Slant 6 Turbo 68Dart Project
There are several things that go into driveability on the street. The main one is camshaft selection. These guys who can't WAIT to get that slant six out of Granny's Duster, so they can swap a 360 into it, are setting themselves up for a lifetime of driveability issues, because the 360 they swap into her 3,300-pound Duster, will very likely spend its life with a camshaft that will give it a rough idle, a high rpm idle, and require a loose torque converter for decent driveability. All of that goes together to make for some not-so-relaxed cruising and poor fuel economy. This camshaft selection will require a rear axle final drive in the low 4's (4.10:1) or deeper (4:56?) or deeper, yet, in order to maximize acceleration at the strip. Then, if you want to make it a hiway cruiser for a trip, or just relaxed freeway cruising, a 3.08 or 3.23-geared center section will be necessary.
This absolutely dictates that you install an 8.75" housing in the car. They don't give those away anymore... for some reason (availability?) they have become unduly expensive.
Slant six cars have an advantage here, in that both Ryan Peterson's turbo car and Tom Wolfe's similar Dart, were tested with a variety of final drive ratios and ended up being quicker and faster using 2.73:1 ring and pinion gears than any other. What that means is, if you have a turbocharged slant six, you have a "one size fits all" final drive situation, which also means, you don't have an use for an expensive 8.75" housing that will accommodate a drop-out center section; you can use a cheap, readily-available 8.25" hiway geared rear end out of a Late '70's Duster, Aspen, or other A Body car. Saves you a ton of cash, there... Maybe enough to buy the upper control arms, spindles and disk brakes to change your front end over to LBP wheels...
Camshaft selection is surely an engine parameter that has a tremendous effect on driveability. Turbo motors of all kinds, don't work well if they are subjected to much overlap. The boost goes out the exhaust valve, which exacerbates the problem of making enough exhaust to spool the turbo effectively. Two avenues of approach are used to prevent this situation (that I am aware of.) Lobe center separation is wider than would be desirable on a naturally-aspirated motor. That minimizes overlap, by itself. It also makes the idle smoother. The other thing that works to make for less overlap is, reducing the amount of time (in degrees of rotation) that the valves are open. Very mild timing is part and parcel of turbo camshafts, for the expressed purpose of minimizing overlap. This smooths the idle further, and makes for an engine with impeccable manners; tons of low end and mid-range torque.
Now, you have an engine that is geared for the road, but still performs well on the drag strip, and idles like your grandmorther's slant six...
There are two other factors that can affect driveabilty, and will...
Spark advance and fuel metering. The subject of spark advance on boosted engines, is far beyond the scope of my understanding; In NO WAY, do I have sufficient knowledge to discuss it, even in a rudimentary way, so, I will leave that to smarter minds... yours, maybe. The only caveat here is, that in order to stay our of harm's (detonation) way, be very conservative with spark advance, keeping it ALWAYS less than 18 degrees if boost is present... even a little.
Fuel curves are vitally important to good driveability, but we have A/F ratio meters to assist us in tuning, but even with their help, it's not easy.... but, time and patience will put it into the realm of possibility. It just take some considerable effort.
The amount of boost present is the difference between a 300, 400 and 500 hp motor; I don't think their driveability would be much different. Just their lifespans... LOL!
My 2-cents... YMMV...:happy1:
Ideally it has to fall into the same spectrum as the current car - be incredibly driveable. If 400hp makes it act badly, then I'll do 300, if 300 is too much of hassle, 250. You know what I mean? This build is for a car that needs to run every single day of its life, even though we have a second car now, I like driving THIS one. This build was never ever meant to be Hemi Destroyer, Ls1 Crusher, etc... it's pure fun in a dependable package. If it makes 300 - cool. Remember my last goal was 200, and I hit that. Now I'm just setting a new one. I may look into some really awesome pistons, but right now I have a basic plan. Keep in mind too I have never ever rebuilt an engine, but I want to do it myself, minus the machine work, which I have no way of doing.
My basic plan is hone the block, and the bearings, etc...020ish over pistons and ring set, a nice functional cam that is maybe more adequate than the stock cam (I still have no idea what that is on turbo, but I am researching these things all the time), I would use the solid lifter head off the current block I have, and maybe try and find some 2.2 (I think it is) connecting rods, to increase the displacement somewhere near 232 or something, then maybe have our machinest dish the pistons a little bit to decrease compression. Right now the head is shaved anywhere from .020 - .040 as far as I can guess just from how many times I've had the head off and previous owners had it off, and the last time .010 came off to get rid of the warp that was in it. I may even do a 4 bbl setup. I also want to simplify my exhaust J pipe, by removing the J-pipe and doing something similar to this:
Credit for that goes to "Thomas S" on the sl6.org site.
:D This turbo setup is nearing 10k miles, and right now I'm still dealing with the block liking to throw rust into the radiator. I was about to buy a brand new Mishimoto radiator for the car (yes they do have one that will fit) but I'm thinking why trash something nice like that with rust and junk flying into it? I don't really know what to do in the interrim, but I'm thinking I'll take this current rad out, shoot 150 psi through it upside down or something and see what happens.
I'm ordering a new Intercooler and coolant reservoir from Mishi. to get the car onto the track. I'm almost in the "lets blow it up" sort of mood, but not quite. I have to continue to stay calm and collected even though this cooling issue is frustrating me right now, and it will be a moment till I can reassemble another slant six. I'm not sure if I can get the other motor for free, but maybe he'll sell it for something reasonable. Shipping would literally be me getting in a forklift, driving 200 feet away, grabbing the motor on the pallet, and driving it back to our shop.
Currently today, I also found 2 of the spark plugs aren't sealing in the tubes, not the spark plug tube seals, but the spark plugs against the tubes. I'm thinking they may need some kind of rubber O-ring or something since the plugs don't have washers on them. I don't know if that would effect anything or not, but oil is just spitting like dog slobber out onto the spark plug wires. Not a lot of oil - but any oil is an annoyance sort of thing.
There's a lot that has to come off it, but he said he only keeps good engines on pallets, bad engines are piled into a corner or in a container, so he has to think about why he has it on a pallet - maybe he intended to use it for something sort of thing.
There are several things that go into driveability on the street. The main one is camshaft selection. These guys who can't WAIT to get that slant six out of Granny's Duster, so they can swap a 360 into it, are setting themselves up for a lifetime of driveability issues, because the 360 they swap into her 3,300-pound Duster, will very likely spend its life with a camshaft that will give it a rough idle, a high rpm idle, and require a loose torque converter for decent driveability. All of that goes together to make for some not-so-relaxed cruising and poor fuel economy. This camshaft selection will require a rear axle final drive in the low 4's (4.10:1) or deeper (4:56?) or deeper, yet, in order to maximize acceleration at the strip. Then, if you want to make it a hiway cruiser for a trip, or just relaxed freeway cruising, a 3.08 or 3.23-geared center section will be necessary.
This absolutely dictates that you install an 8.75" housing in the car. They don't give those away anymore... for some reason (availability?) they have become unduly expensive.
Slant six cars have an advantage here, in that both Ryan Peterson's turbo car and Tom Wolfe's similar Dart, were tested with a variety of final drive ratios and ended up being quicker and faster using 2.73:1 ring and pinion gears than any other. What that means is, if you have a turbocharged slant six, you have a "one size fits all" final drive situation, which also means, you don't have an use for an expensive 8.75" housing that will accommodate a drop-out center section; you can use a cheap, readily-available 8.25" hiway geared rear end out of a Late '70's Duster, Aspen, or other A Body car. Saves you a ton of cash, there... Maybe enough to buy the upper control arms, spindles and disk brakes to change your front end over to LBP wheels...
Camshaft selection is surely an engine parameter that has a tremendous effect on driveability. Turbo motors of all kinds, don't work well if they are subjected to much overlap. The boost goes out the exhaust valve, which exacerbates the problem of making enough exhaust to spool the turbo effectively. Two avenues of approach are used to prevent this situation (that I am aware of.) Lobe center separation is wider than would be desirable on a naturally-aspirated motor. That minimizes overlap, by itself. It also makes the idle smoother. The other thing that works to make for less overlap is, reducing the amount of time (in degrees of rotation) that the valves are open. Very mild timing is part and parcel of turbo camshafts, for the expressed purpose of minimizing overlap. This smooths the idle further, and makes for an engine with impeccable manners; tons of low end and mid-range torque.
Now, you have an engine that is geared for the road, but still performs well on the drag strip, and idles like your grandmorther's slant six...
There are two other factors that can affect driveabilty, and will...
Spark advance and fuel metering. The subject of spark advance on boosted engines, is far beyond the scope of my understanding; In NO WAY, do I have sufficient knowledge to discuss it, even in a rudimentary way, so, I will leave that to smarter minds... yours, maybe. The only caveat here is, that in order to stay our of harm's (detonation) way, be very conservative with spark advance, keeping it ALWAYS less than 18 degrees if boost is present... even a little.
Fuel curves are vitally important to good driveability, but we have A/F ratio meters to assist us in tuning, but even with their help, it's not easy.... but, time and patience will put it into the realm of possibility. It just take some considerable effort.
The amount of boost present is the difference between a 300, 400 and 500 hp motor; I don't think their driveability would be much different. Just their lifespans... LOL!
My 2-cents... YMMV...:happy1: