M20 Cylinder Heads. Is There A Difference?

[maxfield]

Why not get a 325 inlet instead of going through all the trouble. Plus you wouldn't get any gains anyway. Would it increase air flow?

[DelaneyG]

you can get a tool which goes on the end of a drill and push it through, its kinda like a pipe cleaner

[DelaneyG]

gettin the 325 manifolds the best bet

but if you ported and polised the 320 manifold it would make a difference cos the air can flow more smoothly but you have to do the lot to really get the best results


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[Beastly_Bavarian_Beauty]

Where can you get one of these porting/polishing extension (pipe-cleaner like) tools from? Manufacturer names? Places that stock them? Prices? Etc?

[Beastly_Bavarian_Beauty]

Oh yeah... and does this tool fix onto the end of a drill? Like a flexible extension? Any web links to an example would be good too guys. Thanks.

[maxfield]

Why not polish the TB aswell

[DelaneyG]

il find out about the tool

youd wana leave the throttle body as it is, they are already smoothed anymore and they wouldnt work properly

[Beastly_Bavarian_Beauty]

Bravo. Good advice ARGOS. Actually bought a tent at the weekend from Argos also, cut down from £79.99 to £39.99. Seeming to be an amazing place. Great deals and amazing advice. lol

[Turbo-Brown]

I'd guess you woudl lose power all through the rev range as there is no advantage of a smaller inlet.

Eh?

That's not true at all!

A smaller diameter tract should yeild more low end torque as the air speed approaching the engine will be greater in the smaller pipe than it would be in the larger pipe.

Because the air speed is greater, the air approaching the engine has more momentum and as a result of that: more of it goes in, to which the corresponding amount of fuel can be added leading to a bigger bang and thus more power.

However, this can of course become restrictive after a point.

Don't assume that bigger must be better when it comes to the sizing of inlet systems!

[Jhonno]

an itl be more than a 10 bhp gain when its all done

no chance, it will lose to standard 320's when done

better off fitting the 325i cam into a 320i head, bout the only thing that will be of use to you

Argos summed it up pretty nicely imo

[Jhonno]

dont fit a 320i inlet to a 325i total waste of time

also polishing it will achieve basically jack all, the air needs some turbulance to mix properly with the fuel

as argos says the 320i inlet cant be opened out enough for a 325i

[Simon13]

i'm sure i said in this thread the same thing argos did. I guess some people don't read what i say which is nice

[DelaneyG]

Fitting a 2.5 head to a 2 litre would acheive absolutely nothing. Sure, you have 2mm bigger inlet and exhaust valves but you'd drop the compression from an already miserable 8.8:1 to around 8.4:1 so you'd have the throttle response of a lawnmower - any power you'd gain from the bigger valves would be lost with the lower compression.

But a 2.5 head will fit a 2 litre and it'll run and drive okay althouigh the valve top piston cutout clearance is very, very tight. It's not a satisfactory job by any means. A 2 litre head will NOT fit a 2.5 of any desciption. Contrary to popular opinion there is actually very little difference in port size between the 2 litre and 325i heads but the top of the port is a slightly different shape. The reason the 320i is so fartless at low rpm is because the ports are too big causing slow gas speeds. At higher rpm the big ports should come into play but the small TB restricts it badly - a lose-lose situation.

The only mod worth doing to a 2 litre is fitting the 325i throttle body along with a chip. I've done this twice - the first time was by opening out a 320i inlet manifold which is sort of okay but there's not enough meat in the manifold to do it 100%. A far better solution is to fit the 325i inlet manifold complete. To do this you have to open out the inlet ports slightly which is easily done with a 325i inlet gasket as a template and a stone in an electric drill. The 325i manifold will then bolts straight on and the ports will match up. Combined with a chip I reckon this will find you 10 bhp and make a 320i much more lively.

What are you talking about? first off that comp ratio is for an m20 with a cat mine hasnt got one so its 9.4:1 2nd im incresing the comp ratio by taking 60 thousands of an inch off the head and 5 thounsands off the block 3rd im going to adjust all the ratios by calculting the cc of the combustion area and smoothing to suit it. "throttle response of a lawnmower" i think not luckily i am going to build this engine when i take my car off the road in sept so maybe youl see for yourself.

Bigger valves = more air in more air out meaning better responce

Of course itl fit its the same engine!!

For a valve to hit piston youd would need an extreamely high lift cam.

Ports need to be big big and smooth smooth how can a big smooth port cause low gas flow?? are you mad theirs less restriction thats basic engine tuning

[DelaneyG]

dont fit a 320i inlet to a 325i total waste of time

also polishing it will achieve basically jack all, the air needs some turbulance to mix properly with the fuel

as argos says the 320i inlet cant be opened out enough for a 325i

Eh? why would you want turbulance? the idea is to get rid of turbulance if theres no turbulance you can get fuel in quicker it will mix better and you can get it out quicker so the engine can turn over quicker

Smoother=Quicker=Faster!

but their is no point putting a 320 manifold ona 325

[bigkev]

so how does that explain why the bike that won the british supersport championship last year actually had the inlet ports decreased by 25% with epoxy resin
this is to give you more velocity into the cylinder which fills quicker and allows you to have a wilder cam timing (more overlap) as you dont get so much blow back through the inlet port the only thing that dictates flow really is the valve itself

[DelaneyG]

sorry mate i only work on cars i dont know a thing about bikes apart from they rev to 12000 an more in some mad cases!!

[DelaneyG]

the only thing that dictates flow really is the valve itself

yes and no, if the air can get to the valve quiker then that will increase the amount of flow

[bigkev]

an engine is an engine its all the same principal this method is used on harley davidsons in the states for drag racing and they only rev to about 7000 and are also 2 valve pushrod design

[bigkev]

say it like it is argos dont you hold back now

[jmc330i]

dont fit a 320i inlet to a 325i total waste of time

also polishing it will achieve basically jack all, the air needs some turbulance to mix properly with the fuel

as argos says the 320i inlet cant be opened out enough for a 325i

Eh? why would you want turbulance? the idea is to get rid of turbulance if theres no turbulance you can get fuel in quicker it will mix better and you can get it out quicker so the engine can turn over quicker

Smoother=Quicker=Faster!

Everything on the exhaust side needs to be smooth to get the gases out quicker, but on the inlet side you want (to a certain extent) a rough surface to create turbulance, this helps the fuel mix with air to improve combustion.

[Turbo-Brown]

the faster it arrives at the valve, the more gets crammed in on one stroke. This is how four valve per cylinder technology came about.............

Interested to know why you think that, considering that the larger inlet area on 4v engines typically reduces gas speed and therefore low end torque when compared to 2v engines.

Note how Honda have an engine in their armada which uses only one of it's two inlet valves at low engine speeds so as to keep the gas speed and torque up.

[Martinaston]

So as a rough guess from all the comments what we realy need is a manifold with variable bores to keep the air speed constant throughout the rev range

Going back to a comment on page 2 of this thread,
Is there a difference between a 320 and 325 cam ?

[jmc330i]

So as a rough guess from all the comments what we realy need is a manifold with variable bores to keep the air speed constant throughout the rev range

Rover 827s have some sort of trick inlet manifold dont they?
Im guessing its something to do with airflow.

Going back to a comment on page 2 of this thread,
Is there a difference between a 320 and 325 cam ?

There must be, putting the 2.5 cam into 2.0 makes a difference apparently.

[Simon13]

yeah but it's not a straight forward swap is it?

thats why 4v cars typically have less torque low down than 2v

i've noticed it slightly between 24v 2.5's and 12v 2.5's E30's that i have driven

[jmc330i]

yeah but it's not a straight forward swap is it?

What the 2.5 cam into the 2.0? I dont know Ive not done it, but I was at college with a guy who did and his 320i went pretty well

thats why 4v cars typically have less torque low down than 2v

i've noticed it slightly between 24v 2.5's and 12v 2.5's E30's that i have driven

I noticed that when I had my 2.0 8v Cav. The 2.0 16v Cavs and my friends Astra Gsi only really pulled away once they got up the revs.

[jmc330i]

Putting a 2.5 cam into a 2 litre doesn't do anything apart from fuck up the idle. The profile and lift are pretty much the same but the timing isn't - the piston speed of a 2.5 is a lot faster than a 2 litre.

Odd, I know for sure the guy I know fitted the 2.5 cam to his 2.0, plus the inlet and TB.

Is there anything else that could be changed to make it fit/work? Got me interested now as to what else he did to it and didnt tell us

[Martinaston]

I compared two cams alongside each other and didn't see any difference but i didn't check the overlap,
I'll have to have another look when i get a 325 out.

Argos whats this about an E34 M5 ?

[Jhonno]

DelaneyG please stop before you hurt yourself.. You obviously dont have an inkling on how engines work

Argos.. I i thought the 325i cam was higher lift than the 320i cam.. hence why temple320 i believe fitted one in his 2.7 with a 731 casting

as argos said the whole 8v's having more bottom end torque thing is still based very much on the golf gti's of the 80's... the xe lump is a torquey bugger from 1000rpm to redline it is more than likely a seat of the pants thing as they lack top end the bottom end feels torquier

airflow into a 16v head gets split in 2 on each port to go to each valve so air speed is pretty much maintained