TECH TALK - ask your technical car questions

Post by **GT3x24x7** » 08 Feb 2005, 16:42

From "SuperChevy" (link) ...

WHAT IS BLUEPRINTING?

Contrary to its name, blueprinting an engine has nothing to do with big rolls of paper that have strange, blue-colored drawings on them. Blueprinting an engine starts by designing it on paper first. Calculating things like compression ratio, piston pin (compression) height, displacement, and carburetor cfm requirements are all the beginnings of the true blueprinting process. From there it involves properly communicating your needs to the parts manufacturers and to your machinist and finally checking the parts, by hand, to ensure that they all meet your requirements.

That is, blueprinting involves first designing the engine to suit the purposes you intend to use it for, then building it meticulously with (likely custom made) precision engineered parts. You're gonna start with a block, which will need precision machining to spec, and then add those parts and components with care until you have a bulletproof engine. Sounds pretty straightforward..

EmptyWords · Post by **EmptyWords** » 13 Feb 2005, 23:22

whats a stroker engine?

Grez~Supra_RZ-S · Post by **Grez~Supra_RZ-S** » 14 Feb 2005, 02:31

http://www.2quicknovas.com/happystrokers.html

boganbusman · Post by **boganbusman** » 14 Feb 2005, 07:12

In case you don't want to read all of that, stroking is basicallly putting shorter conrods in your engine to increase the displacement.

Of course there are other things involved (like a new crankshaft), but that's basically it.

MarlboroMan · Post by **MarlboroMan** » 14 Feb 2005, 11:20

but i personally think that changing the stroke will gradually change the engine characteristic. i have seen alot 4X4 trucks engine have longer stroke, and most racing engines have shorter stroke. long stroke engine to me is with better low end torque, and short stroke engine can go higher rev. by comparing the of the bore to the stroke, and you know what i mean.

so i guess that if you replace a longer con rod and make it runs a long stroke you will be better low end torque but it the other hand as a trade, you wont get high rev performance.

same thing that if you put shorter con rod you will get high end rev performance in exchange of low end torque.

of course you have to take care of the compression ratio too (special thickness head gasket, or different compression ratio piston...), you don't want to get a blown engine or a low power engine

boganbusman · Post by **boganbusman** » 14 Feb 2005, 14:41

Can one of the mods please make this sticky?

btw thanks for the contribution malboroman

Sweeper · Post by **Sweeper** » 14 Feb 2005, 15:18

Not a question this time, call it more a contribution.
After I asked some RX7 boys to explain Horsepower and Torque to me I finally got the hint.
Now maybe other people than me can get to understand the whole torque thing?
http://www.rx7club.com/showthread.php?t=393712

I hope that can help some people.

MarlboroMan · Post by **MarlboroMan** » 14 Feb 2005, 19:11

not a problem boganbusman, i am still learning, happy to discuss and sharing knowledge with you guys.

the link is very very helpful, MUST see !! thanks sweeper

EmptyWords · Post by **EmptyWords** » 14 Feb 2005, 20:44

whats a bore?

boganbusman · Post by **boganbusman** » 15 Feb 2005, 01:49

The 'bore' measurement in an engine is the diameter (width) of the cylinders.

To 'bore' the engine is to make the cylinders wider by machining the block. Doing this will give you more displacement. Depending on how much you bore the block, you might have to get new rings or forged pistons (or both).

Sweeper · Post by **Sweeper** » 15 Feb 2005, 10:41

Ok, now a question.

Forged pistons.
I understand these are forged in a predesigned shape, but what are they generally made from compared to normal pistons? Is there a point in forging NA pistons?

MarlboroMan · Post by **MarlboroMan** » 17 Feb 2005, 15:22

Sweeper,

i noticed that no one wants to answer this and this for some time and this is my own point of view.....

i bet some of the after market forged pistons are made with better material, most of all the process of forged pistons is the main point here, it is "cut" out from a piece of alloy, i dunno about the physics, but it is proven forged items can take more stress than the mold ones.

is there a point in forging NA pistons...

yes it is, when you want to change the compression ratio of the stock engine to something like 12:1 or maybe more, custom forge piston comes in. sometimes that a high compression NA engine (13:1) like the TRD celica, has more compress pressure in the combustion chamber than the force induction ones, i guess the custom forged piston in this paticular NA engine will do its work of taking high pressure and heat. and they are running octane 100 or more fuel to avoid severe engine knocking case.

* i have heard that the higher the octane the higher the chemical stablity of the particular fuel, so that it can be compressed with very high pressure without "explode" before the spark plugs ignite. diesel engines are "natural" combustion engines, thier high compression ratio will compress the fuel and explode in the cimbustion chamber without any help of spark plug.

EmptyWords · Post by **EmptyWords** » 17 Feb 2005, 21:58

what is compression ratio? hehe....

chimpzrl · Post by **chimpzrl** » 17 Feb 2005, 22:01

A guess to see if I can guess right:

The ratio of the compression of the engine to the normal volume of air. (change in pressure).

boganbusman · Post by **boganbusman** » 18 Feb 2005, 06:21

Oh sh*t . . . I didn't see your question Sweeper

Thanks for answering that malboroman.

And chimpzrl is pretty much right, the compression ratio is the compression of the intake charge in the cylinders. Eg: 10:1 means 10x normal air pressure inside the cylinder.

Oh, and remember that the maximum compression is only reached when the piston is fully extended.

One last thing: When a fuel explodes spontaneously (because of heat caused by compression), like diesel, it's called a 'low flashpoint' fuel. Fuels with a 'high flashpoint' are usually high octane petrols, and that means that they can take a lot of heat before they ignite. (and spark plugs generate extreme heat)

MarlboroMan · Post by **MarlboroMan** » 18 Feb 2005, 06:57

here is a little picture to help understand better for the compression ratio thingy.
this is the image i remember from the "how stuff works" page.
this is a picture of compression ratio 10:1
all together is 11 portions, 10 compressed to the 1 portion = 10:1 compression ratio

Sweeper · Post by **Sweeper** » 18 Feb 2005, 09:51

Thanks Marlboroman and Bogusman you answered my next questions as well about compression ratios.
And a good drawing that explained how it worked in practical solutions.

Now onto the next question which is more tricky, I hear the max compression for a rotary is around 20:1 is it then possible to run it on diesel, more exact turbo diesel?
just wondering what the average compression is in a piston diesel.

boganbusman · Post by **boganbusman** » 18 Feb 2005, 10:38

A turbo deisel with 20:1 comp would just explode I reckon. The diesel would probably ignite instantly and it wouldn't work unless you dropped the compression significantly.

Edit 24/7/06: Diesel engines actually have a compression ratio of 23:1, my bad.

Would a rotary run on diesel? No idea Can a rotary even reach 23:1 compression?

But malboroman probably knows more than I do.

MarlboroMan · Post by **MarlboroMan** » 18 Feb 2005, 12:01

sorry, I don't know much about rotary and diesel engines. recently i have been thinking about how to increase the rotary compression ratio, totally i have no idea about it. I would like to know much.

boganbusman · Post by **boganbusman** » 18 Feb 2005, 12:06

Oh right. Well . . . just go to HowStuffWorks and read up on deisel engines. That might help you a bit.

Or maybe there is someone else here who knows about this stuff.

Sweeper · Post by **Sweeper** » 18 Feb 2005, 12:08

Damn, I got the team stuck, HELL!
I can't ask the RX7 owners again, they will just end up in an argument over some guys homemade diesel and such and never go anywhere.

MarlboroMan · Post by **MarlboroMan** » 18 Feb 2005, 12:48

lol, hehe, yeah man. i dunno much about rotaries and diesel.

well this is not an answer well is my own point of view. if diesel is running a compression around 20:1.

if the 13B rising its compression ratio to 20:1 NA gasoline (thats almost F1 level !! whos would do that ?) it might need a very good fuel with very high octance, perhaps F1 fuel. probably (again) custom made rotary unit (triangular thing) to raise the compression, and alot alot ....worse of all this is alot of money......

the same 20:1 rotary runs on diesel, thoeritically it can, but will need alot things to be customized, rotary compression housing, diesel injection system etc etc...(again thats alot money..)

moreover a diesel turbo same engine, it doesn't matters just lowered the compression ratio, correct boost, fuel air mix ratio but i bet then should work.

anyone else any idea ?

Sweeper · Post by **Sweeper** » 19 Feb 2005, 00:38

Well that was the absolute maximum for the Wankel rotary design according to Dr Felix Wankel himself and his studies.
But I heard from people that it wasn't enough, but seeing as piston diesels runs a lot lower compression I guess a rotary can go diesel too.

I doubt anybody has built a 20:1 rotary because that is like stretching a design to its ultimate limit.
But thanks anyways Marlboro man, you have cleared up a few myths within my head around diesels and rotaries.
Because they said the only way to make a proper diesel rotary was to make the middle rotor of a 3 rotor engine work like an inefficient supercharger, pre compressing the mixture.

MarlboroMan · Post by **MarlboroMan** » 19 Feb 2005, 07:58

did you mean that in that case the mid rotary didn't get fuel and air and play as a dummy ?

Sweeper · Post by **Sweeper** » 19 Feb 2005, 16:58

MarlboroMan wrote:did you mean that in that case the mid rotary didn't get fuel and air and play as a dummy ?

I mean that all the fuel and the air is first feeded into the middle rotor to get a precompression.
Then that precompressed mixture goes to the other 2 rotors that makes the combustion.
Though a such design is not the best in my book.