Math to figure out if your car will run on pump gas.
01-09-2011, 02:33 PM
#21
FormerVendor
I have a question regarding maximum DCR number statements and recommendations. I know a few people who have been racing their stock-cube NA LS1 motors with a DCR of well over 9.5 for well over a year (milled/high-SCR heads). The spark timing has also been advanced over stock, and yet they run fine (and stronger than stock) on 91 octane pump gas. I understand that DCR is important, yet these motors with an abnormally high DCR seem to run fine, and lowering the DCR would not leave them with a performance advantage. They absolutely do run on pump gas. Efficiently? Reliably?? As far as I can tell...
So:
Is DCR for LS motors more important under forced induction applications than NA?
If these motors run just fine on pump gas with a 10.0:1 DCR with proper tuning (even with advanced spark timing over stock), are there new possible high DCR pump gas limits due to advances in engine technology since 1955 when the Gen 1 was introduced??
So:
Is DCR for LS motors more important under forced induction applications than NA?
If these motors run just fine on pump gas with a 10.0:1 DCR with proper tuning (even with advanced spark timing over stock), are there new possible high DCR pump gas limits due to advances in engine technology since 1955 when the Gen 1 was introduced??
Do you have a dyno sheet of one of these 9.5 DCR deals to post??? What's the point of running so much compression if you arent making also much more power and tq from it??? We have some of the fastest and most powerful pump gas engines out there and they don't have really high DCRs at all. Just pretty normal.
01-10-2011, 01:43 PM
#22
With LOW VE you can more easily run higher compression. These engines running super high DCRs are not that great or they would be making huge power and tq increases over normal DCR deals from all that squeeze in reality and I can guess that they are not.
Do you have a dyno sheet of one of these 9.5 DCR deals to post??? What's the point of running so much compression if you arent making also much more power and tq from it??? We have some of the fastest and most powerful pump gas engines out there and they don't have really high DCRs at all. Just pretty normal.
Do you have a dyno sheet of one of these 9.5 DCR deals to post??? What's the point of running so much compression if you arent making also much more power and tq from it??? We have some of the fastest and most powerful pump gas engines out there and they don't have really high DCRs at all. Just pretty normal.
No dyno sheets. The cars did pick up HP/TQ from running higher compression - but not a ton (I can see that above a certain DCR running any higher compression is not a substantial gain). I only ask, because I know people running 9.8:1 or higher DCR on pump gas with advanced timing over stock. The motor I am in the process of building will be at 9.2:1-9.4:1 DCR, with an SCR of around 10.2:1.
Yes I agree about VE (changing my previous comment on efficiency) - but really why I asked is due to how the wording is used and how DCR is commonly referred to, as if a motor will quickly self-destruct if running a DCR higher than X.X on pump gas of X octane. For example:
Math to figure out if your car will run on pump gas.
Race engines, using high octane race gas, can tolerate higher DCR's with 8.8:1 to 9:1 a good DCR to shoot for
Staying below 8.25 DCR is probably best for trouble free motoring.
When contemplating an engine of around 8.4 DCR or higher, measurments are essential, or you could be building another motor.
Last edited by ZexGX; 01-10-2011 at 01:50 PM.
01-10-2011, 06:45 PM
#23
FormerVendor
Yes engines with high VEs cant seem to run as much SCR or DCR is what I am saying in general.
I like analyzing things like DCR as well but some people get carrried away with it meaning more than it does.
I like analyzing things like DCR as well but some people get carrried away with it meaning more than it does.
01-11-2011, 04:45 PM
#24
I used Pat Kelly's calculator when I built my 406 and I'm very happy I did. I had several camshafts in mind and this helped me weed out the ones that "looked good" but weren't actually optimal for my combo.
I built a 10.5:1 static compression, 8.16:1 dynamic, 406 small block with a hydraulic flat tappet camshaft and made 522 hp @6,000 rpm and 514 ft lbs at 4500 rpm on pump gas. I can drive it in stop and go traffic with no issues and it runs 185*.
I built a 10.5:1 static compression, 8.16:1 dynamic, 406 small block with a hydraulic flat tappet camshaft and made 522 hp @6,000 rpm and 514 ft lbs at 4500 rpm on pump gas. I can drive it in stop and go traffic with no issues and it runs 185*.
