No Power Under Load

[Pascal Zundel]

To Jacques: Thanks, for the best joke of the day!

[Chuck Watson]

From my experience it has good power up to about 4500 rpms. Then it falters. I have only had a few track opportunities with it so my experience is limited. But no, it never ran flawlessly under my ownership. The original builder says it was a very fast car that he ran for several years and he is surprised to hear of the current issues. There is a possibility that interim owners replaced parts along with de-tuning the car. Won't know that for sure until a tear down I guess. But I am still under the impression there is a fuel/ignition or compression problem due to the fact it pulls well (until it doesn't)...

[Chuck Watson]

In my mind I keep coming back to the question of what is different under load versus rev'ing the engine in the garage. It revs beautifully in the garage. So the differences I can think of are:

1) More fuel needed obviously
2) More air-flow presumably
3) Is a bigger spark needed?
4) Is the compression any different?

[David Jones]

Chuck, what happens at 4500 rpm. Do you have an EGT gauge? If so does the EGT change. Have you checked for full throttle application. I suspect that if it is free revving in neutral it could be that it is just not getting full throttle under load. It takes very little throttle opening in neutral to get full revs but at full load even 90% throttle will limit rpm.

[Jeffrey Leeds]

Just to confirm: With no load the engine revs. freely well past 4500 but under load it poops out at ~ 4500. At that point it does - or does not - continue to accelerate at some much slower rate?

[Mike Wilson]

I think David is on to it.

[Chuck Watson]

I'll do a physical inspection of the butterflies at full throttle (is that what you mean David?). Interesting point. The issue around 4,500 rpm is kind of a stall or stutter. Enough so that you really don't get much more acceleration from there on. Almost feels like a rev limiter, but it's not (yes I checked the rotor ). I don't have a EGT sensor, but I have purchased a leak down tester and hope to test that tomorrow along with checking the throttle.

[Jeffrey Leeds]

I was thinking along the lines of slippage in the drive-train as the rpms get over a certain level , but David's suggestion makes more sense now.

[David Jones]

Chuck, if it revs over 4500 in the lower gears but stall at 4500 in 4th I would still think there is a good chance that you are not getting full throttle. I have as they say been there and done that. With the F Vee it became routine to do a full throttle check by looking down the throat at every engine check and especially before first practice. I gained 2 secs per lap on one outing with a fresh engine after finding I only had 95% throttle opening. It is not an obvious fault like ignition timing or jetting by reading the EGT. I first had experience of this with a BMW 1800 Ti back in the 60's which had been upgraded to TA with Webers and we eventually found that even though it had full throttle when the engine was off, when under load the engine torqued in it's mounts and put slack in the throttle cable so it backed off full throttle.

[Chuck Watson]

Cautiously optimistic that you are right! IIRC it WAS mainly a problem in 4th. Hope to check tomorrow.

[Chuck Watson]

Unfortunately it not just an unopened throttle. Compression and leak down results below.

#1: 168 psi, 40% dry, 14% oiled
#2: 172 psi, 33% dry, 18% oiled
#3: 205 psi, 9% dry
#4: 205 psi, 14% dry

Wish they all looked like 3 & 4! Hissing on 1 & 2 was mainly from crankcase. So, looks to me like a rings/rebuild issue. I've rebuilt a 911 engine but not a 356 or race engine.

Bummer. Guess I won't be racing anytime soon.

Thoughts, suggestions, advice?

[Dan Epperly]

I was about to post that I had the same symptoms with the engine in my B, so after switching out everything, I finally pulled it apart and there were head leaks all over the place,not bad enough to make the usual racket but bad enough to loose compression. Check your heads for leaks...

[Chuck Watson]

Dan, that would be a welcome problem considering.....

How did you determine the leaks were there? Something that could be determined with engine in place?

[Dan Epperly]

Dan, that would be a welcome problem considering.....

How did you determine the leaks were there? Something that could be determined with engine in place?

I wasn't able to figure it out until I pulled the heads and saw all the carbon marks radiating out from there the cylinders meshed with the heads. I suppose you could possible peer in there with a flashlight looking up to see if you can spot the tell tale carbon marks. Pulling the heater boxes if have them would make it easier.

[Ron LaDow]

How did you determine the leaks were there?

A leak-down test and an ear will tell you.