321 cooling on a runabout

[Tim Weber]

Yesterday I played 302 vs 321.

First off, I ran 302 and got it good and warm for base numbers. The highest temp recorded was 305.

Then changed tower housing only, same prop, same set up, with 302 intake. The max temp was 347.
Then changed to 321 airbox, 348 max temp.

I ran the living hey out of it, taking 5 laps WOT with rpm 7000+.

engine timing 225
air temp 80
water temp 70
air density 101
oil mixture 20:1
3/4" high
1/8" tuck
high rake clever prop
used 302 brass exhaust hole
altitude 1170

I don't see where a runabout will cause an issue.

Tim

[Matt Dagostino]

What do you consider a '302 intake' to be vs. a 'used 302 brass exhaust hole' you reference?? What instrument are you using to measure temperature (also are you measuring head temp or exhaust gas).

[Tim Weber]

Matt,

The 302 intake is the original spray shield and air horn from the 302. Then I switched to the 321 air horn and larger, baffled spray shield.
The brass exhaust is the fitting below the power head on the top of the tower just under the steering bar mount. The 302 fitting has about a 3/8" hole in it.
The 321 fitting has about a 1/16" hole.

I was measuring head temp with a spark plug sensor on the top cylinder.

Tim

[GrandpaRacer]

While you found acceptable temps your data confirms the 321 runs hotter with less safety factor. How did it compare in performance?

This morning I decided to do a dimensional inspection on the tower housings of my 302 and 321. Having measured both I found some interesting numbers. From the cavitation plate to the bottom of the exhaust snout the 302 measures 2.279 inches while the 321 measures 2.202 inches or the 302 snout is .077 inches deeper down then the 321. The second dimension was the placement of the water inlet hole in the snout. The 302 measures .875 inches while the 321 measures 1.00 inches from the bottom of the snout. Now when you add the .077 inches and the.125 inches you find the water pickup hole is .202 inches closer to the prop shaft on the 302. The last dimension I checked was the hole size itself where the 302 hole is 1/64 inches larger then the 321. With these dimensions one can see we might have a cooling issue when we go higher on a hydro, Measuring the exhaust relief hole in the brass fitting the 302 is 5/16 inches while the 321 is1/8 inches. It is my opinion that this has a minor effect on the engine cooling because the water velocity is great enough to only provide for minor heating of the cooling water due to the temperature in the tower housing. Remember the tower housing runs much cooler the actual exhaust temperature. How can we solve the issue. One, we could make the water hole into a race track that goes .25 inches deeper or closer to the prop shaft or we could plug the watering hole in the 321 and move it down .25 inches. Anyone have an idea on how the best way might be to cool the engine? Seems to me by allowing a modification to the watering hole location might be the easiest way to maintain commonality between all 321's and would be easy to inspect for conformity to the rules.

Took my second 302 out of the trailer and the scout is 2.236 inches deep but the bottom of the snout to the water inlet hole is the same as my other engine at .784 inches from the bottom of the snout. So I guess there is some variability relative to the snout dimensions.

[DtwSailor]

Thanks Tim, this also backs up the testing we did in Jesup at the beginning of the season when Mike Affholter ran my sealed 321 with machined head, gear foot, and tower and took 2nd or 3rd I believe in CSR. I'm doing a round of testing tomorrow on the hydros as well share the results, video and whatever other data I get.

[Hydro doc]

We need a solution, soon, as the nbra meeting is nov.5. Could we enlarge the hole in the down housing to the same size as the 302? As the hydros are having problem of over heating, this would be a cheap and easy fix. Has this fixed the over heating problem.?

[Matt Dagostino]

Doc...............as we discussed the 302 back pressure nipple is a 5/16inch diameter brass plug and does relieve much more backpressure than the stock 321 brass plug that is less than half the diameter. Testing is showing that even when running the 302 backpressure plug in a 321 midsection the engine temps are still 40 plus degrees higher than using a 302 entire midsection! The new configuration of the 321 midsection is made to be quiet and has a much different internal baffle. Seems the only real solution for the motor to survive in CSH/20ssh is to either allow a external water pick up as John Adams has demonstrated or lower the class heights a bit. But in the APBA Stock Outboard division it is already legal in any class except the 300ssh to run the 302 brass 5/16th plug in the 321 midsection if you want. TJ and the SORC have allowed all parts between the 302 and 321 to be interchangeable in any class EXCEPT the sealed 300ssh class which runs buried at 1 3/8th and does not experience the overheating issues we see in CSH/20ss. As the Yamato 321 is the new product being offered seems we should do what is necessary to serve our members and do what is necessary to make it operate at the approved class heights we allow. Go SOONERS.

[Tim Weber]

Like I mentioned on a earlier post,
Switch to runabouts!

Just kidding aside, the hydros seem problamtic. Hydros are a bigger part of the category and I'm not in a position to comment.

But.... I've just scratched the potential of the 321 so my numbers are just one test session

I really don't know what I have until once really dialed in

Tim

[Hydro doc]

Inorder not to have to buy a 302 brass nipple, would it be the "fix" to simply drill the 321 brass nipple to 5/16. Is this what SO com. Will recommend?

[Big Don]

Matt where did you hear that it's on the Tech agenda? I don't believe that has been shared with the SORC as I have not heard this.

[Big Don]

Doc, I'm not 100% sure but would be willing to guess nothing will be decided until the meeting in January.

[Jeff Brewster 59s]

The nipple is not on the agenda because there is NO agenda. The agenda will not begin to be formed until I have the 2017 commission in place and they will help me decide what motions will be discussed in LA.

[Tim Weber]

I'll have my temp gauge on board this weekend at Tabor City. So far, all I have is testing data under controlled conditions. The race data will tell us a lot more.

Stay tuned until next week.

Tim

[Tim Weber]

Ok, four heats on the books at Tabor City.

Max temp at 356. I ran it hard all weekend, won two of the heats so no sandbagging.

The air temp was 82, my guess on water temp 65, altitude 110