Seff

Is it possible to tune with a vacuum gauge? For example, I have a vacuum gauge hooked up and can see a difference when driving at 70 kmh in forth or fifth gear - 1700 or 1000 RPM respectively.

The primary rods are controlled by vacuum, does that mean I should always go for max vacuum, no matter the RPMs? Or does higher RPMs mean more air moved, and thus more fuel consumed? I'm at a loss.

Engine info:
Engine: Olds 380 stroker 9.5:1, roller cam, Ebrock performer RPM intake, stock 7a heads with 2" intake valves and a bowl blend port job. HEI off a 403 Olds connected to ported vacuum, set to 19 btdc initial timing.
Carb: 17057253 rebuilt for the old engine, a stock '71 Olds 350 8.5:1. Currently has Third Recipe idle system modifications. Slight stumble off idle when cold.

oldcutlass

Driving while keeping the vacuum at the highest level on the gauge is the most economical way to operate an engine. Vacuum gauges have been used for economy monitoring for decades.

Seff

Makes sense.

I guess fifth gear is out at that speed, then.

When I cruise at 80 kph, it's about the same for the two gears. 1100 rpm in fifth. 10-12 inches of vacuum.

oldcutlass

Vacuum is dictated by throttle opening, engine load, and rpm.

Seff

Will timing have an influence, or only indirectly by affecting power and thus load?

oldcutlass

Timing has a correlation to vacuum. When you tune your engine idle your after the highest vacuum with proper timing and a/f mixture screws on the carb.

Seff

I did that when setting idle screws. Metering at part throttle is done by vacuum and adjusted with the adjustable part throttle screw.

Marx3

How have you adjusted the APT screw?
If your engine is in good tune in relation to the whole setup ( which cam? ) Depending on the size of the cam, I would say keep rpm as low as possible. How much vacuum do you see in idle?
Have you done some testing to see if you get beter mileage in 4th or in 5th ?
I guess your carb has Ruggles parts in it?
A 17057253 is a very fine unit btw. 849 cfm and all :-)

Seff

Drilled a hole into the top of the air horn.

Cam: 221/228@.050 on a 112lsa.

Getting 16 inches at 700 rpm idle. 19 at 900. Still playing with timing, since I have an adjustable vacuum advance.

Yes, Ruggles parts. I followed his suggestion about carb choice.

Marx3

But how did you adjust it... we're did you put it? And why? Tip-in procedure ? :-)

Seff

Uh, I used the one in the carb? The 77 model has one built in.

I used tip in, and managed to bottom out the screw without any effect. So I suspect my rods are too slim for my jets.

Marx3

Okay so the apt is bottomed out. That's what I meant. ( where did you put it )
That sound wrong, what jets and rods do you have in there?

Seff

I agree, sounds wrong. It's 74 jets and D4 primary rods.

Marx3

wow 74 jets... that sounds pretty big for a 380". D4 rods? I have never heard of D4?
Can you remember were you left the main air bleeds on the carb? Did Cliff suggest modifications here? I think that unit had main air bleeds around .130-.140 combined, from the factory, which means 74 jets will be pretty rich. I assume Cliff did not suggest modifications. Did he suggest 74 jets for that engine? I would say 71-72 and a nice full tapered 44 rod.
I think you should sort these things out, so you can do a tip-in that confirms a slight lean jetting and THEN try messing with different PP springs to see if you optimize things a bit.
Did you install one of Cliff's PP springs? if yes, which color? I think your vacuum level would dictate a green or light blue spring.

Seff

Cliff did indeed not suggest modifications to the MABs.

The D4 rods are Cliffs tapered rods. I don't remember their exact size - but I remember that they're smaller than the .030" smaller than the 74 jet which is recommended in his book.

I didn't change the PP spring, but I have a green one lying around... I think. This carb, including the rod/jet combo was ordered for at stock 71 350, not for this engine.

What kind of jets does a stock 71 350 Qjet that was on a Supreme come with? Could I use those?

Seff

Just checked - I have some 73 jets, a green spring, and my primary rods are 44s. According to the receipt, anyway.

Marx3

I dont know what jet/rod combo the 350 Supreme came with, but I am pretty sure the Olds units were calibrated with small main air bleeds: small jets/rods. It wouild propably have come with something like 70 or 71 jets.
either way, that does not matter, since your carb i from 77 and the calibration will propably be different.
Did Cliff suggest using 74 jets with his 44 rods?
Since the size of the main air bleeds is unknown, one can only guess, but I think those jets are too big.
Can you describe how you performed the tip-in ?

Seff

Yes, he put together that set, the 44 rods and 74 jets.

I'll measure the MABs, the rods, and all the jets I have. Dug the jets and rods out of the 71 carb for safety's sake too.

I set it to 2200 rpm, then I set the screw at three turns from bottomed out. Afterwards I tip the choke plate about 1/2-1/4 inch in, and listen for an rpm increase. If not, I lean it up with a turn clockwise on the atp screw. Alternatively, I pull a small vac hose - if the rpm increase, it's rich.

Marx3

well, if Cliff sent you those jets they must be usable for the application. Has the unit been remanufactured by Holley, by any chance? ( small sticker on the side of the carb ) If yes, then there is no telling what size the MAB's has. I just took a ´76 Olds unit apart today that had been worked over by Holley, and several of the orifices where ridiculously big or small.
Anyways, if you could not detect an rpm change by holding your hand over the choke tower, it is propably rich, yes. Maybe you did not choke it up enough? It is my experience that you have to close the choke at least half way, to provoke the slight choking of the engine, that is necesary to tell the accuracy of the jetting.
Have you been in touch with Cliff about this?
or better yet, do you have the opportunity to measure AFR with a wideband to confirm the jetting?

Seff

I'll measure them anyway. Could be a fluke.
No signs of remanufacture.

I choked the engine to the point of stalling, without rpm increase.

Sadly I don't have a wigdeband. Might get one.

Posted the same on his forum, nobody has replied yet.

Edit: I added bypass air as well, didn't make a difference.

Marx3

Well, if anyone knows those sizes, it's Cliff :-) I haven't got the sizes for that particular unit, yet... If you measure them out, I would like to know them :-)

About tip-in: it sounds like you definately had it closed enough :-)
I guess you pulled a vacuumhose?

I recently build a Qjet for a Buick 455. Because the engine had a pretty big cam, I gambled a little and installed jets that were on the big side theoretically ( 75's ). By eye-sight I placed the needles ( full-tapered 44's like yours ) right at the top of the taper with the APT screw. I did this before I put on the air horn.
Tip-in showed a slight drop in rpm at about 2000 rpm: a bit rich. I then took the car for a spin with my wideband to confirm things. It read low 14:1 at cruise. Rich condition confirmed :-)

Yeah, I saw that on his website.

what size by-pass did you install? How much vacuum did you gain by doing this?

btw, I have used this wideband for years. I must have had it up, close to 50 cars' tailpipes at this point. Never let me down! Back when I bought it 6-7 years ago it cost about 3000 dkr. http://www.ebay.com/itm/Innovate-Mot...331835&vxp=mtr

Seff

I'll let you know when I know their size.

Yes, and pulling a hose didn't change much.

You mean you pushed the rods down and then turned the screw until the rods were at that particular setting?

I'll check bypass size as well.

Wideband choice duly noted.

Marx3

Yes, I looked closely at the needle and it's position in the jet. If you look straight down along the needle as it goes into the jet, you can see the needle move sideways as it comes on and off the shoulder of the top of the taper. You might have to do move the PP up and down a few times, to get the eyes used to the detail. Once I had found the top of the taper I knew were to put the PP to have be sure I had the fattest part of the needle positionen in the jet. Usually I try to put it right in the middle of the taper. Gives more rooom for adjustment.
In the case with the 455, though, I knew it was propably jetted a little too generous.

Seff

Makes total sense. I'm pretty sure my rods move sideways even when sitting completely in the jet.

Marx3

and they should! The rod wont completely block off the jet. there is still that .030"'s difference.
Anyways, try it out for size. That way you will know for sure that your rods are positioned in the middle of the taper.
While your'e in there positioning, count the number of turns up and down, to pull the rod to the .044" part of the taper or to the .026" tip of the rod.
Then you will know exactly were your rods will be. Less fumbling in the blind.

Seff

Makes sense.

I'll measure the rods to make sure they're 44s.

Marx3

Yeah, better do that. Cliff doesn't stamp rods, like the factory did.

Seff

Alright, I measured.

Current rods: .44s
Current jets: 74s
MABs: Measure just shy of 2 mm (measured with a drill bit), I figure 1.9 mm * 2 ~= .149" combined MAB. If the MABs are only 1.8 mm then we're at .141".
Idle bypass air: 2 mm each side, a combined .157".

As noted, I have a green spring - but it's double as long as the spring I took out of the carb from under the power piston? Seems odd.

Seff

Addition: I have two sets of 73 jets and a set of 70 jets I could try out.

The green spring is a lot softer than the spring that was in there.

Seff

Hold on. The MABs in the air horn are .070ish, but the one in the main body are .030. Odd.

Further, Cliffs suggestion is jets from 73-75, and for rods to be at least .029 smaller than the jets - which the 44 rods are. So I'll try that combo.

Seff

73 jets and 44 rods, still able to bottom out the ATP without any effect. Mayhaps the ATP doesn't turn far enough down?

Marx3

.030" lower mab's are pretty small / richening. I dont know, I just think it sounds like a very rich setup when combined with 74 jets. The 44 rod will make it possible to lean it out pretty much though, IF the APT works.
Have you confirmed that you are able to place the rods deep enough for the 44" part of the rods to go into the jets?
The green spring is for a slighter lower than stock idle vacuum, afair.
I think it is long so people can trim the lenght for their application.

I cant explain why you have no control over the APT, other than the jet / rod combo being off.

Seff

Thanks.

I'll test drive a bit, see how it acts. So far it certainly runs. Idle vacuum at 750 rpm is 17 inches.

I can certainly drill out the lower MABs, but once that's done it's kinda irreversible...

Trimming the spring is next step.

Marx3

wow, talk about a civilized cam :-) gotta love rollers. I would think a flat tappet with that duration would make lower vacuum.

There is no problems in installing smaller bronze bushings and re-drill the mab holes.
interesting!

Seff

Yeah, I'm surprised this cam is so well-behaved. Not much lump to it either. It was chosen with EFI in mind, though I never got around to that... this year.

I have a set of 0.070 MABs somewhere, that I could reinstall. You think this would lean up the mixture?

On second thought, I might have to ask Cliff about spring trimming.

Marx3

going from .030" to 0.070" will definately lean up the mixture.
If you are calling Cliff, better let him know about the whole APT situation :-)
I know thye are pretty busy these days, so response in the forum may talk even longer than normal.

Seff

The funny thing is that his original suggestion when I moved the carb from my 350 to my 380 was "third recipe idle system mods" which I misunderstood to include the MABs, so I drilled them up to .070 - he advised me against this afterwards. But if you look in the book he suggests 44 rods/74 jets for .070/.070 MABs - and less for my smaller MABs.

Marx3

.070 mabs is suggested in all 3 recipes. I misplaced my book ( for the second time ), but I can remember that the jet suggestions for recipe 3 is about 74. I cant see why your engine would fall in category 3... Maybe he took it for a flat tappet.
Sometimes they are pretty busy at the shop, maybe he mixed things up.

Seff

...I never mentioned roller cam, I think.

Does that mean I should downsize my idle system again? I found vacuum leaks after I enlarged the idle tubes...

Marx3

It is my understanding that of two profiles of equal duration, the roller will always have better idle characteristics. I may have misunderstood things along the way :-) Since your engine produces 17hg at 750 rpm, I dont think Idle can get much better, so the idle system much be spot on. Perhaps a little rich, but who cares about that.
I dont think a 221/228@.050 flat tappet in a 380 cui would produce 17hg in idle, though the 112 lsa helps a bit.
I am no expert on cams, this is just ideas :-)