When you Port a head and pick up flow alot does it usually require more jetting?

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Re: When you Port a head and pick up flow alot does it usually require more jetting?

Post by turbo2256b » Wed Jun 06, 2018 6:32 pm

Most heads i have done for customers tell them to increase jetting 20 to 30%. each holley jet size is about 4.5% increase.
with a power valve in the curcuit might play with the jetting to figure how much to open the PV fuel feed.

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Re: When you Port a head and pick up flow alot does it usually require more jetting?

Post by cjperformance » Wed Jun 06, 2018 7:55 pm

turbo2256b wrote:
Wed Jun 06, 2018 6:32 pm
Most heads i have done for customers tell them to increase jetting 20 to 30%. each holley jet size is about 4.5% increase.
with a power valve in the curcuit might play with the jetting to figure how much to open the PV fuel feed.
So you go up 4 to 6+ jet sizes due to portwork?
Craig.

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Re: When you Port a head and pick up flow alot does it usually require more jetting?

Post by groberts101 » Wed Jun 06, 2018 9:20 pm

cjperformance wrote:
Wed Jun 06, 2018 7:55 pm
turbo2256b wrote:
Wed Jun 06, 2018 6:32 pm
Most heads i have done for customers tell them to increase jetting 20 to 30%. each holley jet size is about 4.5% increase.
with a power valve in the curcuit might play with the jetting to figure how much to open the PV fuel feed.
So you go up 4 to 6+ jet sizes due to portwork?
I can only wish my port work was that good. :shock:

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Re: When you Port a head and pick up flow alot does it usually require more jetting?

Post by NXBOY » Sat Jun 16, 2018 10:48 pm

Just talked to Buddy which just got back from short trip in the Galaxie after jetting it up 3 to stock jetting and said it only got to 210 versus 230 at highest point. I say it was as hot outside or hotter so all is well as being heavy and 3,000 + rpms at cruise he should be in the mains some IMHO.

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Re: When you Port a head and pick up flow alot does it usually require more jetting?

Post by cjperformance » Sat Jun 16, 2018 11:04 pm

NXBOY wrote:
Sat Jun 16, 2018 10:48 pm
Just talked to Buddy which just got back from short trip in the Galaxie after jetting it up 3 to stock jetting and said it only got to 210 versus 230 at highest point. I say it was as hot outside or hotter so all is well as being heavy and 3,000 + rpms at cruise he should be in the mains some IMHO.
Get him to check plugs now, will be interesting to see if it was just too lean or wether a little extra fuel is covering another problem
Craig.

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Re: When you Port a head and pick up flow alot does it usually require more jetting?

Post by 68corvette » Sun Jun 17, 2018 3:56 am

Why does increased head flow need bigger jetting?
Should not the carb meter the fuel for the air which is passing through it?

I understand this with injector engines, but would increasing the jetting mean that engine needs more fuel for same air amount passing through the carb?

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Re: When you Port a head and pick up flow alot does it usually require more jetting?

Post by My427stang » Sun Jun 17, 2018 8:50 am

I think I'd be looking at the ignition curve, especially at or around cruise RPM, exit airflow underhood, and radiator size if it's heating up climbing a hill part throttle.

More fuel may cool it down, but seems an odd way to lose 20 degrees
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Re: When you Port a head and pick up flow alot does it usually require more jetting?

Post by Steve.k » Sun Jun 17, 2018 10:01 am

I think you just added more fuel to fire. More power more heat. Cooling system was likely marginal before. I run 36 degrees total timing in wifes 70 cougar no advance and that thing wont get above 180 anythime. Another thing is exh restrictions with the added output. Maybe a collapsed muffler. That would explain the flat top end.? If cooling system adequate i dont care where you time it shouldn't get hot.

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Re: When you Port a head and pick up flow alot does it usually require more jetting?

Post by groberts101 » Sun Jun 17, 2018 10:56 am

My filthy scratched up penny...

proper radiator/fan shrouding makes a BIG difference in actual air flowing through the core/s.. otherwise the core is effectively reduced to the size of the airflows "sweet spot".

ignition timing does and always has made an impact on heat generation(use a handheld vac pump connected to the distributors vac advance pot and you will quickly see the temp gauge move during extended highway cruise, or even sitting at a light for that matter)

the amount of power produced by an engine to maintain steady state part throttle cruise is very very little when converted to BTU's.. doesn't matter if you change main jets several increments up or down.. the measurable differences should still be quite small from the radiators standpoint compared to WOT runs. If you were to get really lean.. the radiator will likely be at the end of the line in regards to letting you know something's not right.

Running higher/OEM temp t-stats gives less margin during times of cooling system heat saturation.. high ambient temps, up longer grades, carrying extra weight, etc.. and running a much cooler one increases coolant flow rates along with adding "time to reach same heat saturation point". So just because it's rated at 160° doesn't necessarily mean that the engine will run at 160°, because they rarely do, but you will surely have more available margin during periods of increased engine loads and/or higher ambient temperatures.

And finally.. just because a head flows substantially more on a flowbench means next to squat for what it will actually consume during steady state cruise. Or even at WOT throttle for that matter since an engines true measured mass flow rate is not directly tied to head flow % gained on the dry bench. If it's even remotely close to flowing enough to supply the air pump to begin with.. more dry flow will not make a huge difference. Only way that happens is if the baseline cylinder head was so ridiculously anemic during light/steady state cruise that it was literally choking the engine to death in the first place. Would be highly unlikely to occur unless it's one hell of a big stroker motor with tiny little cylinder heads.. not really a normal occurance for any performance oriented type build. When pre-existing parts combo's remain the same after porting, a 1-3 jet size jump is pretty common for a decently improved set of heads. And that's assuming the pre-existing parts combo had plenty of headroom to allow higher airflow improvements to begin with. Beyond those typical jet size jumps.. it's usually only when moving from an unported anemic OEM cast head towards a badass aftermaket casting with hugely improved airflow numbers that will warrant a bigger jet size jump. But even then.. the amount of fuel needed for steady state cruise can easily be handled by a properly adjusted idle/transition circuit with only smaller supplementally increased needs from a larger main jet.

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Re: When you Port a head and pick up flow alot does it usually require more jetting?

Post by Steve.k » Sun Jun 17, 2018 12:26 pm

Also seeing its a galaxie im thinking auto trans. Where is convertor/stall. Maybe more heat generation there? The extra hp may have lowerd cruise rpm to below stall creating more heat. May not be but things to think about. All in all id say rad/cooling issue. Unless its a crack or bad gasket.

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Re: When you Port a head and pick up flow alot does it usually require more jetting?

Post by NXBOY » Sun Jun 17, 2018 4:52 pm

Problem is he wanting to run pump gas with 11 to one compression with Iron heads in a heavy car. I only had him go back to STOCK jetting for carb. He says he needs more elecric fan and part of the radiator is being blocked by it. But if jetting helped any lean cruise ay above 3.000 the combustion temps on them cylinders I would think be cooler. Most my experiance in the past with dual planes was with small block ford where #1 cylinder would run leaner, its the long cylinder and it would happen at a certain rpm not sure of. Timing is locked out at 38 degrees. He goes on two or three hr trips one way, car aint loosen any coolant or burning it. Car cranks 210 psi with all plugs in except one tested. I like him to try 40 or 42 as well to see if it makes a difference. I know under hood temps get real high from headers. He has no complaints, he happy, pulls harder and sounds cool. All new cam with a tighter LSA might add some heat as well?? Just the getting hot on the LONG hilly trips scares me. Hes running a thermostat,dont remember what it was.

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Re: When you Port a head and pick up flow alot does it usually require more jetting?

Post by Steve.k » Sun Jun 17, 2018 5:38 pm

I don't know about anyone else but 210 cranking comp to high for pump juice.Gonna be higher with all plugs out.

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Re: When you Port a head and pick up flow alot does it usually require more jetting?

Post by NXBOY » Sun Jun 17, 2018 9:10 pm

Steve.k wrote:
Sun Jun 17, 2018 5:38 pm
I don't know about anyone else but 210 cranking comp to high for pump juice.Gonna be higher with all plugs out.
I agree it will be higher, he set the cam advanced 4 which I hoped ICL for around 108. Compression ratio is really close as before except Dynamic of coarse and he got by on 93. Ill keep after him to get more fan on it. Only so much I can do. He suppose to get a O2 sensor or something and get some kind of digital ignition box with timing control all working on it. It liked going from a 31 squirter to 35 so I bet some intermediate work on the carb it would like it at cruise. He is very Busy and got a real race car also so thats probably alot to due why he hasn't got to the fan issue yet.

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Re: When you Port a head and pick up flow alot does it usually require more jetting?

Post by randy331 » Sun Jun 17, 2018 11:41 pm

groberts101 wrote:
Wed Jun 06, 2018 9:20 pm
cjperformance wrote:
Wed Jun 06, 2018 7:55 pm
turbo2256b wrote:
Wed Jun 06, 2018 6:32 pm
Most heads i have done for customers tell them to increase jetting 20 to 30%. each holley jet size is about 4.5% increase.
with a power valve in the curcuit might play with the jetting to figure how much to open the PV fuel feed.
So you go up 4 to 6+ jet sizes due to portwork?
I can only wish my port work was that good. :shock:
Why would you assume needing an increase in jet size after porting is a sign of good port work ?

Randy

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Re: When you Port a head and pick up flow alot does it usually require more jetting?

Post by cjperformance » Mon Jun 18, 2018 12:03 am

randy331 wrote:
Sun Jun 17, 2018 11:41 pm
groberts101 wrote:
Wed Jun 06, 2018 9:20 pm
cjperformance wrote:
Wed Jun 06, 2018 7:55 pm


So you go up 4 to 6+ jet sizes due to portwork?
I can only wish my port work was that good. :shock:
Why would you assume needing an increase in jet size after porting is a sign of good port work ?

Randy
That is certainly not my assumption!
Craig.

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