FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: 390rpm on June 13, 2021, 02:18:10 PM
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My dad bought some headers similar to these pictured below. I don't have the part number at the moment, but they look similar to the Jegs version. Should we run them? The only caveat I see is that I think they'll need to be opened up a little to fit the CJ heads. Thanks.
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I checked for part numbers and I think they're Flowtech headers if that helps. If you are familiar with them then you probably already know, but the dimensions are 1.75" primary and 3.00" collectors.
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Well - What is the alternative? If it's these headers vs log style exhaust manifolds then you are probably better off with the headers. CJ heads have four bolts per exhaust port so be aware of that. It's been said that the diameter of the primary tubes (1.75") should be the same size as your exhaust valves in the heads. That grossly simplifies things but it may be safe to say these headers won't be a restriction. If you have power steering you should check about fitment. Similar for a shock tower car. These appear to be painted vs ceramic coated. Hence they will spread more heat vs the coated options.
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CJ heads have four bolts per exhaust port so be aware of that.
As long as the ports match up, the engine won't care if you're using 2 bolts or 4. Four may be better for sealing, but I haven't had any issues with sealing by just using the 2 vertical bolts.
I can't comment on fitment because I've never used Flowtech.
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We'll buy anything that'll work the best. I mean within reason. He bought these several years ago with several other parts at a swap meet, so they were just laying around. We probably wouldn't spend $1000 on a set that only gained a little at peak. I assume they'll work alright. I know LT1/LS1 cars dyno 400-425 RWHP regularly with 1.75" primary tubes, so these should work fine for 400ish gross FWHP build. They looked a little short to me, need to be coated or wrapped, and need to be ported. They seem like they'll clear everything and fit well. guess they're not too bad.
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Since headers are made out of fairly thin metal, you don't want to "port" them. At best you might be able to lightly transition the first 1/4", but even then you better be careful or you'll either bust through the weld or thin metal, or you'll weaken them to where they'll crack at the flange. You can slightly adjust the height of the port by raising or lowering the header, by elongating the holes, but that's about it. Doing that may or may not lead to interference issues elsewhere, so check carefully.
And wrapping headers can cause them to rust out quicker. If they're coated, they won't be for long with wrap. If you're in a moisture free environment, you might be able to get away with it....for a while.
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I guess I'm not really "porting" them. I'm trying to enlarge the roof of the flange a bit, and slot the bolt holes to get better alignment. They feel fairly heavy and not too thin. If they rust out we'll just buy new ones.
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Unless these Cobra Jet heads have been hogged out, that header flange will be a bit larger than the port. How did you verify the roof of the port was being blocked by the header flange? That would be unusual. Is the casting code on these heads C8OE-N? Regardless, FE exhaust ports are nearly all the same. The smogger heads use a port that sits around 1/4 inch lower than pre '67 heads, and of course MR and CJ ports are traditionally located, but are the same size as all those non-smogger ports.
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I remember checking them with my calipers a while back. The ports on the heads were around 1.88" tall, but the ports on the headers were 1.76" tall. If remember correctly, they were almost identical in width-- around 1.30" wide. The heads are lightly ported.
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So, at most, the roof could be +.12" proud of the header flange. Or maybe it is symmetrical is it might be half that. You might want to know for sure before you start fiddlin' with it. And if it were me, I might just be happy to bevel the header flange entry slightly to assist the flow, rather than route it out to match. If you were building a Pro Stocker or an F1 engine, then, yeah. But a truck engine? Even a nice runner? Naw. You'll make a good set of headers weak for not a lot of gain.
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Yeah, I'll have to check them out and get accurate measurements before I decide what to do with them. I live a couple of hours away from the shop, so I don't have them on hand to fiddle with. I'll probably use them. I feel like I read that Jay Brown tested them out, and they were decent.
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Flow techs are pretty good, is this a case of truck headers with a pass car head? If so, likely will have to slot all the holes a bit to get the gasket to seal unless it uses the full flange seal like a manifold
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I'll have to check, but I think they do need to be slotted.
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On my 74 F350, with a 390 and NP435 4 speed, I had a set of Hedmans for 15 years, and then a pair of FlowTechs. Both fit very well, and performance and gas mileage both improved noticeably. Best of all, I was finally finished with replacing cracked factory exhaust manifolds. I find the FlowTechs are great headers for the price. I also have a pair of 1 5/8" long tube FlowTechs on my low 10 second 331 SB Ford bracket car, and had another pair on my 85 Mustang, for the money, you can`t beat them. On a FE truck, to replace the starter motor, the pass. header needs to be removed, or maybe loosened and pulled away, but I think most FE headers are that way.
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I guess I'm not really "porting" them. I'm trying to enlarge the roof of the flange a bit, and slot the bolt holes to get better alignment. They feel fairly heavy and not too thin. If they rust out we'll just buy new ones.
I'd advise coating because replacement quality headers are very expensive - $600 plus not unusual. Lots of good SBF headers for the larger port heads are in the $1K range.