8v 2l Twin Charged -my Little Project
Thought I would pull my finger out and post up some porgress on my twin charged project.
If people are interested I will add more detail as I go. I actually have been writing a doc to cover what I have been doing so I can prob cut and paste bits.
So the aim of this project I am setting out on is to increase horsepower…but why? What do I want the car to do? The 1.8l Alfetta is slow by todays standards, and so I would like to bring it into the 21st century…and then some. It will be predominantly a once in a while street car (probably around 2000km’s per year), but may see the odd track day in the future. So what are the main things I want to achieve then?
1. The car must retain standard lines (no guard pumping etc)
2. The car must be able to be returned to original condition with minimal fuss
3. The conversion must be cost effective without appearing cheap.
4. The horsepower target will be 300 rwhp on pump fuel.
5. Fuel efficiency is important, but due to small distance driving – not the be all and end all.
6. The horsepower must be obtained without engine family change (No twin-spark of other makers engines allowed)
7. The package must be reliable, no point having a dyno queen.
8. Lots of low down torque.
9. It must be a challenge, I like a challenge!
10. It must be street drivable and tractable
Hardware chosen to achieve requirements:
So with the constraints I laid out for myself, a few things became clear. The engine should remain an 8v engine as to keep with the beautiful Alfa design which aesthetically is hard to beat.. It would require forced induction of some description and for reliability and tractability it would probably require fuel injection.
The engine chosen was a late model 8v 2L engine, going with the adage that you can’t beat cubic capacity.
This left me with the decision of what type of forced induction to use to obtain the desired hp. I must admit I ruled out nitrous oxide on the basis that it’s not remotely road legal to have it hooked up….and there's no challenge in it. Next up is turbo charging, but with the 300rwhp target, I worried that the engine would have excessive lag for that instant tractable hp for ‘out of corner fun’. In fact I know this to be the case from past builds I have completed...even with rollerbearing turbos. On the other hand, supercharging tends to become inefficient at the upper rpm range if low down grunt is to be maintained, also the lack of variable boost for roots type chargers is a problem as compromises inevitably creep in. I could have used a vortex supercharger rather than positive displacement charging, but I would still have the issue of lack of low down torque.
I figure a feasible solution would be to supercharge the lower rpm band and turbo charge the upper rpm band. This would give the best of both worlds, low down torque for that small V8 feel, and the satisfying upper rpm surge that turbo’s are renowned for. Best of all, it would be a challenge, actually my mind was made up when I was told I’d been smoking something and it would never work.
So that was it, I was going to build a 300rwhp 2l 8v Alfetta GT with twin charging via roots supercharging and turbo charging.
Existing twin charge examples:
Delta S4 turbo boosts supercharger, then bypasses supercharger), twin stage intercooling
Mazda March super turbo (turbo boosts supercharger till about 3500rpm, then switches to turbo only)
Voltswagon Golf 2007 (turbo boosts supercharger till about 3500rpm, then switches to turbo only
2004 SPI Mini cooper S twin charged (300rwhp claimed)
Stock Eaton Supercharger with Stock Pulley and Garrett Turbo.
Method or forced induction
After reviewing various methods of twin charging from manufacturers and various individuals around the world, I decided on a method.
I plan to pressurise the supercharger inlet with the turbo charger. The turbo charger stage will be intercooled. The turbo will be sized to provide 350 rwhp at 6500rpm at approx 23psi.
I would LOVE to twin stage intercool, but packaging space is at a premium. This will limit max boost allowable, but given my very low comp ratio, I suspect that I will still be able to run 15psi, which is ample.
OK, so for a few photos of the proposed setup - dummy fitted in the shed with modified manifold bolted up.