738 replies to this topic

[claysummers]

They wouldn’t have taken much off, though I can feel the difference. Looked to be virtually virgin prior. I forgot to take the invoice so I will call in on the way home from work (oh yes, work. First day back tomorrow). The cam is pretty tame and doesn’t warrant too much comp. Unshrouding exhaust ports will have added some volume.

I want to do another tank of cruising on the old head to test the fuel consumption before I swap the new one on. So far seem to be using more fuel with the SUs, which I wasn’t expecting.


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[warrenm]

Been a lot of years since I've seen a Holden head with such small valves & not ported.

[claysummers]

Trying to keep the velocity up Warren. Won’t be revving over 4000 very often.


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[claysummers]

Booked the ute in for a dyno tune with Davor Pribicevic at Performance Auto and Dyno, Seaford in the end. He was recommended by the engine shop and he is local. I will fit the new head after the next club run.

He uses someone in Sydney to supply needles etc. so now I am wondering if I may need to richen things up at all. At the moment it is running pretty well, although I’m not sure it picks up as well as with the old cam and tune. It doesn’t crackle and pop on over run like it used to either. May just be difference in the timing.

According to the builder the new head is around 10:1 static. It should flow a bit more and have a bit less back pressure. Cam is very mild spec either 0.435” lift, 109 separation and 205 duration at 0.050”. Factory cast headers, straight through muffler and 2” full exhaust with fairly short secondaries. Currently running TW needles and red springs.


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[yel327]

The head is standard chambers and standard valves? If so will be higher comp than standard LC XU1 but you also probably have twice the gasket thickness so that should compensate I guess. So rule of thumb says 10:1 give or take. Aftermarket pistons sometimes sit a bit further down the bore too to compensate for deck cleanup so that might reduce it a bit.

[claysummers]

Larger exhaust valves.
Forgot to say that the TW needles are sitting in 0.010" jets, HS6 carbs.

I'm hoping for recommendations on needles to suit from the wise ones.

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[yel327]

Larger exhaust valves shouldn’t change compression as they are probably not de-shrouded like you do for bigger inlets.

[claysummers]

Yes, they have been deshrouded a bit Byron. Thinking the slight opening up could require richening things slightly?


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[warrenm]

Having a cam that is close to std, needle selection is harder. Have a look at an Austin Healy 3000 needles, that might give you something to look at.

I built a 173 last year, the new pistons were .040" down the hole, before machining.

[yel327]

I'm no expert but if you have larger exhaust valves and better exhaust (as in X2/S headers and larger pipes) it will probably lean off a bit. From memory that is what happens to a standard red 6 when you put extractors and bigger exhaust on it. I'm not sure larger exhaust valves are going to have any performance increase, but the exhaust should.

 

Stick a magnetic dial gauge on the pistons at TDC and measure the deck height, if its 40 thou down then you might be looking at 9:1-ish compression static. Which should be OK with a small camshaft.

[claysummers]

Been through all this Byron. 35 thou deck height plus permaseal gasket. The only thing I’m changing from the current setup is the head.
Made it pretty….


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[yel327]

You probably did, even posted it but I forgot. Same as I forgot you'd put larger exhaust valves in! You'll be fine with static compression ratio with pistons 35 thou down the bore, but IIRC it will also mean more risk of pinging with them that far down regardless of the static compression ratio.

 

To show the difference it makes I entered info into a compression ratio calculator for a HT-HG GTS350 manual engine:

 

4" bore

3.48" stroke

64cc chambers

8cc valve reliefs in the pistons (effective dish).

10 thou deck clearance.

25 thou compressed gasket thickness

8 cylinders.

 

Comes out at 10.04:1. GM almost always rounded up to the nearest 0.25:1 so this was advertised as 10.25:1.

 

If I change the gaskets to 38 thou compressed (which is typical of these gaskets) and drop the pistons to 35 thou down the hole it drops to 9.22:1. Using 38 thou gaskets with something like 5 thou deck height it is 9.85:1.

 

Have a play with 6cyl numbers:

 

https://www.summitra...sion-calculator

[claysummers]

Thanks, that’s a handy tool. Confirms my calcs based on factory head volumes. 8.5:1 for the old head and 9.9:1 for the 161 head.

What I am asking for though is advice on needles. Helped before (Bruiser)……………


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[Bruiser]

Hiya Clay
I’ve been having a think and checking out that TW against the OA7 on the comparison graph from
https://www.classicm...chnical/needles
also because salamiman has bought it up too.
I am sorry those ones didn’t end up working out for you
I tried them on the advice of someone here with an engine very similar spec to how mine
was at the time, he was using the weaker blue piston spring as well!
Your motor is even more sensible than mine was then, so you should need a leaner needle than I did, logically.
I never got that quite right, I don’t think.
I had a chat a while back on the pm with a fella here who had used 0A7 needles in his su’s
With 3 cams he described as 25/65, 30/70 and with a big crow 35467 as well
He raced a 600hp speedway car, so I guess he knows a bit. I did quiz him on the needles,
and he said they worked fine with each setup.
Maybe the hotter his motor became, the lower he would drop his jet to riches things up for mid to top end,
which brings the idle richness up too. Maybe acceptably (within reason) ?
The OA7 and OA6 come up all the time in discussions, and the comment about “old timers swearing by them” does too.
They both have a fairly even progressive taper on the graphs, maybe that is well suited to the Holden 6 generally(?)
If you are looking to buy (hopefully) the ideal set before your dyno tune, maybe someone else has the knowledge to
give the right advice, but I think the best we could get is a rough guess. And they’re really not a cheap guess, either
Those TWs could be reshaped to be close to an OA7, if you are game and patient enough..
I’ll help you out if you want to have a go

Maybe the dyno feller has an idea, if he’s done a few of these?


Head looks nice, there’s nothing like a brand new one all nice and fresh
I can’t see any deshrouding in the chambers, just a bit of grinding on the exh port floors
Did he need to even them up a bit out something?
I bet having your dizzy regraphed will make a huge difference

[claysummers]

Thanks Bruce. I think the TW needles are working pretty well with the current setup and your advice has served me very well. I just wonder if the new head will change things. I’m still running the numbers on fuel consumption but I get the feeling it is a bit higher than with the twin BXUV-2 Strombergs. Davor the tuner thought it worth getting opinion on what others have experienced, so we might have something on hand just to save some time. Doesn’t really matter, and I speculate it will take a couple of iterations to get it right. I think there are 78 different fixed needles for the 0.010” jets. $70 or $80 plus freight for a set of three from Midel. He said he uses their Haystack software to get the right ones.


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[claysummers]

This thing: http://needle.sumidel.com/


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[claysummers]

What do you reckon about these plugs? No 1 on the right.
I may have damaged some of the valve stem seals when I put the soft springs on, possibly accounting for numbers 2 and 4 being oily. 3, 5 and 6 have pretty unform whitish grey cathodes. Electrodes are pretty uniform, with a small amount of soot. Apart from no 2 the insulators are pretty uniform I think, though 3 has some soot.

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[claysummers]

I think this photo confirms that the valve stem seals were leaking on all bar three exhaust valves. And running lean.

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[Bruiser]

Could explain why the plugs are all patchy, the pairs should be pretty similar with your su’s feeding 2 ports at once.
They do look a bit crudded up with oil, too.
They don’t look as lean as the exhaust valves do, anyway
at least the valves aren’t completely white.
New head with nice guides and seals should make a nice improvement

[claysummers]

Number six plugs set to 0.060" per VH spec for the Bosch electronic dissy. Rockers set to 1/2 turn preload cold. Minor fuel leak on middle fuel bowl to fix, and it will be ready to go for a run.

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Edited by claysummers, 18 February 2024 - 08:34 PM.

[rexy]

The plug straps look a bit hot? Too much advance?

[claysummers]

They were fives so sixes might be cooler? I’m told the blue motor dissies have a fair bit of mechanical advance. Static was at six.


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[yel327]

If you give me the dizzy Bosch number I’ll give you its specs. Not until the weekend though.

[EunUCh]

Speaking of valve stem seals , the rubber square section ones that are supplied with gasket kit tend to harden after a while with heat and oil and then let a bit of oil past . If they were possibly damaged on installation then that is another story. I recently had to "tidy up" some valve seats etc. on a 186 and found every valve stem seal was hard and just broke apart and this thing had done hardly any miles.

Use viton o rings instead of the rubber seals , they handle the heat better than the rubber apparently . i forget what size i used but they are available in a size that does the job.

[claysummers]

Speaking of valve stem seals , the rubber square section ones that are supplied with gasket kit tend to harden after a while with heat and oil and then let a bit of oil past . If they were possibly damaged on installation then that is another story. I recently had to "tidy up" some valve seats etc. on a 186 and found every valve stem seal was hard and just broke apart and this thing had done hardly any miles.
Use viton o rings instead of the rubber seals , they handle the heat better than the rubber apparently . i forget what size i used but they are available in a size that does the job.

Thanks for the tip though I’m sure I damaged them putting the retainers back on after changing to soft springs. I left the shrouds off also and if I recall correctly none were fitted when I got the head. It was only ever going to be a temporary thing.


Running nice now, though I will need to re-set the tappets hot I think. It certainly pulls well. No pinging evident under load.