I just wanted to start a thread where we can talk about theoretical pros and cons of different engine mods; it's just my opinion that specific threads about specific engine questions should be reserved for answering those questions and be directed at the person who originally posted it. If you want to argue your point beyond making a suggestion, maybe refer a final post in the tech question to see the "theory" thread for further arguements. Any proof, testing, before and after comparisons and other reasonable hypothesis might help out. Am I out in left field? As someone once said "It's only the internet" so I don't see the need to get up in arms here. Some of the best scientists in the world don't agree on common subjects. Any scientist worth his salt will admit that we don't REALLY understand how an internal combustion engine works.

Anyone want to start with their theories on head porting or crankcase windage or quench or anything else?

p.s. enough with the name calling and bad 'tudes.

 

OK here's an easy starter for you.

How many of you have actually degreed the cam/cams in your Honda/Acura? What did you find out? What did changing the LSA do for you and why?

 

I've been around nothing but the SOHCs and have never had any experience with adjustable cam gears.

I've read many books on performance, but do to a lack of $$$ the best I did was a homemade turbo kit.

That said:
Degreeing cams should be done on a dyno.

What is the maximum expected gain out of Adj. cam gears?

I feel that it helps the DOHC more than the SOHC

 

I know that honda produces great combustion chamber designs and some honda's are running around with 11.0 compression ratios. But why is it when I mention anything higher than a 9.5CR for my uncles Ford 302 he says he needs 100 octane?

I know how octane ratings work and I understand that. But is there that big of a difference in the combustion chambers that we can run 11.0 on 93 octane but he's stuck at the lower.

 

Actually, degreeing a cam doesn't need to be on a dyno. All that should be done with a degree wheel is to verify [or set] the cam is at the correct relationship to the crank. Sometimes with aftermarket parts or machine work, the distance between the crank and cam centers can be altered slightly, retarding or advancing the cam from their factory orientation. With aftermarket parts, the problem can be as simple as manufacturing variance that causes a discrepency. However, with a degree wheel, adjustible cam gear, and a bit of time, you can reset your cam and keep the stock power angles and peaks as the stock powerband, helping out drivability, while actually increasing power across the band.

As for compression ratios:
The world of V-8s are much different than I-4s, and the biggest difference is in construction. Most V-8's on the market are cast-iron blocks. Good for longevity, bad for heat dissipation and weight. On the contrary, most I-4s are all-aluminum construction, and that is where the first of several things comes into effect when considering maximum compression ratios.

For the sake of simplicity, I'm going to assume that the intake valve closes exactly at BDC, and that there is zero overlap. This means we'll be talking about absolute compression ratios, even though most engines don't effectively use all of their measured absolute CRs.

Now, the reason for higher compression ratios is to make more power. If you can compress the air and fuel more before igniting, the energy output of the burn will be faster and with greater effect [same idea behind pressure bombs for any of you that have seen the movie "outbreak", the opening bomb is a pressurized 55 gal. gasoline barrel with an altimeter trigger]. The limits of this, however, are how well you can control the temperatures inside the combustion chamber before ignition. Here's where your cast iron block falls behind. The coolant in the block can only absorb so much heat, and the material of the block itself is going to absorb and hold the rest. Same is true for the cylinder heads. What that means is that the cylinder temperatures are going to be higher, which also means smooth shapes and more even temperatures inside the entire cylinder becomes of paramount importance. Both of these are primary reasons that the Hemi-head Dodge engines were [and still are now that I think about it] so good at making power.

On the flip side, Aluminum cools much faster, so you can afford to generate more heat per cycle, knowing that it will be wisked away by the cooling system more effectively than in a cast iron block.

I know this is all pretty basic and jumbled, but I'm recovering from some severe streph throat and the associated drugs. I'll read this some more tomorrow and see if I can straighten some things out and/or add to it.

 

LSA matters as much to SOHC as it does to DOHC cars, its just harder to accomplish (the entire regrinding of the cam and all)

i gained 25hp and a much longer torque curve by changing cam settings.. i wouldn't expect nearly as much on a n/a car but its still worth alot if its decently modified

 

Degreeing the cam is especially important if you have the head milled for that extra compression as the shorter distance will retard the cam timing.

For compression I just want to add that the bore size has a lot to do with detonation and the small bores (say 3.189 compared to over 4") create fewer opportunity areas for pre ignition to begin. Also, look at the alum vs cast iron thing the other way; iron retains heat and so requires less compression than aluminum for the same amount of heat-power output. What I mean to say is that two identical heads with one made of iron and one aluminum, the iron head will make more power and the alum will require more compression to make the same power (heat/energy output). Aluminum is easier to machine and is much lighter which is why it is more commonly in use now.

 

Regarding the bull-nose/knife edge issue, there were a few comments that I didn't agree with. First, last year I had the opportunity to rebuild a 1992 Ferrari Formula 1 engine at the shop I was working in for a customer with more money than God. If you know much about them you will know that Ferrari Formula 1 engines are almost never rebuilt by anyone other than being sent back directly to Ferrari and they will never touch one that hasn't been built by them. I realize that technology has changed somewhat in the last 10 years but typically Formula 1 technology is several years ahead of the rest of us as they have relatively UNLIMITED BUDGETS. I can tell you that in those 5 valve heads the leading edges of the dividers on the intake sides were not knife edged but the exhaust were. I don't mean to say that there was a big fat blunt edge there, only that they weren't knife egde sharp. This thinking has been followed by the crankshaft manufacturers who used to knife edge the leading and trailing edges of their crankshafts and now they have almost all moved to a bull nose leading edge and knife shaped trailing edge. I am not a fluids engineer (though I majored in aerospace engineering for a few years in college and took several classes on aerodynamics) and don't have the desire to spend my day researching formulae on the subject but I know what my flowbench tells me and I know how many top manufacturers and racers have designed their products to compete at the highest levels.

 

i've never even seen a formula one engine...
and you got to rebuild one...
I'm so jealous. Can you buy old ones or something?

 

The guy we were building it for just sold his phone company a couple years ago. I went to his shop where he had two former Formula 1 cars in the front part that he does "vintage" racing with. In the back of his shop he had about 30 different vintage racing cars and motorcycles as well as several big rig transporters. He let us take a spin in his new Mercedes S600 - yeah, he has plenty of dough. And yes you can buy used engines, this one was about $250,000 before the rebuild. The bare block runs about $80k. Add $8000 for new rods, $5000 for valves, $1500 for pistons, etc...