Tunnel ram carbs

[solarite_guy]

Agree, it is going lean at low vacuum when the secondaries open.

Agree also, the missing valley pan is not good on a street motor, but not a contributor to this problem.

I sedriously doubt your sam lobes are at issue here too. If there was a problem with wiping a or a couple lobes you would know it. The car would run like crap at higher vacuum too.

Without re-reading everything, have you sprayed the carb cleaner where the manfold and heads meet?

Which intake manifold gasket are you using?

Okay, so let's brainstorm a little bit.

1. Put the brown pump cams back in.

2. The 280H comp will want more main jet than what the stock jets are in the carbs. This could be a contributor. I am making the assumption you are in the mains at this point.

We need some enrichment to occur here. I have been trying to avoid this, but it is coming down to a couple more ways to provide some enrichment. An obvious thing and what the engine needs is some more fuel at this vacuum point.

2a. Options: More jet and rear plate OR rear block, with jet and power valve (one of your first thoughts).

I may have mis-interpreted but can you get into the secondaries slow enough that it wont backfire? If so, what vacuum readings are you seeing?

Let's wait for your feedback on these questions before buying anything.

Cheers

[dunga]

Originally Posted by Mikemuir

Managed to sneak some time out of work and have done a few test runs.
Blue cam didn’t make too much difference.
Hooked up vacuum and noted that hesitation/bog and backfire through carb all happening around 2 or less vacuum
If I keep vacuum in the 10’s when accelerating the motor runs sweet.
Really do think that I need to be looking at low vacuum problem because this is where all the problems are occurring .
Even on 1/4 throttle vacuum is dropping below 4
Maybe I should be checking lobe lift on cam next to confirm cam is ok?
Next step I would think would be to check cam timing
One other thing I noticed when I put new inlet gaskets in was that there was no valley tray fitted . Is this a problem?
I have now gone through a can of carb clean so believe I can rule out any vacuum leaks around the top of manifold and carb.
What are your thoughts?

Cheers

I believe your secondaries are opening too fast I assume they are not double pumpers from memory these don't have metering blocks that the secondary jets can be changed ??? do you have stronger springs I think solarite guy is on the money you have to remember they are not very large primary venturis and will send a strong vacuum signal to the secondaries at wide open throttle (manifold vacuum does not open the secondaries air velocity through the primaries creates the vacuum signal that is sent internally through the carby casting to the secondary diaphrams) you need to richen secondaries and slow their opening just my two bobs worth then again its been a while since I played with holly carbs

[Mikemuir]

Hi guys
Thanks for your help
I guess I am interpreting too much into this and cam should be ok
Any other reasons the vacuum is low?
If I slowly move throttle and keep vacuum above 5 the car runs perfectly with no bog or hesitation/backfire and loves the revs 😃
Over or above 1/4 throttle Definitely bog and hesitation when secondaries open / high velocity through carbs so yes believe I need some more enrichment
There is definitely no vacuum leaks around manifold on top,I have rechecked with carb clean
I did put the black springs in (heaviest) but still the same as above.
Installed new gaskets on intake manifold with gasket seal as well so should imagine they should be good.
Excuse my lack of knowledge with these carbs but everyday we learn something new

Help appreciated
Cheers

[solarite_guy]

Okay, then, as mentioned earlier you need to go up at least 2 jet sizes on the primary side. I believe your carb comes with 53s stock. Be prepared to go more later with testing.

The secondary side will be expensive. The rear plates should be 134-34s. I can't find my conversion chart to map over to jet equivalent. They may be 53s but there is another way to be sure. There is a number stamped on the back of the plate. It may or may not be 34. If so, these are equivalent to 53s. At this point I would recommend going up 4 sizes on the secondaries.

There are 3 ways to go about this:

1. Change rear plates every time you re-jet. This can get expensive.

2. Install a 4160 to 4150 conversion kit, which includes a rear metering block and assorted items to help with the conversion. Initial investment is not cheap, but then re-jetting just requires a jet change.

NOTE 1: Get re-usable bowl and block gaskets. They may already be installed.

NOTE 2: The block in the 4160 to 4150 conversion does not have provision for a power valve. This can be tuned to run okay, but you will wind up using more fuel on a regular basis when the secondaries are open. Option 3 addresses this.

3. More initial investment cost than option 2 and more initial complexity. This involves changing both bowls, front metering blocks and switching the rear plates to blocks with provisions for power valves.

Option 2 may be the most practical though not the best technically advantageous solution.

BTW, FYI for intake manifold gasket installations. Get manifold and head surfaces clean.

Scotch-brite wheels work well. Be sure to stuff clean rags or tape over the ports to keep the crap out.

If stuffed with rags do some careful vacuum work before pulling the rags back out.

A good old fashioned Mr Gasket intake is the best using this method. Once everything is clean, apply very a thin coat of bearing grease to the side which will face the head. At 2 points about half way distance from the center of the intake flang to the end of the flange apply a thin dot of RTV with your finger. It should be about the size of 1 1/2 the size of your finger print.

The next time you pull the intake to will come right off without effort and remain affixed to the manifold. The gasket can be reused many times this way.

At all costs avoid those "print o seal" gaskets and any gasket like them. Highly prone to failure.

Questions?

[Mikemuir]

Thanks for all your guys help.
Think it is in my best interest now to book it in for a Dynatune.
The guys on the Dynos work with these setups all the time and should be able to sort it all out with the Dyno.
I do appreciate all your help so far ,but now think it is more cost effective for me to put it in the shop rather than playing around any further and spending money on additional gear that may not be needed.
I will report back once it has had its tune and advise what changes they made.
Thanks Heaps for all your Knowledge and Help

[solarite_guy]

Yes, let us know what happens.

[solarite_guy]

Hopefully your shop has 1 or 2 situations in place.

1. If they have a stock of test rear plates, then they can zero in on the ones you need and only charge for the ones you take.

or

If they have the tools to modify your existing plate while tuning on the dyno, you will pay the labor to make the mods but not have to buy new plates for each re-jet. Not a lot of shops have those tool anymore, but it is possible. Folks like me have sets.

[Mikemuir]

Hi there guys
Falcon back from the Dyno and running sweet!!!!!!
Here was the fix
They changed the power valves from 6.5 stock to 8.5
They have changed out the primary jets from 51's stock to 55,54
They left the brown spring on the vacuum secondaries
The brown cam for the accelerator pump was used.
Also advised new air cleaners after all the backfires!!!!!!!

Thanks guys for all your help.
I know it is difficult to tune carbs through emails.
The Dyno guys were really good and glad they could sort it.
Expensive but worth every penny

Cheers

[HIPO]

Good stuff! enjoyed this thread & everybody's input!

[solarite_guy]

Great.

Good to hear it's sorted.

Congratulations.

[Mikemuir]

hi
well beautiful day today so thought i should go for a spin

car is running sweet now but noticed that when i am giving it WOT the secondaries are only slightly opening now and definitely not opening right up, no matter how much acceleration i give it!!
I just spoke to the dyno guys and there response was that because they had made the motor more efficient on the primaries the engine is not big enough to want the secondaries to open fully now??
This doesn't seem quite right because they were definitely opening right up before it got dyno 'd
Have they done a quick fix some how and robbing me of some power ???
they said that it still had the brown springs in and the butterflies seem to open manually with my hand no problem
Just want to make sure there story is the correct story!!
Any comments would be appreciated

Cheers

[solarite_guy]

Although, I would not take the path the shop did, it is possible it might be fine.

I assume you are looking at the secondaries while the car is sitting still. Is this correct?

If you don't mind, could you put the vacuum gauge back on and se what vacuum readings you are getting at idle and under different driving conditions?

[Mikemuir]

Hi there
I did put the vacuum gauge on when I got it back and vacuum had not changed (steady 10 at 1000rpm idle in Park)
I understand that the secondaries won’t open while stationary and just revving.
The thing I don’t understand is the dyno guys reply to why the secondaries are now not opening fully: looks like about a 1/4 opening slowly now under hard acceleration on open road,
They did open fully before the tune?
I can see them through the hole in my bonnet while driving
Is there explanation correct
Thanks

[solarite_guy]

Early on I mentioned I wanted to get you back to a softer spring in the rear IF possible. This and the way they approached the jetting shows the difference between their approach and mine. Don't second guess which approach is best.

Let's keep an open mind on their answer for now.

I want to do a bit more analysis on your engine combination first.

When it was on the dyno, what rpm did it hit max hp? What was the hp reading.

Tell me about your exhaust system.
Header primary size?
Collector size?
Exhaust type? Duals or single?
Exhaust pipe diameters? Before and after mufflers?
What mufflers?
Resonators? Which ones?
H pipe? X pipe? How far back located?

Weight of car?
Convertor lock up rpm?
What transmission?
What rear gear?
Tyre diameter?
Single pull rear ? Or dual?

Cheers

[Mikemuir]

hi there
I did tell the dyno guys only to take it to 5000 Rpm as it is mainly used on the street and i didn't want to put too much strain on the motor until it has proven itself.
The max hp at 5000 rpm at the wheels was 238hp .max torque 261

Info that I know and can provide
Header size 1"3/4
Dual exhaust 2 1/2" exits behind rear wheels
H pipe
Single resonator on each bank
C4 trans
9" LSD 4.11 gears
weight approx 1.5 ton

Thanks

[solarite_guy]

Alright, I will run some numbers and get back sometime tomorrow.

I should be able to give you a good top end estimate too.

What brand dyno did they have?

[Mikemuir]

It was a Winpep7 Dynojet

Thanks

[solarite_guy]

Been a little busy, but have done most of the work.

As you can see from the printout, they did not convert to standard hp numbers based on atmospheric conditions.

That is the easiest part, but can't get to it for a few more hours.

With numbers converted to standard then useful comparison can be made.

[Mikemuir]

Hey no worries.
I really appreciate all the good work you have done
Cheers

[Bossxr8]

With the engine being very mild is it possible it just doesn’t need the secondaries fully open? It can’t need a hell of a lot of fuel and air to feed that power level.

[solarite_guy]

That is exactly what I have calculated for 5k rpm, given his specs.

Now I need to convert his measured hp numbers to std corrected using the atmospheric numbers presented on the printout. From that the CFM is derived and compared to what it ideally should be.

[Mikemuir]

Hi
Thanks for this.
I guess my question to you guys is ,Why did I see the secondaries opening right up before tune and now they don't.
Is that because the tune has increased the efficiency and burn of the fuel?
In my line of thought 'the velocity of air/fuel entering the primaries wouldn't have changed,thus how would the jetting and tune have lowered the velocity enough to now not allow enough vacuum in the secondary diaphragm to open them fully ??
The only explanation I can come up with ,Is that because there is now more fuel being mixed there is less air being dragged in.
Is this correct

Thanks

[solarite_guy]

There could be a couple possibilities. I don't want to talk about one yet. The other could be a stop put into the linkage or diaphragm which may be visible.

[Mikemuir]

I definitely can't see a stop externally on the linkage and the secondaries do open fully if I push up on the linkage.
I guess I am right in saying that something else has been changed in the tuning procedure?
And the answer to my original question is that if they have just changed jetting and power valves in the tune up, it should not have changed the secondaries opening?

Thanks

[solarite_guy]

Alright, that helps and you are on to something that I will wait on until I can do the standard air correction.

My SW for this in on my server upstairs and it is hot up there. The a/c is not working up there. As soon as the computer boots up and I get to the SW it shuts down. For some reason it won't run on my laptop. I'll try again in a few more hours.

[Mikemuir]

Man you,re lucky
We have AC on here but on heating not cooling!!
Cheers for your info

[solarite_guy]

Alright. apologies for the wait. It is still hot, 41* outside, no a/c upstairs and downstairs is just hanging in there. Anyhow I bypassed of the checks and bull**** servers do and was able to get this and shut it down.

So the STD Air Correction Factor is 1.0333. Works like this:

238.76 x 1.0333 = 246.71 corrected hp @ 5k rpm.

At this point, don't make judgements, just take the info in.

In my ideal world in which I work, my expectation would be 278.80 RWHP from your combination as measured by a Dynojet inertial dyno. Inertia dynos and load dynos give very different numbers.

That works out to about 7.5% less VE% and ~40cfm less of air compared to what I would like to see.

There is a lot we don't know about the combination. The mufflers and resonators can make a big difference. The lengths make a bigger influence on engine output than most realize. In a closer to ideal world your exhaust would be 2.81" diameter twin pipes. I can guarantee the primary pipes of your headers are too large in diameter. "They" always do that for 2V Clevelands. The lengths? A question mark. Same for your intake manifold runner lengths.

All in all, your power output and carb utilization is probably in the ballpark of where it should be.

The AFRs are on the lean side. Move them from around 13:1 to 12.5:1 under full throttle load and you've got some hp gains right there.

I wouldn't recommend making changes to the exhaust system unless you already have plans for that. Everything you have might be good enough as they are.

You might have some heavy, high tension piston rings that will cost some power. Even the weight of oil the engine was machined for and type of oil pump can have an impact. Electric fans? makes a difference.

Point being, you are in the ball park. Some weekend tinkering stands a chance at making some gains.

Assuming your engine rpm's quicker now could be a reason why the secondaries are not opening as much as before and why the move to the 8.5 PV.

I'd say drive it around and enjoy it. When you decide it's time to tinker with it, give some thought about the bang for the buck. I woukd focus in the AFRs first.

Cheers.

[Mikemuir]

Hi There

Thanks for your calcs.
I am happy with the way the car is running at the moment so agree ,I just drive and enjoy.
Think the 2x 390"s is probably on the larger size of the CFM required for this motor(glad i didn't leave the 2 x 600's on that were on it when I got the car!!)
Maybe i will really wind the revs up one day(over 5000rpm) and check the vac secondaries then
Cheers for all your help