Straight Six Performance and Torque
Straight Six Performance and Torque
(OP)
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- h ttp://www. tractorshe d.com/cgi- bin/galler y/photo_pi c.cgi?pic= http;//www .tractorsh ed.com/gal lery/tphot os/a29587. jpg&fi rstrec=1&a mp;lastrec =15&Pa rameter=da n%20penley &mode= All&wh at=tphotos
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- h





RE: Straight Six Performance and Torque
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
RE: Straight Six Performance and Torque
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://tr
Good luck, it all sounds like a lot of fun.
RE: Straight Six Performance and Torque
http://www.boosthead.com/home.php
RE: Straight Six Performance and Torque
But these guys increased power with a 2 stroke leafblower:
ht
If you go on ebay you can find a bunch of gas powered leaf blowers for less than $100.
RE: Straight Six Performance and Torque
RE: Straight Six Performance and Torque
RE: Straight Six Performance and Torque
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 !!
RE: Straight Six Performance and Torque
http
http://www.allpar.com/mopar/images/ram1.jpg
ht
http://homepages.nznet.co.nz/dodge/engslant6.jpg
http
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.
RE: Straight Six Performance and Torque
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 ??
RE: Straight Six Performance and Torque
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.
RE: Straight Six Performance and Torque
RE: Straight Six Performance and Torque
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.
RE: Straight Six Performance and Torque
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
RE: Straight Six Performance and Torque
RE: Straight Six Performance and Torque
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.
RE: Straight Six Performance and Torque
RE: Straight Six Performance and Torque
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.
RE: Straight Six Performance and Torque
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.
RE: Straight Six Performance and Torque
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
RE: Straight Six Performance and Torque
On the tractor combo I’m running now, You only run one gear, the distance is normally 300ft. We run the motor till it basically stalls at about 600 rpms or spins out the tires, (which happens a lot, because of tire size limits and max. tractor weight we’re allowed to run in my classes from 4000# to 6000#,The way we cut or sharpen the bars on the tires plays into that a lot.) This winter for the current motor I’ll be looking at different cam profiles, (Does the Dyno 2000 from Motion software allow you to test profiles?, or is there a better program to play with?) PATPRIMMER- The heavier flywheel would certainly help, one area I hadn’t thought of looking at. And converting to a electronic dist. is also on line.
One of the discussions that is always taking place on the tractor forums is the best fuel to make power in these types of engines, 102 AV fuel comes up, the 110 racing fuel, and variety of combos. Any thoughts? Thanks again to everyone.
RE: Straight Six Performance and Torque
RE: Straight Six Performance and Torque
It eventually became my test mule and then one day while experimenting with a doomed home made LPG injector.. :(
Godspeed little motor
R.I.P.
The End.
Ok, my .02 dinars is to check crankcase pressure and to verify that the rings are sealing well and consider the benefits of raising the top ring grooves and using thinner rings. Also see if there is a way to reverse cool the block & head.
RE: Straight Six Performance and Torque
Thinking about the camshaft, Pat is right a roller cam with very fast opening and closing rates, and high lift, but keep the open period short. Another simpler way to get started could be to increase the rocker ratio, but a different cam would be much better.
With three siamesed inlets, any sort of induction ram tuning would probably cause more problems than it would solve, just place the carbies fairly close to the head with a heat shield to cover the exhaust.
I have been thinking about an exhaust system. On the surface four exhaust ports are a problem too, but there may be a way to tune it. The front three cylinders have two ports, and the back three cylinders have two ports. If these pairs of ports at either end of the engine were joined by a short Y piece, there would then be two pipes with even 240 degree exhaust firing periods. As the exhaust cam duration is almost certainly going to be less than 240 degrees, only one exhaust valve will be open at any one time in each three cylinder group.
After the Y piece just add a tuned length "primary" pipe length. As this will serve three cylinders instead of one, just tune the length to 6,000 Rpm which would correspond to 2,000 Engine Rpm (or whatever).
For a 700cc cylinder volume, 2,000 engine Rpm (pipe tuned to 6000Rpm) two inch pipe thirty inches long from valve to open end looks like the go. Two vertical pipes should sound glorious.
http://
RE: Straight Six Performance and Torque
RE: Straight Six Performance and Torque
What is the maximum RPM you are allowed to run.
Can you get the head tested on a flow bench. To just test and report does not cost much, but the data helps a lot with Dyno 2000
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.
RE: Straight Six Performance and Torque
RE: Straight Six Performance and Torque
Yes, it does have cam profiles in.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Straight Six Performance and Torque
I have no idea of what is in the working engine of the software, but if it is mostly rule of thumb, I expect it's rules of thumb are closely matched to my application.
I put in some specs for some engines that I knew the dyno figures for and it was quite accurate.
It's predictions for a Mazda Rotary turbo were also accurate.
I will run a few numbers through it and see how it performs.
If someone has a better package, I would be interested to compare the predictions obtained for the same input.
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.
RE: Straight Six Performance and Torque
I think that the matching and sizing of components will be very critical to getting maximum power while maintaining the widest possible power band.
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.
RE: Straight Six Performance and Torque
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.
RE: Straight Six Performance and Torque
RE: Straight Six Performance and Torque
No mater how conservative I went, it wanted to develop maximum power between 3000 and 4000 rpm
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.
RE: Straight Six Performance and Torque
Another (more expensive) software package is Engine Analyzer Pro from Performance Trends, which will go down to 1,000 Rpm, and you can select the Rpm steps above that.
Motion software claim that Dyno 2000 will model anything from a standard single cylinder side valve Briggs and Stratton lawnmower engine, to a supercharged four valves per cylinder Rolls Royce Merlin. I have used it mainly on small DOHC four cylinder engines, and it is extremely predictive, especially good for experimenting with camshaft ideas.
But it also needs some knowledge and care. It cannot predict detonation or over carburetion, and it assumes optimum ignition timing and adequate fuel octane. But if you already have some reasonable knowledge and experience of engine operation and limitations, it is an excellent tool.
Probably the best way to do it is to enter all the parameters for a standard unmodified factory engine and attempt to duplicate the original known torque and power curves. From there you can begin to change things and see the results of each individual change, or changes in combination.
RE: Straight Six Performance and Torque
then noone would ever know unless they took off the distributor cap.
RE: Straight Six Performance and Torque
But EFI would be a whole lot better in that regard !!
RE: Straight Six Performance and Torque
you might also want to unwrap that exhaust manifold, unless you're running a turbo.
Hotter exhaust gas just means higher exhaust backpressure.
I know this runs against what you might read in Hot Rod magazine, but that's why you came to this site, isn't it?
RE: Straight Six Performance and Torque
RE: Straight Six Performance and Torque
Phenolic spacers fitted between cylinder head and inlet manifold will do a good job of reducing heat conduction into the inlet manifold.
Shiny reflective heat shielding between exhaust and intake manifold will go a long way to preventing "toasting" the inlet manifold.