Khibbs

I'm trying to determine what I'm going to do for exhaust mainfolds on my 81 when I do a motor swap this winter. My plan is around 400hp Gen I small block so headers would help but would't be HUGE game changer in performance based on what I've seen. I recently installed the Central Corvette true dual system with Magnaflows and it's great.

I'm on the fence about running a full set of headers like the Flowtech units and having to then modify my existing system to meet them.

If my stock units are in good shape I might weld up the air tubes, paint them with ceramic paint and throw them back on. I'm unsure of how that will go and there is a valve on the passenger side that I'm concerned about.

Has anyone tried these Hedman Block Huggers (68390) units and could they possibly be a direct fit as they look close?




Any advice or opinions are welcome...thanks.

Khibb

Dynra Rockets

The factory 81 headers will not support 400 rwhp. The tubes are too small and the collector is junk. The factory designed them for weight loss only.

The headers you linked, while have larger tubes, have a collector that looks sketchy. I would contact the manufacturer to inquire what HP they claim supports.

Even if you use those the collector will not support a pure bolt on with the stock downpipes. You will need to cut the flange off the exhaust downpipes and weld on the flange provided so might as well get real long tube headers.

leadfoot4

Why not get the Hedman 68300 headers?

terry82

the best fitting headers for your factory exhaust would be sanders or mcjacks headers.The factory headers are a little small if you want 400 hp.The headmans may be a good header but you will have to modify the the pipes to bolt up to them.https://www.bing.com/videos/search?q...35716559EB7EDD

Khibbs

Thanks for the suggestion so far. I'm looking around 400hp at the crank (now rwhp) but I still don't doubt that a full set of headers would be a nice benefit.

@terry82 - Thanks for the suggestion on Sanders. Looked like some good options but I called and they said they have nothing that would fit the stock setup on an 81.

I'm starting to think if I'm going to spend $400 or so on headers I'll bite the bullet and have it taken to a local exhaust shop to have it mated to my existing system.

I can weld so I'm wondering if the Headman 68300 would match up close enough. I've read that the Flowtech point downwards a bit and some work needs to be done.

I thought this video was very informative. Understanding that the stock 81 corvette manifold performs better than a cast iron unit, I was hoping they'd be closer to the short tube header and the loss (If I kept them) wouldn't be that bad.

In this test the difference between mid-length and long tube is 10 Ft/lbs of torque and 6.5 hp at WOT on an engine that's close 500hp. I'm assuming the gains would be less on an engine that's closer to 400hp.

Greasyfingers Nick

Hooker on my 81..with custom exhaust after, headers are ceramic coated, your choice shorter or long..depends how you want to fit em up..while you are at it ..use heat shileded primary sparkplug wires..Performance Distributors..since plug wires will run close to headers...and a custom curved Performance distributor..they will make em to your engines specific needs.
Nick


Hooker 2456-1 for 81

jim2527

So....the keep word is here is stock. Will they work? Yes. Will you need to tweak your existing pipes? Yes. They have 3" collectors and your current down pipes are smaller than that so they'll need tweaking.

As far as I know the only true bolt-on shorty/block huggers are the McJacks. McJacks are available in either a 2" or 2-1/2" collector.

Dynra Rockets

If you have an automatic you can use L98 C4 manifolds. They have very slightly better flow than the 81-82 units, no real performance gain but it will allow you to bolt up to your existing exhaust. You will have to weld the air ports shut.

Here installed in my 69.

Capt. Shark

I used these on my L82 refresh. Bought them at the factory after a tour of the facilities. Very good quality and perfect fit.
So much better than some of the cheap Chinese crap.

https://www.sandersonheaders.com/san...ategory_id=649

sunflower 1972

I searched and searched and then searched some more, and the only shorty header I could find that is a DIRECT REPLACEMENT for the stock cast iron exhaust manifolds were McJacks. I admit they are a little pricey, but they are quality pieces.

kanvasman

Not sure if it's what you are interested I have a set of stock l98 manifolds. Pm me and I'll give you a pretty good deal. Thanks. Jim

Khibbs

Thanks Capt. When you say "perfect fit"...did they bolt right up to the stock Y pipe or were mods needed?

Capt. Shark

Had to take it to the muffler shop and they made the connection from the collector to the existing pipes which are CC true duals, also. Sorry, guess that was kind of vague. They clear the starter and steering, fit to the head perfect and I can actually get to all 8 plugs.
Excellent product, IMO.