289 FIA vintage race engine with Webers

[Gaz64]

Jim,

I think we'll find the belt deflection on the engine stand is some harmonics happening that video can't capture as "true to life" due to frames per second.

A bit like vehicle wheels that go backwards on TV.

Now, your carbs.

I hope some other guys on here will chime in to say what choke size they have.

If Jim gave you 42mm, then your combo of CID, compression ratio, cam profile etc, AND intended use: driving style, peak rpm etc were all deciding factors.

A tuning book of mine shows the ideal intake tract for an IR system, to have the throttle butterfly as the same size as that of the intake valve, and then the choke to be .85 of the butterfly.

Yours would be around these figures.

I would thinking about an air corrector change that will richen the top end, something like 180 as a start. Easy enough to drill them out to 1.85 about No. 73 as a test.
Then buy the correct sizes when you are happy with your testing. A misfire (poor combustion, valve float, poor spark quality etc) leaves unused oxygen, which then shows lean.
You may see that happen as the power falls away.

Gary

[blykins]

I’m still thinking something is off with the crank pulley. Even on the video from the dyno where there is no belt, I see run-out at low rpm. It’s almost like the pulley is bent or it’s not centered on the balancer.

I’m also concerned with the valve float signs on the dyno sheet. Could be the reason the engine is not making the horsepower it should.

[Gaz64]

Originally Posted by blykins

I’m still thinking something is off with the crank pulley. Even on the video from the dyno where there is no belt, I see run-out at low rpm. It’s almost like the pulley is bent or it’s not centered on the balancer.

I’m also concerned with the valve float signs on the dyno sheet. Could be the reason the engine is not making the horsepower it should.

Ah yes, after looking at dyno videos.

More investigation as to the cause of the power falling off, either valve float or ignition system etc.

[blykins]

Originally Posted by Gaz64

Ah yes, after looking at dyno videos.

More investigation as to the cause of the power falling off, either valve float or ignition system etc.

I would say valve float.

If it were just an issue with not enough camshaft, then the power would just fall off in a curve.

In the last 500 rpm of the dyno sheet, we see the power go up, back down, up, back down, etc. That's a tell-tale sign of valve float. I would say that the engine needs a little more valve spring seat pressure.

[Gaz64]

He's making near 1.5 per cube now, but there's probably another 30hp still on the table.

Gary

[1795]

Brent and Gary,

We wil take a look at the possibility of valve float. One contributing factor to those results may be that the dyno had the oldest computer I have seen operating in a long time. I think the last time that I saw one that old it was in a museum. When he was showing me a graphic of the torque curve the dyno operator commented on how this graph showed subtle variations that more modern computers on dyno's even out in the programming. The variations at the high rpms could be an artifact of the older computer and programming not being able to keep up with the input data at higher rpms.

While there still may be 30 hp left on the table, those extra 30 hp and 8,000 rpm redlines do come at a cost. If I am peaking at 6700 rpms and pretty much shifting between 6500-7000 rpms, the engine is going to last a lot longer than taking it to 8000-8500 rpms. I know guys who have engines that are operating in the HP and rev ranges that you guys are talking and those engines are expensive and are getting refreshed or broken way sooner than my little wallet can mange.

Now when I get to be a pro and am driving someone else's car using their money it may be a different story

Thanks guys, I really do appreciate the feedback.

Jim

[Mark IV]

"How fast do you want to go?".........How much do you want to spend?

Jim is playing in a league that has budgets FAR above his. He is smart enough to know he will not be at the front of the pack but as long as he can run mid-level with clean driving, he is a winner. We at Time Machines are proud to be a small sponsor to his efforts and will continue to provide whatever help we can from parts to sweat equity (we have some sway bar upgrades in the works).