Straight Six Performance and Torque 4

[keddano]

First off let me say since I’ve found this site, It has amazed me with the vast amount of knowledge and intellectual conversation everyone contributes.
With that said…I would like to pick your knowledge for one of my current passions. I got involved in “Farm Tractor Pulling” a few years back. I run a semi-modified straight six cyl. engine putting out about 70 Hp(stock 38Hp)10.5 CR. Stock Stroke. Oversize bore, Larger intake and updraft carb and all the common performance work-ups. Max Rpm is 2100.What I am looking for is some suggestions on little things that can be done to still gain more torque and horsepower. (Currently running a cold air filter system, Cool Can, Wrapped Exhaust Manifold).I guess I’m looking for ideas were others generally have not. I would enjoy discussing any thoughts. Thanks in Advance for any suggestions. Dan
Photo of SixGun Blaz'in-

http://www.tractorshed.com/cgi-bin/gallery/photo_pic.cgi?pic=http;//

http://www.tractorshed.com/gallery/...15&Parameter=dan penley&mode=All&what=tphotos

 

[CESSNA1]

KEDDANO: It depends on what is available and how much money you have. Here are some suggestions:

Install a stroker kit
High lift cam with solid roller lifters and roller rocker arms. (watch out for piston interference)
supercharger/turbocharger and intercooler
Nitrous oxide injection
Increase compression ratio to 12.75:1 (watch out for piston interference)
Recurve the ignition

That is it for now
Regards
Dave

 

[Warpspeed]

Once all the small things have been done, it starts to become expensive. Almost doubling your power is a pretty good effort, but you need more airflow and Rpm.

The next step would be some airflow work in the block (side valves ?) and a more aggressive higher lift camshaft.

Here is a Forum I think you may find rather interesting. It is a bunch of enthusiasts that are into building homemade airflow benches and dynamometes. The guy that runs the Forum is a tractor puller himself.

http://tractorsport.com/cgi-bin/forum/cgi-bin/ikonboard.cgi

Good luck, it all sounds like a lot of fun.

 

[globi5]

I'm not familiar with the rules, but since you only need to pull for a relatively short time (I guess) you could install an electric supercharger and run it off the battery. This way you wouldn't have to touch the internals and don't need to worry about a mechanical connection between the engine and supercharger.

http://www.boosthead.com/home.php

 

[globi5]

Again I don't know the rules.
But these guys increased power with a 2 stroke leafblower:

http://videos.streetfire.net/Player.aspx?fileid=AB544E3B-5DFF-416D-9CFD-A1AD23CA9564&p=0

If you go on ebay you can find a bunch of gas powered leaf blowers for less than $100.

 

[Frederick]

If you can't install a blower, multiple carbs to even out fuel distribution would be a plus. Straight six engines tend to have uneven fuel distrbution with the center cylinders running rich and the outer ones lesn.

 

[turbocohen]

Frederick, are you infering that my ole bmw 6 has distribution problems? I think you might be refering to older carureted dinosaurs.

 

[Warpspeed]

Lot's of good ideas here guys, but unfortunately forced induction or "funny" fuels would take him out of his own class and pit him against the big boys.

Much better to be king of your own chosen class and stay within a reasonable budget. Even in the lower classes competition is pretty fierce, jolly good fun though !!

 

[Tmoose]

I'd think at 2100 rpm 100% cylinder filling is not particularly hard to do, so valves and porting are kind of secondary. Some intake/exhaust tuning effects could help boost torque, but 2100 rpm would require some seriously long intake/exhaust tracts. These examples below have power rpm peaks a good bit higher than yours. Even the slant 6's peak power was up around 4000 rpm, so your manifolding would have to be longer still.

http://pic6.picturetrail.com/VOL174/1021972/2732735/65732275.jpg

http://www.allpar.com/mopar/images/ram1.jpg

https://www.hemmings.com/images/editorial/engine-left-EDIT.jpg

http://homepages.nznet.co.nz/dodge/engslant6.jpg

http://warped.org/mopar/pix/slantsix-choke-pocket2.jpg

Inertial tuning might result in embarrasingly small pipe diameters.

A few times I have accidently stumbled over excellent ignition/carburetion settings on engines that I thought were running very well, and the power and throttle response difference can be amazing. A long-runnered 3 carb manifold sporting some SU carbs off an MGB might be fun.

If you could simply raise your rpm to 3000, and the cam was up to it, you'd have almost 50% more power.

 

[Warpspeed]

I think three SU carbs would be splendid for tractor pulling. He probably only has three rather small intake ports anyway, and siamesed ports are not exactly ideal for inertia tuning. I am guessing there may be four exhaust ports.

The updraft carby suggests a fairly early engine design, most likely with side valves and it may not be blessed with too many main bearings.

Dan seems to have disappeared ??

 

[patprimmer]

He last visited the site on 28/10/05

Before any intelligent recommendations can be made, we need to know the limitations that are imposed whether they be rules and regs, or limitations re the original design, like bearing support, block strength, oil flow, air flow(up draft and 2000 rpm might also suggest splash feed).

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[keddano]

Sorry for going MIA. Was away from the tube all weekend. I didn’t know if there would be an interest in this one, Thanks for the info, Guess I should fill in more info, so everyone is up to speed. I run in Div 2, The tractor cannot be stroked, (although sometime in the future it will be when I step up to Div 3)We are limited to a 3 ½ mph speed limit, rpm are suppose to be only 20% over factory specs, It has to be normally aspirated. Currently It runs necked down stemmed S.S. Valves (intake & exhaust, as big as physically possible that we could fit without changing guide locations),The head is a OHV design Waukesha, Ported, polished. The intake manifold is a 3 port shared cast iron log design from a larger engine modified to fit (bigger dia. Runners, port matched to the head,) Exhaust manifold has been port matched. 10.5 CR, I run 110 octane red torco fuel. The Waukesha block runs 3 ¾” bore x 3 ¾” stroke for 248 CI.(fresh pistons and rings this spring) The one place I’m lacking is I’m still running a stock cam Solid tappets(will be changing this winter). The dist. has been recurved, for max. advance at 1800 rpm. It has a squirter oil system for rods. Now that it is broke in I’m changing to Cen-pe-co oil. Thanks again in Advance,Dan

 

[Warpspeed]

Hmmm, interesting, it sounds like the camshaft may be the next logical step. And possibly three SU carbies ?

SUs would be particularly good because as Rpm falls off under full throttle full load the air velocity across the jet is maintained. The carbies could be quite large but will maintain good mixture quality right down to very low engine Rpm at full load.

There is some rather clever computer engine simulation software around these days where you can enter all the various engine parameters, and it will plot power and torque curves on your computer screen. This software is not that expensive, and is especially good for optimising valve timing and trying out various different ideas.

I am using Dyno 2000 from Motion software which cost $160 Australian dollars three years ago. There is a later version out now which is supposed to have several new features. There is also a trial demo version available that can be downloaded free from their website.

 

[ivanheow]

make a 15 inch long inlet for each cly. with 4 1.75 su's on it one carb per cyl.4 inch bell mouth on each carb.
raise compression ration to 13 to 1.encourage squish in the chamber.keep head temp low.make exhaust primaries 70 inches long and 1,5 inch dia. use short skirt thin ring low tension pistons .robert

 

[turbocohen]

Are you allowed to substitute distributorless ignition? If not, can you upgrade to something with more MJ's?

 

[patprimmer]

I'm with Warpspeed.

3 SUs, one for each port, sounds good to me. 1.75"is probably the best size, but that will depend on what rpm it will be used at.

What is the maximum rpm you are allowed.

Do you use one gear only.

Can you change ratios to take advantage of different power curve from the engine.

Can you change gears during the run to accommodate a narrower torque curve.

What is the minimum rpm that the engine sees at full throttle full load.

I would have thought you could run 12:1 CR with 110 octane, but I realise short cam duration and high load low rpm is more inclined to produce detonation, and the detonation will do more damage when compared to something doing 3 or 4 times the rpm.

You can run higher CR if you pay a lot of attention to running the minimum deck clearance that avoids collision between piston and head, and a lot of attention to polishing away sharp edges and potential hot spots.

A higher lift cam should help, especially if you can convert to a roller and keep the duration relatively short, and thereby maintain a wide power band optimised around the rpm you can use. Increased cam overlap will cool the exhaust valve and allow higher CR

A tuned length and dia inlet and exhaust will help. The length and dia's depends on what RPM you will use.

By tuning length, you can get noticeable gains, but only over a narrow rev range. Outside that range, you come back to non tuned length performance, so you don't really lose anything, but you need to carefully choose where to put the gain.

When porting heads to run such low rpm, be careful not to lose to much air speed.

As it seems you hit the load at max rpm, a very heavy flywheel might help.

To determine optimum ignition timing, hold a load on a dyno and manually move the dissy for maximum sustained power (just short of detonation). Repeat at various rpm throughout the used rpm range. Calibrate the dissy to automatically reproduce this. Hold the load for some time, so you can be sure that detonation won't set in after a few seconds. If you can't get access to a dyno, try it in the tractor with a method to control the load to hold the various rpm at full throttle.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ivanheow]

oops should have read '6 su's and 6 inlet tubes ...doh

 

[patprimmer]

Except it seems that it might have 3 Siamese ports.

SU's seem to work well with one carb per pair of cylinders as they seem not to like the very heavy pulsations in airflow that occur with an individual runner manifold.

I think the diaphragm that controls the plunger and needle valve gets confused by the reversion.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Warpspeed]

That can be cured to a certain extent by the choice of oil viscosity in the damper piston and spring selection. It seems to work fairly well on the XKE Jaguar engines. In fact, Jaguar carby tuning settings may not be a bad starting point as the engine size is fairly close, and so will be the uneven pulsing on the outer two carbies.

I would not be at all surprised if three good Jaguar HD8 carburettors worked darned well just as they are, without changing things around very much.

 

[kenre]

Once you have the engine running as best as possible with all the good advice given here, you should look at the back end.
Many older tractor transmissions and diffs are filled with very heavy oils, 85/140 etc. By going to a lighter oil there will be much less drag and more power to the wheels.

Ken