and 20-24 psi..
-sluggish off boost but a beast on boost. what a kick in the pants.

high compression/low boost 10.5:1 and 12-15 psi..
-very peppy off boost even better on boost. not as much of a wow factor but overall more fun and more drive-able.

With premium pump gas I would say 8.5 will be fine.. others may disagree.

[buguy]

I've read that you should stay in the 12:1 dynamic compression ratio. 8.5:1 @ 10 psi is 14.3:1 which doesn't sound safe. I don't know what 99 Ron fuel is though. But with 92 octane you would only be safe to about 6 psi @ 8.5:1according to everything I've read.

[advinnie]

I've read that you should stay in the 12:1 dynamic compression ratio. 8.5:1 @ 10 psi is 14.3:1 which doesn't sound safe. I don't know what 99 Ron fuel is though. But with 92 octane you would only be safe to about 6 psi @ 8.5:1according to everything I've read.

That’s what I’ve read as well and why I’m worried about running 8.5:1 static compression ratio and 10 psi of boost

[buguy]

Yeah I'm not sure how you figure in water injection. Sounds like there are a few guys here running 20+ psi with it. I think having the perfect tune is key. Not easy to do (maybe impossible) with a draw through carb set up. Off boost yours would be nice and peppy. I think I'd try it myself. Sneak up on boost and make sure you have an afr gauge to watch. Maybe try one of the CB black boxes so you could pull plenty of timing out of it until you have the tune as good as you can. Then maybe you could start creeping up timing and boost. Oooooor throw a shim in it to lower the compression one point and have the ability to run more boost.

[advinnie]

I am all ready running the CB performance black box to control the ignition timing it’s a nice bit of kit
I’m not starting to boot till 2500 rpm in third gear due to the large T3 turbo but I do know is that at 4000rpm in their I can hit 13 psi so I need all the help from the compression ratio to get me going in 1st and 2nd

[buguy]

Yeah I have late spool too with my T3. I picked up a small TD04 from a WRX that should help with that. Maybe you should look for a different one too.
Do you have E85 available to you? Wish we had it here!

[petew]

DP1600 had 7.5:1 with some dish top pistons. Car was pretty sluggish down low. Went back to stock pistons and 8.5:1 comp. Heaps better down low and I think it comes on boost earlier too. I'd say err on slightly higher comp ratio. All the modern stuff is going this way. Gives you a broader torque curve and less lag. Most of the guys in the past ran low comp ratios to prevent detonation with a bad tune. With all our modern gismos and easily available wide bands, we can easily tune for higher comp ratios and boost.

With 100ron fuel you should be fine. Course water/meth inject will allow you to run much higher boost down the track.

[buguy]

I think my stocker is around 7.2-7.3 from the factory.

[advinnie]

There is no way near me that sells E85 fuel and just 25L of 110 race fuel cost £85 fuel is not cheap here in the UK .
TD04 turbo I will look into that one. What sizing A/R have you got on your TD04 and do they have the same exhaust manifold stud patten?

[Dan Dryden]

I run a td04-13t from an Impreza WRX.
Spool is good. Noticeably quicker than a T3 turbo.
It has a smaller compressor housing, so the kick of torque in your back isn’t quite as hard.
It uses a different exhaust pattern so you will need to modify your exhaust to fit one.
Also, I’m not sure that they have a carbon seal, so my not be suitable for draw through setups.

[advinnie]

I think my T3 has a .36 hot side

[buguy]

That would be the smallest T3 I have ever heard of. Sounds like water injection might be your best bet. I read somewhere that adding water injection is the same as 25 more points of octane. So 91 octane with injection would be like 116 octane race fuel!
I think AR on the 13T is a 41
Somewhere around a 1.5" inlet size and 1.75" outlet. They also have a weird (ugly!) stud pattern.