Quote:
Originally Posted by oldman
you might want to invest in some sort of desktop dyno software instead of just trying cams. I'd make sure the software can take altitude adjustments:
https://www.enginelabs.com/engine-te...t-to-the-test/
https://www.motionsoftware.com/Dynomation6.htm
It is NOT unusual for large cams to have flow drops or sags in the mid range. Probably more pronounced because altitude is effectively making the engine 10% smaller and the port size significantly bigger. Also sure 112 LSA and large exhaust duration offer "free" midrange power by trading idle quality of a large tug of exhaust velocity on overlap. But this is at standard pressure, you are getting far less air into the cylinder and thus the exit velocity of the gas is low, the extra exhaust duration combined with the 112 LSA is going to cause exhaust reversion (can prove that via software). Close to single pattern cam could have been tried with a 112 LSA. 226 / 230. Basically you have too little air velocity in the mid range and FAR too little exhaust velocity and what in theory should be giving you a strong mid range (112 LSA and an extended exhaust duration), is giving you the exact opposite, too little exhaust tug (the negative pressure area of the exhaust column of burned gas that is going out the exhaust at the same time the intake is open, aka overlap) combined with too little intake velocity. IMO and I probably let you down, I would caution any use of extended exhaust duration and this GPI it is HUGE on an engine at altitude unless sims were run on cam software. For example the GPI cam has 8 degrees more exhaust duration compared to a nearly identical Cam Motion cam. IMO even at sea level the CM cam makes more sense. At elevation I'd whack another 4 to 8 degrees off the CM design.
https://cammotion.com/gen-5-lt-camsh...226-238-113-3/
your original TSP cam:
Cam Specs: 235/239, .645"/.635", 116 LSA
Just an eyeball look tells me the GW cam opens the exhaust far earlier that the TSP cam. This is only going to sag the midrange flow. The suggesting was to hack 10 degrees off intake and exhaust. Not hack 10 degrees off the intake and add it to the exhaust on an engine that is already intake flow limited (due to altitude). TSP cam 3.5 degrees before TDC... GW cam 11 degrees before TDC.
TSP stage one is 227/231 on 116 LSA so GW cam is just way out there on the exhaust duration. |
You may be right, though I have a hard time believing being 2700FT elevation could change this much engine behavior... We are not talking about 10% more like 7%...
This is clearly not what we can call high elevation by any means...
This whole stutt pisses me off so big that I'm considering buying an LT4