Wednesday, May 31, 2006 - 06:07 pm, by: Matt Worrad(Mworrad213)
G'day everyone,
Just wondering if anyone would like to help me with my assignment. I have some questions which need some reasonably qualitative responses. They are as follows:
1. In what ways can an engine be made stronger?(able to withstand higher loads, compression pressures and revs)?
2.How can you make an engine rev more freely?
3.Why do Extractors or headers usually produce a power gain over normal exhaust manifolds?
4.What are the advantages of forged pistons in a race engine?
5. Cylinder head porting can be a complicated and risky task but can be done to vary degrees. What is meant by match porting?
6. Briefly explain what the process of "cc-ing" cylinder heads?
If anyone can help me out with anysort of information it would be greatly appreciated.
Thursday, June 01, 2006 - 06:59 am, by: Matthew Sharpe(Madmatt)
Also for 1) reducing manufacturing stresses by techniques such as shot-peining, using forged components (see 4), component selection etc.
2) Bore & stroke has some bearing on this also - generally a square or over-square (short stroke) engine will rev more freely, but it gets really complicated really fast with how it affects torque etc.
3) Reduced back pressure - exhaust gasses flow more freely, leading to less exhaust stroke power loss, and improved intake and combustion.
Thursday, June 01, 2006 - 02:24 pm, by: Cihan Aday(Cihan)
3.Why do Extractors or headers usually produce a power gain over normal exhaust manifolds?
Manufacturers use cast manifolds with rough walls, sharp curves and short, usually large diameter runners due to space constraints and ease of manufacturing. Sometimes they are un-equal length and usually these designs cause some turbulence and impose a restriction. The use of ideal designs is offset by large scale production costs more than anything.
Power gains because of the effects of exhaust scavenging, where the flow of one cylinder helps the next. If your using a 4-2-1 extractor design with a 4 cylinder engine, runners 1 and 4 will couple together and runners 2 and 3 together. This all works together because the exhaust gasses come out in successive 'waves'.
Increases in primary runner length is associated with increases in volumetric efficiency hence peak torque. Tuned length runners are just that, just like there is a resonating frequency for sound at a certain tube length, there is an idea runner length for a given application. Shorter primary runners promote higher rpm efficiency, longer primaries promote midrange efficiency.
5. Cylinder head porting can be a complicated and risky task but can be done to vary degrees.
- Complicated because manufacturers design cylinder heads using a much larger agenda than WOT driving. Flow benches only tell you a few things things, port flow at different valve lifts. Heads design is based on many other factors and take into account average port velocity at varying revs, subsequent idle quality, response, ideal BSFC and what RPM it occurs, A/F mixture quality etc etc. Simply enlarging ports will usually only go so far. Its possible to go too far and drop the average Mach# of fresh charge through the inlet ports too much, reducing low and midrange torque. Polishing the intake ports also has unwanted effects when the heads actually coupled with a shortblock. Most of the time power is actually lost or increased slightly, even though there is a large flow increase on the flow bench. Think of a golf ball and how it glides through the air, now think of a table tennis ball and how it doesnt.
Cylinder heads should be made to suit the application more than anything. Its only worth increasing port flow to the degree that is useful to your application. Going overboard can result in powerloss because of velocity reduction, especially in non forced induction engines. Larger valves almost always help topend power under wide open throttle IF the valve is smaller than the port. If the valve is larger than the port (like many old school V8's, Gen3 etc) then it has been engineered by the manufacturer to this specification for a reason, probably because it worked best under normal driving conditions to achieve economy AND under WOT driving when economy is the least of your concerns.
4 valve cylinder heads naturally flow better and allow optimal port velocity to be maintained retaining low engine speed port velocity. They also allow large power when revs raise. When compared to a 2 valve per cylinder application on the same shortblock, the advantages are obvious. The RB30 + RB25 cylinder head combination is a very good comparison, and the exchange can net 30% more power with no low end power loss.
Porting a 4 valve head is that much more complicated. The balance between ideal port velocity and maximum port flow can be upset easily resulting in unwanted consequences. The degrees they are referring to are application related.
Your course is very interesting. What job prospects are there learning what you are? Motorsport engineering - What uni/tafe is this at?
Friday, June 02, 2006 - 01:22 pm, by: Matt Worrad(Mworrad213)
Thanks for your help guys,
Cihan, the course is pretty much based around race vehicles. We work on a couple of cars in our workshop, we own a formula ford heaps of go karts a couple of bikes. We also work on cars that are owned by other teams, they'll drop it at the workshop and we will fix it or install things whatever needs to be done. Part of the course is work placement, so we are assessed when we go away with race teams. We do a lot of work with the utes, supercars and formula ford and aussie race cars. Quite interesting, however be prepared to work till the car runs that may mean no sleep or food.
From the first year of the course you will gain a certificate 3 in motorsport. Second year you will gain a diploma in motorsport engineering and if you choose to do the free option of an advanced diploma in engineering you may be exempt from up to 18 months of engineering at uni.
The tafe is located at Wodonga in vic, and if you would like to get in contact with the tafe you can call : (02)60556657. Positions will be open for next year however out of the 300+ applicants last year only 30 of us got in, so dont fart arse around if you want to do it.
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