Questions about the v8 builds

[awJCKDup]

Hey everyone, I didn't want to highjack a build thread so I am posting here. I am thinking about the V8 builds, which has prompted several questions.

1. With the valve covers on, how are the rocker arms, pushrods, and lifters being oiled?

2. When you scale down an engine, do the cam specs, (lift, duration) scale proportionally? I just watched a video of Steve's V4, and it sounded very healthy, is this due to more "performance" like cam specs.?

3. How long do you allow these engines to run at a single time, even being water cooled , do you limit runtier?
Thanks, John

 

[stevehuckss396]

1. With the valve covers on, how are the rocker arms, pushrods, and lifters being oiled?

My rockers will be oiled manually. One drop of light oil will be plenty for the light duty these engines see. At an all day show I will oil the rockers 2 or 3 time a day.

2. When you scale down an engine, do the cam specs, (lift, duration) scale proportionally? I just watched a video of Steve's V4, and it sounded very healthy, is this due to more "performance" like cam specs.?

Duration for most of the model engines I have seen the plans for is 240I/260E. In my opinion, which is worth what you paid for it, duel profile cams are unnecessary in an engine where both valves are the same size. I also believe that a 240 duration cam will make an engine sound sluggish. I think old school thinking was less duration equals a better idle. The Peewee has a 280/280 with .070 lift. I think the longer duration gives a warmer sound at idle and high lift is unnecessary. I don't see the point of stressing the valve train with high lift cams on an engine that runs on a stand.

3. How long do you allow these engines to run at a single time, even being water cooled , do you limit runtier?

What's runtier?

I run mine for a few minutes at a time. Usually just long enough to allow someone to see and hear it run. The cooling systems on an engine this small is inadequate. The only reason I water cool is to extend the run time but it will never allow infinite run times.


So John, when you starting on yours?

Steve

 

[gbritnell]

I have to echo almost everything Steve has stated.
When I built my 302 v-8 I put a fitting into the lifter valley that tapped into the main oil galley. From there I ran 1/16 brass tubing up to both hollow rocker shafts to feed oil to the rockers. The problem was regulating the amount of oil that went there. I played around with restrictors in the lines trying to get it right and then eventually just eliminated it completely. I do like Steve does, before a show I remove my breather caps, one on each rocker cover, and I have a small tube which is attached to the rocker shaft which I squirt some oil into. I've never had a problem with this method.
As far as cam timing, my engine runs a scaled version of a stock 302 camshaft. Without getting into specs it's quite mild. My 4 cylinder is a little more radical but the problem with these little engines is that if you make it too radical you are fighting compression and flywheel needs to keep it running slowly. If it runs well what difference does it make to say that you have a full race profile cam in your engine?
As far as cooling, these things get hot. My 302 has a large heater core as a radiator and from cold I can run the engine about 10 minutes, if I don't rev it a lot, before it starts to get hot. Even at that hot is subjective. How hot? Probably by feel it's about 200 degrees but that's what a full sized engine runs at anyway. It is only for display and not meant to run continually. At a show I run the engine all day for 2-3 minute bursts and have had no wear or other problems.
George

 

[awJCKDup]

Thanks Steve,
I understand about stressing the valve train, my questions about the cam come from hearing some engines that just seemed like they were laboring to rev up, while your V4 sounded crisp and responsive, and has a nice idle. Due to the low compression of these engines I assume that you run no or very little overlap?

What's runtier?-----That was supposed to be run time, I was sure I ran spell check, oh well.

A V8 build is in my future, I just don't think my skills are up to the task just yet.

Thanks George,
Your telling me you run an oil pump in your 302?

"If it runs well what difference does it make to say that you have a full race profile cam in your engine?" Again I don't care about full race specs, but I do care about how it sounds.

I saw, and you started your 302 for me a last years NAMES and I was duly impressed.

Thanks all
John

 

[mu38&Bg#]

Engine that have a hard time revving are more likely have issues with air/fuel mixture than anything else. The carbs are often very simple and getting a good idle mixture than works when hot and or cold can be tough.

 

[gbritnell]

Hi John,
Yes the 302 has a full pressure oil system. When I built it I worked from the factory engineering drawings and duplicated all the oil system, from the pump, to the filter, then to the main oil galley feeding the lifters and then to the mains and the rods through the drilled crankshaft.
As far as the sound that can be deceiving. You would think that my v-8 with open pipes and eight cylinders would make a gosh awful noise but it doesn't. Now take the v-twin with two cylinders, that thing is extremely loud. Part of that has to do with cam timing and some has to do with compression.
My Holt engine sounds very mild when it's revved up but the reason for that is it has two flywheels on it, one very large and another that probably would be adequate on the front of the engine. It was designed and built that way to mirror the full sized engine. The cam timing is not much different than my four cylinder OHV engine but the compression is much less.
In past discussions on this forum we have debated the issues of cam timing, what's good, what it should be, what someone prefers etc. Over the years I have seen many many multi-cylinder model engines. Some run very nicely and others not so well. With all the critical elements required when building anything with 4 to 8 cylinders I feel it's more important that the engine start and run smoothly.
Don't get me wrong, I'm not saying that a little more radical cam couldn't be used but there are so many other issues to be dealt with, fuel mixture, air flow, heat dissipation, ignition timing, compression etc. that cam timing is just a small part of the whole.
George

 

[awJCKDup]

George, your points are well taken. I appreciate the advice from the guys who have been there done that. Thanks.
A pressurized oil system,---wow, I didn't realize the internal detail was that complex.

Thanks again all
John

 

[jpeter]

Hey, check mine out.
[ame]http://www.youtube.com/watch?v=B9zt3SF_Flc[/ame]

 

[awJCKDup]

Very nice Jpeter, I had seen that video several times before. Your engine is quite responsive, and has a nice idle. I like it.

John

 

[jpeter]

Thanks.