Chrysler racing outboards

[FMP]

Nothing Bill Edwards or WPT or the many others who I could name that race and built them don't know. Still lots to learn from some of those guys.
They worked hrs , days, months, years testing different ideas and still hold them close to chest.
Like modified chambers , moving spark plugs etc.lol

[gmjim]

A little more duration on the exhaust or just area by squaring if on a heavier hull. Transfers area, squared on centers and inner side of the outer ports, leaving far outside corners round worked well for the Force race motors, same applies to the Chryslers. Transfers could be raised a bit depending on the stock duration numbers, exhaust and transfers measured using the degree wheel first. Leave the outside port ears at the sleeve, they help direct fresh charge to the center of the deflector.
Chrysler heads are big and small bore, squared corners rectangular shaped head are the later and cool a bit better , the other is the earlier. Don't exchange big bore for small, just cut for psi. Earlier Force can use Chrysler head, they did change the shape again, late Force had slightly different chamber to match the later Merc x flow design.
The Chryslers are 165 psi, the Force a bit less 145-155 or less and not even based on design, a bulletin was issued, except first few years from Chrysler. I run 172psi on 93 with lots of timing and more jetting with 3151 Wisecos. Not sure how much the later Force will tolerate on pump gas but 165 should be fine with jetting.
Chests are a bit different, front case seems a bit tighter, tuner is different between late Force and Chrysler.
Lowers are one or the other, different legs. Powerflow side bullet Chrysler doesn't bolt to later Force. F5 typeA, B, C or D will bolt to 77/78-84+ Chrysler mid, not earlier two piece lower unit leg 60s-76/77.
Like anything older if you are pulling it apart check the ring pins , I have pulled them apart and found the pin moved, piston chipped and just ready to wreck the cylinder.
If you find an F5 that's close by have a look. They take some more work to mod because of the ex stuffers etc but five holes always gives more.
But a well built Chrysler or F4 will turn good rpm and perform.
Minimum 40:1 !

Thanks for the reply! Sadly I just missed a very neat pair of F5 motors...
when I get a motor I while do some measuring and post some numbers, see where I am at!

[FMP]

I would guess that they are a rare thing in Byron Bay

[gmjim]

Yes they are sadly....

[gmjim]

What do you think of these couple? 1x140 hp, 1x115 hp......

[FMP]

The 140 should have dual fuel pumps. The 115 depending on 78-84 year should have the same TC carb size as the 140. Both are 3.375" bore, 140 is 2.875" vs 115, 2.8" stroke. Both should have electronic distributor no points but if convert back to points no issues, very reliable. Both are Powerflow 1.73:1. Grab them both knowing they are good to start a build. But if the later Merc style Force 120 is also available consider that as well.
No real issues for any availability on ign or other parts for the Chryslers except maybe where you are in the world, everything is over here. The FORCE could be easier in that regard.

[FMP]

A comparison of Chrysler pistons, the big ears deflector is from a very late replacement 99/2000 Force F5 powerhead. Not the later Force Merc F3&F4 design.
The other is the Wiseco 3151 with cropped deflector ends and the best choice for a replacement piston, very close to the original Chrysler deflector which was used during the production run for the F5, small and large bore version 89-94.
Mercury decided to change a few things in the late replacement F5 powerhead, ears included.
These late pistons were tried in a stacker 103ci. It didn't go too well. The deflector on the transfer side didn't hold up and pitted and frittered away. Possibly a less aggressive ign advance and jetting could have led to a different result. After all Merc did " improve" them.

The other changes included destroked crank about 0.030" from the 2.876".
Followed by ex duration drop to match. The original big bore had slightly higher ex ports than the small bore specs and more revs. They kept the big bore.
With the new lower ex came more head deck thickness and chamber volume, but the new big ears on the deflector cancelled some of those cc. The squish however is very wide , not tight but stock compression is 155-165psi.

Transfers remained the same.
Original small bore and big bore had tranfers at 121.3°. The small bore ex spec is 103.7°, the big bore I've measured at 102.5°, the late replacement short stroke big bore I've measured at 103.7°, tractor porting that ran out at 5200-5500, although the original big bore does turn some more it's not much more in stock form.

The fresh water intake passage at the bottom of the block above the adapter was widened from the original.

Bosses were cast and countersunk between the first fresh water chamber in the block to the hot exhaust side of #4,5 cylinder water jackets, to be drilled as needed. #4 drilled will likely improve the temp of 4 and 5, mixing some fresh cool with the more heat soaked water at 4 and then 5.

They also went with four pedal coated cages.
Definitely good waterskiing, tube pulling motors, all three versions.

[FMP]

When looking at the fuel burn pattern on the original deflector transfer side , full round port patterns are seen. As mentioned above the squaring of the center ports and inner corners of the outer ports would still aim the extra area at the deflector. If the outer port outside corners would be squared the cut back of the deflector ends would allow more charge by instead of up and over and possibly out the exhaust port s before being restuffed prior to close.
I believe the improved later design deflector was an attempt to contain more at lower and mid range.
It could be and advantage to almost fully square all ports with this deflector.
The piston shape after the deflector is convex in both examples. The chamber is also convex at the top of the ex ramp, level towards the mid and near bottom of the ex ramp and concave at the bottom of the slope.
The tightest area is at the top and center of the chamber as is the tranfers side of the deflector. The burn pattern shows a triangular shape aimed at the exhaust which has more clearance by the shape of the piston vs the chamber. This enables the restuffed fresh charge to be pushed back into the top of the chamber working against the compression of the upstroke. I suspect the reasoning is it's more efficient to dead end the incoming pulse from the ex port into a decreasing wedge prior to ex closing as well as the burn front being forced from tight to loose.

[FMP]

That's a short boat! Looks like an old SE or mod 50 boat

It's not a mod 50 , he has compared them and they are smaller, he says. The boat was previously run with a hot KR15, ran 105.
With a low rake 3 blade cleaver it's very stable. He felt less safe in a larger 18’ 69 Glastron Molinari with BP1250 stacker which he drove back in the 1980s at 90MPH.

[FMP]

Comparing weight of the three pistons.

On the left is the later Merc Force big ear, 687g

Center is Force original cut ear, 671g

On the right is Wisecos +0.030" 3151, 639g
Piston only without wrist pin and rings 520g


All had wrist pins and both rings, no bearings retainers or clips.

All three are for CHRYSLER FORCE style rod not later Merc F3,F4

[FMP]

Show us more of this rig!

Not sure if it's a triple or a 115 but it's as direct injection Tohatsu
https://m.youtube.com/watch?v=uR9A2UEvlrY
It did have a inline 6 on it at one point, read that somewhere.
Just a 70 or 90
https://m.youtube.com/watch?v=Aq7PMMVjnm0
Need a 135/140 or F5

[gmjim]

Found this one thanks to a hot tip, seller says it is a 1995 120hp, looks like it may be the model mentioned previously that uses a mercury crank spline and mercury rods?
Sale is a very good price...

[powerabout]

When looking at the fuel burn pattern on the original deflector transfer side , full round port patterns are seen. As mentioned above the squaring of the center ports and inner corners of the outer ports would still aim the extra area at the deflector. If the outer port outside corners would be squared the cut back of the deflector ends would allow more charge by instead of up and over and possibly out the exhaust port s before being restuffed prior to close.
I believe the improved later design deflector was an attempt to contain more at lower and mid range.
It could be and advantage to almost fully square all ports with this deflector.
The piston shape after the deflector is convex in both examples. The chamber is also convex at the top of the ex ramp, level towards the mid and near bottom of the ex ramp and concave at the bottom of the slope.
The tightest area is at the top and center of the chamber as is the tranfers side of the deflector. The burn pattern shows a triangular shape aimed at the exhaust which has more clearance by the shape of the piston vs the chamber. This enables the restuffed fresh charge to be pushed back into the top of the chamber working against the compression of the upstroke. I suspect the reasoning is it's more efficient to dead end the incoming pulse from the ex port into a decreasing wedge prior to ex closing as well as the burn front being forced from tight to loose.

Piston almost like an omc yet chamber very different

[FMP]

Yes , Mercury leg, lower, rotating assembly,

[FMP]

Piston almost like an omc yet chamber very different

Even the difference between the pure CHRYSLER FORCE and later Merc Force chambers and deflector design is slight but notable. As mentioned before Merc had the chance to do an inline design or anything else like the OMC but only slightly changed the original. I can't say for certain but plenty of any of the designs including Schnuerle will burn down without proper care and tuning.
Some wise guys in the know who raced the original design did mod them by moving the plug and a bit more, picked up a few extra HP. The motors ran very strong!