Thoughts on a 225 rebuild

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ArizonaKid

ArizonaKid

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I have a 1976 super six motor, its probably got at least 100,000 miles on it, and since I decided to put a 318 into my dart, I wanted to set aside some money for a rebuild, and get a parts list ready. The motor is all stock, except for the timing chain I replaced, stock springs, valves, pistons, cam and lifters.

So what I figured would be good was; new pistons for a higher compression, I think these motors were around 8.4 to 1. A new cam, and maybe lifters, I want to know if its better to use new lifters, or keep the original hollow mechanical lifters. New valves and a head job. And finally, new springs.

I wanted to know what you guys used and liked, the compression I would shoot for would be in the 9.5 to 1 range, so nothing too radical or racy cam wise. The motor would be for nothing more than a daily driver, but eventually I might put a turbo setup on it, if I get a good deal on one.
 
Well if a turbo might be in the picture later, keep that comp ratio down around 8.0-1 with some forged slugs and have at it.
 
There's not really a "good deal" on a turbo setup, because they don't exist for the slant. At one time I saw someone selling their entire bolt on setup to put on for $2,000 - Carb and all. After building the setup myself and knowing all the pieces involved, $2,000 isn't bad if they did all the work for you. I think toad is selling off most of his setup if he still has it.
 
Always use new lifters with a new cam; never re-use lifters on another cam or swap lifters between cam lobes. Save them with the original cam if they are not badly worn; each lifter HAS to stay with its cam lobe. The contact pressure wears the lifters and cam lobes in a closely matching pattern and they should never be separated. You can only use a new lifter on an old cam, never the other way around.

Lifters are ground new with a slightly convex surface; this, along with the off-center contact between cam lobe and lifter face, make them spin around and around on the cam lobes, which keeps the waer uniform. As they wear, the convex surface will be come flat and eventually concave and that is 'worn'. The original /6 lifters are hardened through and through so tend to last a long time.

As said above on the turbo plans: keep CR low. For a turbo, and port work can be dispensed with if you are looking to moderate power increases. But your final direction is quite different if you want to stay normally aspirated, so turbo or not is an important decision to make up front.

Shaving the head is the common way for moderaqte CR increase on this engine. You can put in a composite head gasket and lower the CR a bit. The orignal head gasket is a thin steel shim and you will typically lose a few tenths on CR when you swap. Shaivng .050" is supposedly nothing much and shaving .100" is not uncommon.

The real /6 experts are over on www.slantsix.org; lots of good articles to read there. There have been developed a number of rod and pistons variations that can be used. You have a lot of fun reading to do.
 
I have 3 Super Six Engines in my shed and I'm currently toying around in my head with rebuilding 1 of them as a Long Rod 225 with EFI.

Creating a Long Rod 225:

you use your 225 block and crankshaft. And then you use the 7 inch 198 connecting rods and late 80's early 90's 2.2 Turbo pistons like Sealed Power W533P. The Pros of this combo are light, strong pistons and a very long connecting rod. This combination produces 1.7 rod ratio *which is really good* and will push the piston close to the top of the bore. (.040ish negative deck height). A stock 225 rod/piston setup stops somewhere around 0.175" down in the cylinder (negative deck height). Bringing the piston closer in turn raises the compression and also a increase in torque. With unmilled components and a fel-pro gasket. You would be looking at around 9.0:1 - 9.5:1 compression. If you start milling decks, then all bets are off as compression shoots up quickly

So whats the difference? Lets break out the old math:

225 rods and 225 pistons
Stroke - 4.125
Rod Length - 6.700
Deck Height - 10.680
Piston Compression Height - 1.918
225 Pistons have a Compression distance of 1.740
That puts the piston 0.178 down in the hole

-Boring
--------------------------------------------------------
198 rods and 225 pistons
Stroke - 4.125
Rod Length - 7.005
Deck Height - 10.680
Piston Compression Height - 1.613
225 Pistons have a Compression distance of 1.740
That puts the piston 0.127 out of the hole

-YIKES!
--------------------------------------------------------
198 rods and 2.2 Turbo pistons
Stroke - 4.125
Rod Length - 6.700
Deck Height - 10.680
Piston Compression Height - 1.613
2.2 Turbo Pistons have a Compression distance of 1.573
That puts the piston 0.040 down in the hole

-The Sweet Spot


So for a cheap upgrade in pistons/rods you can increase efficiency of the motor and the compression from 8ish to 9ish

If you go the Slant 6 route, I would encourage you to gasket match the intake and exhaust components and run 2.25 pipe to help out where you can.
 
I lost your reasons. If changing to a V-8 later, why rebuild the slant for more power? If the compression is good, your only reason might be to up performance. All oil leaks can be fixed w/ engine in the car. Anyway, visit slantsix.org for ideas. There isn't much choice in pistons for a slant and $$$ for high-end.
 
BillGrissom said:
I lost your reasons. If changing to a V-8 later, why rebuild the slant for more power? If the compression is good, your only reason might be to up performance. All oil leaks can be fixed w/ engine in the car. Anyway, visit slantsix.org for ideas. There isn't much choice in pistons for a slant and $$$ for high-end.
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Im saving the motor for a custom car i'm building later, no sense in throwing out something that can be used, at this point, I'm going to work on the 318, put that into my car, and rebuild the slant to stock (or close) specs, then put it away for later. I've fixed most of the leaks by now anyway, the current one is coming from the oil pump, i'll get to that later.
 
GAmoparman, do you have an approximate cost of this rebuild you can give me? And can I just use the carter 2-barel I have for it, or would another carb be better? I'm also guessing a good header setup would do well for this build?

And thanks to nm9stheham, I've heard you can use new cam, old lifters, and you cant, from a whole bunch of people, so i wasn't sure of whats right.

I figure if the long rod 225 build is a good price, then that will be my way to go, instead of a turbo setup. thanks for the answers guys!
 
after the first of the year I will be doing a build on a slant 6 with long rods and 2.2 pistons, cam, 4 barrel and headers! do you think 2 1/2 exhaust would be too big?
 
9.5:1 is too much for a non quench iron headed engine. Leave it the stock compression and use bolt ons for power such as cam, intake, exhaust, etc.
 
dvboth said:
after the first of the year I will be doing a build on a slant 6 with long rods and 2.2 pistons, cam, 4 barrel and headers! do you think 2 1/2 exhaust would be too big?
Click to expand...
Not too big at all from an engine breathing standpoint. Eventually one runs into the bends fitting under the car as the pipe size gets bigger and bigger.

With a narrow lobe angle cam (more overlap), going up moderately on the CR is OK. Even with a wide lobe angle cam for torque, a modest CR increase over stock is OK; a half point in that case will still work and will add to the engine's zip.
 
Crunched some more numbers for CR with 198 rods and stock 2.2 turbo pistons

Based on the following:

Bore - 3.40
Stroke - 4.125
Head Gasket Thickness - .045
Combustion Chamber as 62cc
Piston Dome volume as -16cc
Piston Deck Clearance as -.040

That comes out to 8.79:1 Compression ratio and 78.74cc Total displacement volume
 
Alright, I see a couple of flaws you'll want to correct.

1. Your bore is going to be 3.45 or 3.504; There may be a size between, I'm not sure
2. What head gasket are you going to use for that thickness? I believe a FelPro is .038
3. Also, did your calculations require a gasket bore? mine usually do...
4. Your combustion chamber looks a little big for stock. I believe mine was 58cc

All of that may mess with the compression a bit. Best of Luck!
 
Thanks for the additional info Brandon! Taking these items into account and plugging them into my calculations.

Bore - 3.40
Stroke - 4.125
Head Gasket Bore - 3.520
Head Gasket Thickness - .038 *Varies between .038 and .042
Combustion Chamber as 58cc *Varies between 56cc and 62cc
Piston Dome volume as -16cc
Piston Deck Clearance as -.040

Based on your numbers, That comes out to 9.28:1 Compression ratio and 74.10cc Total displacement volume

If we shoot for the middle ground with the gasket thickness of .040 and combustion chamber of 60cc, we get 9.03:1 Compression ratio and 76.42cc Total displacement volume
 
I don't understand why you would want to use the 198 rod and 2.2 turbo pistons. 198 rods are hard to find, then they would need "rebuilding"., and the pistons are still just a stock piston.
Just use a stock 225 rod, and piston. mill the block or head to get the CR in the range of 9.0 to 9.5 to 1, depending on what cam you run. We are talking a street engine, here. If you really want a "long rod" motor, do it right and get the Molner or K-1 rods and the Wiesco pistons.
 
Charrlie_S said:
I don't understand why you would want to use the 198 rod and 2.2 turbo pistons. 198 rods are hard to find, then they would need "rebuilding"., and the pistons are still just a stock piston.
Just use a stock 225 rod, and piston. mill the block or head to get the CR in the range of 9.0 to 9.5 to 1, depending on what cam you run. We are talking a street engine, here. If you really want a "long rod" motor, do it right and get the Molner or K-1 rods and the Wiesco pistons.
Click to expand...

That was kinda my point when I mentioned what I did about compression. The long rod thing isn't really worth snot on a street car. Plus, if he'll have the same compression with either setup, what's the point?
 
Charrlie_S said:
I don't understand why you would want to use the 198 rod and 2.2 turbo pistons. 198 rods are hard to find, then they would need "rebuilding"., and the pistons are still just a stock piston.
Just use a stock 225 rod, and piston. mill the block or head to get the CR in the range of 9.0 to 9.5 to 1, depending on what cam you run. We are talking a street engine, here. If you really want a "long rod" motor, do it right and get the Molner or K-1 rods and the Wiesco pistons.
Click to expand...

By 198 rod, I'm referring to the length. I agree that the Molner rods would be the ones to source. As far as piston selection goes, unless you'll doing some wild things on the motor, why would you spend extra on a piston if the "stock" 2.2 turbo piston can handle it.

The reason for the change over isn't just for compression ratio increase as milling could handle this alone..your adding torque due to the longer rod and also improving the rod ratio which improves multiple areas on top of increase the compression ratio. This change would fall under the "Improve efficiency" category of motor building to use with add-on's such as intakes, cams, headers, etc.
 
You obviously have no clue who Charlie is, I can tell. He's been racing slants longer than a lot of people have been alive. Trust me, he knows everything you're sayin and probably knew it before you did. He certainly knew it before I.

First, longer rods have zero effect on torque. Say it with me. Zero. However, a longer crank throw (stroke) would. All longer rods "do" is allow the piston to dwell at TDC a little longer and "supposedly", "possibly" increase the power stroke a little. It's a difference you'd never feel in your butt and likely not see on the dyno.....at least on a slant six.

All that said, it has been proven that shorter rods are actually better on the street, because they keep piston speed up at TDC thereby helping to fill the cylinders faster. This isn't secret information, it's all verifiable online in many, many different places. Even after all that said, once again, we're splittin hairs talkin about a street slant six. Were we talking about a mega cube stroker big block used for racing, it might be different, but we're not.

Also, the other "benefit" is the reduction of friction on the cylinder walls and piston skirts due to the reduced angle on the rods by being longer. But again, with the slight difference we're talking about, it's splitting hairs at best on a slant six street engine. Again, see my reference above to the mega cube stroker big block that we are not talking about. lol

You might want to read all about it here:

http://www.slantsix.org/articles/stroking/stroking.htm

Everybody else has.
 
GAMoparMan said:
By 198 rod, I'm referring to the length. I agree that the Molner rods would be the ones to source. As far as piston selection goes, unless you'll doing some wild things on the motor, why would you spend extra on a piston if the "stock" 2.2 turbo piston can handle it.

The reason for the change over isn't just for compression ratio increase as milling could handle this alone..your adding torque due to the longer rod and also improving the rod ratio which improves multiple areas on top of increase the compression ratio. This change would fall under the "Improve efficiency" category of motor building to use with add-on's such as intakes, cams, headers, etc.
Click to expand...


I am aware of the 198 rod length issue. There is really no reason to use the "long" rod on a mild street engine. On a slant six the main advantage of the long rod seems to be the engine is less prone to detonation. The long rod on a slant, has not shown a measurable increase in torque.
As you said "As far as piston selection goes, unless you'll doing some wild things on the motor, why would you spend extra on a piston if the "stock" 2.2 turbo piston can handle it". Why spend the extra money on a 198 rod. They are hard to find, and over priced when found, then still need to be reconditioned.
 
And just one example of his mistakes. When I was reading and learning about early Hemi engines after I got my 331, I used his pages as a source of reference. I also joined a couple of Hemi forums. After I became familiar with the engine, I tore it down and began cleaning it up to prepare it for the machine shop.

Now, I will give him this much. My engine is somewhat of an anomaly. It is a 1956 331 Power Giant truck engine and they are a bit different than the automotive engines. However, he had them lumped in with the automotive engines.

Had I gone by his information, I would have had my machine shop deck the block over .070" from where it was in an effort to blueprint the deck height. When we found out it was that "tall" I immediately called Bob Walker at Hot Heads.

When I told Bob where I had gotten my information on deck height, he almost dropped the phone laughing, saying that while the Victory site has some good info, a lot of the specifics are either left out, or wrong altogether. He gave me the correct deck height and mine was only out like .013". All of the guys on the forums I joined also echoed the Victory site's good information and it's mistakes as well.

So be careful where you get your information from. Get it from many sources and compare. I like listening to guys who use dynos and build engines for a living and guys who use the drag strip. Although there is room for error depending on which dyno you use, what it's corrected to, blah blah blah, there's no substitute for experience. There's also no better result source than the drag strip. Trap lights do not lie.
 
The high rod ratio of the 198 rods with a 198 crank can be a bit misleading; most of that high number comes from the short crank stroke, not the 5% increase in rod length. When the 198 rods are used with the 225 crank, then you only get the 5%; not all that much of a change. Using the 2.2 pistons may be an advantage in getting the piston top closer to the top of the bore, doing the quench thing, etc.
 
Actually as far as the OP is concerned, all this discussion is mote. This discussion has turned into more "high tech" then necessary. The OP is building a mild street engine. I think he is more interested in "bang for the buck", which would leave out a long rod combo.
 
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