Compression & Ignition Question

Robert

Sounds like Sweet Music!

Paul

 

Very Nice.......... Like Mike says a larger W/P pulley is in order.
Ray

 

Thanks.
The belt system confused me a bit.
I have a 69 400cui and there is a little smaller pulley onto the balancer. The WP pulley has almost the same size like the balancer pulley, maybe a little smaller.
When i bought the 455 engine there was no belt,alt,oil or something else assembled.
I would take the complete belt system from my 400er engine. Because the bigger WP pulley doesn't fit with the 455 balancer pulley.

 

Sounds like you had the non-AC pulleys on your 400 which will work great especially with that new water pump. I believe the WP pulley for that setup is slightly larger than the balancer pulley for a slightly underdriven waterpump. They will also free up a few HP compared to the way overdriven AC pulleys.

 

That AIR pump pulley is normally on a long WP and that is why it aligns OK on your short water pump which is what the 400 would have had so your early pulley set should work.

 

Troubles....

They engine is not runnig at idle speed. Heavy shaking at 750rpm.

At 2500 rpm with light torque it runs great. Lambda is 0.92
But When the secondarys are open, the engine runs to rich like 0.69-0.70.
Timing is 35* at 2500 rpm.

I guess the carb 750cfm is has wrong size of jets. Tomorrow i will try a with the orginal 850cfm from this engine.

Any suggestion?

Need help, the engine builder isnt a buick guy....

I run the engine with the stock collectors ... 320hp@5000 and 500nm to weak for this setup...

best regards

Robert

 

Robert

Have you done a compression test?

What is the initial timing at idle?

The 750 carb is too small.

Paul

 

Compression test was good. All Cylinders 12-13 bar.
Initial timing was 8* .
Cliff means its enough...

Thanks for the help paul :beer

 

At peak torque or around 4000 rpm, the Lambda should not be less than 0.85.

At idle the Lambda should be just under 1.0

These are just good starting places and you will need to fine tune from there

Paul

 

That cam with basically no overlap at .050" should be idling almost smooth. I'd check the spark plug wiring, 18436572, again.

If not that, I hate to say but, I'd be pulling the valve covers and checking that each valve is opening all the way either while running or while cranking over. Hopefully no lobes are wiped. You can usually just do an eyeball check to see if they all look like they are coming up the same amount. Start it up and watch one side at a time. For how bad yours is running it should be noticable.

500 NM = 368 lb ft so that is about right for you HP reading but IMO HP should be around 400(at least) and torque should be something north of 400 for your setup even with the exhaust manifolds.

.92 = 13.52 so that isn't bad but you are right the .70 = 10.29 A/F ratio is way rich. Unfortunately a bad lobe could do that so I'd be checking them.

Changing the carb wouldn't hurt but if the carb is even working close to right it wouldn't make more than a 20ish number change. Was it on your engine before? Are the secondaries opening all the way?

 

We have a big vacuum 0.7 bar but i didnt remember at wich rpm.
The man who owns the dyno isnt a buick guy. Now im not sure is my carb correct connected ---> look picture

The carb was installed on me gs400 und it runs good. But after disassembling the carb i found on these 2 red spots (picures) fuel, much fuel, they arent seal. Can the fuel drain in the intake?

I removed the valves covers and 2 lifters arent load right, they was soft. So i remove the loadspring and run with the starter to load these. After 6 Tries with breaks they are now stone hard. After that i checked the compression again 12-13 Bar.

Next pull, same results... i removed the vavle covers again and checked the lifter, stone hard again. hmmm

Thanks for the help!

Robert

 

Those go right into the fuel well around the jets and they are prone to leak. Usually it is minor. If you take the base off you can get to them easily. Clean the area and epoxy them to keep them from leaking.

 

short timing question :Smarty: . I asked the man from the dyno about the timing. He said the total timing is 45* with vacuum ahmm i guess the correct timing should be 36* right?

Someone can me recommend a Holley carb for this engine? 81870 ?

 

It sounds like he is including vacuum advance at part throttle for your total timing so 45 sounds OK. You mentioned 36 total earlier which may be a few degrees too much especially with those heads. If it is on the dyno I'd try taking a couple out of it and see if it adds any power.

As far as the vacuum advance goes I'd disconnect it completely for WOT power checks and only have it connected if you are checking part throttle cruise conditions on the dyno. The vacuum advance should go away when you go to WOT but why even have it hooked up to add some possible confusion when looking for max power.

How's the shake at idle? That is your most important concern. Playing with the timing won't make a difference there.

 

Mike, now i have fixed the leaks of the Q-Jet. Now the engine is idle very smooth @ 1000 rpm much better than before. But when the secondaries open, the lambda is the same 0.69-0.70 from 2500-5000 RPM.
Torque is now 540nm little more hp the same...

I haven't jets rods so i want to change the carb to a holly 80870 its a 870cfm electric choke with vacuum secondaries.

I guess the engine has two problems.

First is the bad Air/fuel ratio @ WOT

Second is a ignition problem. When the engine want to idle, it hears like the ignition has a short fail, like ch ch ch ch silence ch ch ch ch silence. Its also possible that the carburetor make those problem also?

What u think about the carb? i must use a adapter plate for the square bore...

Thanks

Robert

 

I'm not sure what you mean by the sound effects but it sounds like an arc-over somewhere. Try looking at the engine while the lights are out in the room to see if there is any flashing. Is there a chance there is a cracked spark plug?

From my direct experience with the 870 Avenger your engine will make about the same peak power on the dyno, maybe a little more, as the smaller Q-Jet. Where the Holley vacuum secondaries fall down on the Buick is they just won't open as fast as the Q-Jets can in real life so the midrange gets shortchanged and consequently they barely work as good as the Q-Jet at the track. However if there is some problem with the Q-Jet the 870 will run better and it is much more tunable to get everything right on the dyno. I'd say it is worth the change to see if there is some big HP pickup.

I don't think you will need an adapter to bolt the Holley to the intake. That looks like an Edelbrock so all you should need is the correct base gasket. Ive done that many times. At most you would need one of their thin plates that make sure all the holes on the bottom are covered but I've never needed one.

http://www.summitracing.com/parts/EDL-2732/

One thing to check on the Q-Jet are the secondary throttle blades opening to about 90 and more importantly is the secondary air flapper on the top of the carb opening to about 90. You can check that with your finger. It should go almost straight up and down. That would make a difference in carb tune. Most of the Q-Jets used always have some sort of angle less than 90 to the secondaries. Some times it is very steep. It was GM's way of changing the airflow rating of the carb to better match the engine and type of intake. There's a tab on the side of the carb that you can grind away to fix it.

 

I bought the 870 Avenger after i saw this test . The engine builder has a lot of experience with carburetors from Holley and has also the proper jets to get the right AFR. I hope the engine produce more power with the correct AFR...

Thanks for your support mike!

Robert

 

First an Avanger 870 from holley doesn't fit onto edelbrock Preformer intake. The throttle flaps hit the intake. No problem, i mounted the spread bore to square bore adapter between the intake and carb.
The engine produce now 50 hp more and 40ft/lb torque:

370hp@ 5000 RPM (with stock collectors and open exhaust)
420ft/lbs
Timing @ 30* to less?

After 5250 RPM the engine cant rev higher, reason?
I hope the +4 Advance are not to much. Rev. limiter set @ 6000RPM
It sounds like the ignition system has a problem. The engine idling now much better with the avenger carburetor. But there is still a problem. It idles nice @ 750 RPM, but all 3 seconds or more it will shorty stumble a 1/4 second only one time than next 3 seconds good idle, than again short stumble.
Next step is, i would try my old distributor with cables, should i take the sparks too? That will show is the distributor the cause or a cable.

regards

Robert

 

What was the Lambda readings.

What does each spark plug look like for color.

If you are around 300 meters in altitude try timing at 32 and 34.

Paul