Long ram intakes. Solid rollercam. 496" Stroker...

[BigBlockMopar]

I agree all the symptoms point to a vacuumleak, or lack of fuel.
I can fatten up the idle AFRs easily by opening up all the mixture screws a half or 3/4 turn. But this has no noticable effect on the surging.

This setup, intake and carbs, has been working good before the camswap. The carbs have never been off the intakes in the mean time.

But I will spray some brakecleaner around the intake-ports tomorrow to see if that changes anything.
If the ports seem tight I might have to open up the carbs and check the floatlevel up slightly perhaps.
I also want to add spacers under the carbs if possible because they still get very hot after a while. (Surging also occurs with a cold engine).

Ignition inital is currently at 25.
There's 10deg mechanical advance in the distributor.
When I had the initial at 14, the surging was less. But overal power was down ofcourse and the engine sounded/felt lazy.

[squirrel]

Might be worth recurving the distributor. I assume you mean you have 10 crank degrees advance in the distributor, not distributor degrees? see if it works better with 10-12 degrees initial, then advancing to 35 total (or whatever total it runs best at).

Usually with a bigger cam you need to run it pretty rich at idle

[BigBlockMopar]

I swapped one of the carbs today for another one, because I thought I noticed some play on the secondary throttle blades on the driversside carb. But after the swap the surge was still present.
The carbs on the intakes I bought new in '98 and haven't seen much running time.

As a test I richened up the idle mixture screws way upto 11-12:1 AFR, but made no difference in the surging.

I'm expecting the 2nd AFR-gauge to arrive tomorrow so I could install it in the car that evening. Hope I can notice a difference in carb behaviour with both gauges hooked up, but I'm not sure I will see much.

I might try recurving or swapping in a stock distributor again for testing, if that would help.
But I'm starting to get the impression the cam just doesn't create enough vacuum for the carbs to keep supplying fuel through the idle-ports.
When I had the Edelbrock Performer RPM intake on the motor with just one carb, engine-idling was lousy aswell and I had to increase the idle-rpm to prevent it from stalling aswell. Maybe I do need to drill the throttleblades.

[BigBlockMopar]

Ding ding ding!
Squirrel wins the fridge and now goes to the next round

After I installed a 2nd AFRgauge I could somewhat equalise both carbs, but no avail.
Only when I backed down the timing to 11-12 initial the idle smoothed out and the engine became usable again.

In a minute I'll post 2 clips of the engine and gauges shown while idling.

[BigBlockMopar]

2 clips of the engine,
- First clip shows the engine running fairly ok and usable again.
- Second clip shows the gauges inside, starting with the car idling nicely in Drive.


1st clip...

2nd clip...

[Barry Donovan]

awesome setup. never saw one in life.

I instantly thought of the rotax aviators engine. aligning carbs.

home made manometer

and there is a fancy gadget, can't find it..its in video though.

to work it, they do not want the two halves of intake to be connected. yours is like that permanently it appears.

I'll look for vid.

I had a dual timing belt subaru doing that on an optical distributor (no advance retard). one intake.

here is another one. this is not the first one I found. fancy though.

http://youtu.be/GDc65eq0CqM

[Scott Liggett]

I think Barry Grant and Edelbrock have the equalizer tool you need for multiple carbs since both sell multiple carb setups.


I always thought the longer the intake runner, the lower the rpm of torque. It's why Hilborn injection setups have choices of very short to very long stacks.

[wyrmrider]

Running very short or very long stacks on the hilborns brings back some memories
Caddo Mills Texas AHRA nationals 1962
Track was very greasy
we took off the stacks completely and retarded the spark to kill the low end

[BigBlockMopar]

That, sounds like fun!

Small update on the longrams tuning,
The surging is down to acceptable levels with the timing at 10-11 initial.
I've played with recurving and timing the ignition some more, since the engine pings very easily once you get onto the throttle a bit.
In order to try and get rid of the pinging I've tried to richen up the mixture a bunch, but that didn't help.
Only limiting the mech. advance to 26-28 total would take care of the ping.
I'm thinking the cam and the longrams combined simply create too much cylinder pressure at midrange for the fuel to handle.
Running the engine with full 35 degrees advance is no option.

Another thing that's noticable, eventhough the engine's temp stays below 190, there's still a lot of engine-bay heat present under the hood. Probably because of all the aluminium engine parts giving off heat.
With the carbs located in the corners of the engine bay, them sucking in all that hot air doesn't help either. I've been thinking I need to louver the hood to rid of that enginebay heat somehow.

I've pointed a heat laser-gun at various engine parts, and even after 10 minutes with the engine off and the hood open, I've measured temps of around 110-120 on the carbs and 155 on the heads, waterpump and radiator.