Engineering student tinkering. (Long post)
11-22-2015, 11:31 PM
#1
Teching In
Thread Starter
Join Date: Mar 2010
Location: Socorro, New Mexico
Posts: 40
Likes: 0
Received 0 Likes
on
0 Posts
Engineering student tinkering. (Long post) I'll cut to the chase. Has anybody managed to make an excel sheet that can be used to estimate the results of a given head/cam/bore/rod/stroke combination? I think I got something going here, so I don't have to shell out for software that gives me black-box information.
Here's what I did.
I made an excel sheet for my Machine Design class last semester to find the load of a rod bolt, but I've since modified it to give me piston speed, instantaneous potential CFM demand, and a few other bits and bobs that I can integrate.
Check this out.
4.125" bore, 4" stroke, 6.077" rod 1.163" piston, 9.24" deck.
I assume that I lose 50 degrees of camshaft duration before I get to meaningful valve lift for the upper RPM limit.
For a camshaft, I assumed that if I close 41abdc and open 7btdc. 228, .551" lift. On a 330 CFM cathedral head, that build is supposed to run out of swept air at about 5500 rpm, and then the 10% of chamber volume to scavenge becomes a variable, but the motor should drop torque from that point, and the power peak should be near 6000, definitely flat at 6600. For my 7 degree overlap, I need like 800 CFM at 1 psi to scavenge it. So basically, it's hard to really wing the power out of this thing. We actually want lots of overlap.
As for power figures, the 41abdc says I get 91% of my 427 plus whatever I can scavenge from the combustion chamber, so I should make upper 400's for torque at 1200RPM, and then up a ways at say 3K, 500 Ft Lbs, up to potentially 553 foot pounds at 5500 rpm, 579 hp. If I can't get the big V.E. and don't make it past 100%, 502 foot pounds is a good goal. If I can scavenge that motor, but just not at that speed, then the torque peak lands wherever the hell my headers and intake make it land, with whatever pressure differential I can get. Probably like 4.5K
On a bigger engine, (put this port and valve on a different chamber so it aims into the bore properly.), say 4.5" stroke, 4.5" bore, 6.7" rod, if combustion works, she's out of V.E. at 4100. Out of scavenge at 4500, out of air at 5000. Conversely if I use a 254 cam, I run out of valve closing event. So, I open it at 14btdc and close at 67 abdc. I get 76% volume loss, and keep 10% in the chamber (86% v.e.), so she should make under 580 foot pounds down near 3K. I'll be nice and give it 6% points more as benefit of the doubt for low-lift flow tricks. 92% v.e. 616 foot pounds. Since my 572 thinks it's a 491, it should rev up like a 491 does, so I multiply my 4800 by 572/491 and she should actually spin to 5600 to make that power, but with the crappy torque of 580. 618hp. But with the 228 cam and the right intake/exhaust, it should make 750 foot pounds. I think that would be more fun than the 620hp build.
On a small engine, like a 360 cube 4.125" bore. 3.375" stroke, 6" rod, 8.85 deck, Excel says 7500 RPM out of air, but my (572/491) scalar says I need to spin it more to get there, and the number is 8800, and then whatever % i'm nutty enough to wing on those valve springs. (the 428 looked like a turkey, but this thing is even more odd.)
Here's what I did.
I made an excel sheet for my Machine Design class last semester to find the load of a rod bolt, but I've since modified it to give me piston speed, instantaneous potential CFM demand, and a few other bits and bobs that I can integrate.
Check this out.
4.125" bore, 4" stroke, 6.077" rod 1.163" piston, 9.24" deck.
I assume that I lose 50 degrees of camshaft duration before I get to meaningful valve lift for the upper RPM limit.
For a camshaft, I assumed that if I close 41abdc and open 7btdc. 228, .551" lift. On a 330 CFM cathedral head, that build is supposed to run out of swept air at about 5500 rpm, and then the 10% of chamber volume to scavenge becomes a variable, but the motor should drop torque from that point, and the power peak should be near 6000, definitely flat at 6600. For my 7 degree overlap, I need like 800 CFM at 1 psi to scavenge it. So basically, it's hard to really wing the power out of this thing. We actually want lots of overlap.
As for power figures, the 41abdc says I get 91% of my 427 plus whatever I can scavenge from the combustion chamber, so I should make upper 400's for torque at 1200RPM, and then up a ways at say 3K, 500 Ft Lbs, up to potentially 553 foot pounds at 5500 rpm, 579 hp. If I can't get the big V.E. and don't make it past 100%, 502 foot pounds is a good goal. If I can scavenge that motor, but just not at that speed, then the torque peak lands wherever the hell my headers and intake make it land, with whatever pressure differential I can get. Probably like 4.5K
On a bigger engine, (put this port and valve on a different chamber so it aims into the bore properly.), say 4.5" stroke, 4.5" bore, 6.7" rod, if combustion works, she's out of V.E. at 4100. Out of scavenge at 4500, out of air at 5000. Conversely if I use a 254 cam, I run out of valve closing event. So, I open it at 14btdc and close at 67 abdc. I get 76% volume loss, and keep 10% in the chamber (86% v.e.), so she should make under 580 foot pounds down near 3K. I'll be nice and give it 6% points more as benefit of the doubt for low-lift flow tricks. 92% v.e. 616 foot pounds. Since my 572 thinks it's a 491, it should rev up like a 491 does, so I multiply my 4800 by 572/491 and she should actually spin to 5600 to make that power, but with the crappy torque of 580. 618hp. But with the 228 cam and the right intake/exhaust, it should make 750 foot pounds. I think that would be more fun than the 620hp build.
On a small engine, like a 360 cube 4.125" bore. 3.375" stroke, 6" rod, 8.85 deck, Excel says 7500 RPM out of air, but my (572/491) scalar says I need to spin it more to get there, and the number is 8800, and then whatever % i'm nutty enough to wing on those valve springs. (the 428 looked like a turkey, but this thing is even more odd.)
11-23-2015, 01:34 PM
#3
Teching In
Thread Starter
Join Date: Mar 2010
Location: Socorro, New Mexico
Posts: 40
Likes: 0
Received 0 Likes
on
0 Posts
Very true.
Have you built any engines and modeled your dyno chart (using DCR data from another known build) before you pull the dollar trigger on it?
Here, I'm missing the pressure differential and the valve closing curve. So i only get idle behavior and peak hp rpm.
It's a crap shoot because we need valve events to make headers. They really need to be matched.
Have you built any engines and modeled your dyno chart (using DCR data from another known build) before you pull the dollar trigger on it?
Here, I'm missing the pressure differential and the valve closing curve. So i only get idle behavior and peak hp rpm.
It's a crap shoot because we need valve events to make headers. They really need to be matched.
01-02-2016, 01:13 PM
#4
Staging Lane
I assume that I lose 50 degrees of camshaft duration before I get to meaningful valve lift for the upper RPM limit.
I think the effective duration is closer to nominal - 30 degrees or so for a fast ramp.
Instantaneous CFM (I assume based on piston position and velocity) is a bit too sensitive to plenum buffering (volume, X-section area, and distance to the throttle) to be really useful.
I think the effective duration is closer to nominal - 30 degrees or so for a fast ramp.
Instantaneous CFM (I assume based on piston position and velocity) is a bit too sensitive to plenum buffering (volume, X-section area, and distance to the throttle) to be really useful.