Thread: 8v 2l Twin Charged -my Little Project
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Old 05-18-2008, 10:08 AM
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ToonRboy ToonRboy is offline
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Hey Buzzed,

Nice Alfetta. Ambitious plan. I like it & I hope you "git 'er done!" ;p

I understand what you're attempting to achieve with regard to the challenges to overcome with turbo lag and target HP. Especially when starting out with just 2L. Naturally, if you have a bullet-proof engine, you can get your taget HP (and more) with 1.5L. Problem is the open block design. Very difficult to seal those kind of combustion pressures when you exceed stock output by well over 100%. Not to mention component failures.

Anyhow, since it's been done (and documented) there's not much to argue. However, I'd like to make a few points.

Quote:
I plan to pressurise the supercharger inlet with the turbo charger.
-Just seems to me that a Roots type SC is a big impediment to airflow & a major heat-sink (maybe not so good for the longevity of your SC, but hey, maybe it'll act like an intercooler!) This makes sense for an airplane, but at the altitude of an Alfa, I kinda' like the VW idea. Roots feeds turbo, cuts-out and gets bypassed when turbo gets up to speed. BTW - great diagrams Greg!

Quote:
The turbo will be sized to provide 350 rwhp at 6500rpm at approx 23psi.
Turbo too small. If you gotta run 23psi to get 375hp, you might want to consider a turbo that flows 550-600cfm at just > 1 BAR. The other part of this is trying to contain that 23psi. ibid - open block not so good.

Quote:
My mass flow is calculated on 20-25psi, 4500-7500rpm
Remember, that was a rotary engine, which flows gasses more like a two-stroke, & doesn't have rods, valves, or rings to blow out (just apex seals). Not the same as you are working with now.

Quote:
This will in fact help to make my relatively large turbo (not the one in the photo, but a GT3071R) spool up as though the engine were a larger displacment engine.
GT3071R flow rating is 694cfm max. Found a compressor map: http://www.rbracing-rsr.com/turbo/Tu...0rcompress.gif (doesn't show rpm's tho) but you can see at the flow you need to make your target HP (>35lbs/min, you're already at the top edge of this compressors VE. Here again, I would say pay more attention to cfm flow at 1BAR rather than just boost in psi. High boost means heat & not necessarily flow. For instance, a TD04-12a flows 325cfm at 1BAR, but I can run it at 1.5BAR (and produce a lot of heat), but it won't really flow any more air, which is what you need to burn fuel, which is what you need to make power.

Interesting to see someone taking a look at this. Waiting in anticipation to see the outcome.
Last edited by ToonRboy; 05-19-2008 at 09:28 AM. Reason: Fixed typo ">35lbs/hr" to ">35lbs/min" doh!
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