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-

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[keddano]

Thanks everyone, This is just what I was looking for…Only now you all have me jumping father ahead and thinking of building a completely different engine that could run in a less limiting, no rpm or speed go fast div 5 class. The Waukesha six cylinders do have 3 Siamese ports. The next size up engine from a 1650 Oliver can be pushed up over 400 CI. With a forced oil feed crank. I’ll let everyone know when I start on that one. It’ll take some time to start locating basic parts. What is the going price on a tri-power set of Jaguar HD8 carburetors? In this area, Michigan, USA they are rare.
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.

 

[ivanheow]

having taken a gipsy moth 4 cyl engine at 4 litres from 123 bhp to 186 at wheels in a 1928 riley ,on my rolling rd..i can deff say that tuning for torque is a good idea with a rpm max of 2500 we got something around 400 lb ft ,this without the one off cam i designed for it ,which i think would have topped the 260 bhp mark. pulsing on su's is greatly alleviated by a balance pipe across the inlet tracts . if siamesed then deff 3 carbs .i feel that 3 hif 1.75 inch carbs are your best bet ,prob off a BL engine down the scrappy .regards .robert

 

[turbocohen]

Long ago I rebuilt and turbocharged a 1963 vintage 230 inch chevy inline six that had already accumulated a couple hundred thousand miles in an old pickup using 1978 vintage Buick v6 turbo and ignition parts. In search of fuel economy and enough power to out run a v8 I pulled the head and nickel welded a partition between the siamesed intake ports. Also added a small partition to the intake manifold in an attempt to improve distribution and wound up with another ~10hp on top of the ~280hp it already produced before splitting the twins. The mods allowed MBT spark advance at about 10psi boost using amoco 93 pump fuel but while siamesed the knock sensor detected knock at slightly less boost. I later found even more power by substituting longer rods and clearance fitted pistons .030" from the head. The piston had thinner top rings for less drag and less wasted crevice volume. When I ran out of money and needed to move home from college in Big Rapids, Michigan it made about 330hp at best and the ole grandma's grocery getter I-6 engine torque was enough to humiliate damn near anyone with a V8 and a sense of humor when I revved what sounded like a humble tow truck engine.

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.

 

[Warpspeed]

The best source of SU carbies may be off e-bay, especially from the UK.

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://www.btinternet.com/~mezporting/exhaust_length.html

 

[keddano]

Turbocohen -I forgot to add it does have 6 exhaust ports

 

[patprimmer]

keddano

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.

 

[turbocohen]

Keddano, are you running points and condenser or an electronic distributor?

 

[GregLocock]

How does Dyno 2000 cope with 'odd' engine configurations? I get the impression that it has a lot of built in rules of thumb, and may not cope well with strange engines.

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.

 

[patprimmer]

I have a copy, but I only used it on SB Chev V8s.

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.

 

[patprimmer]

For the application, I would expect that best results would be obtained with maximum power developed at or just short of maximum allowed RPM, with the widest torque band possible.

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.

 

[patprimmer]

Dyno2000 will not calculate power nor torque below 2000 rpm, so it is meaningless for your application as I think you need figures down to say 500 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.

 

[keddano]

The maximum Rpm Differs with which club I pull with, In one club that does check every time, it can only run 1925.At the other club I can get away at run about 2500-2600 safely. I have to run a stock appearing distributor, currently it runs points and a hot coil. I’ll be putting in a electronic conversion kit this winter. I’ll have the head off to do the cam, That is a good idea to have it flow tested while it’s off, Then I would have a starting point to help with the cam decision. Thanks

 

[patprimmer]

The work I did on Dyno 2000 indicated you need a VERY short duration cam, like 10/35, but with lift around 0.400"or more. I guessed valve size at 1.8 and 1.4.

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.

 

[Warpspeed]

I believe the latest newer version of Dyno 2000 goes down to 1,500Rpm, but that is probably still marginal for this application.

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.

 

[carnage1]

With a little machining you can put a chrysler slant six reluctor on your existing shaft and replace your point plate with a pickup from a chrysler distributor. if the distributor you are starting with is big enough you might be able to fit a chevy ignition module inside, if not you can fit a motorola MC3334D (if your comfortable with a bit of basic electronics).
then noone would ever know unless they took off the distributor cap.

 

[Warpspeed]

I have been thinking a bit more about carbies, the big advantage of SUs is the improved atomisation of fuel at low Rpm high load compared to fixed venturi carbies.

But EFI would be a whole lot better in that regard !!

 

[Rob45]

Dan,
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?

 

[keddano]

Rob45,So it would be better to wrap the intake to keep the hot exhaust gases away from it? Everyone's been alot of help and left me with some new ideas for the future.Just a quick update,at the National Pull I was at this weekend I tok a 2nd place in the #4000 Div 3 class I ran in.I didn't compete in the other 3 class because of a brake-down,no not mechanical,I dropped the front end too hard at the end of the pull and taco'd the front rims and snapped the front weight bracket.,After some running around for repairs,Sunday we took one 1st place in 3750# Div#3 and a 3rd in 4750# Div# 3,so overall it was a fun outing.I'm sure I'll be back with a few more questions as I dig deeper into the new motor. I'll be watching and add If i have anything that will help. Thanks Again Everyone,Dan

 

[Warpspeed]

Heat wrapping the intake may only serve to keep in the heat once it has heat soaked.

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.