Compression ratio

[justin]

what about the new corvette c6 that runs 11:5, or the 2007 ferrari 599gtb fiorano running 11:2:1 and the 2007 lamborghini murcielago that is running 11:0:1? you can still run pump gas.

 

[Jac Mac]

what about the new corvette c6 that runs 11:5, or the 2007 ferrari 599gtb fiorano running 11:2:1 and the 2007 lamborghini murcielago that is running 11:0:1? you can still run pump gas.

Yes & all have smaller dia cyls, centrally located spark plugs, evenly disposed squish/quench areas and a computer that will taylor the fuel ignition etc to what the engine needs or can stand at any given time, unlike the average pushrod 4"+ bore V8 with 2 valves per cyl, plug, squish areas in whatever space is left.

Jac Mac

 

[justin]

Yes & all have smaller dia cyls, centrally located spark plugs, evenly disposed squish/quench areas and a computer that will taylor the fuel ignition etc to what the engine needs or can stand at any given time, unlike the average pushrod 4"+ bore V8 with 2 valves per cyl, plug, squish areas in whatever space is left.

Jac Mac

the corvette c6 has a 4.125 bore

 

[CliffBeer]

what about the new corvette c6 that runs 11:5, or the 2007 ferrari 599gtb fiorano running 11:2:1 and the 2007 lamborghini murcielago that is running 11:0:1? you can still run pump gas.

These are vastly different engines that allow for materially higher CR. To put some context to it, the 599 and the murcielago engines are all 4 and 5 valve engines (in contrast to our humble two valve SBFs) which allows for a more even and dense distribution of the fuel and a better burn avoiding premature detonation. Premature detonation is the main reason to back off the CR. Similarly, these engine have sophisticated fuel injection and engine mgmt systems supplying fuel at amazingly high pressures (creating better atomization of fuel), all this having the same effect - allowance for higher CR.

The list of significant differences is lengthy. IMHO you just can't compare a SBF to one of these engines...

 

[Lynn Larsen]

You are starting to see what has been talked about for the last 3 years and is finally hitting the market now: gasoline direct injection (GDI). Mazda is touting this quite heavily now. What is it? In simple terms, it is injection ala a diesel engine. The fuel is injected directly into the cylinder in a precisely timed fashion. With this technique, I believe, preignition/knock will become a thing of the past and much higher compression ratios will be possible.

The $64K question then becomes, will we see any retrofit GDI setups? I wouldn't hold my breath (or delay a build) waiting for it, but there is great promise for extracting more power and, maybe even more worthwhile, more effeciency out of existing engine designs.

Lynn

Wikipedia:GDI

 

[DBLDREW]

Julian,

I side with the flat top guys and I would steer away from hypereutectic. Rather, I would suggest a good set of forged pistons; the few dollars extra will be worth the peace of mind.

I don’t think anybody should really be that concerned about going with a Hypereutectic piston. Now it is true that a forged piston is stronger and as you build more and more hp the Hyper will fail before the Forged, but the thing that you need to remember is that as you are building more power your transaxle will fail long before your Hyper pistons will. If you are planning on building a 600-700hp motor then yes you should drop the extra money for the forged pistons, but if you are going 400-500 then the Hypers will be fine. My car is living proof of that. I have a Mustang that I pulled out the 302 and dropped in a 351 about 13 years ago. The Car has to pass emissions so the combo isn’t that radical, but I did put a 100 hp shot of nitrous on it. The car runs 11.80 and I’m using Keith Black Hypereutectic pistons. I’m on my 3rd tremec trans and the original motor is still running strong! To be honest I’m surprised that the pistons are holding up as well to running nitrous on them but I can’t argue with the results.

 

[Russ Noble]

The hypers get a lot of bad press and apparently are not as tolerant of a faulty tune, particularly on NOS, as forged pieces. But I think DBLDREW is right. When my Rover V8 big bore, big stroke,(for a Rover!) gave up the ghost with severely cracked crank and rods, the KB hypers were still 100%. Although one spiroloc had started to disintegrate which remains a bit of a worry.

I'm sure hypers would be absolutely fine in a road motor. But what price a little more insurance in the form of forged? Also isn't it nicer to be able to impress everyone with forged pistons!

Cheers