2009 EngineMasters, What's new?

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MadBill
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Post by MadBill »

Dan, re the mixture variation, I have seen this on Dellortos when using ram tubes of more than say 2-3" length. In one case we had to go up 7 sizes on mains and up 4 on air correctors to compensate when 3" tubes were replaced by 8" ones (I believe there are special extended length aux venturis for use with ram tube that minimize such acrobatics.)

Even though the average power is likely to be down, you could try a pull with short or no air bells, just to see if it quells the AFR variations.

Also, the emulsion tubes usually affect the very bottom end of the range, especailly tip-in. David Vizard's method for tuning them is to place contenders on a table with the tops 'as installed' facing towards you. Now look at the size and placement of the holes. The further away from you, the higher the RPM they affect and the greater the area of holes in that region, the leaner the mixture will be.

One last note: I recall discussions some time ago re venturi size for your app, and while I don't doubt that some have had sucess with chokes of 90% or more of throttle bore diameters, many havec come to grief thus. It might be worth a pull or two with chokes of no more than 80% of TB diameter to see if that improves the fuel curve.
Felix, qui potuit rerum cognscere causas.

Happy is he who can discover the cause of things.
dan miller

Post by dan miller »

Thanks, Bill

We're pretty much out of time/ideas/enthusiasm/money, etc. lol

Going back to the pump one more time on Tuesday to check out some different exhaust systems. If they provide no change, we feel we can probably eliminate the headers as the cause of the lean spike.

I'll show up with a shorter (256 vs. 266) cam that we can plug in if nothing else helps. I suspect that we might have too much cam, but on the other hand, peak power is at 6500, and I can't imagine that the camshaft is causing a lean spike.

Danny
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Post by ausbullet »

MadBill wrote:Dan, re the mixture variation, I have seen this on Dellortos when using ram tubes of more than say 2-3" length. In one case we had to go up 7 sizes on mains and up 4 on air correctors to compensate when 3" tubes were replaced by 8" ones (I believe there are special extended length aux venturis for use with ram tube that minimize such acrobatics.)

Even though the average power is likely to be down, you could try a pull with short or no air bells, just to see if it quells the AFR variations.

Also, the emulsion tubes usually affect the very bottom end of the range, especailly tip-in. David Vizard's method for tuning them is to place contenders on a table with the tops 'as installed' facing towards you. Now look at the size and placement of the holes. The further away from you, the higher the RPM they affect and the greater the area of holes in that region, the leaner the mixture will be.

One last note: I recall discussions some time ago re venturi size for your app, and while I don't doubt that some have had sucess with chokes of 90% or more of throttle bore diameters, many havec come to grief thus. It might be worth a pull or two with chokes of no more than 80% of TB diameter to see if that improves the fuel curve.
I recall when I did a V12 with 6 x Weber IDF's, once we had a 'bit of cam' in it it would not get on the plane with the ram tubes at all, (boat application).
We had tried every combination we had at the river and no success, even different accelerator pump arm positions, one run I didn't refit the ram tubes and away it went, came back fitted the ram tubes, it would not get 'on the plane'.
It ran its first few races with nothing on top, then for aestheitics we cut off the tubes and just flared the short casting of the top cover plate.

This engine, V12 Jaguar, had relatively straight inlet ports, at WOT with the valve open you could see the piston and/or bore.
It always suffered with fuel standoff.
The Weber 44 IDF's had machined oversize venturi's.
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Post by nitro2 »

MadBill wrote:Dan, re the mixture variation, I have seen this on Dellortos when using ram tubes of more than say 2-3" length. In one case we had to go up 7 sizes on mains and up 4 on air correctors to compensate when 3" tubes were replaced by 8" ones (I believe there are special extended length aux venturis for use with ram tube that minimize such acrobatics.)

Even though the average power is likely to be down, you could try a pull with short or no air bells, just to see if it quells the AFR variations.

Also, the emulsion tubes usually affect the very bottom end of the range, especailly tip-in. David Vizard's method for tuning them is to place contenders on a table with the tops 'as installed' facing towards you. Now look at the size and placement of the holes. The further away from you, the higher the RPM they affect and the greater the area of holes in that region, the leaner the mixture will be.

One last note: I recall discussions some time ago re venturi size for your app, and while I don't doubt that some have had sucess with chokes of 90% or more of throttle bore diameters, many havec come to grief thus. It might be worth a pull or two with chokes of no more than 80% of TB diameter to see if that improves the fuel curve.
X2!

Long ram tubes on carbs can do strange things to carburetion, particularly if the ram tube is not much bigger in diameter than the throttle. Very good chance this is the problem.
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Post by CamKing »

MadBill wrote: One last note: I recall discussions some time ago re venturi size for your app, and while I don't doubt that some have had sucess with chokes of 90% or more of throttle bore diameters, many havec come to grief thus. It might be worth a pull or two with chokes of no more than 80% of TB diameter to see if that improves the fuel curve.
I'm also thinking there's something going on in this area.
What is the venturi size you're running?
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Post by JonKaase »

I'm sitting at a race in Budds Creek, MD. Waiting for the rain to stop. Wishing I was at home working on the Enginemasters entries. Both engines have fuel curves ( o2) that look like the Swiss Alps. At 3600-4000, both engines go down to 9.5/1 air fuel. Both tunnel rams with 4500 dominators. I think that this is the point where the manifold lengths are such that they are on the wrong side of the pulse. Or the manifold and headers work against each other. It's not a carb issue. A bigger plenum would help, but I can't make it any larger by the rules. One thing that makes it worse than a 4bbl, is that all the runners are the same length, so they all come into and out of sync at the same time. 1 week left. ... Kaase
dan miller

Post by dan miller »

Hello Mike

I believe that they're 48's. On a previous session (last year's engine) we tried removing the vents. No joy.

I'm opening up the choke on the merge collectors that we have been using. I made them 2.500", but on the OD. That would make them around 2.375" on the ID. I don't know how choke points are described, but suspect that 2.375" might be a little small.

I'll open them up to 2.750", as soon as someone smart 'splains whether it's ID or OD. lol

My current thinking is that bigger is probably better than smaller (if you're as lost as us), and will probably opt for 2.750" ID

Danny
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Post by dan miller »

Hello Jon

You have such an honest face, and are such a likable guy, that I'd like to believe you. lol

But my evil side figures that you're at about 12.5 to 12.51 start to finish.

Really looking forward to the Challenge. There should be more interesting things there than in a college cheer leader room.

Danny
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Post by CamKing »

dan miller wrote: I believe that they're 48's.
Well, there goes my only idea. I calculated it needed 49's, so that's not the problem.
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dan miller

Post by dan miller »

Hello Mike

What's your take on the cam timing needed in a deal like ours?

We currently have 266@ .050" with 108 lsa. Several folks have offered that the cam was the probable cause for the lean spike. I dunno. However, I sent a larger cam to Doug Engle yesterday, and he ground it to a 256 (same lift and lsa) and headed it back my way.

So if worst comes to worst, and we still can't get a handle on it when we go back on the pump on Tuesday, we'll stab it in. If it has the same or more power, we'll leave it, if not, out it will come.

We're leaving Thursday morning, so I'd really prefer not to do the cam swap-o rama.

I've also heard that dual pattern cams with less exhaust duration are recommended for Webers. Any feel for that? We typically run single pattern cams in all our engines.

Thanks, Danny
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Post by CamKing »

What's the stroke in the engine?

We always ran single pattern or 4 degrees longer on the exhaust.
We'd run the same cams we ran with the mechanical injection.
For some reason, I remember most of them liked a 108 LSA.
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Post by 1989TransAm »

PipeMax states to use the OD of the tube with the tubing having a .0625" wall. So your 2.5" pipe with that wall would have an ID of 2.375" as you stated. So if you got the 2.5" choke from PipeMax than that would be correct.
rmcomprandy

Post by rmcomprandy »

Ha - Ha - Ha,
After only a few pulls with a tunnel-ram manifold my engine had an almost flat 02 Fuel curve which varied only about 1 ratio from beginning to end.
Of course it also didn't have nearly enough points to even make any noise about - I'd gladly take a mountainous fuel curve and a lot of points, LOL.
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Post by CamKing »

rmcomprandy wrote:Ha - Ha - Ha,
After only a few pulls with a tunnel-ram manifold my engine had an almost flat 02 Fuel curve which varied only about 1 ratio from beginning to end.
Of course it also didn't have nearly enough points to even make any noise about - I'd gladly take a mountainous fuel curve and a lot of points, LOL.
To be honest, I really don't understand the choice of a tunnel-ram for this application.

With having to make power from 3,000-7,000, I would think you'd give up a lot on the bottom, and before it started helping on top, you'd be up against the restriction of the mandated mufflers.

I have a feeling that the engines that do well will have a 4.040"-4.125" bore. a 3.75"-3.875" Stroke, a single plane manifold, and a single 850 carb.
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rmcomprandy

Post by rmcomprandy »

Oddly enough, the tunnel-ram made more torque average while the upper range horsepower average remained about the same as a single plane and single 4 barrel.
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