Max Compression for Street/Strip Use
- Thread starter Bayrunner
- Start date
Any fancy electronics? EFI w/ o2 and knock sensor? Ignition box with easily adjustable timing and maybe a knock sensor?
'68falconohio
Well-known member
Aluminum or cast iron cylinder head?
We can get 110 octane leaded or 100 octane un-leaded fuel out of the pumps here, but it's only ~$7/gallon.
We can get 110 octane leaded or 100 octane un-leaded fuel out of the pumps here, but it's only ~$7/gallon.
Im sure not an expert on high end builds but with some smoothing in the head and with efi and its knock sensing and timing control shouldn't he be able to be closer to 11? Or is the head design just that crappy?
Howdy Back:
TJH- the combustion chamber shape is not too bad. The miss-match of the chamber wedge and the piston dish is unfortunate, but still not too bad. The small diameter bore also helps to minimize knock. The problems are more likely due to the short stroke design, high cylinder pressures and designed to run at low rpms (lugging). Yes, smoothing and rounding any sharp edges in the chambers will help by eliminating hot spots and minimizing carbon build up, both of which can cause pre-ignition. EFI doesn't sound like an option(?) but a computerized knock sensor and timing control would help to deal with higher CR. However, the gain of another point of CR would hardly be worth the effort and expense. Getting to a zero deck height will also help with quench which will minimize spontanious combustion- another cause of knock.
IF we're talking an alloy head here, that is another plus factor for a little higher CR. I guess Bayrunner needs to specify the details of this build.
Adios, David
TJH- the combustion chamber shape is not too bad. The miss-match of the chamber wedge and the piston dish is unfortunate, but still not too bad. The small diameter bore also helps to minimize knock. The problems are more likely due to the short stroke design, high cylinder pressures and designed to run at low rpms (lugging). Yes, smoothing and rounding any sharp edges in the chambers will help by eliminating hot spots and minimizing carbon build up, both of which can cause pre-ignition. EFI doesn't sound like an option(?) but a computerized knock sensor and timing control would help to deal with higher CR. However, the gain of another point of CR would hardly be worth the effort and expense. Getting to a zero deck height will also help with quench which will minimize spontanious combustion- another cause of knock.
IF we're talking an alloy head here, that is another plus factor for a little higher CR. I guess Bayrunner needs to specify the details of this build.
Adios, David
'68falconohio
Well-known member
And running on the ragged edge as far as what octane is available could be a bad thing if you plan on driving it often without opening it up, right? The carbon build up bumps the CR up over time.
Many modern engines do it all the time. Sounds like thats what he is building. Guess we will await the details.
hi all, i have run this cam (crow 14650) with 11.0:1 comp and it was fine on OZ 98 octane fuel which is 92.5 octane in the US.. the alloy head helps as does the zero deck hight. i even had the std 36 degrees of total advance for some time but i now make more power with only 32-34 degrees all in at 3000rpm.. carbon build up is common in cars which run a bit rich from factory but a well tuned carby with a good inlet like the aussiespeed will almost have no carbon build up over a long period of time. the quench area in the AU x-flow head works very well with the dish on the piston of the 200-250 motor due to equal areas around the chamber being the same as the highest part of the piston edge. i have done dyno runs and removed the head to see the flame paterns and there was no pre or secondary detonation when using the correct deck hight.. the head that George is using has no bad chamber (hot) edges and i have also built a motor with 11.6:1 comp which runs on AU 98 octane and booster and makes 365hp@6000rpm. i will be working on a 400hp x-flow soon with 12:1 comp but i havent worked out the dynamic comp yet.. cheers
Bayrunner
Well-known member
Glen, yes on my Xflow. 10.5-7:1 will be the mark as we previously talked about.
Originally, this post was a general consensus Question to get an idea where people felt a comfort zone. Most of my cars had or run 10:25 and up. They all have aluminum heads of some sort and the tune is key as Glen mentioned. On this build, fellas, I have good advise. I was even thinking of another build as a strip setup increasing to 11.5:1 using an alternate Xflow head. We will see. I would like to get this one up and running first.
Cheers
Originally, this post was a general consensus Question to get an idea where people felt a comfort zone. Most of my cars had or run 10:25 and up. They all have aluminum heads of some sort and the tune is key as Glen mentioned. On this build, fellas, I have good advise. I was even thinking of another build as a strip setup increasing to 11.5:1 using an alternate Xflow head. We will see. I would like to get this one up and running first.
Cheers
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