OT garage question: Type 4, Cylinder Head Temp Options

[malcolm2]

I have been trolling The Samba Bay Bus forum with hopes of needing some info once I pull the trigger on the Bus purchase....

But I ran into a CHT post. I gave them Jakes INFO post from here. Those guys seem to think that 425 is ok for a bus.

My thought was that Jake was talking about a type 4 engine, regardless of what it was pushing.

Last post I saw the guy basically is accepting 425 and knowing the engine will not last.

Yes the bus is heavier, but shouldn't the goal be to keep temps down?

My L-Jet 914 cruises on the interstate (70 and 3400rpm) at VDO gauge temp of 340-to 350 with 12.5 - 12.9 A/F. I have gotten 29 mpg. So I think I have this one dialed in. I want my future bus to be dialed in too.

[Mblizzard]

As the direct quote says:

"420F+
Well your engine has been damaged. Go home...."

This is a mechanics of materials question not an engine question. With the alloys and materials that the heads and valves are made of they are all pretty close between Typ4 and the others. At above 400F things just start breaking down and cracking will start regardless of your engine type.

To accept that it is ok because it is a bus to run at that temperature to me would indicate a basic failure to understand the limitations of the materials your engine is made from.

As a comparison you know the Type 4s that are extensively modified for use as an airplane engine? Here is what they say about CHTs "CHTs above 400°F should be considered abusive, and grounds for "doing something right now" to bring them down."

If the materials in these heavily modified engines don't like 400F you can bet a stock one wont either.

How do I know?

400F+ =

[malcolm2]

That is very well thought out and big words were used.... (IMG:style_emoticons/default/dry.gif) I would certainly take engine, or car in general advice from this State Educated car guy.

Thanks. I might copy and paste to The Samba. I think they have lots of guys that could use help from 914 guys. (IMG:style_emoticons/default/wink.gif)

Go Vols

[malcolm2]

This is the picture that made me sick for the guy. It is an up hill run at 428 CHT. But 45 mph. 2000 rpm WOW. gotta get those REVS up. Can't see the shifter in this picture but 4th is my guess.

[Mblizzard]

This is the picture that made me sick for the guy. It is an up hill run at 428 CHT. But 45 mph. 2000 rpm WOW. gotta get those REVS up. Can't see the shifter in this picture but 4th is my guess.

Screams poorly adjusted timing! But as you said 2000 RMP in 4th is not going to make that any better!

Ok I know it is correct to have the CHT under the plug rather than attached to the head. You get the quickest response and see temp increases likely before they become a problem in the engine.

A couple of time on long hard sustained hill pulls at Okteenerfest I saw some temps climbing towards 400F. Because of the CHT location I could do something before the entire engine got saturated to that 400F temp. Down shift get out of it a little bit and the temp falls. Just can not even understand how someone could look at that and not do something. at that temp you had to be losing power and beginning to ping!