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HM Headers HM9C

Started by _CraigA_ , Sep 21 2009 08:51 PM

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129 replies to this topic

#1 _CraigA_

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Posted 21 September 2009 - 08:51 PM

Does anyone use HM Headers type HM9C on their LC/LJ?

I'm just about to start the build of my new engine and was thinking of moving away from the factory headers to the HM ones.

What mods are needed? In their catalogue it says that the floor needs to be modified and an engine mount relieved to get the required clearance. :dontknow:

Or are there any other suggestions for high performance headers/extractors? Brad Merrick has had the '73 Bathurst ones remade - are these the go?

Has anyone had some custom pipes made?

Edited by CraigA, 21 September 2009 - 08:54 PM.

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#2 VitcLJ

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Posted 21 September 2009 - 09:52 PM

Have had HM9C on the car for years. They fitted without any engine mount mods or floorpan mods. If you haven't already, get yourself one of the small high torque starters else any problems with starter means removal of the HM9C's. The HM9C's are used by a lot of the group Nc historics. They really do fill the space betweem the engine and the inner gaurd with the tri Y design there may be a neeed to heat insulate the wiring to the starter and the altenator.

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#3 _CraigA_

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Posted 21 September 2009 - 10:10 PM

Great news. I didn't really want to start bashing the floor around!!

I'm already using a small starter and insulating the wiring will be straightforward.

Appreciate the response. :spoton:

The engine builder wants to have a first hand look at my 9 port head before advising which pipes to use. I'm chasing 250+FWHP and I don't think the XU1 headers are going to cut the mustard.

Attached Files

ports.jpg 421.54K 103 downloads
ports2.jpg 426.09K 120 downloads
valves.jpg 362.75K 84 downloads

Edited by CraigA, 21 September 2009 - 10:14 PM.

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#4 orangeLJ

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Posted 22 September 2009 - 09:58 AM

Last I knew of HM9Cs were no longer available unless you ordered some ridiculous quantity.

Jason (Jklummp) has just got hold of a set, I think my old man is going to fit them for him some time in the future.

is this the new motor for the XU1?

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#5 _CraigA_

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Posted 22 September 2009 - 10:35 AM

Thanks Chris.

Yes, its for the new motor for my XU1.

Like you, Toranafest has spurred me on to get off my lazy arse and get the car going. The XU1 has been sitting there for six months and I'm hanging out to flog the crap out of it again!!

By the way, your car looks great. Looking forward to seeing it all back together.

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#6 orangeLJ

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Posted 22 September 2009 - 01:55 PM

Thanks Craig!

Any other specs on your new motor? what cam, rods, pistons, la la la you know the deal

I know what you mean about wanting to flog the crap out of it, Its only been like 4 months for me, and Im so freaking excited to get it back together!

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#7 _jklumpp_

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Posted 22 September 2009 - 02:26 PM

Last I knew of HM9Cs were no longer available unless you ordered some ridiculous quantity.

Jason (Jklummp) has just got hold of a set, I think my old man is going to fit them for him some time in the future.

is this the new motor for the XU1?

Yep, I managed to find some in a repco clearance shop in WA or SA or somewhere!...Amazing price too, even with freight to NSW..... but that doesn't help you.
I think the HM9c's are back in production - got positive responses when I phones around - only a few days to get them in.....?
They are sitting on my work bench, 1/2 port matched, so can't help you with how they fit.... Assume you're running triples?

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#8 _CraigA_

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Posted 22 September 2009 - 04:03 PM

I met with the engine builder today and he also thought the HM9C's were hard to get??

Assume you're running triples?

Yes, 45mm Weber's.

Any other specs on your new motor?

Here's what I presented to the engine guy. Final specs will change a little, especially cam choice/compression, based on his personal inspection of the head.

Head (use existing)
Head is 9 port small chamber style (149/161)
Full Service (possible new springs/valves) springs depend on cam choice
Modification to suit Unleaded Fuel
Currently running 1.5 Erson roller rockers/pinned studs

Block
New 3.3 blue motor to be sourced. Greg (ozbox) is on the job right now
Crack Test
Water jackets pressure cleaned going to be sent to Redistrip
Bored 30"
New Bearings (camshaft, crankshaft)
New Pistons/Rings (ACL Race Series)
ARP rod bolts
New Welch Plugs
Gasket Kit (ACL Race)
Water Pump (cast impeller type)
Adjustable steel cam timing gear
Counterweighted crank, snout drilled to suit Romac balancerbolt (I will supply balancer) crank to be knife edged
Flywheel/Pressure Plate machined (I will supply Yella Terrasteel unit)
H.V Oil pump rebuilt or replaced
Crow Camshaft - two choices I'm looking at:

P/N 35626 IN. 34/68 EX.70/32, 238/244 Deg duration @50", Valve Lift 0.486"/0.495" (2800/6200rpm)

P/N 35803 IN. 34/68 EX.70/32, 246/246 Deg duration @50", Valve Lift 0.490"/0.490" (3000/6400rpm) most likely this one

New pushrods
New lifters
Full balance
Possibly high capacity sump

Current Induction
Triple 45mm Weber's on Warneford long runner manifolds (need to be checked for flatness/straightness/match ported)
2" or 4" Ram tubes
Current Exhaust
Factory XU-1 headers (need to be checked forflatness/straightness/match ported/new studs fitted)
Single 2.5" exhaust
Low restriction muffler with Dual 2" Outlets
Possibly replace XU1 headers with HM Headers HM9C?

Current Ignition
Electronic Distributor
High Energy Coil
Current Driveline
Yella Terra explosion proof steel flywheel
Ceramic Button clutch (planning to move back to organic)
Exedy high clamp pressure plate
M20
Choice of 3.55 locker, 3.55 LSD, or 3.08 LSD 3.55 to be used

Current Cooling System
3 core radiator
15 psi cap
16" Thermofan (no mechanical fan used)

Current Fuel System
VK Commodore mechanical fuel pump (sealed type)
Malpassi Fuel pressure control valve (3.5 psi)
3/8" fuel lines on carb side of pump

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#9 orangeLJ

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Posted 22 September 2009 - 04:15 PM

sounds like it should be a nice little package.

Cam choice is similar to what ended up in my LJ by the looks of it, Im only going for 40mm webers though on a warneford design short runner manifold.

what sort of compression are you looking at?

I think I ended up with about 9.8:1 compression using flat top ACL pistons and decking the block.

it definitely gets up and boogies alot better then before, so Im hanging out to get up it with the webers.

Only thing really holding back my 202 is the head, could do with alot more work.

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#10 _CraigA_

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Posted 22 September 2009 - 04:38 PM

what sort of compression are you looking at?

This will depend upon head inspection/cam choice/piston choice.

I'm sure the Weber's will wake your car up even more.

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#11 _jklumpp_

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Posted 26 September 2009 - 07:55 PM

seriously think about doing a 12 port conversion to your head to get the best from the webers - 1 carb/ cylinder.
I bought my head already converted (some sort of epoxy used to divide the port behind the post), and then I made some fins and welded them in to bring the divider to the gasket face)

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#12 _oldjohnno_

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Posted 27 September 2009 - 09:00 PM

seriously think about doing a 12 port conversion to your head to get the best from the webers - 1 carb/ cylinder.
I bought my head already converted (some sort of epoxy used to divide the port behind the post), and then I made some fins and welded them in to bring the divider to the gasket face)

How well did this work out for you? Any flow or hp numbers? I only ask because my own experiments with dividers in 9 port heads didn't go well at all with flow numbers that were even worse than before, especially at higher lifts. I appreciate the advantages of a true IR intake - and to be honest the typical weber setup with 6 throats feeding 3 ports never made much sense to me - but at the end of the day I just couldn't get anything resembling decent flow. Quite possibly I was doing it all wrong; that's why I ask.
I haven't played with 9 port heads for ages but I have a suspicion that a 1.7" valve with a good bowl/seat/short turn and with minimal port enlargement and no bolt sleeve (capscrew in floor) would be the ideal. Possibly use a tongue or lump on the floor (a la stovebolt Chev) to keep the velocity up and then couple this with triple HSR42 Mikunis on an IR manifold (or what passes for IR with siamese ports). I'd be very surprised if this didn't make more peak hp than webers and with substantially higher average hp..

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#13 _jklumpp_

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Posted 30 September 2009 - 12:56 PM

You've got me Old Johnno - I really don't know :surrenderwave:

To be honest, I have just taken the advice from people in the know - and when you're talking about a mechanic with a 'stock' xu-1 that delivers more HP than a current gen V8 commodore, and an engine builder that has been building speedway red motors since they were new technology, I just listen & follow what they tell me to do!....
My Rebuild included completely re-built block & internals, new head, new webers, new manifold, etc, etc - so I have no comparision of the difference
Sounds like you have a better tech understanding than me....

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#14 _jklumpp_

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Posted 30 September 2009 - 01:04 PM

oops

Edited by jklumpp, 30 September 2009 - 01:06 PM.

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#15 _oldjohnno_

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Posted 30 September 2009 - 03:29 PM

You've got me Old Johnno - I really don't know
To be honest, I have just taken the advice from people in the know - and when you're talking about a mechanic with a 'stock' xu-1 that delivers more HP than a current gen V8 commodore, and an engine builder that has been building speedway red motors since they were new technology, I just listen & follow what they tell me to do!....

Fair enough.

Sounds like you have a better tech understanding than me....

I wouldn't count on it! :dontknow:

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#16 _CraigA_

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Posted 19 October 2009 - 07:03 PM

Ordered some HM9C's from American Auto's in Sydney. One week to supply, about $500.00 or so with club discount.

New engine is now well underway with a target completion of about 4 - 6 weeks.

Thanks to Greg (ozbox) for the virgin bore blue motor bottom end. Has been hot tanked and looks very good. +30" ACL pistons and rings ready. 'Starfire' rods have been tidied up and will be balanced & shot peened soon. Sump (thanks Ben) is off to Australian Specialty Racecraft tomorrow to be modified as one of their Comp Circuit pans with an external oil pick up.

The head has been hot tanked & stripped and turned out to be an original 'Superflow' unit from the early '80's.

Just needs a small bit of extra port work around the valve area and ready to go.

Cam choice is close to being made. The current one turned out to be a Watson Heatseeker solid - stage 4 grind. Will more than likely move up to the next stage. Will post final specs soon.

Crank is being knife edged and balanced. Was using a Yella Terra 10.6kg steel flywheel but engine guy has recommended a lighter version.

Still trying to choose the right clutch. Tossing up between just a heavy duty one or a cushion button.

Has anyone used a cushion button behind a Holden 6 cyl?

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#17 _Drag lc_

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Posted 19 October 2009 - 07:21 PM

dont know much about cusion button but we are using a npc sprung centre button one in our lc and is streetable.

Cheers Hayden

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#18 _CraigA_

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Posted 19 October 2009 - 07:27 PM

Thanks Hayden, I was hoping you'd provide some feedback :-)

I'll make contact with the NPC guys and see what they can offer.

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#19 _Drag lc_

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Posted 19 October 2009 - 07:44 PM

yeah look we have only had one clutch problem and that was prolly our fault and that was red mota pcd we are now using blue mota pcd one. from my memory Doug is the bloke to talk to at npc carnt talk highly enough of them . and quite cheap from memory pressure plate and friction disc was around 300 i think.

Cheers Hayden

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#20 _CraigA_

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Posted 28 October 2009 - 02:51 PM

Ended up buying a cushion button from Clutch Industries. Didn't get a chance to talk to NPC but will keep them in mind for the future.

HM9C Headers have arrived and are at the engine builders for port matching, as are the intake manifolds. Once this has been done they are off to Hi Octane Performance Coatings

Head is completed, with some extra porting work carried out and heavier double valve springs fitted.

Weber's go off soon to be fully reco-ed and replated by Nigel at Xtreme Fuel Systems.

YT9044L flywheel ordered and delivered by tomorrow.

Erson rollers rockers are worn (flat spots) on the valve roller and are being replaced with Yella Terra units.

Getting closer Posted Image

The only other things I need to cover off are a carby heat shield and air intake box.

For the carby heat shield I was thinking of using the ACL Heatshield material, either fixed to the bottom of the intake manifolds to to fit an XU1 type heat shield and extend it with the ACL stuff.

Posted Image

And for the cold air box I wanted to use a fabricated box to cover the RAM tubes and then use a single air filter/pick up behind or below the grill somewhere. Anyone done something similar?

Anyone got experience they can offer with either of these things? All help and advice appreciated.

Edited by CraigA, 28 October 2009 - 03:03 PM.

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#21 greens nice

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Name:Kevin
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Car:EH Holden
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Posted 28 October 2009 - 03:46 PM

if your after some heat shield go to the wreckers and look for a newer model falcon, a six cylinder one, they have then and wreckers will probs only want $10 for them, thats what i got on mine. that stuff works a treat aye Posted Image

cheers kevin

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#22 orangeLJ

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Posted 28 October 2009 - 06:11 PM

Sounds awesome craig!

Any chance you could let me know how much the reco + replate on your webers is worth?

I was thinking of hi-temp painting mine (black) as they are a bit dirty and worn from years of use.

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#23 _CraigA_

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Posted 28 October 2009 - 10:22 PM

Any chance you could let me know how much the reco + replate on your webers is worth?

The cost to redo the Weber's is $660.00 and includes the manifolds.

We've used Nigel's services before on various styles of carbies and his work is first class.

if your after some heat shield go to the wreckers and look for a newermodel falcon, a six cylinder one, they have then and wreckers willprobs only want $10 for them, thats what i got on mine. that stuffworks a treat ayepublic/style_emoticons/default/spoton.gif

Great tip Kevin, thanks plenty for that.

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#24 _jklumpp_

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Posted 03 November 2009 - 06:19 PM

What's the hi-temp coating on the HM9c's worth?
Was also thinking about doing this...

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#25 _CraigA_

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Posted 03 November 2009 - 07:30 PM

Have been quoted $280 in silver, $310 in black. Turn around 3-5 days.

I'll be doing mine black.

Can anyone recommend somewhere in Sydney that will make me a catch tank? Or maybe a forum member can help?

I want to put one in place of the factory washer bottle. Must have a breather, drain, and two inlets. There's a few around that are ready made that would work but I'd rather something that sits neatly on the inner guard.

And where's the best place to get some 12AN fittings and hose? Need to plumb up the rocker cover to catch tank.

Edited by CraigA, 03 November 2009 - 07:41 PM.