Compression ratio for 500hp turbo build

[Hags86]

Originally Posted by CSG Mike

Lots of experience doesn't mean it translates to this platform.

It's like saying a high end shop with decades of experience tuning/repairing CRT televisions can do the same with LCD televisions.

Specifically, unless they have significant experience with DI and dual injected platforms, they're basically starting from scratch like everyone else.

I recommend you talk to as many local tuners as you can, and pick one based on their experience with this platform, as well as their other experience.

I did that a year ago when I started this journey and made my choices. It comes down to trading off a little direct experience for the fact they are easily accessible.

I'm inside a 10 minute drive of arguably the best Motec tuning house in Australia, Holinger's R&D and manufacturing plant, Motec's head office and the engine builder who has the Subaru contract to do all their engine warranty work. Are they all experts on this platform? Maybe. But with some help from others we're making it work as best we can. They all know each other and work together routinely. Hell, the Mainline Dyno head office and software development team sublets the upstairs floor my Tuners shop!

[CSG Mike]

Originally Posted by Hags86

I did that a year ago when I started this journey and made my choices. It comes down to trading off a little direct experience for the fact they are easily accessible.

I'm inside a 10 minute drive of arguably the best Motec tuning house in Australia, Holinger's R&D and manufacturing plant, Motec's head office and the engine builder who has the Subaru contract to do all their engine warranty work. Are they all experts on this platform? Maybe. But with some help from others we're making it work as best we can. They all know each other and work together routinely. Hell, the Mainline Dyno head office and software development team sublets the upstairs floor my Tuners shop!

The best part, is that with a Motec, you can live, tune, and can accomplish more in 1 hour, than a full day of Ecutek tuning!

Sounds like you're in great hands.

[Hags86]

Yes. I had a software issue with Motec and they couldn't reproduce it on their simulator. I drove there and took the developer who does the software for a drive in my car, expained the issue and they fixed it. That sort of accessibility is very helpful.

[armstrom]

I've been giving this a fair bit of thought lately as well. I think one thing that is missing from the discussion is the availability of E85 and how that factors into the decision.

In my case E85 is pretty much impossible to find so I'm stuck with 93 pump gas. Most of the higher power builds I've seen are only able to achieve 400+ RWHP with stock compression using E85. Has anyone seen a good counter example?

I'm close to the point where I'm either going to pull off my SC and sell/trade in the car or go for an engine build and install a small pulley on my Harrop.
-Matt

[Hags86]

Agree. This conversation is premised on e85 being the predominate fuel. I have, and will keep, a 98 octane map with the flex fuel as e85 is not exactly readily available in the city/suburbs, but you can do it if you plan ahead. But it is impossible to find in the bush. I'm OK with little/no boost and very conservative ignition timing on 98 to get me home. It's already saved my bacon once.

[armstrom]

Yeah, my challenge is that I'm currently running a supercharger. Turbo systems have the advantage of being able to run a high boost/high power map for E85/FlexFuel then a lower boost map for regular pump gas. When you go with a supercharger boost control isn't really possible. If I want the most versatile configuration possible I suspect a lower CR build coupled with a high-boost pulley (~14-15 PSI is the max, I believe). In that case I can tune for max power on pump gas and maybe a bit more on E85 just through ignition advance.

A good example is TJ Hunt's car. He ran a built engine with stock CR and the a 14psi pulley on a Edelbrock SC. He made 420RWHP on E85 but had to pull so much timing to keep avoid knock on pump gas it only made 270RWHP. I bet if he could have dropped the boost down to 10-12PSI or so he could have made 300RWHP or more on the built motor on pump gas.

So, will an Edelbrock SC make 400RWHP or more on pump gas? Probably not. If you lower the CR to keep the engine safe you can't increase the boost enough due to the minimum pulley size and max RPM of the SC. But could you maybe make 350-370RWHP on pump gas? Maybe... Wish there were datapoints for this type of configuration.
-Matt

[CSG Mike]

Originally Posted by armstrom

Yeah, my challenge is that I'm currently running a supercharger. Turbo systems have the advantage of being able to run a high boost/high power map for E85/FlexFuel then a lower boost map for regular pump gas. When you go with a supercharger boost control isn't really possible. If I want the most versatile configuration possible I suspect a lower CR build coupled with a high-boost pulley (~14-15 PSI is the max, I believe). In that case I can tune for max power on pump gas and maybe a bit more on E85 just through ignition advance.

A good example is TJ Hunt's car. He ran a built engine with stock CR and the a 14psi pulley on a Edelbrock SC. He made 420RWHP on E85 but had to pull so much timing to keep avoid knock on pump gas it only made 270RWHP. I bet if he could have dropped the boost down to 10-12PSI or so he could have made 300RWHP or more on the built motor on pump gas.

So, will an Edelbrock SC make 400RWHP or more on pump gas? Probably not. If you lower the CR to keep the engine safe you can't increase the boost enough due to the minimum pulley size and max RPM of the SC. But could you maybe make 350-370RWHP on pump gas? Maybe... Wish there were datapoints for this type of configuration.
-Matt

Actually, you can boost control with a supercharger as well. Harrop even has a kit for it!

I've also helped many people do this with a centrifugal to meet p/w requirements on racecars.

[armstrom]

Originally Posted by CSG Mike

Actually, you can boost control with a supercharger as well. Harrop even has a kit for it!

I've also helped many people do this with a centrifugal to meet p/w requirements on racecars.

hmm.. interesting. Do they just vent through the bypass valve? I've seen the systems that drive the supercharger with a CVT to provide a wide range of boost levels and maximize boost at low RPM.
-Matt

[CSG Mike]

Originally Posted by armstrom

hmm.. interesting. Do they just vent through the bypass valve? I've seen the systems that drive the supercharger with a CVT to provide a wide range of boost levels and maximize boost at low RPM.
-Matt

Yes.

[CSG Mike]

Originally Posted by Alltezza

Any recommendations for forged pistons with stock compression?

I'm not able to find any except for SuperTech

CP or JE.

[JoeeStacks]

Originally Posted by Alltezza

If you're keeping stock compression would there be even a need to upgrade your pistons?

Are the stock pistons good enough when paired to forged rods?

I was under the impression that the piston was shaped a little odd, which makes it hard to fit aftermarket rods to it. Unless you shave the piston and make the rod fit.