Quote:
Originally Posted by 1795
If you do not decide to replace your oil cooler, then minimally you need to flush the oil cooler and lines with some solvent and then run some fresh oil through them to make sure that there are no metal particles still in the system. Flush until you see very little oil in the solvent and then with fresh oil and run that through until it is as clear as it was going in.
I have a question regarding compression ratio and iron heads. A couple of people have said that they would cap CR with iron heads at around 10:1 and that you can go higher with aluminum heads. I recognize that for the most part modern aluminum heads flow better than standard iron heads. However, there are iron heads that flow better than standard iron heads. Is it the potential flow or the material that contributes to this thought?
My first car was a 1974 Buick with a 340 in it that had 11.25:1 compression with iron heads. My 289 race engine has 12.7:1 compression with iron heads, in fact unless aluminum heads were used on a race car when it was raced originally, all vintage race cars must run iron heads. There are people in vintage racing running up to 14:1 CR with iron heads. Of course, we are running on higher octane gas (110-112), but fuel does not seem to be the issue.
Looking forward to some education here. Thanks.
Jim |
Fuel is the issue. Today's pump gas, at 92-93 octane, auto-ignites at a much lower temperature than the high octane race gasoline. In fact if it was not for the fuel going through a phase change (liquid to a gas - latent heat of evaporation) and cooling the air charge, gasoline would auto-ignite at 10:1 compression. This is the main reason why we take the AFR from 14.7:1 down to 12.5:1 at WOT. We are using the extra fuel, that we cannot burn, to cool the air charge and prevent detonation. The un-burned fuel is also making some extra pressure, as it expands from the heat. Kinda like making steam pressure with fuel. From a detonation point of view, gasoline is a poor fuel choice, but other merits make it the top choice used.
The head material is what matters, not the flow. Aluminum conducts heat much better than cast iron (About 4 times better, if memory serves). Therefore aluminum is much less likely to have a hot spot, and it can transfer heat to the water much better, thus its surface in the combustion chamber is cooler. Additionally aluminum can be machined easier and have a smoother surface. Way less potential to have a spot hot enough to act like a glow plug, and the combustion chamber runs cooler. This make aluminum capable of running higher compression, with gasoline.
Now the flip side is that conducting heat from the combustion chamber to the water is an energy transfer, therefore less power and efficiency. A trade off that is well worth the price.