Fundemental car question - Page 2

Unit 5302 · 10-06-2001, 01:14 AM

Quote:

Originally posted by crazy horse gt:
hey unit 5302 in about 2 year's , how much would you charge me to help me build my 4.6 i'm kidding , but not really you seem to know

I know very little about the Mod engines, but I'm seriously considering buying a new GT in late winter.

Most of my knowledge comes from the theory of operation and what not. As far as doing engine work, I wish I actually had a place suitable for that. I've got a 427FE waiting for a lot of that, but money needs to make itself a little more accessible first.

That and a car to put it in!

Crazy Horse GT · 10-06-2001, 01:38 AM

ok thank's unit ,later. pkrwud will probably give me hell jk. see ya. oh by the way i know aguy who has , 2 70 boss 302's he is selling one & should just sell the other one, also hell iv'e known him for 7 year's & they just sit in his garage , it's sick, i even offered to help him get one of them going but they just get more & more dust build up on them . sad but true.later.

------------------

[This message has been edited by crazy horse gt (edited 10-06-2001).]

I hate Rice · 10-06-2001, 01:17 PM

Question: What is a dished piston? Is it similar to a domed piston but the other way? What are the benifits of it? Thanks

Unit 5302 · 10-06-2001, 05:57 PM

PKRWUD has a ton of real experiance diggin around in engines, and you'd be better off having him help you with building stuff up. He's got the facilities to work on that kind of stuff, and he knows what he's doing.

I hate Rice a dished piston is exactly what you think. It's a concave piston which drops the compression ratio. Dished pistons are beneficial in a couple different circumstances, most notably, high boosted applications. In those circumstances, you want the compression ratio lower to allow for a higher boost level. It also comes in handy on some of the older cars that had very high compression ratios, that maybe you want to run on 87octane pump gas now. Installing dished pistons will drop the CR way down, and allow you to do that.

For a naturally aspirated engine, no real benefits come to mind. Heh, maybe you wouldn't need to flycut? LOL!!

[This message has been edited by Unit 5302 (edited 10-06-2001).]

Rev · 10-06-2001, 06:28 PM

I think originally, the dished pistons were just a crutch to meet emissions standards. The Big Three using dished pistons could lower compression with the same old heads, add an air pump, EGR valve, leaned out carb, cats, and voila, they were there. Also retarded timing and high gears.

Those engines put out a whopping .5 HP per CI. I know because my '75 Granada 351W did just that. Fortunately, I was able to tweak it a little once I had figured out what they had done.

Rev

------------------
'66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph
1/4 mi.

[This message has been edited by Rev (edited 10-06-2001).]

1965GTO · 10-07-2001, 01:12 AM

PKRWUD you obviously haven't been taught too well if you think displacement alone has nothing to do with torque. It is the number one factor. Stroke isn't nearly as important as you would think. Stroker engines make more torque and horsepower because they increase displacement not because of the longer stroke.

PKRWUD · 10-07-2001, 04:15 AM

65 goat-
So, in other words, you're saying that, with equal compression, a 351 will have more torque that a 347, because of displacement? I don't think so.

Take care
~Chris

------------------
Retired Moderator
MustangNet

My site: JimPorterRacing

RACECAR spelled backwards is RACECAR

HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

Unit 5302 · 10-07-2001, 12:49 PM

There is more to torque than just compression ratio and displacement. The compression ratio is only part of the cylinder pressure.

If everything else was equal between the two engines (which is impossible) the 351 would develop 1.1% more torque than the 347.

Bore is more of a component of displacement than stroke, and thus, it is more important than stroke in the overall torque of an engine. The only problem comes in when you have an existing engine, increasing bore is much more difficult than building a stroker for it.

84LX89GT · 10-07-2001, 05:34 PM

People have been very thorough on this subject so i don't think there's very much i can add.
I learned that in in two identical displacement engines (in theory). The one with a larger stroke will get worse gas mileage because of the increased friction from the rod angle and will also wear out the rings faster because they're forced against the cylinder wall harder from the rod angle. BUT.......it will have better emissions becuase there's more tumble and atomization on the intake stroke because the air/fuel is pulled farther and the tendancy of the air/fuel is to "tumble" into the cylinder because of the angle of entry.
The advantage of a large bore, short stroke engine, is as stated that there's less friction and as a result can produce more power over the rpm range and because of port angle and cylinder fill rate, flow more air through the head at higher RPMs (port angle has advantages for both large stroke and large bore engines).
Another thing that i've read is that because of cylinder pressure and atomization of the air/fuel as well as the increased leverage of a longer stroke crankshaft, an engine with a larger stroke will produce it's peak torque and horsepower at a lower rpm than a large bore engine which has to generate more torque by increasing it's rpm operating range.
A stop-gap measure taken in the early 70's to come up with better emissions was to increase the stroke of existing engines and to engineer large stroke small bore engines. Some examples are the 400 Chevy engine, 400 Ford engine, (i think) the Chevy 305 engine, the Chrysler 400 engine (not sure on this one either) and a great example is the ford 255 made from '80 to '82 (or around those years). It had a decreased bore and the 3.00" stroke and was designed to be an emissions oriented engine. Remember that crap variable venturi carburetor, all of those were meant to lower emissions, but of course, didn't come into the public's favor.
-summary-
In terms of power, a short stroke engine will have a larger power band and can keep power in the rpm range better, but since it's operating range is higher in the power band it may lack some torque on the bottom end. A long stroke engine breathes really well at lower rpm and has increased leverage from the crank and better burn of the air/fuel mixture, but loses power on the top end faster because of friction.
If anyone disagrees, i'm open to any other ideas

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10-06-2001, 01:38 AM	#22
Crazy Horse GT Registered Member Join Date: Aug 2001 Location: Sale Creek, TN. C. S. A. Posts: 4,652	ok thank's unit ,later. pkrwud will probably give me hell jk. see ya. oh by the way i know aguy who has , 2 70 boss 302's he is selling one & should just sell the other one, also hell iv'e known him for 7 year's & they just sit in his garage , it's sick, i even offered to help him get one of them going but they just get more & more dust build up on them . sad but true.later. ------------------ [This message has been edited by crazy horse gt (edited 10-06-2001).]

10-06-2001, 01:17 PM	#23
I hate Rice Registered Member Join Date: Aug 2001 Posts: 81	Question: What is a dished piston? Is it similar to a domed piston but the other way? What are the benifits of it? Thanks

10-06-2001, 05:57 PM	#24
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	PKRWUD has a ton of real experiance diggin around in engines, and you'd be better off having him help you with building stuff up. He's got the facilities to work on that kind of stuff, and he knows what he's doing. I hate Rice a dished piston is exactly what you think. It's a concave piston which drops the compression ratio. Dished pistons are beneficial in a couple different circumstances, most notably, high boosted applications. In those circumstances, you want the compression ratio lower to allow for a higher boost level. It also comes in handy on some of the older cars that had very high compression ratios, that maybe you want to run on 87octane pump gas now. Installing dished pistons will drop the CR way down, and allow you to do that. For a naturally aspirated engine, no real benefits come to mind. Heh, maybe you wouldn't need to flycut? LOL!! [This message has been edited by Unit 5302 (edited 10-06-2001).]

10-06-2001, 06:28 PM	#25
Rev Registered Member Join Date: Nov 1998 Location: Houston, Tx. Posts: 3,887	I think originally, the dished pistons were just a crutch to meet emissions standards. The Big Three using dished pistons could lower compression with the same old heads, add an air pump, EGR valve, leaned out carb, cats, and voila, they were there. Also retarded timing and high gears. Those engines put out a whopping .5 HP per CI. I know because my '75 Granada 351W did just that. Fortunately, I was able to tweak it a little once I had figured out what they had done. Rev ------------------ '66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph 1/4 mi. [This message has been edited by Rev (edited 10-06-2001).]

10-07-2001, 01:12 AM	#26
1965GTO Registered Member Join Date: Jul 2001 Location: Dupo,ill Posts: 219	PKRWUD you obviously haven't been taught too well if you think displacement alone has nothing to do with torque. It is the number one factor. Stroke isn't nearly as important as you would think. Stroker engines make more torque and horsepower because they increase displacement not because of the longer stroke.

10-07-2001, 04:15 AM	#27
PKRWUD Junior Member Join Date: Mar 1999 Location: Ventura, California Posts: 8,981	65 goat- So, in other words, you're saying that, with equal compression, a 351 will have more torque that a 347, because of displacement? I don't think so. Take care ~Chris ------------------ Retired Moderator MustangNet My site: JimPorterRacing RACECAR spelled backwards is RACECAR HEY !!! Are you ASE Certified ??? If you are, ask me about iATN. The best tool you'll ever have, and it's free !!!

10-07-2001, 12:49 PM	#28
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	There is more to torque than just compression ratio and displacement. The compression ratio is only part of the cylinder pressure. If everything else was equal between the two engines (which is impossible) the 351 would develop 1.1% more torque than the 347. Bore is more of a component of displacement than stroke, and thus, it is more important than stroke in the overall torque of an engine. The only problem comes in when you have an existing engine, increasing bore is much more difficult than building a stroker for it.

10-07-2001, 05:34 PM	#29
84LX89GT Mustangs Join Date: Jul 2000 Posts: 1,938	People have been very thorough on this subject so i don't think there's very much i can add. I learned that in in two identical displacement engines (in theory). The one with a larger stroke will get worse gas mileage because of the increased friction from the rod angle and will also wear out the rings faster because they're forced against the cylinder wall harder from the rod angle. BUT.......it will have better emissions becuase there's more tumble and atomization on the intake stroke because the air/fuel is pulled farther and the tendancy of the air/fuel is to "tumble" into the cylinder because of the angle of entry. The advantage of a large bore, short stroke engine, is as stated that there's less friction and as a result can produce more power over the rpm range and because of port angle and cylinder fill rate, flow more air through the head at higher RPMs (port angle has advantages for both large stroke and large bore engines). Another thing that i've read is that because of cylinder pressure and atomization of the air/fuel as well as the increased leverage of a longer stroke crankshaft, an engine with a larger stroke will produce it's peak torque and horsepower at a lower rpm than a large bore engine which has to generate more torque by increasing it's rpm operating range. A stop-gap measure taken in the early 70's to come up with better emissions was to increase the stroke of existing engines and to engineer large stroke small bore engines. Some examples are the 400 Chevy engine, 400 Ford engine, (i think) the Chevy 305 engine, the Chrysler 400 engine (not sure on this one either) and a great example is the ford 255 made from '80 to '82 (or around those years). It had a decreased bore and the 3.00" stroke and was designed to be an emissions oriented engine. Remember that crap variable venturi carburetor, all of those were meant to lower emissions, but of course, didn't come into the public's favor. -summary- In terms of power, a short stroke engine will have a larger power band and can keep power in the rpm range better, but since it's operating range is higher in the power band it may lack some torque on the bottom end. A long stroke engine breathes really well at lower rpm and has increased leverage from the crank and better burn of the air/fuel mixture, but loses power on the top end faster because of friction. If anyone disagrees, i'm open to any other ideas