What are the important points for a LSR engine buildup?

Moderator: DLRA

Post Reply
User avatar
NMBRPL8
Posts: 12
Joined: Sat Jun 08, 2013 10:55 pm

What are the important points for a LSR engine buildup?

Post by NMBRPL8 » Sat Jun 15, 2013 7:09 pm

Gday all, despite searching and reading i reckon close to 75% of all the posts in this forum, and asking google and reading other forums, cant seem to shed a whole lot of light on the subject. Ill understand if everyone wants to keep tight lipped on the specifics, it is a competition sport after all, but in a very general sense, what should one aim for when building an engine for a land speed attempt? Is RPM key? more revs equals more speed potantially but then you need the torque to get the gearing there, so is torque the key, should I go for as high a compression ratio as i can safely manage? And besides those basics, what should a newbie (to lsr) like myself be watching out for as far as engine design goes? I think i have a decent plan in place trying to get a good balance of rpm and torque, and keeping it all together and safely able to sustain the revs i want out of it without anything heating up too much and binding up or melting down. Roller bearings throughout, oil squirters to the piston crowns etc, that kinda thing.

So go easy on me, im new to the thinking behind holding an engine on redline for a sustained period of time, so there is lots i probably have yet to consider, any hints/tips/links/shove in the right direction would be muchly appreciated.
Cheers :)

User avatar
JonB
Posts: 268
Joined: Wed Oct 06, 2010 6:35 pm
Location: Brisbane

Re: What are the important points for a LSR engine buildup?

Post by JonB » Sat Jun 15, 2013 8:15 pm

Hi
Hp is your friend, build as much as you can reliably, gear it for your target speed and put up with abusing your clutch to get off the line if it bogs a bit.
Your only down in the revs once per run unless you have ultra-wide gears.
Guessing your project will be a bike engine seeing as you have a Kawasaki symbol as your avatar.
Generally means your gears are close-ish and you have 5 or 6 so once your up in revs you can stay there.
What fuel class are you running?
How resistant is your head design to detonation?
It's no use adding a heap of compression if your chosen fuel makes you back the timing out to keep from detonating.

All just my opinion.
jon
DLRA#1115
Underhouse Engineering

User avatar
ChrisACT
Posts: 111
Joined: Thu Nov 10, 2011 7:39 pm

Re: What are the important points for a LSR engine buildup?

Post by ChrisACT » Sat Jun 15, 2013 8:46 pm

I'm a newbie to this style of racing too so I'm very interested to hear the opinions of the experienced racers here.

I'm running a small air cooled two stroke (100cc).

The plan is to go for the revs I know the engine can handle on a circuit, minus a bit. I know it'll rev to 14,000RPM all day at the track so I'm building it to run at 13,500RPM on the salt. Obviously it only spent a very short amount of time at redline for circuit racing (end of the straight) but it will have to run at redline for at least a quarter of a mile for my class (which is hopefully about 9 seconds if I'm hitting my target speed right at the start of the timed zone).

The porting and pipe will be a lot wilder than I used to have as I'm aiming for peak HP and a wide enough power band only to avoid bogging down on gear changes. Each gear change will only drop the revs to a point which will still be above peak torque.

I'm also planning to run it on Methanol instead of Avgas to help with cooling and detonation. I'm not planning to increase the compression at all from how I used to race it on Avgas (which was at 12:1 CR anyway) so I'm hoping to be able to keep detonation under control even if I advance the ignition a bit for the methanol. Besides, high compression ratios actually make it harder for two strokes to rev. Great if you're riding on dirt and you want lots of bottom end and midrange but not so good on a circuit (or presumably the salt). I'm also planning to coat the piston crown and combustion chamber with a heat reflective ceramic coating to try and keep more of the heat coming out the pipe instead of heating up the head and piston.

I'll be running EGT and CHT temp sensors on it so I can shut it down before things get too hot if need be. Also going to run an O2 sensor.

I expect the weak point in the engine will probably be the small end bearing.

I'll no doubt find out what kind of grenade I've built when I get it to Lake Gairdner.

Stayt`ie
Posts: 907
Joined: Fri May 13, 2005 11:47 pm
Location: Mackay

Re: What are the important points for a LSR engine buildup?

Post by Stayt`ie » Sat Jun 15, 2013 10:55 pm

use all the tricks to get peak horsepower as high in the rpm range as possible, also keep your torque curve from falling away to quickly after peak torque, (the flatter the better), then gear to make the most advantage of what you have, :wink: ,, how you go about achieving this depends on the type of motor your running, 2 stroke, 4 stroke, flat, hemi, pent, :),, their all indivuals,,,,

from the avater you have, are you planning on running a W1 ?, :D ,,,
First Australian to ride a motorcycle over 200mph at Bonneville,,,

User avatar
NMBRPL8
Posts: 12
Joined: Sat Jun 08, 2013 10:55 pm

Re: What are the important points for a LSR engine buildup?

Post by NMBRPL8 » Sun Jun 16, 2013 5:21 pm

Correctamundo, building a couple of wizzas at the moment, the one im building for the salt im hoping to be able to sustain about 10,000rpm but we shall see if that holds together well :p I think it should do what i want from it, i just know myself and know that if it does ill just keep on pushing it to see how much more it will do :/ was hoping someone would say revs arent everything haha. All my math adds up to being more or less ok, peak hp not looking too impressive but a nice fat torque curve. May have to make myself a new cam to really make the most of it. Ah well all good fun :p I too am sure ill find out how long the fuse is on this grenade when I get it out there, thinking of running my egt and wideband on there as well to keep an eye on it, would be a shame to break too much of it, hard to get parts for :/

momec3
Posts: 720
Joined: Tue Mar 01, 2011 10:36 pm
Location: Cedar Grove Qld

Re: What are the important points for a LSR engine buildup?

Post by momec3 » Mon Jun 17, 2013 5:24 pm

Hi and welcome aboard,

Big oil capacity, bigger oil cooler. Deep sump if wet or better dry sump if you can.
Oil temp just keeps growing and growing on a run and oil pressure then goes south.

Big duration cam, flat torque. Max HP at the expense of torque. Biggest carbs (cfm) that you can find. You cannot go too big.

How this relates to your build or bike motors is up to you, just my thoughts and 20cents.

Chris.
Chris

Stayt`ie
Posts: 907
Joined: Fri May 13, 2005 11:47 pm
Location: Mackay

Re: What are the important points for a LSR engine buildup?

Post by Stayt`ie » Mon Jun 17, 2013 6:34 pm

be interesting to see how a W1 goes, all we need now is somewon to rockup on a XS1 yammie, youse could then have your own little battles, :lol: ,
i know jackshite about the W1 motors, but seem to recall that thay would "pull a pig out'a bog" with the grunt thay produced :) , maybe leave the motor asis, give it a run at next years event to get a firm baseline, then build from that, :wink:
anywhay mate, give it ya best 8) ,
First Australian to ride a motorcycle over 200mph at Bonneville,,,

User avatar
NMBRPL8
Posts: 12
Joined: Sat Jun 08, 2013 10:55 pm

Re: What are the important points for a LSR engine buildup?

Post by NMBRPL8 » Mon Jun 17, 2013 9:38 pm

I might throw a stock ish motor in the van as a spare and see if i dont blow up the built one :p all brass bushes converted to roller needle bearings, freeing up the oil pump to just take care of the crank and rocker gear, and the squirters for the piston crown. Its dry sump anyway with 3 litres oil capacity i could easily enlarge the oil tank though if oil capacity is an advantage. Had not planned on an oil cooler but if it is adviseable then I will fit one. I like the sound of the Accusump devices as a bit of an oil pressure buffer, might give enough of a window to avoid real damage...

Interesting on the ideas of cant go too big on the carbs, dual high flow petcocks on the fuel tank and extra capacity float bowls were on the list but i would think anything over and above what the engine can flow would in fact be too large, am i missing something there?

Cheers for the adivce/tips, keep em coming! Hadnt meant it to be specific to my engine, just a general question :) If i catch salt fever (HA, if i catch it lol think i already got it without getting out there yet...) i may have to bring my daily ride for a bash, thats a w800 the modern descendant. Id would like to see what she does one day once the bugs are all worked out of the turbo and microsquirt conversion. But the wizza is the current favourite rescued from a pile of rust and corrosion, coming back to life so i dont *want* to destroy it on the salt, but if i have to overstep the limits to find what they are, then so be it :p A mate of mine rides an XS1 i will be having some road battles with him for sure :p

momec3
Posts: 720
Joined: Tue Mar 01, 2011 10:36 pm
Location: Cedar Grove Qld

Re: What are the important points for a LSR engine buildup?

Post by momec3 » Tue Jun 18, 2013 8:46 am

Think too big carbs then think Pro Stock.
No such thing and to make the thing keep on winding can't be to big.
My opinion and it worked for me

Chris
Chris

User avatar
NMBRPL8
Posts: 12
Joined: Sat Jun 08, 2013 10:55 pm

Re: What are the important points for a LSR engine buildup?

Post by NMBRPL8 » Tue Jun 18, 2013 10:29 am

OK no worries, wasnt questioning the logic or your experience, im a mechanic by trade and cant stop my brain going to the technicalities of it, over-carbing is my pet hate on most of my customers bikes, kills any kind of rideability. I have to get myself into salt racing mindset i guess and remind myself im only supposed to be concerned about a narrow rpm range up top. Ill bring a few options with me and test them out before hand, hmm thats given me a bit to think about there thanks crhis.

User avatar
gennyshovel
Posts: 823
Joined: Tue Mar 29, 2005 10:10 am
Location: Broken Hill

Re: What are the important points for a LSR engine buildup?

Post by gennyshovel » Tue Jun 18, 2013 2:07 pm

I couldn't get the blown 250 to run at anything over 1/8th throttle with the 42mm carb, and I tried every jetting/ needle/slide combo I could. It's cfm rating was twice the engine needs.
With a 34mm carb, no problems
Tiny DLRA# 484
Postiebike Racing , created & funded by TwoBob Engineering

Stayt`ie
Posts: 907
Joined: Fri May 13, 2005 11:47 pm
Location: Mackay

Re: What are the important points for a LSR engine buildup?

Post by Stayt`ie » Tue Jun 18, 2013 5:09 pm

with cars you are talking a lot of cubic inches and i can see what Chris is saying,, motorcycles, "big ones" are around 100c", imho, given the rpm some bikes run at, air speed is more important then quanity,,
First Australian to ride a motorcycle over 200mph at Bonneville,,,

User avatar
NMBRPL8
Posts: 12
Joined: Sat Jun 08, 2013 10:55 pm

Re: What are the important points for a LSR engine buildup?

Post by NMBRPL8 » Tue Jun 18, 2013 9:54 pm

OK, thats a lot more inline with what i know and what makes sense to me, i would guess Chris is more a car guy then? Anyhow appreciate all the tips, i have a selection of carbs i can try out anyway, though the flat slides i was planning to use are sized just a little over what i calculate the engine should flow, with some more port work and a valve job. Was hoping to be close to spot on, erring to the too large side so as to not restrict it (same reason for the flat slides, less restrictions) But i will test some others out and have a couple in the wings. Typical newbie ill probably overprepare and lug a bunch of useless stuff out with me and back, but id rather have overprepared than under i guess.

Whoops looks like i missed an earlier post sorry Jon, im running gas class, straight old fashioned pump fuel. Plans for nitrous went out the window when i found even standard pistons are unobtanium and having forged ones made would about triple my budget, i was going to let it triple itself over time bit by bit rather than all at once on two pistons. So pump fuel it is, as for compression ratio im still undecided i will probably adjust with base plates, was thinking in the 12:1 range, they were only 8.7:1 when new, but i reckon ill be able to get away with a tad more than that ;) Im all for abusing my clutch, i will need to only having 4 gears to play with (I am looking into cramming a modern 6 speed gear set into a spare gearbox i have but i doubt it will be finished before 2015
)
So the advice as it stands: Oil pressure, oil volume and oil temperature. RPM is good, a big flat torque curve is also good, move peak hp higher up in the rev range and of course gear it appropriately.

So thats about it, people dont get too technical with it just some real basics? If so, cool my simple old contraption ought to go ok :)

User avatar
NMBRPL8
Posts: 12
Joined: Sat Jun 08, 2013 10:55 pm

Re: What are the important points for a LSR engine buildup?

Post by NMBRPL8 » Wed Jun 19, 2013 1:51 am

Gennyshovel, love yourr blown 250, thats what i cut my teeth on (sans blower) and loved every minute of it. Shame about the holed piston, cool vid on youtube though. Must have read your build thread a dozen times, keep it coming! Im stealing your oil squirter design with my own twist, hope that was ok...

User avatar
gennyshovel
Posts: 823
Joined: Tue Mar 29, 2005 10:10 am
Location: Broken Hill

Re: What are the important points for a LSR engine buildup?

Post by gennyshovel » Wed Jun 19, 2013 1:40 pm

Yup, steal away, it's not as though I've thought of anything new, after all
Back in the '70's, a local bloke one of your Kwackas, we were going away somewhere at night, he got all flustered and pulled over, complaining his header pipes were glowing red, lol, they weren't, it was the lead bikes tail light reflection in the chrome .
I dunno what we were up to back then, 'cos another mate was in front, heading to Mildura, right in the middle of prime 'roo time, we all chickened out trying to keep up, as there were too many near misses with the pesky hoppers.
When we stopped for fuel an hr later, he asked "who is leading ? , I can't catch him !
He was chasing his own hi beam indicator light perched next the tacho ! as it turned out.
I seem to remember drink driving may have been encouraged back the ?
Tiny DLRA# 484
Postiebike Racing , created & funded by TwoBob Engineering

Post Reply