How Much Compression on Low Octane?
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Ahh Now your build is making much more sense to me.
The air pressure at 4000 ft is 40% less than at sea level.
That makes a much different build.
And changes your CR & your DCR needs.
That's why your DCR can be so high! And "off" the chart.
Some of us (like me) live at sea level in the hot & humid east coast.
That's a whole different build too.
And that's why sea level builds run so poorly at altitude, they are gasping for breath!
The air pressure at 4000 ft is 40% less than at sea level.
That makes a much different build.
And changes your CR & your DCR needs.
That's why your DCR can be so high! And "off" the chart.
Some of us (like me) live at sea level in the hot & humid east coast.
That's a whole different build too.
And that's why sea level builds run so poorly at altitude, they are gasping for breath!
still over 200 psi on a compression check.
Old Pro Solo Guy
Joined: Dec 2017
Posts: 8,082
Likes: 4,431
From: Marlton NJ
Yes you are correct there and I made a mistake.
Got tripped up by a metric data table in meters. Oops.
I still stand by the fact that the higher altitude is the only thing that allows you to run a DCR that high and tolerate regular gas.
Most of us do not have that luxury.
Try your car at sea level and I will bet it will need premium.
Got tripped up by a metric data table in meters. Oops.
I still stand by the fact that the higher altitude is the only thing that allows you to run a DCR that high and tolerate regular gas.
Most of us do not have that luxury.
Try your car at sea level and I will bet it will need premium.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Yes you are correct there and I made a mistake.
Got tripped up by a metric data table in meters. Oops.
I still stand by the fact that the higher altitude is the only thing that allows you to run a DCR that high and tolerate regular gas.
Most of us do not have that luxury.
Try your car at sea level and I will bet it will need premium.
Got tripped up by a metric data table in meters. Oops.
I still stand by the fact that the higher altitude is the only thing that allows you to run a DCR that high and tolerate regular gas.
Most of us do not have that luxury.
Try your car at sea level and I will bet it will need premium.
The altitude compensated DCR accounts for the loss of air density giving you a lower effective DCR despite the actual mathematic DCR. The 7.99 accounts for loss of air density.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
I'm looking at the AFR 180 and Pro-Filer 185 heads.
I ordered a Scat stroker rotating assembly with D-dish pistons.
I'm evaluating cams now, intake closing will probably determine which head I go with for combustion chamber size.
If I can't find one close enough I'll consider milling a head.
I ordered a Scat stroker rotating assembly with D-dish pistons.
I'm evaluating cams now, intake closing will probably determine which head I go with for combustion chamber size.
If I can't find one close enough I'll consider milling a head.
I, of course, am a bit biased on head choice. I do know that the cnc'd heads from AFR will be exactly 180cc not something bigger. Also the chamber will be as advertised and not bigger. The valves use smaller stems for less moving mass and the springs are pac springs. All told a decent package.
I would determine CR then get the cam to match that and get the DCR you want in this scenario.
where is it going to be most of the time? Build it for that.
You could get a cam with more overlap/duration and then put in a higher stall torque converter to get you into the meat of the torque when you need acceleration.
below peak torque or near it is most likely for detonation. Above peak torque less likely as less time is available for it to occur and peak pressure has already been reached.
You don't have to tear up your hood to get CAI. The L82 system is a good option, ugly to me, but effective.
