I can get them done for $595.00 plus shipping if anyone wants some done (that's my cost, no mark up).

71



72

BTW, I removed the heat riser assemblies from both manifolds, dyno test wil be done with a single long bolt through both of them to fill the holes.

Even at 6 hun ... that is an awful lot of $$$ to just push some abrasive and clay through cast iron.

Chris the rib on the 72 is to hold the heat stove for the air cleaner, in case you didn't know that

It seems to me that you could accomplish the same as Extrude Hone with a wet sand blasting set up.

I can't remember the name now,
but I am pretty sure I had a small electric pressure washer (German ?) in the 1980s that came stock with a nozzle that would suck in sand and blast it out with the high pressure water.

a quick Google search found this:

http://www.pressureparts.com/None-C-SandBlas-Pressure-Part-391510.aspx

I admit that it would be hard to get even an extra long shank carbide burr inside some of the exhaust manifold passages but the wet sand blast nozzle should work

If you blow enough hot air through them you can accomplish the same results.

Ok,

This just in.......

Had my 340 dyno'd this week, I don't have the dyno sheets yet but I do have a report on Extrude Honed Manifolds VS stock manifolds. With ZERO changes other than removing the EH manifolds and replacing with stock unmodified originals (both sets were nice originals of 1971 A-body 340 manifolds, one set EH, the other stone stock, bead blasted clean, no repairs, heat risers removed and blocked off).

A grand total of 4-5 HP difference basically accross the board. Pretty much what I expected.

Additional notation, removing the stock air cleaner netted an additional 8-9 HP gain using either set of manifolds.

This was on a 426 Cube stroked 340 running a hydraulic cam and pump gas friendly 9.7:1 compression, VERY stock 71 TQ carb, intake, etc. (FAST style build 340 but compromised big time by hyd cam choice and lower compression for streetability).

thanks for posting that rear wheel dyno result

is the 5 hp gain
with the Extrude Hone exhaust manifolds
about 1.5% or so
of the maximum horsepower?

Thanks for the update Scott, I was waiting for it!

Can you say where that motor is power wise? Obviously the manifolds would make even less difference on a smaller cubed motor. Sounds like it's not worth it except for the very few looking for every last hp and constrained to use stock manifolds.

Cheers,
Dave

Scott , thanks , question , what were you using for an air filter element ? Also did they just pull off the top of the air cleaner or remove it completely ?

The dyno test was run on an engine dyno (not a Chassis dyno). I wanted the engine to be dyno'd with most accessories installed to best simulate what it would really be once installed in the car, stock air cleaner, pullies, ex manifolds etc.

Unfortunately the dyno shop only had headers available for a small block and due to this his exhaust hook ups were only for headers. Of course this didn't come up until 2 days before the run so I had to go out and have a muffler shop cobble up some ex mnfld collector adapters and short ex pipes which ended up reducing the 2.00 ex mnfld outlets to 1.75 diam tubing (pretty serious cork).

At any rate, the engine HP peaked at 439hp at just under 5,900 RPM (hyd cam or intake manifold volume being too small likely factors there) and 480 somthing ft lbs or torque.

Nothing earth shattering but a solid showing considering the build combo and the restrictive exhaust pipes. I'm thinking with some minor tuning and a good exhaust setup 450HP plus should be a no brainer once in the car. If I ever decide to go with a roller cam even more HP could be available, I built the short block to take anything I can throw at it in the future so there's a gob of room for improvments down the road.

As far as Extrude Honing and the difference it makes. I think there is a limit to gains you can expect but IMO every engine will benifit differently from it. As I've said before, you chase the bottle necks in the combo, if the bottleneck is the manifolds it will make a bigger difference and push the bottle neck to some other area needing improvment to gain more HP.

John I can't answer the AC questions yet but I'll ask, I believe it was removed completely, I also believe it was a stock filter.

Hey Scott, can you post the sheet...and what happened to the "15 to 20 hp" ??? You could easily loose or gain 5hp with the choice of muffler you run and on a real 340 CI motor the gains would probally be less than 5hp. I remember when Dulcich dynoed a 440 and gained 2-3 ftlb of tq with the extrude honed BB set...not really worth the effort and expence AND I hear that some exhause manifolds will crack over time. I would like to have seen that 426 run with a nice set of TTI headers as well as the manifolds.

Keep in mind that If I were building a race or bracket engine this would have been an entirely different build.

My goals were a bit complicated but along the lines of a STOCK appearing ( all correct externals for 1971, carb, intake, exhaust, air cleaner, etc.) PUMP GAS (lower compression for safe no detonation street duty engine that would require MINIMAL maintainance (hydraulic cam, no removing valve covers, etc.). There's an outside chance that I could someday run it in a FAST event and I wanted it to be a viable canidate for that as well.

Due to all of the above I didn't run header tests, roller or solid cams, better carb or intake, high compression, etc. Of course in electing to side step all of those I walked away from a couple hundred HP as well, something I can always add or change later if I choose to do so even if I left the compression alone.

The bottome line is that if you want every available HP available to whatever combo you need to make choices with nearly every aspect of the combo, not just one item. Extrude honing is a viable choice but can result in a minimal gain for the money spent, it's not for everyone. As far as cracking due to EH them, I doubt it, you can't even see dimensional changes in the manifolds, they simply look polished inside, I doubt there is any appreciable thinning that could lead to cracking, in fact the deburring action of polishing them probably decreases the likelyhood.

This old saying comes to mind "Speed costs money son, how fast do you want to go?"