Weber IDA, timing question

[Chuck]

I am looking for some input from those running Weber IDA on a SB Ford.

I have been told by my engine builder that timing should be set at 32 degrees and much more can cause all sorts of nastiness.

I have been told by a carb expert that Webers require advancing the timing to 38 degrees and ignore what the engine builder says.

The carb expert and engine builder live far apart and have not met. Probably a good thing.

So what is the correct answer?

 

[Jac Mac]

Chuck this probably wont help give you a definitive timing number, but it might help you understand why the above comments were made...
The lower number of degrees advance your motor requires to make good power the better the design of chamber/piston crown/cam choice etc you have, so therefore if you only need say 30° total adv to make full power you have done a better job than the guy that needs say 38° to get the same HP numbers. The problem ( if thats the right thing to call it ) with webers is that they seem to require a richer setup than a typical 4bbl setup to perform the same job, this is mainly due to the fact that they are one venturi/one cylinder with the resultant stop start airflow that entails.

Hope that helps.... so I would suggest that both the gents you spoke to are right, especially if your engine man plays with 4bbl stuff & the carb guy works with webers, from my point of view ( & Im a 4bbl guy ) around 32° total is a good figure for any healthy SBF, start there & advance with caution.

 

[Randy V]

Hi Guys,

My engine is a flat top piston 331 with Dart Pro1 heads, Weber 48IDAs, Inglese designed "Weber" cam (the hotter of the two offered but I don't have the specs/nbr here).
The engine has never had a 4bbl on it - so, break-in and Horsepower tuning all took place with the Webers on a Superflow Dyno with 92 Octane unleaded fuel.
With the carbs tuned and timing set to optimum we were at 30 degrees total.
I will say that the tuning could be a it better, but we started running into light detonation at 31 degrees. That may have been influenced by fuel mixture but I doubt to a great degree.

 

[Cliff Beer]

Chuck, I'm no Weber expert, but I do know a thing or two about these carbs.

Frankly, I'm surprised your carb guy is saying the webers require 38 degrees. My bit of experience has been that the greater the advance the greater the reversion effect up the venturis....thus requiring an increasingly rich mixture (which is not fully/ideally atomized). As JacMac pointed out, this is a problem which is more relevant to Webers than a four barrel due to the individual intake runners rather than a common plenum, which tends to moderate reversion.

You could do a few dyno runs but I'd tend to steer more towards your engine builders timing #'s. That's just me though.

 

[Chuck]

Jac, Cliff, Randy

Thanks for the info. It is currently set at 32 and I will leave it be for now.

Jac: that explanation was helpful.

Now I am starting to wonder if the reversion plates on the original were more significant to the engines performance than I had previously thought, keeping vaporized fuel in close proximity to adjoining carbs. I have seen very little in print regarding the use of reversion plates.

 

[Glenn B.]

This is a direct quote from Jim Inglese's technical discussion on his website:

"THE IMPORTANCE OF IGNITION TIMING
This is one of those things I can't stress enough. I wish I had a dollar for every time somebody had a Weber setup that ran terrible, that was corrected by timing. This is the single most common issue with a badly-running Weber system, bar none. Very few people have an understanding of, nor pay enough attention to ignition timing. So I will say it plainly: WEBERS NEED A LOT OF IGNTION TIMING! IT IS ABSOLUTELY CRITICAL. Set the total advance at 38 degrees BTDC and forget about "intial" timing; whatever it is, that's what it is. Initial timing means nothing; total advance is EVERYTHING. If it's too retarded, you'll have a lazy, rich, engine with farting and popping carburetors, and way too much heat in the heads, which can make the carburetors boil the fuel in the bowls...and drip. It will cause all sorts of issues...none to do with the carburetors...but they'll get the blame most of the time."

Cam selection is critical to gain the maximum from Webers. Again, from Jim:

"Any cam is fine as long as you pay attention to the lobe separation angle. A 110-114 degree lobe separation is ideal for Webers. I generally discourage the use of anything tighter, like 108, or 106. The problem with a lot of overlap is that it causes "reversion"...reverse pulses from the exhaust stroke that have nowhere to go but up into the carburetor. This disturbs high rpm airflow and causes the engine to think it's too lean at high rpm’s. Without a plenum, the flow is pulsed backward up into the carburetors because there is noplace else for the reversion pulse to go. To find your cam's lobe separation angle, check your cam card. Just add the intake centerline and exhaust centerline and divide by 2."

More to be found here:

Home

I followed his guidances to the letter, and now the Webers on my Lola are terrific. My suggestion: Call Jim. He'll give you the straight story.

Hope this helps.

 

[Randy V]

I have all the respect in the world for Jim Inglese. However - I cannot agree with a blanket statement about ignition timing like that. There are too many variables - particularly between cylinder head designs and efficiency. Ford small blocks typically need much less timing (overall) than do Chevy small blocks. This is due to the design of the cylinder heads / combustion chambers and has literally nothing to do with the induction system.

If I put my engine at 38 degrees total advance it would not be long before it was damaged due to detonation.

 

[Randy V]

Here's a link to the dyno pull video

[ame=http://www.youtube.com/watch?v=HBqWB_4ZZuI]Carriage House Customs 331 Ford with Webers - YouTube[/ame]

 

[Chuck]

Glenn

I am well acquainted with Jim and very familiar with his recommendations. I have a lot of respect for him as well.

It was the direct conflict between my engine builders 32 degree dyno setting and Jim's 38 degree recommendation that prompted this post.

I was looking for those with real world experience. I have yet to hear of anyone running 38 degrees on a SB Ford with an engine set up similar to Randy or mine.

Would be curious to know what your engine set up is and its timing.

 

[Cliff Beer]

Chuck, my experience is with dialing in IDAs on a 289 install in a Mustang....with tons of experience messing with other webers over the years, and studying their operation pretty closely. My GT40 has a Holley (which will soon be replaced with webers).

Jim obviously knows what he's doing with webers. On the 289 the reversion was getting quite extreme as the full advance became more aggressive (38 degrees)....to the point where there was some concern about the risk of fire. There was no room for anti-reversion plates unfortunately, nor a full/proper air cleaner (which would have helped with the fire concerns...). The car seemed to pull just as strong (butt dyno) with considerably less advance. In the end I think we settled upon somewhere between 30 and 32 degrees max advance. We had an AFR plumbed into the exhaust and it seemed to run equally well with less fuel at 32 degrees than with greater advance.

That's just my experience and I'm no expert.

 

[Ron R.]

Knowing what (little) I do about tuning carbs, I thought that reversion was more a cam (valve timing) issue, not so much an ignition issue.

I've spoken with Jim, and got some jetting and cam advice when having my engine built, but I thought that valve overlap was the big problem. Webers don't like it, the more overlap, the more reversion (and the more likely you're going to have a fire).

Please explain how ignition timing comes into play..I must be missing something.

On the other hand, timing has everything to do with properly controlling/timing the flame propagation for maximum power, without inciting detonation.

Am I being too simplistic?

 

[Glenn B.]

As I mentioned, my Weber set up is on my Lola, not on my GT40. So, it's a SBC, not a Ford. I'm running a 9.7 to 1 CR, 112 degree LSA on the cam, and timing set at 38 degrees full advance. Pulls cleanly like a train, no backfire/reversion issues and no detonation. The lower CR combined with 93 octane in Texas may be contributors to the positive outcome.

I agree with the earlier post...reversion is typically more of a cam issue with Webers. What's the LSA of your cam?

 

[Ron R.]

Glenn,

Not sure if you were directing this to me, but I can't recall all of my specs off the top of my head. but I think I'm at 110 LSA, with 35 degrees total advance, 393 ci, 11.95:1 CR with AFR 205 heads, solid roller.

I'll check tonight, I'm curious.

Ron

As I mentioned, my Weber set up is on my Lola, not on my GT40. So, it's a SBC, not a Ford. I'm running a 9.7 to 1 CR, 112 degree LSA on the cam, and timing set at 38 degrees full advance. Pulls cleanly like a train, no backfire/reversion issues and no detonation. The lower CR combined with 93 octane in Texas may be contributors to the positive outcome.

I agree with the earlier post...reversion is typically more of a cam issue with Webers. What's the LSA of your cam?

 

[Tim Kay]

Is there any reason not to "lock" the dizzy and set it at full advance (what ever that may be for your motor). I currently have full advance come in at 2,400 rpm (webers) and I'm curious what the effect will be if I come in sooner with full advance.

 

[Robert May Eng.]

I am looking for some input from those running Weber IDA on a SB Ford.

I have been told by my engine builder that timing should be set at 32 degrees and much more can cause all sorts of nastiness.

I have been told by a carb expert that Webers require advancing the timing to 38 degrees and ignore what the engine builder says.

The carb expert and engine builder live far apart and have not met. Probably a good thing.

So what is the correct answer?

Armchair timing figures are just that, there are way too many variables to set a figure for total advance. I think the best bet is get it fired up and head for a dyno.

Bob