Driveability: Patriot Heads 59cc vs 64cc
09-07-2007, 08:04 AM
#23
TECH Senior Member
iTrader: (23)
Join Date: Aug 2005
Location: Watertown, NY
Posts: 8,797
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by aero_ub
A lot of people seem to be missing the fact or not understanding that your static compression ratio due to running 59cc heads doesn't mean much at all when determining if you can run them on 91 or 93 octane. You could have an engine with a 12:1 static CR that runs fine on 91 and another with a 10.5:1 static CR that needs race gas to not get detonation (you get the idea). What matters is your Dynamic CR. That is determined by when your intake valve closes on the compression stroke (degrees ABDC) and that is determined by your cam. The cam is what’s important here.
So, how many people here running the 59cc heads actually calculated or know what their dynamic compression ratio is with their specific cam? Where is your DCR and what octane are you running?
My issue right now with making my H/C selection and calcs is that I do not really know at what DCR does running on 93 octane because an issue? What is a reasonably safe DCR to run on an LS1? I know that once you get in the area 8.5:1 and up you better start paying attention. But, there are many aspects of an engine/head design that effect and determine when you are going to get into a dangerous area.
aero
So, how many people here running the 59cc heads actually calculated or know what their dynamic compression ratio is with their specific cam? Where is your DCR and what octane are you running?
My issue right now with making my H/C selection and calcs is that I do not really know at what DCR does running on 93 octane because an issue? What is a reasonably safe DCR to run on an LS1? I know that once you get in the area 8.5:1 and up you better start paying attention. But, there are many aspects of an engine/head design that effect and determine when you are going to get into a dangerous area.
aero
09-07-2007, 04:30 PM
#24
Originally Posted by brad8266
You aer 100% correct on that, DCR is what really matters. Mines around 8.7-8.8 DCR. I would imagine that a stock cam in an LS1 matched with some 59cc heads is going to make a lot of DCR. Im too lazy to run the numbers right now though.
For a daily driver, with variable qualities of fuel, I'd leave well enough alone at that. Keep in mind, this is installed at a 115* ICL; advanced two degrees brings that up to 8.73 DCR. Many Comp cams are ground advanced 4 degrees, which would likely put you over the limits of 93 octane at 8.86 DCR.
aero_ub - general rule of thumb is to get your DCR up to 8.5 for best power and throttle response through the mid-range. 8.5 to 8.7 is a safe acceptable range for 93 octane fuel without major attention to detail in engine assembly and tuning. To squeeze more than 8.7 out of 93, you need the tightest quench you can safely run (.034 - .030) without risking a piston rocking into the deck surface of the head. An excellent drivability tune with emphasis on spark timing and AFR in high load, low rpm areas is critical.
Keep in mind, this is specific to the LS1. I wouldn't advise anyone try that with a larger bore or lazy combustion chamber, such as 400 gen1 SBC or any BBC.
09-07-2007, 06:46 PM
#25
Staging Lane
Thread Starter
Join Date: Oct 2006
Location: Bradford, Canada
Posts: 96
Likes: 0
Received 0 Likes
on
0 Posts
Originally Posted by hammertime
The 212/218 .558/.563 115* LSA cam yields a rather high 8.08 DCR with stock LS1 chambers and stock MLS .053 thick gaskets. Just dropping down to a .040 thick gasket bumps that to an 8.31 DCR. Further reducing the chambers to a 64cc LS6 style head give an 8.59 DCR.
For a daily driver, with variable qualities of fuel, I'd leave well enough alone at that. Keep in mind, this is installed at a 115* ICL; advanced two degrees brings that up to 8.73 DCR. Many Comp cams are ground advanced 4 degrees, which would likely put you over the limits of 93 octane at 8.86 DCR.
aero_ub - general rule of thumb is to get your DCR up to 8.5 for best power and throttle response through the mid-range. 8.5 to 8.7 is a safe acceptable range for 93 octane fuel without major attention to detail in engine assembly and tuning. To squeeze more than 8.7 out of 93, you need the tightest quench you can safely run (.034 - .030) without risking a piston rocking into the deck surface of the head. An excellent drivability tune with emphasis on spark timing and AFR in high load, low rpm areas is critical.
Keep in mind, this is specific to the LS1. I wouldn't advise anyone try that with a larger bore or lazy combustion chamber, such as 400 gen1 SBC or any BBC.
For a daily driver, with variable qualities of fuel, I'd leave well enough alone at that. Keep in mind, this is installed at a 115* ICL; advanced two degrees brings that up to 8.73 DCR. Many Comp cams are ground advanced 4 degrees, which would likely put you over the limits of 93 octane at 8.86 DCR.
aero_ub - general rule of thumb is to get your DCR up to 8.5 for best power and throttle response through the mid-range. 8.5 to 8.7 is a safe acceptable range for 93 octane fuel without major attention to detail in engine assembly and tuning. To squeeze more than 8.7 out of 93, you need the tightest quench you can safely run (.034 - .030) without risking a piston rocking into the deck surface of the head. An excellent drivability tune with emphasis on spark timing and AFR in high load, low rpm areas is critical.
Keep in mind, this is specific to the LS1. I wouldn't advise anyone try that with a larger bore or lazy combustion chamber, such as 400 gen1 SBC or any BBC.
