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06 800 head 13 to1 compression ratio

5K views 32 replies 5 participants last post by  Daag44 
#1 ·
Hi guys it's been a while I use to be known as vintage 30 but my acct got messed up when I got a new phone . I'm getting ready to start back up on my 06 motor build again . Anyone in Michigan running a13 to 1 compression head on pump gas I was going to try it but think I'm gonna have it machined to be bit safer maybe 12.5 to 1 .
I'm running crank shop trail ported cylinders And this year I'm going to add a summit air box off the 07 as well as the exhaust with DJs helix. I put in a new crank and got the snow x dual ring Pistons installed on the rods started thinking about the head which is a slp for 0 to 3000 feet elevation which is 13 to 1 they claim it's safe but I'm leaning toward it isn't . I really only bought it to help with cooling the motor . Just wondering if anyone is running 13 to 1 with no issues on our crappy pump gas...thanks

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#7 ·
13 to 1 on premium pump gas is not advisable. 12.5 is about as high as I'd want to go on pump gas. With a splash of race gas I think you could get away with it. But your jetting and pipe selection would be critical.
Thanks I don't think I'm going to even attempt it . I'm gonna do a squish test then have head machined to get me around 12 to 1 to 12.5 to 1 ..

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#9 ·
Thanks I don't think I'm going to even attempt it . I'm gonna do a squish test then have head machined to get me around 12 to 1 to 12.5 to 1 ..

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Darren, something I have learned from working with 600, 800, and 1000 owners is that the squish test is best done mechanically with an accurate depth gauge or dial indicator to get the same measurement as Ski-Doo. Otherwise you can easily get a squish that is far too tight. I have noticed and remarked this problem throughout various builds on DooTalk and it worries me. I noticed that engine builders who do use a medium like solder to measure squish also have their own specs for these engines that are different from Ski-Doo. So if you use solder I recommend using the spec from the builder. Hope that helps.
 
#10 ·
A quick calculation says you need to gain 1.65cc's of compressed volume to go from 13/1 to 12.42/1 on a 400 cc swept volume. That's .012" added to your squish, or 1.65 cc volume cut from the chamber. Have you actually measured your squish? You need to do a cc on the assembled engine to know your actual theoretical c/r, and know what you need and have for a squish height.Contact the head maker and get the spec. There can be differences in cylinder and case height that can vary it. It may be called a 13/1 dome when you buy it, but it can vary + or - some. Guessing can cost you dearly. A few thoughts.
 
#12 ·
Geez, even knowing can cost you dearly. That pipe action is a wild card that can raise cylinder pressure higher than you account for. A nice cushion in octane level is necessary if you're going to stray to far from the stock 12/1.
Why are we only beginning to hear about this??? I have been waiting patiently for you to bring this up. Here is a excerpt from a 4 stroke topic, only because recently I was looking for runs from Marcel Corriveau, but there are more for two strokes. Pipe pressure is everything.

Even if we tried to add fuel afr dropped but Pyro and exhaust pressure went higher.

http://www.dootalk.com/forums/topic/439654-top-speed/#entry3251319
 
#13 ·
Not the same thing at all,daag. I was talking about the increased efficiency the negative wave adds to the induction process, and the raise in cylinder pressure by the stuffer phase.Unlike the formula for theoretical or actual compression ratio,there is no mathematical way to calculate this amount,not that I know of,anyway.Perhaps an engineer can calculate it? I call it the wild card, because it can raise the 'squeeze' above the octane level you have calculated it needs.Which,of course is why you want the most efficient pipe you can buy/make/borrow/design,increased volumetric efficiency. 4 strokes use the same negative wave during overlap to aid in scavenging the chamber, and produce a low pressure in the chamber to aid cylinder filling and ram effect.I saw a pic of an F1 car a few years back that had what looked like an expansion chamber on it. Could they have got induction on a 4 stroke working well enough to be filling the pipe with unburned charge, and stuffing it back in? Anyone have any thoughts or knowledge on that? A pic of a KTM works motocrosser my son has what looks like a diffuser and convergent cone on it.I'm sure the motocross guys on here have seen that.Interesting stuff.
 
#15 ·
Are you saying we can't use center pipe pressure as a measure to detect if more or less unburned charge is being stuffed back into the cylinder?
It wouldn't tell you anything about the charge quantity that's getting stuffed or vacuum signal.The wave effect happens all through the pipe,and also happens in a reverse direction because the diffuser has a taper that acts as a convergent cone on the returning wave that is farther down the pipe, albeit in a much smaller way, due to the small angle.I'm a 4 stroke guy with limited 2 stroke and expansion chamber knowledge.I would say its very complicated, and like port directional flow and port timing, much easier to get it wrong than right.
 
#16 ·
Zxmodv, the following links will give you a better idea of what I was referring to. Monitoring the center pipe is something I first learned from the few MachZ guys that knew how to tune their sleds. Then I noticed Dynotech were doing the same thing with a write-up on it, then I found it on Gus Bohne's MachZ, the Arctic Cat stock 800, the Ski-Doo Summits and Backcountry, then I found LRD's post which led to pipe builders. That is the reason why some months ago I couldn't understand why monitoring center pipe was not useful. I've only monitored AF but heck few even believe this is possible and still choose to adjust a fuel controller using EGTs. How on earth can the EGT tell you if you're nearing lean or rich misfires??? First you make a baseline without a fuel controller, then the fuel controller is installed to make adjustments. The lower the numbers the higher the fuel flow. I just don't get why we are over a decade behind the Arctic Cat owners. But knowing how much you like two strokes I figure I'd bring it up.

The graph was provided by BRP to dealers some years ago to help educate the effects of aftermarket mufflers. I have read the complete article from BRP and copied it somewhere, but somehow misplaced it :headbang . Krm could probably get us a copy. It was worth the read.

http://www.dootalk.com/forums/topic/218137-xp-500ss-full-wet-450lbs/page-8

http://www.dootalk.com/forums/topic/992753-silencing-the-can/#entry10951553

http://www.omega.com/pptst/DPG3500.html

Digital Pressure Gauge from Omega - NEMA 4X Case with Min and Max readings

Measuring instrument Electronic device Technology Font Auto part


800R Muffler comparison for the REV

Rectangle Slope Font Parallel Pattern
 

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#17 ·
My 770 has an egt in the centre pipe,daag. I'm putting fittings on the other pipes I have to use on it and the 800r. The wave action and the fact that the exhaust gas from a firing stroke not exiting the pipe in one pulse make reading 02 in the exhaust stream inconsistent, unlike a 4 stroke. That's why I don't use it.And to me, egt's are an indication of a process, not a tuning device.IMO. I rarely look at the egt's when I'm riding, in fact I avoid looking anywhere except far ahead. If it blows, so what. If I make a mistake because I didn't read the terrain for 200ft and go into the forest,well, the egt's don't matter. It has a high memory, and I get it tuned before I even turn it on.TT670 advised me on that.I like getting it set up, then just riding it.And I use only the stock muffler and ear plugs.I couldn't care less about cans. How 20 years ago.
 
#22 ·
If u don't mind me asking who are u gunna use to machine the domes? I'm also in the same boat and bought an slp head that has wrong elevation domes in it than what I was told when I bought it.
I use a local guy here in Michigan to do any machine work I've ever needed doc fang engineering in clarkston mi .

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#23 ·
You might change your mind with an ETEC.
Not likely. When and if I own an etec it will remain bone stock. There is thousands of them out there with happy riders at the pinnacle of 2 stroke technology that just ride, no tuning required. As close to 4 stroke gas and go as you can get. Why would you want to alter the sophisticated DI system? I agree with that saying " It doesn't have to be difficult to be good".
 
#24 · (Edited by Moderator)
Not likely. When and if I own an etec it will remain bone stock. There is thousands of them out there with happy riders at the pinnacle of 2 stroke technology that just ride, no tuning required. As close to 4 stroke gas and go as you can get. Why would you want to alter the sophisticated DI system? I agree with that saying " It doesn't have to be difficult to be good".
I am quite surprised on the bold. Say you bought a new 2015 ETEC 600, never checked the plugs as you say, then it burned down due to a lean failure. Would you say it doesn't matter I have a warranty? What happened to all that sophisticated technology that you spoke about? If you would like to argue that it has a knock sensor, I will save you time and respond that it used to protect itself against low octane and not extended lean conditions. The muffler temperature sensor is what is used to protect against a lean condition, but that's still playing with fire, literally. 800C (1,472F) is when the ECM detects the muffler is overheating. This is pretty much standard across two stroke sleds. Before it reaches this temp the ECM will go into a fuel enrichment mode. The ETEC has the advantage of adding oil to match the increase in fuel, which is great. But riding these conditions for extended periods is not good and won't help the life of the engine. There is also the oil ratio equation. Your new sled will be setup from factory to run the appropriate amount of XPS Synthetic oil, but it is still your responsibility to monitor oil usage. What if your sled delivers 10 percent less oil and 10 percent less fuel for whatever reason, and runs with 10 percent higher muffler temps? Will you waste your time blaming Ski-Doo while waiting for a new shortblock? Your best engine is your factory engine with brand new parts and this is worth paying attention to. This is one reason why I am a proponent to getting the fancy gauges that read the muffler temps. If you decide to plug a fancy accessory, you also want to monitor voltage. It doesn't need to be complicated.

Now if you want to pull the Ski-Doo engineering card on me, I will be happy to pull the Ski-Doo engineering history and there are many. In 2003 the 800 SDI was as you say, at the pinnacle of 2 stroke technology. What do think happened to those engines? In stock form they failed and Ski-Doo stopped making them shortly after. Ironically those engines are the most sought out engines for their cylinders in Ski-Doo history. Most don't even know of their value or how well those engines performed, an even less why they failed.

What I'm trying to say is that if there are any signs of trouble with heat, wether it be coolant, or muffler temps, or troubles with oil consumption, or troubles with fuel consumption, or trouble with the electrical, a blind fold with the words pinnacle of 2 stroke technology broidered onto it won't change a darn thing for reliability. Most people call it.......luck of the draw. Well you and I both know that luck doesn't play into it as much as it is advertised.

Here are some of things we can do with newer sleds. When we are riding with out buddies we can compare fuel and oil consumption, coolant muffler and clutch temps, and voltage. Folks do it all the time with fuel and coolant temps, so it's not a stretch to do this with the other variables and follow with appropriate action. If a problem is found with say fuel or oil, then we have the choice to switch sleds to eliminate the variable of rider style - read throttle control. Then if a problem is confirmed the sled can be monitored against a benchmark. It can and should also be brought to the dealer, but we play an important role, especially if the problem doesn't get resolved quickly. Read the multiple power fade topics for a refresher. That is where a forum like DooTalk comes into play. We don't need to pack our sleds full of gauges to go riding stock sleds, but we do need to be conscious of the needs of our two strokes which haven't changed a bit with the ETEC. DooTalk is an extension to Ski-Doo engineering, one that if used wisely makes a HUGE difference. Believe me, Ski-Doo does pay attention to the chatter.
 
#25 ·
Wow. I think your way over analyzing it Daag. All the tuning has been done before it leaves the factory. Leave the gauges off and just ride. Like I said, there is 1000's out on them. And the etec is the pinnacle of 2 stroke development.Not an '04 sdi 800. They hardly made any, and the few that want those cylinders have difficulty finding them. That doesn't make them the most sought after. Nor does an sdi 770 make any more power than a carbed version. They just cost more. And if you think Doo engineers are paying any attention to what you or anyone else is saying on here regarding exhaust temperatures or lean injectors, you should seek counselling dude.
 
#26 ·
Agreed! Daag, if you think that etec consumers owe it to BRP to go out and buy EGT, pyro, wideband O2, and water temp gauges just to carry out field testing for BRP you are crazy!

Don't get me wrong, I love gauges. I have an EGT and water temp gauge on my sled and love to watch how they are affected by riding style, temp, conditions...etc.

But these new etecs do not need that. They are tuned from the factory to operate over a wide range of conditions for idiot consumers that put cheap gas in them and hold it to the bar all day. They are not living on the edge.

Also...you just don't hear about lean burn downs on etecs that are caused by tuning issues. I would say that all etec failures are due to air leaks, injector failures or bearing failures. Not fueling...

Sure there may be a handful of dootalkers that would like to have that level of data. But most do not. And I assure you that BRP would not use your data to make engineering decisions. It's just too uncontrolled for modern engineering and system performance modeling. They may follow trends on the forums to look for reliability issues so THEY can conduct further testing. But they aren't going to use Joe Shmoe's egt and wideband data to make changes to their fueling.

Sorry man...you are just a bit overboard on this. I love your enthusiasm...but it's too much for the average gas and go rider.
 
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