188 With a Twist - Is this buildable?

When I can't sleep my mind drifts and I think of things.

One of the things I thought about was building a 188cid engine with off the shelf parts; no specially made crank, rods, or pistons.
These are the parts I came up with:
Stock 200cid seven main block - 3.68" bore, milled 0.020" leaving a 0.018" piston recess
170cid seven main crank (they do exist) 2.94" stroke
255 V8 flat top pistons - 3.68" diameter, 1.585" compression height
200 rods - 4.715" length
The bore and stroke gives me the 188 cubic inches I want and the compression ratio with a 0.053" head gasket and 53cc head is 8.8:1.
I would like to have the CR up around 9.5:1. In order to accomplish that the head would have to be milled so the combustion chamber displaces around 48cc.

My mind drifted some more.

So then I placed all of the variables in a spread sheet and started playing with the different stock pistons, rods and cranks, and came up with this combination:
Stock 200cid seven main block - 3.68" bore, no milling. Centerline of crank to top of block - 7.808"
170cid seven main crank - 2.94" stroke
200 flat top pistons - 3.68" diameter, 1.511" compression height
144cid rods - 4.855" length.
Now with this combination the displacement is still 188, but the compression ratio with the same 0.053" head gasket and a 56cc head jumps to 9.47:1. MUCH BETTER!
An additional plus with this combination is that the Rod to Stroke ratio is 1.65, which is in the ideal range of 1.65-1.80. This should result in less side loading of the piston
(less cylinder wear) and allow the engine to rev higher.
The downside is that the piston sticks out of the block 0.028", but with a 0.053" head gasket, it would be the same as a zero decked 200 with a stock steel 0.025" head gasket.

What I'm wanting to know is whether the piston sticking out of the head that much is a concern? Can this engine be built with these components and not have a piston hit a valve?
If it can be built, what are my cam limitations in regard to lift and duration?

Here is my calculation. See if I missed something.
Centerline of crank to top of block, stock 200cid block - 7.808"
170 stroke - 2.94"
CH 200 piston - 1.511"
144 rod - 4.855"

7.808 - 1/2(Stroke) - CH - Rod Length = Piston Recess (+), or stickup out of deck (-)

7.808" - 1.47" - 1.511" - 4.855" = -0.028"

Some of you may be asking why I would want to do this. My answer is the same that I tell people why I have a 6 cylinder instead of a V8, because everyone does that and I want to be different.

All input is appreciated.

I don't have enough experience to have much input, but I saw your listing in the wanted section for the 170 7 main crank and I'll keep my eyes peeled.

Stephen

IIRC the 188 & 221 were offered in Brazil or Aregentina

Yes, but why? Just curious.

I mean theoretical efficiencies aside, and I do grant that they are there, if what you want is an engine that goes vroom and makes power, there are plenty of less proprietary ways to get there than starting with an extremely rare crank as your centerpiece. I'm guessing what you want is to be able to rev to 7000 or something like that, but you start by losing 12 ci. Couldn't you gain the same revvability in a 200 with carefully lightened pistons, rods and crank?

Oh, wait. I just read your last sentence. well then, hell yeah, go for it! Make sure you use a dual exhaust though, because i want to hear the recording of this thing flying past at redline

82F100":2y8kx4e6 said:

IIRC the 188 & 221 were offered in Brazil or Aregentina

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And Australia

If this crank is that hard to find, have it magnafluxed then ground with special attention to the radius.
Don't buy any special parts until the crank checks good.

If the pistons stick out of the block too much, it wont hurt to shave a little off of them.

I think it should be fine with a thick enough headgasket. If it is marginal, it's pretty easy to get valve reliefs cut in the pistons.That will reduce the compression loss.

Mockup will let you know how close things are.

Why go to all this trouble for less cubic inches?? A 200 and a 170 are almost identical. You know the old saying, no substitute for cubic inches.

Using the 200 pistons +0.030 with a 170 crank will yield 191 cubic inches, +0.060 pistons will yield 194 cubic inches; If I went
with oversize pistons I wouldn't be losing much displacement.

The benefit of using 144 rods is that the rod/stroke ratio is within the ideal range of 1.65 to 1.80 which
reduces piston side loading (wear) and would allow the engine to rev higher. A cam could be used that would take advantage of
the higher revs to increase HP. Gearing could be changed to 3.55 or higher to offset the low end torque loss.

Of course all is dependent on a better breathing head.

The major thing I am concerned about is deck clearance. I'll just have to take the advice of wallaka and others to do a mockup and cut valve reliefs or mill the pistons if necessary.

Yes you can build this.

This is what I originally was trying to build but could never find a seven main 170 crank.

I also contemplated offset grinding the rod journals to 1.889" Honda journals to make a destroked 2.6L motor that would love to rev.

dagenham":1yx6195q said:

Why go to all this trouble for less cubic inches?? A 200 and a 170 are almost identical. You know the old saying, no substitute for cubic inches.

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all i can think of when i read your post is a V8 guy asking why i'm keeping my six

i've seen more innovation out of this forum than any half dozen mustang forums you'd care to name, it's just another way to get down the road, nothing wrong with it

Would the ability of this engine to rev higher more than offset the difference in cubic inches? I saw an equation for power on here and i know RPM was in it but I can't remember where it was.

you're losing 12 CID, i'd bet the higher RPMs would more than make up for that

HP = rpm x torque/5252

So yeah, being able to rev several hundred or a thousand RPM higher will easily make up for a piddly 12 cubic inch loss.

Rocklord I ran outside last night to look at the 170 I pulled out of the bronco and it was a 4 main darnit.

When I got my JE forged pistons they have a 1.500" deck height, not 1.511"

Some piston makers do this to compensate for having block surfaced.

Once upon a time I mentioned the feasibility of getting a block spacer that was cut to match the head gasket and then getting the block sleeved to match the spacer so you would up creating a 1" taller deck height which would allow for a 5.7" rod.

This is exactly what some of the big RB26 engine builders are doing to create a RB30 stroker motor.

In this day and age of water jet cutting getting a 1" thick piece of steel stock cut probably would not be that hard.

Not sure about the cylinder sleeve's.

What kind of improved rpms would this theoretically gain?

6k? 7k? with the right head cam and springs?

How if you went to oversized at .060 would that take the bore stroke ratio to far out and then you lose the efficiency?

Anlushac11":2pbq0z6u said:

This is exactly what some of the big RB26 engine builders are doing to create a RB30 stroker motor.

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The Aussie blokes are putting the RB26 head on the RB30 block.
BTW, the RB30 is quite easy to find in Australia, probably less so there.

That may be the RB motor that is in some of the Aussie Holdens.

What I was referring to was this. The advantage is it keeps the strong RB26DETT block.

There is also an 'RB30DETT' kit manufactured by OS Giken of Japan, which bolts an extension on top of the RB26 engine block, and fits liners, to give an 86 mm bore x 86 mm stroke. It is available as an assembled short block, containing billet chrome-molybdenum crank, billet chrome-molybdenum H-beam connecting rods, forged pistons, and costs ¥1,500,000.

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