86 replies to this topic

[klevliend]

Is this still with the 1 3/4" SU? Its a great build so I'm keen to know what power its making. Reliable info on power figures etc. is hard to come by

[Bruiser]

Thanks Warren, I am leaning towards 2 3/4 pipe funny enough. Backyard diy exhaust job anyway so if it’s droney or too loud back to the drawing board.
Commodes are a different layout to toranas anyway, with the main muffler amidships just in front of the diff - luckily right around the pipemax predicted length of
64ish inches from collector. Room for a decent round muffler too, just before rear bumper to get some fair amount of the mufflage done. I have squeezed in a 6” round and 16” long one in there at the moment, pretty effective at keeping the volume down.

Yerss, still have 1 3/4 su’s on there, using oa6 needles kindly traded to me by our Clay. Had spent many hours polishing down some old needles attempting to approximate KU and oa7 measurements, creeping up on it using a wide and o2 meter. Was trying to go close to oa6 when along comes a set of proper ones

Although the exhaust needs doing, I suspect the dizzy timing may be responsible for the top end power iffyness
Had to re-do a new one because the old recurved one was well worn and playing up
Had to learn how to modify the timing curve and after much research went with the “ total timing in as fast as possible without pinging” school of thought.
Ended up with 20 degrees initial, 32 degrees total all in by 2200 rpm. Heard no pinging so left it. Since read a few things suggesting too fast a curve can kill top end power, so have just had another crack at it, all in now around 3000.
Can’t see a dyno visit in the near future, the best I can do is use this nifty little gps speedo I got of eBay
It has a 0 - 100 timer on it which can vaguely be converted to 1/4 mile times which can then be vaguely converted to horsepower
Not very impressive numbers yet, but she leaps off the mark like a rabbit on fire

Don’t know why I am sitting here typing, car is sitting in front of me waiting for a test run with new dizzy settings
Will let you know if it worked or not

[Bruiser]

Yep big improvement, pulls much harder up top now
Even sounds sweeter from 4000 to 6000
Hit rev limiter quicker and wanted to go further
Bugger me, live and learn, eh?

[Bruiser]

Can I also ask what anyone’s experience of this kind of change is?

[klevliend]

What kind of dizzy are you using? I had a crack at rebuilding a stock blue HEI but it kept jumping time gears when revved hard. Was infuriating, went through a range of different washer combinations to adjust the dizzy shaft play to no avail and ended up wondering if the camshaft thrust was worn and causing it to jump ... 
Never got around to ever modifying the timing curve and wrote it off in frustration thinking I'd get scorcher to do it for me. But your results make me think I should try again (new motor so I know the cam is good this time) and play with the timing curve. At the moment I'm running triple 1 3/4" with a decent head (not a patch on yours though) and crow 35872 solid cam, but a stock dizzy. What your saying is making me think I'm loosing more than I realise with the stock curve 

[warrenm]

I done an HEI Holden dizzy last week for an engine that I built for a 71 GTR, timing all in by 2500/3000, initial 14°, max timing 28° was only a baby cam 218° duration.

Never had an issue with jumping teeth klevliend, I run the LJ to 7200 without issue, same dizzy for the last 15 or so years.

[Bruiser]

It’s a Bosch blue motor dizzy, they’re surprisingly easy to get apart and back together again.
Very easy after the 6th time in and out experimenting with spring tweaks.
This is the guts of the old dizz, you can see the wear on the throw out weight pivot posts.
The weights could flop every which way
This was causing the timing to be all over the place up and down

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No jumping teeth for me, either. Using a steel cog from an oil pump, too.

The trickiest part for me has been figuring out what numbers to shoot for in the first place
more than actually making the adjustments to achieve them.
I’d bet you could find some improvements over the stock blue motor curve. The previous worn out dizzy
was limited to 16 degrees mechanical for 16 initial and 32 total. That was with a cam of 226@ 50, fair bit smaller than
your 35872. It loved that much initial timing, same as the bigger cam loves it’s 20 now.
Easy to feel results of more initial timing on low rpm response with seat of pants, for me total timing 28, 30, 32, 36?
at high revs not so easy.
Need better calibrated pants

[Bruiser]

I done an HEI Holden dizzy last week for an engine that I built for a 71 GTR, timing all in by 2500/3000, initial 14°, max timing 28° was only a baby cam 218° duration.
Never had an issue with jumping teeth klevliend, I run the LJ to 7200 without issue, same dizzy for the last 15 or so years.

For a cam of that size, 14 initial makes perfect sense, I might have even chosen that number myself
But what led you to choosing 28 for a total number?

[yel327]

I'd love a writeup on how to calibrate your pants. That would be gold!

[Bruiser]

Can they be calibrated by the average backyarder with worn out tools?

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Edited by Bruiser, 03 August 2023 - 01:21 PM.

[warrenm]

For a cam of that size, 14 initial makes perfect sense, I might have even chosen that number myself
But what led you to choosing 28 for a total number?

Most Holden 6's don't handle much more than about 30° on 98 fuel before they start to ping(cam dependant), so down a couple of degrees for safety, especially in country areas as 98 fuel turn over is lower. When I last ran my other engine(10.8 comp) on avgas, 36° was it, no more mph, as tested on the track, the current engine(12.6 comp) I run at 34° on methanol, it's been tested up to 40° & no more mph past 34°, so that's where it stays. As for the need for special tools, a dial back timing light is it, the rest is just normal hand tools. I fit lighter springs & adjust the bob weight stops, some dizzies have different weight bob weights, they vary 3-4 grams, I don't know which cars they originated from, just the collection I have accumulated over the years.

[Bruiser]

Cheers warren I appreciate sharing your knowhow