Vacuum with the new head / other first impressions

80Stang

Well-known member
A question for those who have installed the new head: what happened to your vacuum figures?

Mine dropped to a tiny 5-6HgIn at idle with the 274-110 Classic Inlines / CSC cam. Yes I still have a few hours of tuning to do but this is the first impression that I'm down on vacuum big time. Well the new head and intake are much more volume on on the intake side, and kind of "single plane" setup so I do expect somewhat lower figures at low rpms. While steady driving I see pretty much the same values as it was before. Low vacuum seems to cause troubles at idling and low at rpms when transition to the main circuits are happening.

I'm running the new head on a 200, CR about 9.5+, headers & 2.5" exhaust, 390cfm 4V Holley with 61/59 jets and 6.5 PV. The 390 carb was fitted with Quick Fuel secondary metering block, which utilizes normal holley jets for the secondaries, thus my secondary jets are now easily changeable and does not change the appearance of the carb any way.

After the first ride it seems like the previous ignition setup actually was damn good (Duraspark + MSD6A + Motorsport SVO coil) and very possibly I'm swapping back to it from the DUI tomorrow, changing secondary jets up to 63 and maybe I'll need to play with secondary spring a little as the thing goes way lean at the point it starts to open the secondaries. I'll also swap the PV down to 5.5. It runs on the lean side all the way at the moment, so I'll richen it anyways.

On Sunday we have a day at the race track, so if I'll get it tuned better tomorrow I'll give it a heavy foot at the track and can compare to previous times at the same track. Now I can rev this thing way more
as the weak valve springs are history with the log head and I fitted the alum head with 302 exhaust valves, getting 90lbs seat pressure and adjustable valve train. Today at the first test drive I let it ring to 6K and it did it easily.
 
Mines only running 8" of vacuum but it was doing that with my other head so..... :)

Did you check the fitment of your intake manifold gaskets to your head? The gaskets I got were way off and I had to modify them so they didnt protrude into the intake passages. I have a large vacuum leak as of tonite so I'm going to make a new pair of intake gaskets for mine tomorrow.

I'm running a 600 vacuum secondary Holley and I'm stagger jetting mine because its running lean on the middle 4 cylinders.

#68 jet on the right side of the carb and a number 70 jet on the leaft side of the carb. Also I'm running a .036 squirter and the long yellow vacuum secondary spring.

Take a very hard look at what your going to do as far as a aircleaner/cold air setup. I stuck on a large hood scoop and sealed the carb to it with a aluminum tray and foam. It was good for a 3/10 incresace in the qtr mile tonite in 85 degree weather.

Just slapping on a 10 edelbrock air filter (like I did) with a K&N 2.25" x 10" element creates a large restriction in the system. Its not a big enough filter and doesnt flow enough air.
I'm looking at a 11" K&N filter with the K&N filter top plate and am going to install that to see if it flows enough?

Have fun! :D :D

Later,

Doug
 
Doug,

yes I checked the supplied intake gaskets and tossed them. I fabbed my own in there and applied a little gasket sealer around the ports so no vacuum leaks there for sure.

Air cleaner...another topic from last night tells something about that issue. So far I'm running my test drives without anything in there as I don't have any that would fit...I have to find something for tomorrow. For future needs I have ordered 4" air plenum part# 865-9849 from Jegs plus 4" ducting and a cone type filter element. They will be installed on 7th-8th July after they arrive here.

I have the luxury to be able to test all these on it if I want to: Holley 350 & 500 2V, Autolite 2100 1.14 & 1.21 2V, Autolite 4100 480cfm 4V, Holley 600 VAC 4V, Holley 750VAC 4V. When I bought the head I took both carb adapters with the intake, the 2V and 4V.

Jetting on your engine seems very high. We have run 370HP small blocks on dyno with 66/73 jetting in a 600 double pumper up to 7200rpm. My setup runs stoich but slightly on lean side except while the secundaries need to open when it goes totally lean. I'll first upgrade the jets and PV and the see if I have to touch the secondary spring. My impression is that it opens the sec too early. The 390 currently has 30cc pump, 25 squirter and the cam that it came with, don't remember its color.

Now back to garage...
 
80Stang":1ebgp969 said:
Doug,

yes I checked the supplied intake gaskets and tossed them. I fabbed my own in there and applied a little gasket sealer around the ports so no vacuum leaks there for sure.

Air cleaner...another topic from last night tells something about that issue. So far I'm running my test drives without anything in there as I don't have any that would fit...I have to find something for tomorrow. For future needs I have ordered 4" air plenum part# 865-9849 from Jegs plus 4" ducting and a cone type filter element. They will be installed on 7th-8th July after they arrive here.

I have the luxury to be able to test all these on it if I want to: Holley 350 & 500 2V, Autolite 2100 1.14 & 1.21 2V, Autolite 4100 480cfm 4V, Holley 600 VAC 4V, Holley 750VAC 4V. When I bought the head I took both carb adapters with the intake, the 2V and 4V.

Jetting on your engine seems very high. We have run 370HP small blocks on dyno with 66/73 jetting in a 600 double pumper up to 7200rpm. My setup runs stoich but slightly on lean side except while the secundaries need to open when it goes totally lean. I'll first upgrade the jets and PV and the see if I have to touch the secondary spring. My impression is that it opens the sec too early. The 390 currently has 30cc pump, 25 squirter and the cam that it came with, don't remember its color.

Now back to garage...

Yep, I seen on your other post what youre planning on for a air cleaner but that was after I posted here 1st! ;) :LOL:

I only jet at the track. Warm up the car with a couple of practice runs, then make 3 passes, jet 2 sizes higher and make 3 more passes. It keeps going faster so according to my Holley book I keep jetting it up until I reach a point where the et's start to fall off then you are supposed to jet back 2 sizes and thats supposed to be the optimim jet size for drag racing.

It also states that you automatically jet 2 sizes higher if you are running the carb sealed to a hoodscoop.

When I race it I run no air cleaner element at all so there is no restriction.

I'd be interested in seeing what the Autolite 4V vs the Holley 4V results would be.

Later,

Doug
 
Ok, got the jets to 61pri/ 66sec, PV down to 5.5, nozzle up to 28. My two problems are:

Idle. The idle fluctuates and the whole engine feels breathless right of the idle. Much of this came along with the swap to DUI and that is what I wonder.

Bog at the transition from primary circuit to secondary. The whole thing goes lean.

After the above changes my test drive was nice and now I really felt the engine wanted to go. It bogs but as soon as it gets around it WOT the car really moves. It rings beautifully at 6K+, I saw the needle go to its stopper at around 6300...

So I thougt the secondaries open too early and swapped in a stiffer "black" spring instead of the silver. Got worse, so in the morning right before the 250mls road trip to the track I'll change to one step softer than the silver. Then I'll have that 250mls to look at the A/F meter and with my buddy we can plan changes to setup at the track.

I got the air cleaner temporarily solved. I modified the base plate of my old 14x2" round cleaner and it just clears the camber/caster plates by less than 1/4" now. Same with the hood...but thats how its gonna be tomorrow. I'm going to take a ton of tools and spare parts along with me, including the old ingnition setup, all Holley tuning pieces, a Holley 600 VAC and so on.

Doug, I'm also interested to test the 4100 4V on this, and possibly will do on the dyno rolls later this summer. So we'll have a nice comparison.
 
Doug, have you considered using a velocity stack on the carb when racing? Supposedly, it increases air flow by as much as 18%, which is quite a bit. Might be worth trying a cheap Mr Gasket version.
 
Timing, compression, lobe separation, duration, divided plenum versus open plenum, idle mixture and quality of the mixture all affect man vac.

9.5 might be a little less than optimum compression for an aluminum head with that cam. Compression = man vac.
If the 110 is lobe separation, it should help with man vac.

First, you need to make sure the idle circuit will feed the engine properly.
You should be able to make the engine too rich and too lean with the idle screws. This should be possible with a race oriented Holley but might not be possible with an OEM type setup.
The flip side to this is, if the carb is capable of an extremely fat idle and you have an efficient engine with high velocity ports, it will be difficult to obtain a quality mixture.
I have seen carbs that fed a stock 454 not even come close to feeding a 350 race motor. It is simple when you put it into perspective. A stock 454 will pull 18 to 20 inches of vac with a steady needle on the vac gauge. A performance cam will have reversion which will make the vac gauge bounce, these are pulses. If the engine is capable of pulling 15 in of vac with reversion, it might not be able to pull enough fuel from the idle circuit and end up with a pretty good idle and only 10 in of vac. It would also be a little lazy compared to a properly adjusted carb.
You should also consider the fact that the fuel for the idle circuit is also responsible for the off-idle transition. Now we are getting into air bleed and emulsion tube territory. I will mention that, a lot of engines that suffer from an off-idle flat spot, don't have a properly setup idle circuit.
Another factor is the PCV port on the carb. You will notice that all of the PCV air bypasses the butterflies. This means that you will have to open the butterflies more if you plug this hole, which can cause idle and off-idle problems. This is more of a problem with OEM carbs on performance motors, but should be kept in focus.

Advancing the timing will also give more man vac. The difference in the advance curves on the two dizzys can cause differences in vac, jetting, and driveability.

I have always setup the idle with a vac gauge. This requires adjusting Idle speed, timing, and mixture. Often times, it has to be done more that once before you get the optimum mixture. Think about it, you get the idle rpm set and after you adjust the mixture, the rpm needs to be set again. This is expected, however, after lowering the rpm, the idle mixture needs to be set again. If you are using a vac gauge you will notice that a lower idle = lower vac. I interpret this as the vac signal is what you are using to pull fuel thru a fixed metering device. If you have less vac and fewer pulses, you will benefit from adjusting it.

You will also notice an increase in vac when advancing the timing. Timing is a whole other discussion, however, it is a very important part of the idle circuit.

This knowledge comes from building 350 cu in race engines for "Pure Street" cars. I can build a 350 with 11.25:1 comp, 286AH8 Comp Cam,26 degrees initial adv and a Quadrajet carb. It will pull 16in of vac @ 850 rpm. It is amazing what you can do when they use man vac as the limiting factor. This became the most important factor when building the engine and we learned about several factors that influence it. I was forced to learn carbs and what I learned was, they are a part of the combination and subtle changes that most people never consider will net HUGE benefits.

http://www.carburetion.com/books.asp

The second book down from the top is one everyone should read, even if you don't plan to ever build a Quadrajet.
 
A few thougth here and there:

- CR. Calculated it now, and it is pretty precisely 9.5. I would have wanted to get more with this setup, but I didn't want to mill the head as it will be used to my two 250 buildups in the future, and there I have an issue with too much CR...this 200 was decked zero and there are the HSC flat top pistons, so milling the head or block would be the only ways to get the CR up easily.
- the cam is a 110 LSA.
- timing is pretty well done now. I've got about 13* initial and 37* total.
- the secondary butterflies were adjusted a little bit open from where they were initially. This is one of things I'm going to redo, as I suspect it affects things.
- float levels were way high and were adjusted at the track. No effect on the two issues I have but solved most of another problem that occurred while going around the Slalom track we made

Anyways, on the track and while cruising the highway it is very driveable and WOT operation is satisfactory, with the jetting now pretty much where it should be. There is a lot more power than before and the usage range is now wider thanks to finally stiff enough valve springs for the cam and of course the head's ability to breath all the way up.
 
Seems I was a little bit wrong in jetting as it enjoys more juice. First of all I swapped back to my old ignition setup and got most of the idle problem solved. Possibly there is a small vacuum leak thru throttle shafts but that is minor at the moment.

Then I stepped up to the stiff "black" secondary spring once again which now helped, plus swapped the 61 primary jets to 63. It is getting better and is now much more driveable. Changing springs is a pain without the easy change kit so I ordered one, as well as Quick Fuels adjustable secondary diaphragm. I'm too busy not to take advantage what is available out there...

With the Duraspark I now have some 16 degrees of initial advance. That is intentionally so as the dizzy only gives some 18-20* centrifugal.

I feel a small hesitation still during the phase the secondaries open but I'm not willing to swap the primary jets any more bigger, so if it still bothers I'll go and swap the sec jets bigger and see what it does to the setup.

What comes to vacuum I didn't measure the current idle speed with the timing lamp, but it reads less than 1000 maybe some 900 on the tach and there is about 11inHG on the gauge...this is getting better hour by hour of tuning.
 
That's the cool part of playing with cars. Keep exploring and you will discover more. 8)
 
Updates to my journey with the alum head:

- Advance 14*, about 34* total, vacuum not hooked as the 390 ported port gives vacuum all the time...
- Jets 61 / 68
- 6.5 PV
- acc pump: 30cc, 25 nozzle, orange cam, postition 2
- Idle about 800-900 with some decent about 10InHG vacuum
- Quick Fuel adjustable secondary diaphgram controls the secondaries; adjusted to quite stiff setting at the moment
- finally got the MSD6AL instead of the MSD6A. Limiter....at 6000.

Next steps:
- More total advance but the thing won't tolerate more at lower end so I'll be grinding the dizzy centrifugal slot to make more movement to it
- Pri jets to 62-63
- PV back down to 5.5
- acc pump adjustments leaner
- actually, one major next step is a carb swap. This 390 has very worn shafts and I'd say any and all of my current problems are due to that. I borrowed one Holley 450 VAC that will go in within 48 hours and will see 800miles next weekend.

Last weekend I drove some 650miles and got a decent 11L / 100km on the highway, so the MPG didn't drop at all from the previous iron head setup. At WOT the engine goes wild and works well, but currently I leave some smoke behind as the accelerator seem to be adjusted too rich. City driving and stop & go eats a lot of fuel at the moment.

After the coming weekend I'll let you know more, I'll try to get some videos and pics of action too.
 
That document seems proper and may help out with some things. Thanks.

The MPG was achieved with a little leaner jetting than with the previous setup, and doing a long drive on the highway with not many accelerations or such. That measurement is not perfectly accurate but it gives a guideline where we are at the moment. It is nice to know that MPG (on highway) didn't get ruined with the new head and the power possibilities it gives. But with such a good head you can expect MPG improvements while cruising, so I still have tuning to do.
 
Well the plan changed. The 450 I borrowed has the plate at the end of the primary shaft so big that it hits the intake, and I can't put 1" spacer in there due to hood clearance. So the 450 won't get tested.

Instead, I did put a Autolite 4100 480cfm in there. It worked amazingly well right from the start, and then I had to swap the jets bigger. Although with jetting in decent range and idle tolerable, the performance was not so good as with the Holley and it accelerated way worse. It just didn't rage like with the Holleys. Well I had the leaky 390 on the table and took out the 4100, so why not test a Holley 600 VAC. I had a dirty 600 laying around from our 351C project, so I swapped in 63 jets and put it on. Needs more tuning but performs pretty much like the 390, which makes me wonder about the talks of too big carbs on engines...the quest goes on. With a brand new 600 in the warehouse I'm tempted to go that way, but I'll play with dirty old carbs a little more.
 
80Stang":448h6c8f said:
Instead, I did put a Autolite 4100 480cfm... the performance was not so good as with the Holley and it accelerated way worse.

You mean to say you did not experience a 20% increase in horsepower over the holley?

;)
 
Bort62":2hy2km58 said:
80Stang":2hy2km58 said:
Instead, I did put a Autolite 4100 480cfm... the performance was not so good as with the Holley and it accelerated way worse.

You mean to say you did not experience a 20% increase in horsepower over the holley?

;)

And you point would be??????
 
Bort62":3djn2qx8 said:
You mean to say you did not experience a 20% increase in horsepower over the holley?

I'd say the Autolite was 20% down from the Holley 390.

Anyways, todays quest was to finally rebuild the throttle cable with the Lokar 36" piece, and it went nicely there with just one bracket I had to fabricate for it. Yesterday I got my stock cable stuck at WOT and thanked the rev limiter I installed a week ago.

I had an idea to use the 600's throttle plate with 390 main unit but it didn't work out as the secondaries had no room to open. It could be fitted there though with a few minutes of grinding. So I printed the document Quick 8 referred to and started learning about setting the Holley up for good performance. Basicly I had the trouble to set the idle screws right (the filosophy that idle speed be not set only with the primary idle speed screw but in perfect syncro with the screw for the secondaries too). This seems to pay off a lot but with this spesific 390 with the loose shafts the things are never going to be 100% right. Anyways I have the 390 in there with the best setting so far, and that is what will see the roadtrip to Ford Mustang Club of Finland's main event of the year 400miles away from here.

With the 390, this car roars in a way I never thought a N/A L6 would do. Seemingly the 390 is about the ultimate size of carb for the new head on a 200.

I had a friend and 2+ hours of time to install some goodies to the rear suspension of my car too. GOt the Maximum Motorsports rear LCAs in there, with some SN95 rear springs and Koni Red shocks. Time didn't allow to install the upper CAs. With the softer parts I couldn't do burn outs on asphalt as the rear axle started jumping, but now we are leaving two rubber lines behind with no jumpy axles...
 
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