Stroking a 173

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Page created by T Mar 5th 2007:

This page is a Work In Progress with submissions from WBJailwagon (Jeff), Ben Simpson, Circlotron, Campbell, Sketch, Q-Ball, bf6379 (Brett), v8slrtorana, T and others.

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Holden 173 Engine. Image by Tim. Click to Enlargen.

The Original Thread:

Clearly much thought is required on a project like this and the experience, expertise and
co-operation of Old Holden Members is both appreciated and vital. Here is the original thread [Stroking a virgin bore 173] which provides fuller detail.

Follow up thread.

Further follow up thread.

Custom Conrods

Jacks' Shed

A convenient shot showing the dishes pistons in a blue painted
202 at TDC (see Joshua's shed. The engine has 202 cast in it). A larger image is available at Joshua Bowden's Shed. Photo by Joshua. Click to Enlargen.


Not so long back a contributor to Old Holden posted that a 202 crankshaft could be fitted to a 186.

It may have been Ben Simpson here.

The result in a 186 block would be 202 in capacity.

Stroking a 186:

In that situation the use of 202 Pistons (which have the same diameter as 186 pistons) and having the 202 Main Bearings ground down so that they would fit the 186 block made for straight forward stroking.

While it's evident that simply buying a 202 would simplify the process, the intention here is to develop a cost effective way of increasing the power output from a 173 for a relatively
small outlay.

In the case of a 173 Engine making the best use of the existing investment is attractive especially if you already own a good 173.

A 173 Piston is on the left and a 202 is on the right. Photo by Q-Ball. Click to Enlargen.


A list of concerns are being identified and investigated and the project is untested at this stage. Readers should not attempt the project since the final results are not in yet.

1. The fitting of the Crankshaft.

2. Camshaft Clearance.

3. Piston to Crankshaft Clearance.

4. How far the Pistons extend from the top of the Bores (to be evaluated).

5. How far the Pistons extend from the bottom of the Bores (yet to be established).

6. Whether re-working the existing pistons, sourcing replacements, or sourcing and modifying replacements is required.

7. Top and bottom Piston Ring ridges in the Bores to be removed.

8. Compression Ratio.

9. Displacement.


Fitting the 202 Crankshaft seems straighforward once the Main Journals have been turned down.
Standard Red Sixes Holden Engines have the same Big End Bearing and Journal dimensions. The larger Main Bearing and Journal dimensions on standard 202's being the only exception.
The cutaway 173 Piston is on the left and a 202 is on the right. Photo by Q-Ball. Click to Enlargen.
Cutaway 179 Engine. Click to Enlargen. Photo by Jacks.
Cutaway 179 Engine. Click to Enlargen. Photo by Jacks.

Camshaft Clearance:

Holden publications indicate that Red 202 and Red 173 Camshafts have the same grind which
eliminates some concerns about which Camshaft can be used.

Blue 2850 and 3300 Camshafts are identical to each other but different to 202 and 173 camshafts.

Piston to Crankshaft Clearance:

Looks good as per Q-Ball's piston comparison image.

Compression Ratio:

The Compression Ratio is a consideration. Having run a 173 head on a 202 since 1989 has
produced benefits for me (about 10.5:1). It's estimated that the Compression Ratio of the
stroked 173 will be increased from 9.4:1 to about 10.2:1 (to be confirmed).


Jeff has estimated the final displacement from a virgin bored 173 to be 187.5 cu ins.

Piston Dimensions:

Dished Pistons allow for the compression ratio to be preserved after a rebore, a desirable attribute for anti-pollution engines given that high compression produces emissions.

The piston dish is made bigger in the oversize piston and the compression ratio is preserved.

A large image of the dish in 202 pistons is available [here].
The image displays Jeff's (WBJailwagon) info (see the original thread).

Joshua's shed has an image of the engine with 202 cast in it [here].

Joshua Bowden's Shed

Bore Stroke Ratio:

This will change from 3.5" x 3.0" to 3.5" x 3.25" making it less of a big bore short stroke engine and closer to being square bored.


Stroking a 186



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