srp

We will be testing on a 350 next week, it has been ported by Sandtrax in Tulsa. It has small carbs, factory air box and currently runs T4's and is well known in our area for being a good tuned and fast bike.

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Excellent, Thanks for the data sheet.

Andy, What are the exact port durations on the 421? Banshee or Blaster style pistons?

ETA is about thirty days for the In-frames. There are pieces to the silencers that are not here yet to have a clear picture of cost. I'm not sure if Jim will post any more dyno sheets being so close to them being ready. What we want to see is real world feed back from the track. I do think we are going to dyno a hard running Fast Racing stock cylinder 4 mill. If we do I'm pretty sure it will get posted.

If they are inframes I have seen the CPIs shine with alcohol. May be so close you will need to dyno or run it on the clock.

The scientific standard is calculated in bars (9 bmep low) (11bmep high). Your formula divided by 14.7 will convert to bars. The 492 is somewhere around 8.85 bmep. If a 492 is tuned to 11 bmep@10700 it would make 131 horse-power. This shows more tuning can be done to extract more power. The engine in my drag bike is a 10.88 bmep Passion 421 Cub on gas making 105 horse-power@10150. This shows my engine is very close to maximum output. By your comments you seem to be knowledgeable and on your game. The first number I look at when rating an engine is bmep and then horse-power second.

BMEP is brake mean effective pressure. It is a way to calculate potential engine horse-power before the engine is actually built and will tell you if an existing motor is putting out maximum horse-power. A well built 2 stroke on gas will be around 11 bmep and on alcohol can be close to 13 bmep. The equation for for two stroke bmep is 75.4*torque(lb-ft)/displacement(Ci)/14.7

Projected heat and flange inside diameter will dictate the angles and body diameter of a correctly designed pipe. A high Bmep 421 and a low Bmep 510 will take a similar pipe. On engines such as a high Bmep 510 Cheetah will need a bigger stinger to bleed of heat . Sniper will offer this type of mod for big bore and hill shooting, both needing to bleed of heat to combat power fade. We dynoed with the small bore small flange out of frames Mailman was talking about on 6/3/2010. The inframe Assassins dynoed 5hp stronger with 2 more foot pounds of torque on a 421 cub.

We are looking at removable silencers for the OOF. I have removable stingers on most of the OOF drag pipes. Being able to change the stinger diameter and length at the track will help combat power fade in high gear.

The stingers welded to the the expansion chamber will have a 18 degree mandrel bend so they will hug the frame and clear the air box and filters. Then the tail pipes will slide straight on to them.

Lonnie and Ed both liked the output of the in-frame Assassins. Ed did all of the tuning on the engine when the pipes were switched out to keep the air/fuel ratios the same. Ed and Lonnie both give me some good info on silencer design too.

Maybe Andy can get everybody together after that new track opens up. We enjoyed coming to old Nowata track and don't think we missed even one race. We have not been out in almost a year. There is just no where to go around here. Is meeting up at Whitefield OK for some hand flag races too far for everybody? Going to a all day test and tune somewhere would be better. If everybody got together and wanted to race at Extreme world, Maybe David would open the track for that but last time he had a race there were only three racers that showed up. So everybody can see why it is closed.

We just had a window of one hour on Saturday. If we would have had more dyno time we would have changed pipes and tuned. We mainly wanted a base line on alcohol. We will go to the track for testing. Our drag strip in Tulsa is closed all of this year. To test three sets of pipes and tune all of them on gas and alcohol is going to take more runs than we will be able to make on one Friday session at Atoka. What about Mooreland? When will they test & tune again? If there is a more known dyno shop than Santrax's close to us somebody will need to tell us where it is. Two really big builders know them and has use them many times being Mccoy and Andy. They could probably tell you more about them than I could. We would like to go to another dyno for a second opinion to validate our pipes. We have dynoed many times on Fastracks Dynostar with all of the prototypes with virtually the same results but he is just now getting his name out there and is not well known yet. By looking at the temperature and humidity, the run conditions were better on the day of the gas test. One thing the correction factor don't do is compensate for the water grains in the air and it was bad on Saturday. 99 on Saturday with a density altitude of 3,546 and 61 and 2,755 density altitude on the Thursday that we did the gas runs. The true correction factor on Saturday was actually 109.1 and not 106. We did not really give the alcohol test a fair chance not raising the compression and adding some timing but we will do it again.

(9000 Rpm) With a 54 stroke its 3189 FPM,58 stroke-3425 FPM,61 stroke-3602 FPM,64 stroke-3780 FPM,68 stroke-4016 FPM. All are safe RPMs. 11300 RPM is 4004 FPM on a stock stroke engine and 14100 RPM is 4996 FPM on a stock stroke. As you can see bigger strokes will raise the piston speed. You would need to have some kind of road racing pipe and porting to get anywhere near redline.

A data recorder with about ten transducers would do the trick.

Our pipes that are tweaked for builders will have a tab with that builders name on it. The builder will know what porting configuration his pipes will work best with. So that information will not be hard to get and our variations will have tabs stating deference's. We will work very close with the builders especially with our drag pipes looking for that last couple of horse-power. Our drag pipes will be four piece stamps just like the inframes making them adjustable at the header and belly.

Piston speed dictates maximum RPM, maximum safe RPM is 4000 feet per minute, absolute max is 5000 feet per minute. Fuel,Air/fuel ratio,compression,exhaust port duration,tuned expansion chamber length,baffle angle and stinger back pressure will dictate what peaking Rpm you actually get from your motor, just as Andy said lots of variables. Lonnie at Sandtrax's said stock ignitions seem to start dropping cylinders at a certain RPM. I would like to know if anybody has experienced this and at what RPM.

You will very rarely see anybody using volumetric efficiency as a way to tune a two stroke mainly because of the returning wave of trapped air being forced back into the motor at exhaust port closing. This raises the delivery ratio to close to 1.4 with a highly tuned pipe, meaning a 350cc engine will burn 490ccs of air/fuel. That is supercharging and the better pipes will have a higher PSI amplitude than a bad pipe will have. Mopedarmy.com has a good animation of this. If I knew how to setup a link to it I would.

Lectrons I have are old and the chokes don't want to stay up and that is not helping things when I have the PVL on the bike.

I can see why they would be good on a flattrack. The light flywheel makes them explosive rolling on the throttle. I have had luck like you on reliability and I really take good care of my stuff.

I agree that they are good and if you can launch in second and not ever bog they are an advantage for the racing we do. If you are getting 6 years out of them you are doing something right. What about starting?

I have been running PVLs for years and have dynoed them against stock ignitions and there is not a nickels worth of difference between them unless you had a problem with one or the other to began with. PVLs have less rotating mass and makes launching in second gear with a lot of paddles difficult. But if you are launching in first they are awesome. PVLs need to have the wires going to the coils supported at the coils to keep the wires inside at the connectors from losing continuity( zip ties work good). Hard to start is a under statement and that is why I am back to stock ignitions. A word of advice if your are running PVLs is to buy one spare primary coil and one spare secondary coil because they do go out regularly.

You are right about volumetric efficiency not being 100%. The only way I know to check VE is to put transducers in the crankcase and in the intake manifold and a MAF sensor connected to a data recorder, then compare the pressures to the atmospheric pressure at your altitude. If you have just a MAF reading in (Lb/Min) and the temperature the day of the test I can figure the volumetric efficiency from math. But seeing the pressures differences between the crankcase and manifold at reed closing would tell me more.

Wow Cam, that is some good data. I will check that out.