Mercury Snowmobiles Discussion Board

by **nitrofa340** » Sat Mar 13, 2004 6:21 pm

I already asked this question some time ago and no one replied, so I thought I would try again. Has anyone out there ever tried the SuperMod porting specs for the K3402rs engine as found in the TwisterTipster bulletin? How much of a performance gain was found? I had my cylinders cut to these specs last summer, and never had the chance to race the sled this year. The engine is in a lay down mod chassis. This sled will be used for 500ft drag racing. So far all I know is the engine still starts/idles great,....hot or cold. Thanks in advance for any feedback anyone might have.

by **SHewelt** » Sun Mar 14, 2004 5:47 pm

My experience has been, the MERC Tipsters are not the answer. I've tried the 76 specs & the engine turned into a peaky mess, with no low/mid range...it couldn't get out of it's own way below 8000 RPM's. This made clutching & gearing nearly impossible. I've heard the same horror stories from others who tried the tipster suggestions. I just spoke with a guy last week (he own many MERCs) about the tipsters. He spoke with one of the engine designers from years back who said to throw out the tipsters, as they do more harm than good....seems to be a common experience. I think the Kohlers were pretty close to ideal stock. The 76 T-bolt CDI is pretty good, the pre-76 Prestolite gives up some power though. Perhaps some head work to bump the compression and some internal port clean-up, then work on clutching / gearing from there on....just my opinion.

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by nitrofa340
 I already asked this question some time ago and no one replied, so I thought I would try again. Has anyone out there ever tried the SuperMod porting specs for the K3402rs engine as found in the TwisterTipster bulletin? How much of a performance gain was found? I had my cylinders cut to these specs last summer, and never had the chance to race the sled this year. The engine is in a lay down mod chassis. This sled will be used for 500ft drag racing. So far all I know is the engine still starts/idles great,....hot or cold. Thanks in advance for any feedback anyone might have.
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by **nitrofa340** » Mon Mar 15, 2004 4:45 pm

Scott, thanks for the reply. I will give a report on how the performance changes, whether good or bad, with the new porting after testing the sled on the electronic timer next winter. I am not that concerned if some low and mid range performance is lost, as the sled will only be drag raced. The only throttle positions the sled will see is "on-off". I can understand though, that on an oval sled low and mid range losses would be unacceptable. Thanks again for the information.

by **SHewelt** » Tue Mar 16, 2004 11:18 pm

You are exactly right, I was refering to usefulness of powerband for oval racing. For drags, I'm sure it will give you more upper HP. My 440 that was mod, per-tipster, pulled so hard when it did launch I broke the #35 chain...never did that on any other MERC. It may be the hot-ticket for 500 ft..WFO! I'm looking forward to hearing the outcome & get pic's...I'm sure there will be a roster-tail when it hooks up!

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by nitrofa340
 Scott, thanks for the reply. I will give a report on how the performance changes, whether good or bad, with the new porting after testing the sled on the electronic timer next winter. I am not that concerned if some low and mid range performance is lost, as the sled will only be drag raced. The only throttle positions the sled will see is "on-off". I can understand though, that on an oval sled low and mid range losses would be unacceptable. Thanks again for the information.
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by **waynehaner** » Tue May 04, 2004 3:51 pm

We race both a 340 and 440 Sno-twister in the oval circuit. We have always been successful with the mods recommended for the 440 but the 340 has alway been a dog.

Last year the 340 was ported exactly as the 440 mod specs. We used the 440 pipe on the 340 and the thing kicks ass. I don't have the technical knowledge that SHewelt has but our engine guy is pretty sharp.

Just thought I would pass on the info.

Wayne

by **waynehaner** » Tue May 04, 2004 3:54 pm

Just to add to my previous post. We couldn't pull more that 8900 rpm with the 340 before the mods. Now 10,000 rpm is no problem.

Our guy said if these mods don't work, then we will run over the engine with the truck (LOL).

Wayne

by **SHewelt** » Thu May 06, 2004 11:58 pm

Wayne, that makes perfect sense, as the 340 & 440 are the same stroke (same lower-end), so porting height will result in similar performance (raising the exhaust port is what increased your RPM). The difference in the 440 ports is mainly width. If you tried to widen the 340 ports to the 440 suggested width, you would likely catch a ring, so height was probably where the ports matched up. I know on my 340 & 440 twisters, the 440 pipe is just a slight bit larger diameter, nothing you can really see, I only notice it when measured. The larger diameter pipe may have helped with the more volume you moved through the ports. Lengths of the pipe determine the RPM peak, & the 440 & 340's run nearly the same RPM range, so that also worked out in your favor. Thank God the engine ran good & wasn't necessary for any Kohler 4-wheeling!....Scott

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by waynehaner
 Just to add to my previous post. We couldn't pull more that 8900 rpm with the 340 before the mods. Now 10,000 rpm is no problem.

Our guy said if these mods don't work, then we will run over the engine with the truck (LOL).

Wayne
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by **waynehaner** » Thu May 13, 2004 5:58 pm

Scott,

Thanks for the technical explanation. I know the 340 and 440 bottom end are identical because we have been forced to sacrifice the 340 motor for the 440 on a couple of occasions. Lack of parts you know. If you can help, let me know (LOL).

If we could get a decent hole shot with the 340, we would be unbeatable. It seems like we get a poor hole shot and spend the entire race working our way back from 6th to 2nd or 3rd. Those damn ThunderJets seem to have our number in the 340 class.

Any information on Merc mods you might have would be appreciated. We are especially interested in any pipe manufacturer/design that may help us out. We have a local guy (Darcy Rosentreter) who is suppose to be one of the best but we race against his brother so we are concerned about getting the real deal (probably just paraniod).

His brother runs a 1973 starfire and has beat us out the last four years in the Canadian Championships in Beausejour. We had his number all year in Beausejour and Roseau but he always gets the big one.

I just noticed that you are associated with a CDI manufacturer. Is there any inprovements over the stock unit for the snotwisters?

Thanks for the excellent posts.

Regards,

Wayne

by **SHewelt** » Mon May 31, 2004 11:20 pm

Wayne,
The T-Jet's really handle, but they shouldn't have any HP on you...they may be a bit lighter though. Good pipes are tricky to find. I talked to Scott at Label-X (Maine) last year, and he either did make, or was working on some pipes for the sno-twisters. Label-X has a webpage for contact if you wanted to see what he has available. Many of the front-runners at Eagle river were running something from Label-X, if that helps. I have the MERC Tipster recomendations for the pipe mod's, but really it was ment to allow the higher rev's from the porting (shortens the pipe) & probably alone won't add any HP, just RPM. Regarding the CDI's, the FIREPLUG will pull harder in the mid RPM's compared to stock. The top end is nearly identical to stock (timing profile), but additional energy may help out with higher compression & idle. Dyno results have shown a mid-range increase in HP over stock. Good luck with the set-up!

by **75sno-twister** » Tue Jan 03, 2006 4:34 pm

[quote]Originally posted by waynehaner
 We race both a 340 and 440 Sno-twister in the oval circuit. We have always been successful with the mods recommended for the 440 but the 340 has alway been a dog.

Last year the 340 was ported exactly as the 440 mod specs. We used the 440 pipe on the 340 and the thing kicks ass. I don't have the technical knowledge that SHewelt has but our engine guy is pretty sharp.

Just thought I would pass on the info.

Wayne
<hr height="1" noshade id="quote"></blockquote>Any info on timing and porting changes for the 340 that you could share would be very useful to me. I also drag race a k3402rs. Also did you cut the piston skirt? and how much

by **nitrofa340** » Sat May 08, 2010 9:52 am

Just a quick up date to an old post of mine regarding my 340 f/a engine with the Tipster sheet specs. I am currently racing that engine in my mod stock Rupp F/A chassis. The sled runs good, in spite of the fact that I am still running the complete stock Rupp exhaust system along with 38mm carbs. The sled is currently about .20-.25 faster in 500 ft on ice than my 340 Rupp stocker. Also I could hit 75 mph in 500 ft on the GPS while out testing, which I thought was outstanding. It did win the 340 ModStock F/A class at Waconia this past winter, so it must not be a complete slug. Two weeks later at the Waseca drags, however, I cracked a piston on the second run of the day and it was done for the day. Gotta love those GPI pistons. I might try other pipes on it for next winter to see if I can get a little faster.

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