Exhaust ports on 58cc Jegs heads

outlaw66 · Dec 5, 2006

Picked up a set of the Jegs aluminum heads for the SBF with 2.02 and 1.60 valves. Everything looks great except the exhaust ports are more round than rectangular and come no where near matching the Hooker header ports. Should exhaust ports be matched like intakes? I don;t know how much material is in the lower portion of the port so am reluctant to do any grinding to match. There is probably a good quarter inch on the lower port that would need to be removed to match the header ports. why are the ports more circular on these heads vs stock, and do they need to be port matched. Its a street ride, will have 10.1 CR, .512 lift, and I believe 290 duration Lunati non roller cam.

Outlaw

D.Hearne · Dec 5, 2006

The Header ports need to be a little larger than the head ports. That's the problem with "bigger is better" heads, you end up having to buy other parts to match them. You'll likely need bigger headers now. The bigger ports are there because the stock port openings are the bottle neck in small block Ford heads. With those heads and that cam you're short changing the heads somewhat.

mikemustang289 · Dec 5, 2006

How wide do the exhaust ports on the heads measure? For comparison, my AFR's measured 1.300 inches wide and my crappy headers measured 1.100 wide, a pretty big difference.

I was able to open up the headers to 1.150 but I have since ditched them for a set of FPA headers which are exactly 1.300 inches wide at the exhaust port, and yes the headers are not cheap.

You can port your headers but you risk cutting through the welds, a lot of guys will weld around the header tube to the header flange in order to gain clearance on the inside of the tube. Unless you are concerned about getting every last bit of horsepower out of the engine then I wouldn't bother.

I talked to one guy who flows heads and he always flows the heads with the headers installed. His hooker headers only flowed 92% of what the heads flowed without the header. The FPA's flowed 98%. I don't know what that equates to in horsepower but probably not that much.

outlaw66 · Dec 6, 2006

D Hearne...thanks for the insight, but I 'm not sure I understand what you mean when you said "With those heads and that cam, you're short changing the heads somewhat". Do you think I need more cam, i.e. lift? The cam is new, but an old grind that I don;t think Lunati even manufactures anymore, so I am not ruling out purchasing another cam. The heads are supposedly limited to .580 lift. Please give me your recommendations. I will be running an Edelbrock 2X4 intake, at least initially, but if its to finiky, I'll switch to a single 4V.

Mikemustang289...Your guess on the width difference between headers and head ports is probably pretty close, but the vertical difference is more concerning to me. Like I said, there is probably a 1/4 inch more that could be taken off the head (lower side of port) to match the headers. I find it interesting that your "head flowing" buddy only saw a 6% increase in the more accurate FPA headers. I agree with you in that I don;t know if that equates to any significant increase. My headers are jet-hotted so I can't weld on them but I could grind a little I guess, but for 6%, I don;t know if its worth it for a street car.

Thanks for the info guys...how bout a cam recommendation?

outlaw66

SoCalCruising · Dec 6, 2006

If you have flow numbers on the heads, one good rule-of-thumb is to subtract 10% from the peak flow number and use that as your target lift on the cam. The reason is that the "quality" of flow diminishes as the flow reaches peak. You can kinda see that by noting that marginal flow drops as you reach peak. That is, you see big increases in flow in the mid-lift region, then less increase in flow per 0.1" increase in lift afterward - a leveling off of flow when plotted against lift. So, if those heads are leveling off around .600" lift, then a cam with lift arounf .540-.550" or so would be a pretty good choice. To use less cam would sacrifice hp by not taking advantage of all the "quality" flow. If the heads flow over .600", then use more lift on the cam. Anyway, that's how I think about lift for a particular head.

What is the displacement of your motor? And how will you use the car? What intake do you have?

outlaw66 · Dec 6, 2006

The engine will be a 308 cu. in. and I will start with the Edlebrock 2X4 setup. Its a street car with maybe an occasional trip to the strip. The cam and 2X4 intake are currently on a 289, which I just removed due to a vibration problem that I never really determined the cause of. Building the 308 now, so I wanted to at least start with the 2X4 setup, but it can be changed if necessary. Your discription answered a lot of questions regarding lift selection. I'm getting a little grief from my buds on the duration/lift of the Lunati. They're saying its just to much cam for the street. I love the sound and it pulls good above 3500. Fairly rough idle but I like the way it sounds. I would lke to match the components up as best I can. Thanks for the insight.

Outlaw

66bluepony · Dec 6, 2006

You have the better raised exhaust port heads, any grinding on bottom of head will hurt flow.

D.Hearne · Dec 6, 2006

Do not lower the port floor of the head. Most of the flow happens up top. If the header matches up pretty well there and on the sides, make that call as to open the header port up on top and sides or get larger headers. On my Canfields & tri-Y's, I welded the outside of the header tubes then ported the insides some to blend the flow. Reason I said that about your cam is the specs, it's obvious it's an older grind. Look at the @.050 duration, the duration you posted is the @.0005 (or advertised ) duration. Low lift plus relatively long (advertised)duration spells an older cam grind, Your heads would benefit with a newer cam grind, look towards a late model flat tappet grind for EFI with a long LSA. That will help your carb setup by improving the at idle vacuum. In my 331 I used a Ford Z303 roller with a 3x2 carb setup and it worked fantastically. The Ford Racing rollers are EFI type grinds with less overlap. They give you a stronger vacuum signal at idle. Stronger vacuum equals better carb performance down low that's especially important with multi carb setups for street use.

outlaw66 · Dec 7, 2006

thanks 66bluepopney and D. hearne ...and you're exactly right D, it is an old camshaft. It was new in box but over 10 years old. Thanks for the clarity on the head ports, but especially the info on the camshaft. I am looking at Comp cams now, trying not to exceed the .580 lift limit advertised with the heads, but was not planning on a roller. I have the E303 in my Ford crate motor in the Cobra and it works fine but only has a single carb. I want the Mustang to have a "wicked" idle if possible but maintain the strong vacuum signal necessary for multi carb engines. I realize the overlap has a major impact on idle quality, but even with the Lunati 228 @.50 ( 280/290 @ .0005) camshaft it had a great sounding idle yet it still had about 11-12 inches of vacuum. Is that sufficient vacuum for the 2X$ setup I plan to run? The cams I've been looking at are around 106 to 110 degrees LSA. The "old" Lunati mentioned above had 106 degrees. I do have concerns about piston/valve clearance. On the Lunati I had .191 the exhaust with 9.5 pistons. I 'll have to check again with the 10.1's going in this engine.

outlaw

D.Hearne · Dec 8, 2006

I never measured the vacuum on my 331, all I know there is from the actual experience. I was pleasantly surprised with the outcome. Ford's description of the Zcam is a little misleading. With 1.7 rockers it had a lift at the valve of .585, duration @.050 is 228 degrees. LSA is 112. It idled well at 6-700 rpms, but still had a nice sound to it, not as radical a lope as I had with a B303 in a 302.

outlaw66 · Dec 8, 2006

I'll check the Z out as well, although I have 1.6 rockers that I will be using. Thanks for all the help. I'll post when I get it assembled.

Thanks for the help

outlaw

S-Car-Go · Dec 9, 2006

I'm pretty sure those Jegs heads are 170cc, 18*, Canfiled heads. The exhaust ports are D shaped. 58cc chambers?

Cams have come a long way in 10 years. Spring fer a new one.

S-Car-Go · Dec 9, 2006

http://www.canfieldheads.com/sbf_standard_intake.htm

Don't touch the exhaust ports unless you know what you're doing. They are shaped that way to keep velocity up.

brianj5600 · Dec 9, 2006

I would not be change the shape of the port, but a smoothing any rough areas with a dremel and sanding drum would help. I would leave redesigning to a pro.

outlaw66 · Dec 11, 2006

I believe you're right S-Car-Go, the heads have the same spec as the Canfield specs you provided. I had no plans to enlarge the D shaped exhaust ports unless I found some good info that recommended doing so.
Thats why I asked on this site. Thanks for the info. And I am looking for a new cam to replace the old Lunati. thaks guys

Outlaw66

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