Engine theory

[jgrh64]

Does anyone know what makes certain motors able to rev and other makes can only acheive low rpms? if you have a 4.25 bore and 3.5 stroke you would think this short stroke would enable this motor to rev up high but it is known as a truck motor so everone dismisses it and says why do you need to go fast? (duh) Is it just a matter of the cam specs ? The carb cfm? The old ford flathead can now have multiple blowers and run like a scalded cat yet was known for a while as a slug Any Ideas?

[jasonrmorrow]

What makes an Engine rev...i have this little thing about people calling engines motors...

but anyways, the ability for an engine to reach high rpms is based on several factors, piston speed is one of the big ones, a longer stroke will cause the piston to reach a higher speed which can cause it to score and overheat if not properly lubricated or coated.Rotating mass, the heavier the crank, con rod, and piston the tougher it is to sling it around efficiently. Light but very strong forged parts will allow for a lighter rotating mass and allow the engine to rev up quicker and continue onto higher rpms without much stress. If you have seen a new gen III small block there is basically no piston skirt,which reduces weight and the pistons are teflon coated to limit friction.

Valve float can also limit rpms, valve float occurs when the vlave physically cannot open and then close in the time it takes the piston to come back up for compression. This can be helped by adding solid lifters and stronger valve springs, but then you get into reliablitly issues and things like stud girdles and other exotic and expensive add ons.

Lubrication would be a big concern of mine though, there are a lot of engine builders that can build your engine to rev and know the proper passages and galleys to open up or block off to improve the flow and prevent failure due to lack of lubrication.

Some of the guys at work went to a tech training course with gm and the new vette engine, with the rev limiter disabled, is good to 15 000 rpm, according to one of the engineers, which means it may run at that speed but not for long, kind of like a race engine.

Read up a bit on that or the smaller import engines, there are just certain limitations to each engine design.

[Frizzle Fry]

Strength of the rotating assembly, ignition consistency, valve train, and lubrication (if you want it to stay together).

[jgrh64]

Well I beleive it may be rotating mass in this case- it's the 305 V6, piston is same bore as a 454 but stroke is shorter would be about a 370cu in engine if a V8 as far as I can figure out.I know I should just go to a small block chevy but I have this engine w/ 79,000 mi that still runs good after 41 years and I would rather use it than spend extra money that could be used elsewhere. I WILL adapt a small 4bbl to it one way or another, I have an elctronic dist. conversion from crane cams and can regrind the cam and I guess thats about all I can do .Thought about milling the heads .100 not sure what that will cost though.

[rwgregory]

Want to put a set of headers on that V-6?? Look up my post on the 60-66
parts section.

[Fred T]

The GMC V6 was designed to be a high torque, low speed engine. Massive crankshaft, low compression and heads with small valves and runners were used to achieve this goal. If you want to make it turn fast be prepared to throw major bucks into it, and expect to be disappointed. I'm not saying it can't or shouldn't be done, just know what you're getting into. But you will find it cheaper to put in a V8 than to build a V6 to do anything other than lug.

When operated as designed, and properly maintained, you can easily get 200,000 miles out of the engine. Abuse it by running wide open all day long and it will chunk rods like there's no tomorrow.

If you haven't been there, go to http://www.6066gmcguy.org . Jolly has a wealth of info on the V6.

[jgrh64]

Yes I belong to that club too. Milling the heads will raise compression. I'm not going racing just want to have some fun with it, someday it'll be a smallblock but for now I'll make due with what I have. In the spring I'm ousting the SM-420 in favor of a pass. 4 speed w/ hurst shifter.

[jgrh64]

Looked around the site couldn't find your listing for the headers .

[rwgregory]

As of Fri. nite it was the 23'rd posting from the top of the '60 thru '66
parts section on the first page of this site. Last activity was listed at 12:29
AM on 10/6'05 .
Thanx,
rwgregory

[jgrh64]

found it - little too much for me but thanks.