aluminum heads vs. iron and compression
i was reading on another board (www.hotrodders.com) and a guy posted a question about the difference between the two.
and someone said that aluminum heads lower the compression ratio 1 full point "due to lack of thermal efficiency". given a set of iron heads and aluminum heads both have the same combustion chamber CC. and no one said different... i've never heard of this? i know you can run more compression with aluminum heads, due to heat dissipation. but i was unaware that they 'lower' the compression ratio. |
Re: aluminum heads vs. iron and compression
Al. heads don't lower CR but because they are more inefficent than an iron head they need about 1 point more CR to be equal as far as combustion efficency
|
Re: aluminum heads vs. iron and compression
:) I will take a 10 to 1 motor over a 9 to 1 motor, all things but head material being equal anyday. :eek: :D
|
Re: aluminum heads vs. iron and compression
Well I knew there was a difference in Iron and aluminium but could never put my finger on what it was.
So there is a combustion chamber comperssion tempture difference theory it looks like. To me it makes a lot of sence. Al counducts heat 6X better than Iron and if the compression charge is the same volume but the temp is different (lets say cooler) your pressure will be lower. Well that gave me some thing to think about to day. The comperssoin ratio is cylinder volume @ BDC / cylinder volume @ TDC If you have 64cc Iron heads with say 2.02 and 1.60 tuliped valves then replaced them with 64cc aluminium heads with the same head gasket and valves and keep the same type of spark plug your compression raito will stay the same but the engine will now run a little different now. I knew that an engine would run a little different (usaly better) after a Al head swap but never realy knew why. |
Re: aluminum heads vs. iron and compression
If you built an iron head 10:1 engine that experiences detonation with 92 octane, switching to aluminum heads with the same size combustion chamber will probably eliminate the detonation. The fuel detonation would react like the engine was only 9:1 so you could run a higher compression ratio with less octane using an aluminum head.
|
Re: aluminum heads vs. iron and compression
Originally Posted by Stephen 87 IROC
If you built an iron head 10:1 engine that experiences detonation with 92 octane, switching to aluminum heads with the same size combustion chamber will probably eliminate the detonation. The fuel detonation would react like the engine was only 9:1 so you could run a higher compression ratio with less octane using an aluminum head.
In another case: What if you have two identical engines (like above) one having aluminum and the other having iron heads(identical except for material), and you can change the compression ratio/timing curves to get both engines to run at max performance, right at the edge of detonating? What engine could you get more performance out of? Ignoring flame propagation problems etc caused by altering the compresion ratio with a dome. My one semester of thermo tells me that you would want the iron so you could keep as much heat as possible in the chamber. What am I missing? Dustin |
Re: aluminum heads vs. iron and compression
At the same CR, assuming no detonation, iron heads do make a little more power. You can coat the chambers of Al heads with a thermal barrier though and get the best of both worlds.
Rich |
Re: aluminum heads vs. iron and compression
Originally Posted by rskrause
You can coat the chambers of Al heads with a thermal barrier though and get the best of both worlds.
Rich I love modern chemistry! :D |
Re: aluminum heads vs. iron and compression
I heard that the iron head flows a little better...
Anybody know if there is any truth to this? |
Re: aluminum heads vs. iron and compression
Originally Posted by viperkiller210
I heard that the iron head flows a little better...
Anybody know if there is any truth to this? Rich |
Re: aluminum heads vs. iron and compression
yep. In practise the big advantage of aluminum is:
a) the weight savings over the front of the car b) the ease of machining/porting aluminum over iron c) the huge aftermarket possibilities with aluminum heads (almost none in iron). |
Re: aluminum heads vs. iron and compression
d) it is a LOT easier to "fix" aluminum heads than iron heads.
Personally, I'll give up that very small power difference for the weight! |
Re: aluminum heads vs. iron and compression
:cool: DITTO :cool:
|
Re: aluminum heads vs. iron and compression
Higher compression is all ways good if you can run it.
|
Re: aluminum heads vs. iron and compression
The actual compression ratio is relevant at best. It is the actual amount of 'push' exerted on the piston crown that is what is important. That is what the discussion, in this thread is about. It doesn't matter that the engine CR is 20 to 1. If 90% of that (potential) energy is absorbed into surrounding surfaces (and subsequently into oil and coolant), the engine will not be very efficient.
|
All times are GMT -5. The time now is 09:53 AM. |
© 2024 MH Sub I, LLC dba Internet Brands