whitepunkonnitro
Well-Known Member
Coming to the end of the year..my first year of messing around with a Slant, and I'm still trying to get a basic handle on the characteristics of these engines.
Lots of thought, along with cross breeding ideas from my experience with Fuelers, Stockers and everything in between, has led me to a few conclusions..I figured to share them here, because I know a lot of you are going through the same thing.
The car I'm working with is an extremely lightweight Dart that currently has a "mule" 225, stick and 4:10 gear. Immediate goal was to get it into the 12.90s on motor alone, and then spray it down for some grudge action. Car has a 175 horse plate on it, but so far it has never been turned on.
So, this is what I've learned so far.
The 225 is a bit of a paradoxical engine. Its not a typical drag engine with its under square, long rod ratio bottom end. Before I built this thing, I watched countless videos as well as live passes and always saw the same thing..an engine that was very sluggish on the initial hit, but that would turn on just a few feet out. The automatic cars all sounded like they were in pain.
I thought I could beat that system. After all, anything with a 4.15 inch stroke HAS to make low end torque, right? Just needs to be coaxed out of it.
Wrong.
My initial engine setup..again, just a mule to learn with, consists of a cast crank, stock rods, stock pistons (turned around in their bores), A Comp Cams RV grind and head that has been ported to smooth flow, but not increase port and bowl volume beyond what was necessary to get proper contour. The idea here was to build as much low end velocity as I could, to beat that lack of instant grunt.
The head was shaved .100,and installed with a steel shim gasket.
The intake is an Offy 4 barrel that I reoriented the carb on to face North/South, so that there wouldn't be any questions when it came time to tune the carb. Carb is a 600 AFB that I have set up so it can be run on only the primaries, half secondary and full secondary (I immediately found those options unnecessary..the engine seems to want all it can get)
I did have to jet the carb WAY down to get happy plug readings. Currently it has .098s in the primaries and .081s in the secondaries. (Out of the box was .103/.100). At anything over 3000, its as happy and snappy as any 225 6 banger could possibly be.
Timing is locked out at 34 degrees.
So, initial test hits were all done with a 904, and stock converter.
Right away I knew something was wrong. No matter how I tuned or drove this thing, it was flat out dead at the hit.
Dozens of launches, every conceivable combination of timing, jetting, carb opening, pump shot..dead. I could barely get the converter to stall at 1800..the first five feet, this thing would just ooze out of the hole. After that, hang on! From around 3000 to 5800-6000 its an animal...very happy with the way it runs out.
I considered a few converter options, but ultimately converted the car to stick just to eliminate any of those expensive variables.
So, that is how I cured my issue. First time out, it obliterated the standard issue Slant clutch, and the car is apart right now and getting a HD, B&B, intended for a 273 Commando.
Back to the lack of grunt, and geometrical issues that led to them.
The stock 225 bottom end, under square as it is, and with a 1.8 plus rod ratio and tiny bore, does not have enough rod angularity to generate an effective push off TDC at lower rpm. As crank speed increases, the pressure front at the top of piston begins to better match journal speed as it swings past TDC, and suddenly real torque generation takes place.
Where that long rod ratio and extended dwell time would actually be beneficial to generating torque is the same place where the Slant runs out of cylinder head. Geometricly speaking, the 225 WANTS to be a 7000 plus RPM engine, but getting there is near impossible because of the flow characteristics of its head.
I had considered trying to work with a 170, to better match the size of the ports available, but the situation in terms of rod ratio is just as bad as the 225, and you're giving up 55 cubic inches...and in engines at this scale, that's HUGE!
Right in the middle, you have the 198…and it would be the perfect foundation for a Slant if someone was to produce a cross flow Hemi head and valvetrain that could sustain 10,000 rpm...that ain't happening. The rods are vertical for so long in those engines, making any meaningful torque under 4000 rpm is impossible.
So, there are three choices in stock configuration, and none of them are very well suited to getting a drag car off the starting line with any real anger, but, if we do a little mixing and matching, we might be able to come up with something that will work.
Over the winter, I'll be building what I think will be the most effective combination for one of these things.
I am going to fit a 198 crank into a 170 block. Using the stock length 170 rods, my ratio will be a much more drag friendly 1.56. I also plan on using reverse offset pistons to help that angularity along even more, dropping the effective rod ratio closer to 1.5.
It looks like the crank will fit with just a touch of grinding at the bottom of the bores. I'll post updates on it as I move forward on it.
This could be the magic Slant bullet!
Lots of thought, along with cross breeding ideas from my experience with Fuelers, Stockers and everything in between, has led me to a few conclusions..I figured to share them here, because I know a lot of you are going through the same thing.
The car I'm working with is an extremely lightweight Dart that currently has a "mule" 225, stick and 4:10 gear. Immediate goal was to get it into the 12.90s on motor alone, and then spray it down for some grudge action. Car has a 175 horse plate on it, but so far it has never been turned on.
So, this is what I've learned so far.
The 225 is a bit of a paradoxical engine. Its not a typical drag engine with its under square, long rod ratio bottom end. Before I built this thing, I watched countless videos as well as live passes and always saw the same thing..an engine that was very sluggish on the initial hit, but that would turn on just a few feet out. The automatic cars all sounded like they were in pain.
I thought I could beat that system. After all, anything with a 4.15 inch stroke HAS to make low end torque, right? Just needs to be coaxed out of it.
Wrong.
My initial engine setup..again, just a mule to learn with, consists of a cast crank, stock rods, stock pistons (turned around in their bores), A Comp Cams RV grind and head that has been ported to smooth flow, but not increase port and bowl volume beyond what was necessary to get proper contour. The idea here was to build as much low end velocity as I could, to beat that lack of instant grunt.
The head was shaved .100,and installed with a steel shim gasket.
The intake is an Offy 4 barrel that I reoriented the carb on to face North/South, so that there wouldn't be any questions when it came time to tune the carb. Carb is a 600 AFB that I have set up so it can be run on only the primaries, half secondary and full secondary (I immediately found those options unnecessary..the engine seems to want all it can get)
I did have to jet the carb WAY down to get happy plug readings. Currently it has .098s in the primaries and .081s in the secondaries. (Out of the box was .103/.100). At anything over 3000, its as happy and snappy as any 225 6 banger could possibly be.
Timing is locked out at 34 degrees.
So, initial test hits were all done with a 904, and stock converter.
Right away I knew something was wrong. No matter how I tuned or drove this thing, it was flat out dead at the hit.
Dozens of launches, every conceivable combination of timing, jetting, carb opening, pump shot..dead. I could barely get the converter to stall at 1800..the first five feet, this thing would just ooze out of the hole. After that, hang on! From around 3000 to 5800-6000 its an animal...very happy with the way it runs out.
I considered a few converter options, but ultimately converted the car to stick just to eliminate any of those expensive variables.
So, that is how I cured my issue. First time out, it obliterated the standard issue Slant clutch, and the car is apart right now and getting a HD, B&B, intended for a 273 Commando.
Back to the lack of grunt, and geometrical issues that led to them.
The stock 225 bottom end, under square as it is, and with a 1.8 plus rod ratio and tiny bore, does not have enough rod angularity to generate an effective push off TDC at lower rpm. As crank speed increases, the pressure front at the top of piston begins to better match journal speed as it swings past TDC, and suddenly real torque generation takes place.
Where that long rod ratio and extended dwell time would actually be beneficial to generating torque is the same place where the Slant runs out of cylinder head. Geometricly speaking, the 225 WANTS to be a 7000 plus RPM engine, but getting there is near impossible because of the flow characteristics of its head.
I had considered trying to work with a 170, to better match the size of the ports available, but the situation in terms of rod ratio is just as bad as the 225, and you're giving up 55 cubic inches...and in engines at this scale, that's HUGE!
Right in the middle, you have the 198…and it would be the perfect foundation for a Slant if someone was to produce a cross flow Hemi head and valvetrain that could sustain 10,000 rpm...that ain't happening. The rods are vertical for so long in those engines, making any meaningful torque under 4000 rpm is impossible.
So, there are three choices in stock configuration, and none of them are very well suited to getting a drag car off the starting line with any real anger, but, if we do a little mixing and matching, we might be able to come up with something that will work.
Over the winter, I'll be building what I think will be the most effective combination for one of these things.
I am going to fit a 198 crank into a 170 block. Using the stock length 170 rods, my ratio will be a much more drag friendly 1.56. I also plan on using reverse offset pistons to help that angularity along even more, dropping the effective rod ratio closer to 1.5.
It looks like the crank will fit with just a touch of grinding at the bottom of the bores. I'll post updates on it as I move forward on it.
This could be the magic Slant bullet!
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