Quote:
Originally Posted by blykins
Well, I disagree about the cam timing "games" and about the bore determining the ballpark the engine would be in. I'm also curious as to what lab engine was used, that allowed a difference in stroke by 2" increments.
I play the cam timing game on every engine, not necessarily trying to move hp/tq curves around, but trying to clean up the bottom end manners on street engines. Advancing cam timing helps attain a clean idle, more vacuum, better throttle response, etc, etc. Even on heads that flow over 400cfm, I play that game...
As for the bore determining the ballpark, we have to watch what generalities we use. Remember, the Cup guys are making 900 hp with a 4.125" bore. That is very small compared to the 4.360-4.600 bores of a factory and aftermarket 460 block, and extremely small compared to the Mountain Motor bores.
However, XB, what he said really doesn't help your mission statement. His last sentence is true, especially about spinning it faster and getting less torque. That's what happens....the higher the hp peak goes, the less torque and usable power you get. Adding displacement and stroke helps that because it makes the torque curve broader at lower rpms. Taking away stroke makes the engine very peaky and you get nothing down low.
We were discussing the VTEC engines the other day.....remember that those engines are zippy, but the transaxles also have 4.4:1 final drive ratios and overdrive gears.
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Bill the lab engine was a single cylinder, designed for experimental work like this. I believe it was a flat head design. The professor that wrote the book I am referring to had formulas for calculating power and fuel consumption for every type of internal combustion engine know to man. Radial air craft, turbine, diesel, 2 strokes, and even two pistons running in the same bore. It was interesting.
I do not 100% believe everything that was written. The book was written 60 years ago and a lot of things have be invented and learned since then. However a lot of the fundamental theory has not changed. I played with desk top dyno programs for hours testing this guys theory and they all seemed to prove out. Granted that is not a real engine, and my running computer simulations does not match up to your real world experience. Truthfully I believe you have given great advise here, and I would personally go for more stroke and less rpm.
The guy is set on building a short stroke engine, so I gave him the information I have that might help him.
Some personal observations over the years. I have seen some 289 Ford and 283 Chevy engines eat big blocks alive back in the day. There street manors sucked. In the early seventies we could stroke a 400 sb Cchevy to around 460 cid. Nobody (bar a few mega dollar race teams) could figure a way to get them to breath. It was a waste of money, and we were de-stroking them with a 350 crank and rods.
Today there are great heads everywhere, and strokers are the rage. Before there were good flowing heads, it was a waste of time.
As far as the cam game goes, look at the duration and lift that Sean Highland (hope I spelled that right) wrote in his book on the 4.6 ltr Ford. I think he was under 230 duration at 0.050 lift and a max lift of 0.480" at the valve. With ported 4 valve per cylinder heads, he was making good low end torque and peaking the Hp over 7000 rpm, normally aspirated. This is proof enough for me that you don't need to go radical on the cam if the head flows good. Granted a two valve per cylinder head will likely never compete with the 4 valve per cylinder heads.