Valves per cylinder and Turbo

[charger69]

so, since the valve per cylinder is a thing that matters, does it mean 5 valves per cylinder can handle bigger turbo's? has anyone had any experience with that, and is it possible to turbocharge a 2 valve per cylinder engine? I have heard it can but they get short life after it and can't handle bigger turbo's.
question is does the more valve per cylinder give the engine less stres of handling a bigger turbo?

 

[obi_waynne]

It's more to do with how large the valves are than how many there are. In any application you need to match the boost with the flow rate into the engine.

It may be possible to do a large valve conversion to the head so it flows better.

There were a few 8 valve 4 cylinder engines which were turbo charged in the 80's and 90's

 

[HDi fun]

Valve timing and overlap will player larger roles than the number of valves. Many 8 valve fours were turbocharged. AR MG Montego and Maestro Turbo models. Bentley's Mulsanne Turbo was a 16 valve V8. Loads of four cylinder 8 valve diesels were turbocharged.
The more significant fact is that 4 valve per cylinder engines have pretty much replaced 2 valve per cylinder engines in both naturally and forced breathing configurations.

 

[obi_waynne]

Then VW came along and created a 5 valve per cylinder head!

 

[HDi fun]

Yes indeed. Yamaha has done something like this too in the motorcycle world.

 

[charger69]

Fiat has the 2.0l 20v HGT engine. but isn't it somehow like bigger valve holes = more valves? something that can make the engine handle the turbo?

 

[obi_waynne]

Have a read up on this subject on these pages....
https://www.torquecars.com/tuning/intake-valves.php
https://www.torquecars.com/tuning/porting-polishing.php

 

[HDi fun]

There's no specific number of valves required for a turbocharged application. The benefits of more valves are twofold:

1. Increased total valve area.
2. Smaller and lighter valves allow higher engine speeds before valve bounce becomes an issue.

 

[charger69]

can valve bouncing damage valve holes?

 

[obi_waynne]

The problem with bouncing valves is that they pop open when you want them closed which loses compression and messes up the suck, squish or bang, exhaust phase. They are designed to take quite a beating so I doubt damage would occur but I wouldn't rule it out completely if the bounce was really severe and metal fatigue was also a factor.

 

[charger69]

how about widening the valve holes?

by the way is it possible to do swaping the valve head on different types of engines?

 

[SLEEPER]

With turbos it is all about air flow which means the head has to be able to flow the air the turbo needs.
Some heads flow naturally better than others so wont need upgrading untill the turbo size increases dramatically . Some heads are the opposite . Some can take oversize valves some cant so the answer will never be black or white. But if you can find a better design head and it fits thats a real help if the head cant flow the air.
To answer your question it isnt the valves that decide the size of the turbo you can use ; it is far more complicated than that.
To flow the air that a larger turbo needs you need to be able to flow that air. Unless you are putting a really large turbo on most well sorted engines will be ok with a slightly bigger turbo but because of the way a turbo works the power will come on later with a bigger turbo (assuming similar design etc)
To flow more air you also have to be able to get rid of it as well. So a bigger turbo means often a different exhaust will help as well.
It really is engine specific and the good news is that whatever engine you have someone will have done it and these answers will be a matter of record and easily available. I can recite the facts for rb engines and if you have a cosworth OG will surely be able to do the same as will claymore with volvo engines but the answers will be different .
You need to ask about a specific engine to get a specific answer.
Finally fitting a large turbo will give you top end power but more lag and a larger one more so . With some engines this can be helped by increasing the capacity and then of course all the answers change again.
So which engine is realy important

 

[charger69]

take an example Fiat's 1.3l SOHC engine

 

[SLEEPER]

Not sure on this engine specifically but on most 1.3 SOHC engine i would be looking at an engine swop as I imagine this would be far more effective in most cases.

 

[HDi fun]

Honda had a SOHC 16 valve motor in the 1990s. This must put a hell of a load on the poor little solitary camshaft.