Turbo vs. Standard Heads: differences?

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Brandon Atwell

Well-Known Member
Joined
Mar 11, 2012
Messages
1,202
Hey guys!

I know this is an age old topic, just looking for some clarification

Switching over, is there any changes to the head itself, as in Changes required in bowl volume, head clearance?

Life expectancy of turbos vs. standard?

Thanks in advance,

Brandon
 
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cost................. (and not the good kind)

The rest us not really worth the change..

Yes.. you can pick up a few RPM (noted years ago by a few) but one miss cue on the course and that few hundo RPM dont mean S^%#%

I would place my extra cost if you must spend it into fuel.. and test time.

Grim
 
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Turbo type plugs can give a considerable (500+) RPM advantage in smaller size engines; typically under .45 cu in. They take up a much smaller part of the chamber in smaller displacement engines which may explain why they work well. The apparent fact that they are the preferred plug type used in high performance pylon racing engines operating at a continuous typical RPM of 29,000+ RPM validates their continued use. As far as the cost, the Nelson turbo plugs are $5.00 / plug. What enables these type plugs to give the advantages previously stated will be determined by the accuracy of the seat on the plug body & in the head button. Notice on the posted print the 35* + or - 1* angle is approximately .0375" wide. A precision pre-ground tool cuts the seat in the head botton & a precise CNC machine cuts the angle on the plug body. The 11 /32 thread on the plugs body is machined to a + or - .0015" tolerance. The head design used for this type plug is a double bobble design running at .018" deck clearance with 190*+ exhaust timing. The plugs & their matching seats are extremely durable. They are the only type of plug that is used in my Nelson .45 cu in long stroke outboard engines.

Jim Allen

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Jim,

Is the .018” deck clearance you mention the clearance between the top of the piston and the head button at top dead center?
 
Here's an example of, both, a "standard" head button and a "turbo" head button. For the new "2017" OPS .45 Marine. I can't easily distinguish the differences? (I have'nt been able to perform any detailed measurements yet either)

OPS_.45Marine2017_HeadButton,Stand-PartNo.574451_July2017_01.jpg

OPS_.45Marine2017_HeadButton,Turbo-PartNo.574452July2017_03.jpg
 
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Jim,

Is the .018” deck clearance you mention the clearance between the top of the piston and the head button at top dead center?
Yes. The squish band is flat & the piston crown is also flat. We have tested the .45 Nelson long stroke engine at timings as high as 196* with a .022" deck clearance. The engine is approximately 500 to 800 RPM faster on the high end but it is more difficult to pipe up when used in a pylon plane taking off from the ground. This appears to not be a problem in a boat. Look carefully at the posted pictures of the double bobble combustion chamber. Notice how the intersection of the smaller top chamber is flush with the bottom of the plugs flat surface.

Jim Allen

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Jim

Do you shim the sleeve up to get timing at 190*..? Or cut sleeve?

Gary P. Told me to run 0.010 for old style @ 50% fuel. Does long stroke need more clearance to run better for boats or just plyon?

Sent from my SM-N920V using Tapatalk
 
Jim

Do you shim the sleeve up to get timing at 190*..? Or cut sleeve?

Gary P. Told me to run 0.010 for old style @ 50% fuel. Does long stroke need more clearance to run better for boats or just plyon?

Sent from my SM-N920V using Tapatalk
Alan,

We never cut the sleeves flange. We use .001", .003", .005", & .008" sleeve shims to set the timing. We also use a .200" thick gage block to raise the sleeve above the cylinder, piston crunch point. Typical measurements with a depth mike will be .287". Subtracting .200" gives .187". Adding .003" brings the dimension to .190" which corresponds to the 190*exhaust timing. As I have previously stated many times, no degree wheel is ever used to set or check the timing of a miniature size engine. Subtracting .185" (head button's depth) from .190" gives .005". Add whatever head shims are necessary to give the desired deck clearance. For my engine this is a .008" head shim plus .005 = .013".

I'm not sure what is meant by the old style. Long stroke engines began to appear in 2006. A short stroke engine has a stroke of .706" & the long stroke engine has a stroke of .790". The usable deck clearance will be determined by the fuel. I run the .45 long stroke FAI outboard engine with a OS Max 9B (.4724" bore, twin needle carburetor) & 65% Technology fuel with 5 ozs of Blendzall Racing Castor added to each gallon. The engine's timing is 190* & the deck clearance is .013". With the .013" deck & the 65% fuel the engine is very slightly under compressed. The Nelson heavy duty turbo plugs last forever.

Jim Allen

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The old style engine (I think) has the smaller cranks. I use the os-9b as well. I'm guessing the 0.187 gauge block helps with tbc issues of piston fit..? Working against you (right)?

Sent from my SM-N920V using Tapatalk
 
Jim

will this work the same on any engine size. With 0.200 gauge block?

Sent from my SM-N920V using Tapatalk
 
Alan,

Any size block can be used as long as it is enough to prevent the piston from sticking in the top of the bore. If the piston sticks, accurate measurement of the timing & deck clearance will be impossible. When new pistons are fitted to newly honed cylinders, they are pushed into the cylinder until they stop. This is done after both parts are carefully cleaned. We measure how deep the piston is in the cylinder when it has stopped. We are looking for a .265" to a .285" dimension for the crunch amount when both parts are new. This is the reason for machining piston in .0001" steps that will be fitted to random sized cylinders.

NOTE: I should also mention that the head must fit in the cylinder with about .0001" or .0002" total clearance.This is the reason we machine heads in .0002" steps.

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When I bought my engine it came with a stack of head shims but only one .005” liner shim. Neither Gary Preusse, or John Otto had plugs available so I sent the engine down to Steve Wood and he made a head button for standard plugs and set the engine up with no liner shims and .012” button to piston clearance. I seem to remember him telling me my engine had 190* exhaust timing without any liner shims. He machined the head button so the standard plug was flush with the top of the combustion chamber and the chamber volume was the same as the factory Nelson head button but with a single radius chamber, not the double bubble. I’ve had no complaints with the engines performance thus far, but recently scored some HD Nelson plugs, so I’m anxious to run it with factory head button and Nelson plugs.
 
I don't know who you bought your Nelson engine from or what type Nelson engine you may have in your possession. However, after building more than 2000 Nelson engines of various types, at Aero Precision Machine Inc., including Q-500, Q-40, FAI speed & outboard engines, none leave the factory without a complete set of sleeve & head shims. No engine would have a stock timing of 190* without some sleeve shimming!

Jim Allen
 
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Bought it through John Otto, he ordered it direct from Mr Nelson. It took what seemed like forever to arrive. I dont have the tools to measure port timing, so I never personally measured it. Im going off of memory from what Steve Wood told me, and I could quite certainly be mistaken on that number. I bought the engine new the year before Novarossi announced their line of .46 engines.

6F61432E-672E-4170-901C-D0569D9FFCF2.jpeg9C1AEC03-8E66-46D6-A006-E81F81B457EE.jpeg

The shims in the photo minus the ones under my head button are the only ones that came with the engine, only one liner shim and it measures .005 .The head button in the photo is the standard plug head that Steve made. If I was supposed get a full compliment of liner shims with the engine they never made it into the plastic bag the engine was packed in.
 
When I bought my engine it came with a stack of head shims but only one .005” liner shim. Neither Gary Preusse, or John Otto had plugs available so I sent the engine down to Steve Wood and he made a head button for standard plugs and set the engine up with no liner shims and .012” button to piston clearance. I seem to remember him telling me my engine had 190* exhaust timing without any liner shims. He machined the head button so the standard plug was flush with the top of the combustion chamber and the chamber volume was the same as the factory Nelson head button but with a single radius chamber, not the double bubble. I’ve had no complaints with the engines performance thus far, but recently scored some HD Nelson plugs, so I’m anxious to run it with factory head button and Nelson plugs.
Larry,

I spoke with Henry Nelson this morning about your outboard engine. Outboard engines come with only 1 sleeve shim to set the timing at 190* & 4 head shims to set the deck clearance. Heavy duty Nelson turbo plugs have always been available from Nelson Competition Engines or Aero Precision Machine, Inc.

JA
 
Hello Jim, I think it was Larry Conrad that showed me the carb that came with his outboard engine. My question is, why can't the supplied carb be used for boat use. Thanks in advance. Richard
 
Richard,

The pictured carb, which is now made in delrin, is used for the Q-500 pylon racing engine. It does not have automatic fuel metering & would make throttling up & down for model boat use difficult.

PC080009.JPG
 
Richard,

The pictured carb, which is now made in delrin, is used for the Q-500 pylon racing engine. It does not have automatic fuel metering & would make throttling up & down for model boat use difficult.
I run the turbo plugs and agree with sealing off the volume of the threads from the combustion chamber because that unusable volume is robbing compression from every stroke. Is the percentage low? Yes it is, but when you are trying to get it all you want every advantage in your favor and you have to consider this. I also love the way the turbo finishes off in the dome with its small footprint too. The conical seal not only seals off the thread volume from the compression ratio but also provides a small heat sink band that is located right at the end of the plug and that is an advantage as well. I agree with Jim that these small advantages would be more of an advantage in the smaller engines but an advantage of any size is what I look for. I have had fast engines with both styles of plugs. I personally believe that the Turbo plugs are better. They are not cheap and if your engine eats plugs like pop corn due to you over twisting your third channel needle when you are getting your butt kicked or if your engine is a heat sink nightmare, you are going to be looking for a cheaper plug so that you can afford to race. I feel like the turbo plug is an advantage but everybody has their own ideas about this. I wont waist my time arguing with anybody about it either.

I like the Nova Rossi Turbo C6TF plugs. I run these in my 3.5 and 7.5 O/B Tunnels with great results!

-Carl
 
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