Looking for Advice on Header, Fitment

[CP82AERO]

Hi all,

I've been researching the forum for header and exhaust options for my MKIV build, and finding the usual noise vs. back pressure tradeoffs. Ahead of that, however, I'm concerned about header/sparkplug fit and access wrt the DS footbox. Most of the footbox is assembled, however, if it makes sense to modify it, now is the time--but perhaps I don't have a problem. Any advice? The motor is a Dart block 351W/427 with Trickflow heads. I plan to pull the trigger on Gas-n 1-7/8" headers and one of their exhaust options.
Thank you.

[KDubU]

I can attest that the plug closest to the driver is a pain with the setup you will have. I had to modify a small spanner by grinding it down a bit. Still was a pain though and if there was a simple mod, I would have done it. Maybe someone else has? I also had Gas-N headers and pipes.

[CraigS]

My 351 was a pain like KDubU says. But it is just that one plug. I found it easier to get at it from below than above. Also, unless you have some problem, you won't need to get at it. Over 15 years I bet I removed plugs at most 5-6 times.

[GoDadGo]

Question:

Could you possibly use a "Tite-Reach Extension" to get to those pesky plugs?

https://tite-reach.com/products/3-8-professional-tite-reach-extension-wrench

I have one (3/8" Drive) that I've used to remove plug numbers #6 and #8 on my old C-4 Corvette.

Steve

[CP82AERO]

Thanks all--good stuff. I'll get some iridium plugs and that should take care of many, many miles/years.

[65 Cobra Dude]

Another less elegant option is to make an access panel in the drivers inside footbox wall for easier access. Also makes getting those header bolts more accessible

Henry

[Jim1855]

CP82AERO,

I'm nosey and curious. What's driving you to the 1-7/8" primary tube diameter? I didn't see anything on engine size or expected use.

I run 1-7/8" on my 427. I've also run 1-3/4" and 2". I got more low-end power from 1-3/4" and more upper range, 6,000+, from the 2". I think Gas-N offers some options. Different header designs and sidepipe configs will probably change things but I think diameters will affect things.

With less than 427 cubes there MAY be a low-end torque advantage in a smaller diameter header. The smaller tubes may also provide more room for header bolts and sparkplug access. But if you're spinning a 302 to 7,000 then the bigger tubes will probably help at the expense of bottom torque.

I was fortunate to have the original manufacturer provided headers and a friend that was building specialized pieces.

And the #7 plug is a bugger to get out because it aims at the #8 tube. I worked with a slotted spark plug socket, stubby open/box end wrenches and a few other customized tools. The #8 may be bad in an FFR because of the driver's footbox.

Good luck with your build.

Jim

[CP82AERO]

I'm thinking just that. I see a fair number of broken header experiences. Pull down the carpet, drill out the rivets (lower profile than screw protrusion) and good to go (with a bit of RTV removal).

[CP82AERO]

Hi Jim. It's not a radical motor, and it should be good for 520-530 HP with 10:1 compression and a Weiand Stealth intake that taps out at about 6000 RPM. I came across a formula which resulted in the 1-7/8" primaries--which Gas-n offers--however, if going to 1-3/4" primaries materially helps with space/interference--that trumps any real or imagined HP loss. It should breathe really well up to that point as I've port-matched the intake to the 205cc TrickFlows and the exhaust ports are v. large.

[Jim1855]

CP82AERO,
Sounds like a great engine and that you are right on a boundary line, one might be a bit small, the other a bit big. I'm there with carb sizes, my current 780 runs great, or did when I had it in a car, but by the simulation software an 850 might be just what I'm looking for. I know a 940 was too big until 6,500, then it was great fun, same with the 2" headers.
I don't think you'll be "wrong" either way and you may not really notice the difference.
With physical clearances sometimes just a bit of extra room can really help.
Keep asking questions. You might not always like the answers, but education and understanding are always beneficial.
Jim

[CP82AERO]

"Keep asking questions. You might not always like the answers, but education and understanding are always beneficial".

--Thank you, Jim, that's why I asked.

[D Stand]

I went with GasN headers with the 3” spacing for the bolts which makes getting a wrench on the header bolts better. However, these headers having a 3/8” thick flange, I had to source lower profile pan head bolts because with a standard header bolt I could not get a socket on the plugs…. Just like others have said, I had to make a custom wrench for that #7 as it is pointing right at the header tube. You can get a deep socket on it but you can not get the ratchet on. The socket with the flat spots to put a wrench on is too long. I basically welded a 3” long, 3/8” extension to the side of a deep socket to tighten that plug. I found it much easier to access from the bottom side as well.

My 2 cents,