Understanding The Slant Six

there's a surprising amount of interest in the slant-6 engine especially considering the fact that it's not a performance motor it was the economy it was the bread and butter you know just get to school get to the store get to work you know commuter engine in its earliest earliest incarnation it was a bit of a performance motor but that kind of changed like almost immediately like it went into production and it was its performance status I've always loved this lamp because of its simplicity its unique its its agricultural it's just reliable its world-known it's it's legendary for its reliability I have been involved in every type of high performance every type of racing there is from street racing to Top Fuel and over the years I've had dozens of slants and I've rebuilt dozens of slants set them up for just driving but I never built a performance one so a couple of years ago we put this together now this engine right here is a mule it's something I put together to learn and what it ended up doing was kicking my ass because I applied everything I could think of that's worked in every type of performance application I've encountered and no matter what I did to this thing it wouldn't respond it would you could actually get out you could fly punch this thing get out and walk alongside of it then come around 2,500 rpm it would just come alive and I couldn't figure out why well after a lot of head-scratching and a lot of studying I mean a lot of studying like I spent probably two months really in the guts of one of these engines I found the answers now the purpose of this video is not to teach you how to build a slant-6 this isn't a tutorial use this cam do this to the head you know we use this exhaust I didn't think there are way too many variables and specific combinations for what you would do to your own car and there's there's lots of that material out there you know lots of step-by-step fold up the ABCD and get 260 horsepower or whatever it happens to be you could find those the purpose of this video is to help you understand the slang sex because the slant sex as a performance engine operates in its own unique environment it is unlike any other engines and the Saba corsets this is an inline 6 it's because of the bore and Stroke relationship the proportioning of everything that's inside the engine so if you take what I'm gonna lay out here and apply it to what you've got going on under your own hood it'll help you decide what parts to use what things and and and we'll go from there so the first things first is we got to look at the history of the engine so if you're really interested in the original engineering and development of the slant there's a lot of good reading out there you can find it on all par and some other sites but what I'll do is I'll just give you a quick rundown the engine was originally designed in it started in 1858 and the purpose was the American car makers wanted to have compact sub compacts to compete with the European cars General Motors was going with the core there and they were following the pattern of the German cars a rear engine your rear mount engine air cooled you know like the Porsche the Volkswagen Chrysler decided to go with the more you know Italian and English makers and they were gonna go with conventional front-engine rear-drive but they wanted a very low hood line and they wanted a very light nimble package so the engine was originally designed as a 170 and that's important now because everything that happened in the history of the slant or the development of the slant right up until they stopped production 87 is all hinged on the fact that the engine is originally designed and outlined for the 170 size now you're gonna remember something in 1958 59 when this thing was on the drawing board we lived in a 50 mile an hour world there were no interstates the average travel speed was 40 50 miles an hour 60 was ripping down the highway these engines were designed to move a 2700 pound car with a manual transmission and a 3 series gear 323 355 down the road at you know 50 miles an hour that's it's happy place and the 170 is perfect for that actually I remember reading in a couple places one in particular where one of the design engineers and this is like another Chrysler engineer from the Golden Age of engineering Chrysler engineering saying that little 170 was the perfect engine and I am going to agree with that the 170 as it was originally laid out is the perfect engine this one here is on our 64 Dart it's a filthy mess but it's also been a continuous service since 1964 as far as I could tell this thing's never going to part it has way over a million miles on it and it keeps chugging on strong it's a 170 a lot of the engines legendary durability comes from this 170 size now the 225 came along as an afterthought it was it was a bean-counter engine so essentially it was a slant six was a clean sweep engine and then at the very last minute they says well you know what as long as we've got a six-cylinder let's use this thing in the midsize cars the full-size of the mid-sized cars and light trucks and so what they did was they added an inch of stroke they went from three point one five inch stroke to a four point one five inch they left the bore size exactly the same in three point four inches and the purpose of that was to have an engine that would have basic torque to get the big load moving and then a super heavy crank shift with a flywheel that'll you know move the thing down the road it'll go up and down the road but it was never intended to be a performance engine there were actually some oiling system from not even oil assist problems there were oil burning problems when they increased the stroke ten inch they're also increased the deck height the engine also I said I had to do some trick things with the Rings to get this thing to seal at the 225 size now the 170 while it's the perfect engine is too small to be used in what we would consider to be a performance application today and there's also the problem of the cylinder head where the 170 has a bottom end that's good to 6500 7,000 rpm the head shuts off at about 5500 and we're gonna get to that in a few minutes but anyway that's where the slang comes from and what we're gonna do is you have three sizes you have a 170 to 198 in the 225 the 170 it's in a place of its own the 198 was a bean-counter engine basically what happened was in 1969 1970 when car started to get a little too heavy to use the 170 is the base the bean-counters wanted a step-up option so they've used with a there was eight they put a short-stroke crank in the 225 block and created the 198 the 198 was just a bean-counter engine nothing good can come from 198 it's the throw away now like I says what they did they did that so that the base car you know you bought it you bought a dart 1970 dart the base engine was a 198 and they could suck an extra 30 or 40 bucks out of your top grade to 225 that's the only reason 198 ever existed so anyway let's look at the bottom end of the 225 and try to get a wrap wrap your head around what makes this engine unique and why it's so hard to build as a performance engine now this is critical this applies to the 225 and it's an abnormality that's inherent in the design on the engine and when I say abnormality what I mean to say is that in the world of cars that burn rubber they're hot rodding drag racing that sort of thing where we're going to where we focus our attention the fact that it's an undersquare design makes all of those the roll everything is hinged on this all right so on the square all right let's go back almost every performance engine you're going to come across is over square so let's use like common examples like the this the 350 Chevy you know it's four inch for three point four inch 48 inch stroke the small-block Ford is a four inch bore 31 302 44 inch for three inch stroke the 426 Hemi for a quarter more 3.75 inch stroke okay they're all over square the 170 was also designed to over square it was three point four inch bore and three point one two five inch stroke when they increased the stroke from to create the 225 they left the more size the same so think of it this way the bore is the size of a firecracker the stroke is the size of a mailbox that you're trying to blow up so what happens is you've got this tiny combustion chamber you've got a tiny surface area and you've got a tiny combustion chamber and you can only get so much fuel and air into that package so what happens now is that that charge is used up early on in the stroke the rod is only just starting to lean over when this thing is exerting its maximum force we're advancing the timing on most engines will increase slanted performance you notice either the pants snap it actually has the opposite effect I'm at 225 because you're whiting off the mixture too soon before top dead center it's already being used up before the piston the rod comes around and starts its down stroke now also what happens with is that because the piston is moving away from the from the disorder head the combustion chamber is getting bigger it's using up all of that energy in that first few degrees at that point the rod is barely swung over it's barely starting to push into the direction of rotation it all starts to come into sync at around 2000 2500 rpm anything below that and it's just you're fighting award it doesn't want to move it doesn't want to make power as speed increases as rpm increases the amount of time that the combustion chamber is in any given position decreases and so the flame front which is going to be consistent will actually push that much further down and that's where the power comes on that's why these engines start to work at around 2500 rpm alright now there's a very common modification that people make to these things and and this is important I okay like like look it look me in the eye okay right do not use 198 rods in a 225 you're actually aggravating this situation the longer rod keeps the piston at top dead center increases the amount of dwell time which means that that flame front is being used while everything is completely upright like this and it slows the reaction to angularity so the piston the the rod means over a few degrees later in the stroke you're throwing away power a warm right engine is good as long as you're talking about something that's going to happen it's 6,000 7,000 8,000 10,000 rpm long rods are great but the syllabus slant-6 loggerhead cannot support that kind of rpm you're completely wasting your time you wanted to use a short run as possible if you were to pick in an ultimate slant-6 combination it would be the 172 short 170 block with the short 170 rod and the 198 crank but she didn't barely squeeze into that block this employment has to be done you end up with about 2 or 2 cubic inches but you went up with a geometry that's far more capable of making at low rpm power you need to get the car off the start month now I talked a lot about reversing the piston offset in stock engines because what happens is by changing the offset you're actually hoping the rod leaned into the direction the crankshaft rotation a couple of degrees sooner actually giving it the effect of having a shorter a lot so just keep that in mind if you put in one of these engines together stock put the Pistons in backwards believe me you know are a lot of engines you can't really feel the difference on the slant you will feel the difference if you go for an aftermarket piston that has the pin you know centered you know unfortunately you can't do that but if you're rebuilding using stock Pistons turn them around backwards not just face in the back there is no downside to it now the crankshaft on a slant is another area where there's a lot of bad information a lot of misunderstanding right conventional wisdom says if you build on a performance engine you want to go with a forged steel crank and all slide set cranks were forged from 1962 beginning in production until 1975 beginning in 1876 the intro to cast crank and that crank ran until 1981 1981 they went to a lightweight cast crank now here's a chart on the stand about the slam right normally aspirated if you're gonna get 250 horsepower or so out of a normally aspirated slant I mean that's a stout engine turbo charging nature supercharger okay so let's say you get yourself into the 350 to 400 horsepower range again right super super strong slant-6 but the original forged steel crankshaft to it now understand it was designed extra heavy to create a flywheel effect those cars back in the day use three-speed cranks of three speed transmissions non synchronized three-speed transmissions so you spent a lot of time in traffic in second gear you needed that heavy heavy crank shift for the flywheel effect for the quarter you know accelerate and and and not react every little you know upset in speed in 76 when they went to oh wait back to the original cranks that original runner cranks use the same size bearings as the 440th were above the the fourth our team back in those days which later became before 26 before 26 Hemi this the original slant uses the same bearings as a 426 Hemi when they redesigned it in 76 the cast crank they narrowed the bearing journals now this actually has an effect a positive effect it takes less oil and to keep the smaller bearing happy you've got way way more than enough journal area on the cast crank to support the kind of power that you're going to make one of these things and then you get to the 1981 to 1987 engines and that's what this crank is this crank is 20 pounds lighter then the earlier ford steel crank and why is that because by the time they got to 1981 you didn't really need that flywheel effect you know yeah the transmissions you know the the automatics had manuals fed fully synchronized so you downshift the first no big deal the automatics had part right I'll kick down so you didn't need that giant flywheel effect to keep everything spinning they sucked 20 times out of this if you're building a performance engine if you build a performance slant you want to go to 1976 through 1987 casting and actually I prefer as far as as far as the the block itself goes the 1981 through 1987 block is actually super lightweight they sucked about knowing that they take 20 pounds out of the crank but they took about 20 pounds I'm gonna walk as well no detriment the soles are exactly the same they just took extra metal wolf to block the original slant the concept kind of slant was that it was mostly built of aluminum and so die cast aluminum so everything in the original block is extra thick because it was supposed to be cast out of aluminum when they gave up completely on that idea again the early 1980s when they took the extra cast iron out of the block and created you know basically the ultimate slant now those engines 1981 through 1987 were also had draw ik lifter motors but that doesn't affect if you're building from scratch there's no difference in the in the in the camshaft galley there's no difference in the in the in the in the the lifter galleys so you want to build it but the solid cam of the earlier years solid valve train but you want to use the 1981 to 1987 block and you want to use them 1881 to 1987 crank if you break one of these things you've done something drastically wrong because there is no way you're going to put three or four hundred horsepower through this and hurt and that brings us to the real cork in a bottle the solder head so the first thing you have to know about these things is it everything is scaled to the 175 the ports the valves the general configuration now there were a couple of running changes through the course of production there was a special head designed for the aluminum block but it again configuration is exactly the same they went from the thirteen sixteenths plug with the drool tubes to the peanut plug sometime in the middle 70s 1981 they changed the valve cover mounting area so valve covers don't have to change between early and leader motors but the essential head itself is unchanged from the original 170 size now here's the essential limitation with the head chrysler engineers while they were copying like you know the European motors they were looking for that free-revving you know they were also limited and that they had to keep because the engine was slanted they intake and the exhaust had to be on the same side even back on 1950s the manufactures that were copying we're using things like overhead cams and and hemispherical combustion chambers cross flow cylinder heads but Chrysler was stuck with this this is what they had to work with so cylinder head basics 101 yep optimum configuration is always going to be a cross-flow head with the valves in line with the mixture like a Hemi regardless of the combustion chamber shape you still want the intake and the exhaust in line with the ports so you have your intake port here you can take valve here exhaust off here exhaust port here and what that's doing is reason that's important is because during that period of overlap from both the intake and exhaust valves are open what you're doing is you're pulling this the broadest amount of mixture through the intake hole from the exhaust that's the whole purpose of overlap is to get that column of mixture moving through the intake valve into the chamber before the exhaust valve closes completely and what the Hemi does were the centralized you know cross flow head does is it deposits the the kernel of that mixture into the center of the chamber then you get to the much more common wedge right where this is a wedge but on a typical you know like oak but your v8 engine you've got the intake on one side the exhaust on the other what you've got is you've got essentially the same kind of thing going on intake mixture is coming through it's kind of heading diagonally across the chamber so instead of the floor coming this way she's coming this way it does shorten the area that it's able to pull through so it's not quite as efficient you'll get quite the punch but it's still a basic cross flow configuration the column of mixture and exhaust is all moving in the same basic position then you get to this where you've got the intake and the exhaust on the same side and what happens with this is a low rpm where everything is relatively lazy it'll work pretty much as as much as well as any wedge cylinder integral but as rpm increases what happens is the band that the exhaust is pulling the intake through shortens so what's happening is it'll pull all of its mixture through just to one side and leave this side empty and that's what that's the the essential limitation of having the intake and exhaust on the same side because the the higher the RPM the more extreme that scent that that that short area becomes now that's the limitation that's what you got a work bus up to about 5,800 6,000 rpm you're okay after that H is just not gonna make any cow with the thing the other issue is valve size and port size lettuces this is all design that's all scaled to the 170 only one to two 225 they didn't change any of us now there are two schools of thoughts on us first is that you can increase the size of the valves to better match the cubic inch of the 225 and yes you will pull a greater mixture through but with the essential limitation of this engine being it's extremely long rod and extremely lazy pull away from top dead center what's happening is you're going to lose a lot of velocity through those holes this engine is velocity challenged one of the reasons why it makes so little horsepower at little more PM so my train of thought my school would be to leave the valves the same size and hopefully keep the velocity up to better full better fill the chamber better pull the mixture through so you know but it's six of one half dozen of another your engine builder the way you want now the plumbing into and out of these engines is also very unique and very very misunderstood so let's start with the basics okay well slant sixes came with this configuration intake meaning that you've got three different lengths runners and essentially mounted carburetor naturally the vast vast majority of them were single barrels then you have the super six with the two round Carver they used to be BDS a just about the same as the one on a 3/8 now you've got aftermarket stuff like this for barrel one and also there was one factory high-performance 4-barrel intake manifold the hyper packin we're going to get to that in a minute but here's the genius behind what's going on with these intake manifolds nobody ever talks about it right back in the 1850s chrysler engineers were very tuned in to the idea of sonic pulses sonic tuning right so basically what happens is as a column of a mixer is coming through the runner the intake valve closes on it and what that does is it stops the mixture right and that creates a pulse that travels back up the runner then when the intake manifold when the intake valve opens again that pulse turns around and it actually shows the intake mixture into the chamber the longer the runner the higher the lower the RPM it Tunes it so let's just say you're building an engine to run it 2,000 rpm you are a super warm water you're building an engine to run it 4000 rpm you want a mid-range runner you build an inch will define 6,000 rpm you want a short little runner it all has to do with the amount of time that it takes that a pulse to travel back and forth from the intake valve to the plenum of the manifold what Chrysler did here was pure genius every slant sessions the intake manifold consists of three separate length runners the two outboard cylinders use the longest runner the to center or inboard ones use a shorter runner and then the two center cylinders use the shortest runners and what this does is it broadens the motors operating range it broadens the torque curve of the engine because you've got these so long as a tuning it let's just say 2500 rpm these solders are tuning at 3500 rpm these soldiers are tuning it 5500 rpm so you're spreading the torque curve out without actually hurting anything along the way that's why these manifolds are designed that way and now the hyper pack that is probably one of the miss most misunderstood intake systems ever okay so what the Hypertech did and you could look at pictures of these things with the high compacted was it mounted single four-barrel carburetor right about over here which super long runners and this tune at about 3500 4000 rpm the reason for this the only reason they did this was because of a class that they were gearing up to run that they wanted a dominate and it was NASCAR's sport compact class this was supposed to be a series that was going to be run out you know nationally and but actually the first race was featured on live TV and it was dominated by slant sixes now the reason that they went with that hyper pack style intake manifold had much less to do with the actual performance of the engine but more to do with the limitations of the transmission now remember back then Chrysler was limited to the a 903 three-speed trans which is a non synchronized first gear transmission this is a road race series so there's a lot of like you know tight turns and very you know slowing down and whatnot so because the transmission had an unsynchronized first drivers in Chrysler cars couldn't pull that down shift to motor out of a turn so what they did instead was build a stout torque curve into the engine by tuning that in take those intake runners as long as they were so that the driver could leave the car in second year and torque their way out of the turns so that's the only reason that manifold existed so it was supposed to be a regular series but they ran it only for the one year and then they dropped it and Chrysler I guess had cast up a bunch of these manifolds and he exhaust to go it and we'll get to that in a minute so they did was it just put it in a park and they offered it is a dealer install package until 1960 early 1962 I think they stopped with that but that's the story behind the hyper pack if you're building an engine for the type of performance that we're doing the type of performance we're talking about where you know you know that that broad range you definitely want to stick with a shorter runner intake like this often has or Clifford I'm not gonna tell you which indict manifold to use I'm not gonna tell you which covered or what size to use that's a completely different animal I'm just explaining the dynamics behind the intake plumbing why they did things the way they did and that breaks this city exhaust that the exhaust side slant-6 is unique like everything else about the motor but this is the typical exhaust manifold now there are a couple of different configurations as far as ribbing and whatnot goes but this is the factory exhaust manifold and they're all of this basic configuration the only exception would be the hyper pack manifold what gets it out in a minute so ideally when you're the only one in line six you want to separate the exhaust shoulders one two and three and so on is four five and six should be separate and that's because you'll get optimum evacuation by spite by breaking them into those two groups and essentially that's exactly what the stock exhaust manifold does it's a shorty header you have beautiful individual runners that come out and meld into this common pipe and then they come here they've joined at the outlet pipe all slant six by the exhaust manifolds have the same two inch outlet so essentially what the factory design here was a three into three common collector header you really can't improve on it now some people will try to run dual exhaust off from one of these things and they'll split manifolds and stuff like that wanting this a dual exhaust on a slant is shooting yourself in the foot and here's why there's actually as several reasons but the first is that the motor just does not have enough capacity to flow those two two pipes one 3-inch pipe will flow as much as two two-inch pipes and that's because of the parasitic losses along the inner surface of the exhaust now if you ever listened to a slant with dual exhaust as you're driving down the road let's say you'll see you'll hear it pulsates the sound comes and go and the reason for that is because as you're driving along the exhaust slows down as it gets past the mufflers into the tailpipes the heat goes away and the velocity goes away the only heat is the lubricant of exhaust so the further out you go the less heat there is the less that column wants to move and the motor doesn't really have enough push to keep it moving solidly so what happens is you'll actually hear it quiet down a little bit as the exhaust begins to stall in the back part of the system when the back pressure builds up enough there the forward part of the system shoves that out and the sound comes back and that's why they've got that pulsating sound as they go down the road your optimum exhaust system for a slant six is a single two and three-quarter 3-inch pipe to the back of the car it keeps the heat up it keeps the velocity up it works perfect and it's out of all the exhaust systems you can put on the car it's the best sounding now headers are definitely a good plan for the slap the stock exhaust manifold is good how does it better they'll do that job of pulling that column of fuel it's that mixture through the intake and doing a lot as long as you same rule applies you want to run them into a large diameter single exhaust the function better and they'll sound best that way now all of the headers are currently on the market or of that three cylinders there are three into one and three into one configuration there was one six into one header that was available through like direct connection in the mid 70s but they discontinued that and as far as I know nobody has done anything since the same rules apply when you're running the header single exhaust to the back of the car if you're running them open the two collectors are fine because there there's no heat loss there's no parasitic loss beyond them said it has all function exactly the way they are supposed to this is reset in the beginning of this video I love this plan and we actually plan on doing a lot of stuff with them we have that 67 dark race car we're building a lightweight motor for it now but again you know it takes time we've got so many other projects you know be patient before you see any results with that thing we've got this this engine is just gonna be a basic freshen up we're going to try to make some horsepower with it using nothing but the stock parts and stick it in our white 64 and you know just a driver but we do have a lot of slant stuff planned for down the road now you guys right away in the comments you're gonna be like what came for the is what didn't take should I use what copper to show you is but you know what I'm not going to answer those I'm gonna heart them but I'm not going to answer them because there are formulas out there that you can follow or if you want my opinion on these things you're gonna have to wait until we actually go ahead and build it and get the actual results ourselves I'm not going to give you formulas the purpose of this video was just to try to explain the dynamics of this engine and the unique environment that it operates in so that's pretty much it see you tomorrow

Channel: Uncle Tony's Garage

Views: 624,997

Rating: 4.8774981 out of 5

Keywords: slant six, slant 6, /6, inline six, 225 slant six, 170 slant six, 198 slant six, slant six racing, slant six performance, slant six build, slant six history, hyperpak slant, aluminium slant six, four barrel slant six, slant six headers, slant six exhaust, dodge slant six, plymouth slant six, classic car, dodge, plymouth, dart, valiant, barracuda, charger, challenger, duster, demon, duster twister, scamp, swinger, uncle tony's garage, tony defeo

Id: b8Y96xywS-E

Length: 33min 34sec (2014 seconds)

Published: Tue Jun 04 2019

Reddit Comments

[u/[deleted]]

Understanding the Slant Six

Vapor lock

[u/TigerUppercut08]

I've seen this guy on YouTube, big time mopar head.

[u/GiddeeeUp]

Had a slant 6 in my Duster back in the day. The engine never quit while the body disintegrated around me. lol

[u/TeleKenetek]

Ive always wanted to build a big power slant.

[u/Haematobic]

As a bit of an update, he has just released a part II.

[u/wolf2600]

Awesome. First car was a 74 Dart with the 225.

[u/taratarabobara]

I remember when you could still find aluminum block slant 6's in junkyards. A friend of mine pulled one and paid $30 for it I think. A curiosity then, probably quite rare now.