GARY C wrote: ↑Sun Apr 22, 2018 1:24 am
mtmvette wrote: ↑Sun Apr 22, 2018 12:50 am
Ok. Most guys here build for horsepower...wherever the torque ends up so be it. I'm building kind of the opposite. Thinking my horsepower will be in the mid 300s. gnicholson, carnut1, and B original are on the right track for my build.
Compression is not your friend on a low rpm high torque build, especially with the crap gas available. Lower compression and correct timing events will yield big torque numbers in low rpms. As compression increases, the power will increase in a higher rpm band. The engine masters challenge is not a good example of what I am trying to accomplish. I guess there is not to many people trying to make this type of engine.
Thats completely opposite... If that was so then a diesel engine would not make massive tq at low rpm and 20:1 compression.
True the fuel has to be factored in but 10:5.1 can be done with careful planing and tuning on 87 octane.
Gary obviously understands the dynamics behind compression motors. It's all about cylinder pressure and more of it makes more torque EVERYWHERE. Makes a smaller motor feel bigger due to a fatter torque bands that start earlier than and easily surpass a comparable 9:1 motor. And more importantly, can be achieved at LOWER throttle angles which means LESS engine loading and faster rpm potential needed to get the same job done. So, in that sense you need LESS throttle to accelerate the engine which reduces engine throttle/loading requirements and IMPROVES part throttle detonation resistance. Instead of using 4/10's of the motors available power to get moving.. you only need use 3/10's of a motor generating more torque at similar or reduced throttle angles. Induction velocities and carb signals are also improved with added compression. Street engines need part throttle driveability and torque output.. not everything needs to be about WOT power and tendencies for detonation.
To the compression naysayers, it appears that you don't like to push boundaries or maybe even fully realize what gains you're missing out on. Adding compression is not all about PEAK gains.. but much more about AVERAGE gains throughout the entire operating range. And many posting here sound like they're still stuck in the 80's. Probably still using the near factory recommended high single - low teens base timing figures too? And maybe ported vacuum sources for the distributors vac advance pot? Those were some dismal days for the performance oriented street engine builds.
Even a tow truck motor could and should be considered a performance oriented build with what it has to deal with. I remember many shops doing my machine work warning about going over 9-9.5:1 SCR on 87 octane when I'd end up around 10.75:1 with iron heads.
Another thought. Look at the timing maps on some of the EFI engines these days, yes.. those in trucks too, as they approach near 50° and beyond part throttle/light cruise timing advance. It's not the computer or EFI itself that makes that possible, all engines of somewhat similar designs can do the same thing based on the very similar combustion dynamics, they only allow the process to be automated and give failsafes for people who know nothing about motors and/or how to tune them and/or care to maintain them correctly. And even then.. EFI tuning is very big business because the OEM's still leave much on the table.
Just a little sad some guys will only take input from those who they want to believe since this seed has already been so deeply rooted. Seems all these "need low compression for pulling loads" notions have obviously been heavily preconceived. On the other hand, nothing wrong with adding safety margins that'll run even if you literally piss in the fuel tank. You'll definitely have plenty of safety margin left over with a 9:1 motor build.
