Powerband manipulation 2

[540ZCar]

I want to build a Ford 302 with a redline of 6750 that has peak power at 6000. I rather have a broad powerband instead of high numbers so I want to fabricate intake and exhausts with different diameters and lengths for different cylinders.

Right now I'm thinking of setting up cylinders 1,4,6, and 7 tuned to peak power at 6000. Then cylinders 7 and 4 tuned for peak power at 5250. Cylinders 3 and 5 for peak power at 6750.
Then I was thinking that maybe it would be better to have cylinders 3 and 5 set up for 6750, 2 and 8 for 5250, 4 and 7 for 5750, and finally 1 and 6 for 6250 might be a better idea.

Which one do you feel will be the better route, and while I'm at it are there any formulas that you all know that will calculate what length and diameter would be ideal?

 

[evelrod]

Is this something you came up with after a few too many beers?

Rod

 

[BrianPetersen]

On a normal V8, you are never going to get proper exhaust tuning to work evenly on every cylinder anyhow, because of the 90-degree crankshaft that results in the pulses entering the collector from the primary header pipes at uneven intervals. From that point of view, this is an answer to a question that nobody asked, or a solution in search of a problem, or something of that sort.

In my world of 4-cylinder motorcycle engines with an even firing pattern, it's not unusual to have the intake runners a different length on the inner pair of cylinders compared to the outer pair, and it's rather normal to have the exhaust primary pipes join 1-2 and 3-4 (uneven pattern of pulses, 180 - 540 - 180 - 540 into the first junction). On some carbureted engines, the inner two cylinders are jetted differently from the outer two, and on fuel injected engines, they are often mapped individually to each cylinder. From that point of view, your idea is not completely out to lunch ... but on a V8, the exhaust is already asymmetric, so there is nothing extra needed to achieve that ...

 

[Tmoose]

http://www.lolat160.com/db4/00394/lolat160.com/_uimages/144-4479_IMG.JPG

 

[540ZCar]

I got the idea from reading a book about big-inch Chevy small blocks where the guy talked about having some cylinders running a bigger diameter primaries and others running smaller diameter primaries to broaden the powerband.
I was making the design around the idea of using sequential fuel injection and individual coils. I was also hoping to run boost one day so I was going for a design that uses a plenum. I also want it to be a compact design like the LS1 intake manifolds.

 

[YvesLLewelyn]

540ZCar - I suppose you could take your idea to extremes by actually having the cam lobes for the cylinder pairs you mention ground to different durations/profiles etc. so their power bands were at different RPM. It would be interesting to see what effect it would have as I have never heard of this ever being tried before.

 

[540ZCar]

I didn't even think of that. That would be interesting.

 

[FeX32]

I thought there were known ways of getting max torque from say 1500 to 6000.
We could call VW, as their new GTI certainly has its max torque from 1800 to 6000.
I can vouch for that.


Fe

 

[NickJ67]

I think the VW method is very careful attention to detail in forced induction systems - twin charging in some cases.

I would have thought the drawback with using different tuned lengths and even different cam profiles in different cylinders would be the need to control the fueling and ignition separately to match. While this is possible to do, it certainly isn't particularly simple or cheap and there are easier and cheaper ways to go - like forced induction.

Nick

 

[evelrod]

I think some of y'all need to do a bit more research. Aside the current trends in VVT technology, some of the older engines used multiple cam timing, cylinder to cylinder. This is all pre WW II stuff. Really old technology.

Indeed, my Kent SP 310 and SP 296 camshafts ARE ground with differing profiles. That's what the SP stands for "scatter pattern". It arranges different timing events for the center and the end cylinders of my Mini Cooper's race engine.

My first post was, admittedly, factitious. However, seriously, have a few more beers and perhaps you can come up with some other "off the wall" ideas. They are a hoot!

Rod

 

[FeX32]

What about building a large version of those RC nitro engines. I know they don't work on the Otto cycle, but the power to weight ratio is unheard of.
Come on 2 Hp from 2.1cc .
Sure you would have to pay 200 dollars every 15min for fuel....but who cares


Fe

 

[patprimmer]

Nitro methane fuel also gives VERY high loads on internal components normally giving an engine life of seconds, or minutes at most.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[540ZCar]

You make it sound like off the wall ideas are bad, I believe there are no bad ideas because even if they don't work for what they were thought up for they can at least serve as a muse for something/someone else.

 

[YvesLLewelyn]

The SP cams are meant to compensate for the odd effects of the siamesed ports in BMC A and B Series engines - not to spread the torque/power over a wider band.
The only real way to spread the torque etc. is with a genuine variable duration cam - and, for all practical purposes, such things do not exist.
I agree with 540Z - even extremely odd ideas should be investigated - you can never tell where they may lead.

 

[FeX32]

I thought variable duration cams were used extensively in F1?
Something of the like of the camshaft had a '3D" profile manipulated by moving it along its axial direction.


Fe

 

[evelrod]

Ah well! Semantics. The "scatter pattern" camshafts that I use in my Mini are designed to compensate for the five port cylinder head design. To what purpose? Why, to spread the power and torque over a broader rpm range not normally possible using a "std" ground camshaft profile with the antiquated port design.

As to the rest of it, VVT, VCR and, even variable valve lift have been used in the past. One odd design utilized a four valve design that opened the "second" valve as rpm increased. Not sure where that one went, it was in the 1920's or 30's. One newer version of that scheme was to use two seperate intake manifold runners for each intake valve. Hmmmm? Wasn't that the Yamaha deal at Ford?

Tmoose's link to the BBC/Lola manifold from the CanAm era was cool. One thing for sure, when you got passed by one of the CanAm cars using that configuration, it sounded like music to the ears. It was also awfully loud. BTDT!

Stay with it, guys. Sooner or later something will "stick"!
Watched a video of a F1 engine test run...Don't know what technology was involved to get a powerband of over 10,000 rpm. Sure looked/sounded good, though. I could almost "SEE" the $$$$$$ coming out the exhaust...;-)

Rod

 

[YvesLLewelyn]

FeX32 - Variable duration cams are not used in F1. I think that even the more basic "variable cam phasing" is also banned.
The "3D" cam is an often-suggested idea for variable duration but there are apparently real problems with the geometry of the tilting follower that is needed.
Ferrari did a lot of work with 3D cams but I don't think they were ever in a production Ferrari.

 

[FeX32]

Thanks for the info Yves.
Good to know.


Fe

 

[Marquis]

The Porsche Cayenne V8 has a patent where by the cylinder that is effected most adversely by charge robbing, has an individual shorter profile to compensate.

There's nothing to stop you from doing this- and the exhaust tract could be designed to do this also in league.
I would use 1 D cycle simulation to investigate.
This is what I will do for my Mopar engine and a Jaguar XJR (should I ever get around to buying one).

http://www.auto-scape.com

 

[BrianGar]

''You make it sound like off the wall ideas are bad, I believe there are no bad ideas because even if they don't work for what they were thought up for they can at least serve as a muse for something/someone else.''

Thats the truest statement Ive read In a long while.