Turbo 1.8L Plenum vs. 1 into 4 performance concerns

[tigretr]

I am building a Sunbeam Alpine 1.8L turbo motor and am currently trying to decide whether I should build a plenum to distribute the charge or would it be better to build essentially a reverse header 1 into 4 and force the air directly into each port. Conceptually I would think more flow and more even distribution could be achieved using the 1 into 4 approach, but are there any performance concerns?

I am running individual throttle bodies for each cylinder, 12 psi boost, and the plenum / inverted header would all be upstream of the butterflies.

In the event the plenum is the preferred method, how big should it be?

Any help is greatly appreciated,
Thanks

 

[jomor]

Tigretr,

I'm no expert, but will the butterflys handle the 12 psi boost? Possibly so with individual Idle Speed Valves/Systems. My understanding is that the throttle body is normally upstream of the turbo. I would be interested in how this turns out. Keep us posted. Possibly you coud use a type of poppets or globe valves for throttling instead of butterflies, your change in throttle area would be more linear, controllable, and less flow losses if done properly. You could also design some swirl into the flow stream. If you took this route, my opinion is that the plenum with the apropriate taps would have less flow losses. I would rather see data though.

Interesting!

jomor

 

[kradicke]

The butterflies will behave fine, we have run supercharged systems (and turbo systems) configured with the butterfly after the compressor. There are even some factory setups with this turbo configuration.

Kai @ Wishbone Classics

http://www.wbclassics.com

 

[Warpspeed]

I agree the butterflies will be fine. Engine usage best determines the optimum induction setup.

Long runners will give you better low end off boost torque, but the same long runners can be restrictive for top end airflow.

Long runner induction systems will work best where boost pressures are fairly low, and engine compression reasonably high. In other words a mildly boosted stock engine. Or put another way a turbo assisted engine.

Short runner systems work better for a more highly tuned higher Rpm application. Compression would be lower, cams more radical, boost pressure pretty high. An engine like that will be a slug off boost, all the performance comes from the turbo alone. No real attempt is made at induction tuning, all the air comes from the turbo.

It really depends what you want to use the car for.

 

[BillyShope]

The plenum is usually only a consideration with a naturally aspirated engine. The effect will always be there, but it becomes quite marginal at the high boost you're using. In short, I wouldn't fool with it. It's a whole lot easier to increase turbo boost.

Some effort should be expended to assure equal flow, of course, but, unless you really screw up, this shouldn't be a problem. The cardinal rule in fluid flow: Avoid transition losses.

 

[patprimmer]

I pretty much agree with BillyShope and Warpspeed, however I feel equal flow is fairly important, especially if port injection is used and the ECU cannot individually tune the cylinders.


Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[DesignOutsourcing]

Since you're not staying original, why not drop in 289-302 or a roller 5.0 Ford and a T5 or toploader? It will be worth more-- some good "algers" are going for $30k plus!

If you want to do a turbo, do a search on this site and google for plenum design. I recall someone saying that the plenum helps to balance the flow between cylinders and a plenum volume of 2-3 times engine capacity works well. There are pulse tuning benefits but it's more complex than NA engines due to the pressure changes. For better balance the plenum should extend beyond the last runner and the better ones I've seen are tapered down in volume from inlet to end.

cheers, derek

 

[kradicke]

2-3 times engine capacity is absurdly large. We have had good luck with plenums 0.8-1.2x engine capacity. Attention to the transitions in each runner - proper radiusing - yields more in terms of flow than varying the displacement of the plenum by leaps and bounds.