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Dave's "track-spec" 1600
http://ozdat.com.au/forum/viewtopic.php?t=8460		 Page 21 of 21
Author:  Dave [ Mon Oct 14, 2019 10:28 pm ]
Post subject:  Re: Dave's "track-spec" 1600
Well, Challenge Bathurst time means it "fix the Datsun" time.

I missed last year's CB for family reasons (daughter's Year 12 formal and graduations were on the same weekend), this year is the grand "50th anniversary of the zed" celebrations so can't miss it.

1600 is still broken, for various reasons (holidays, home renovations, illness, got right into motorsport officialling - I'm now qualified as Bronze Event Command so can act as Clerk of Course at up to State level events - and not forgetting sheer laziness.....). Finally got around to doing something with it lately but its only going to be a refresh of the existing engine. So far, been concentrating on getting the head ready to be refurbished. It blew a head gasket, so will be off to the machine shop to check for hardness and straightness, get a few water galleries welded up (they're just a lilttle corroded but getting close-ish to the head gasket fire ring), new valve guides (I put new guides in last rebuild, its probably only done 1000k's or so and they're worn already ??), and I've treated it to a new set of valve springs plus going up a few sizes in cam from a 72 degree to a 76 degree (should work OK with the S15 closer ratio box).

I'm also tidying it up a little before dropping it off at the machine shop. Its always had the two end exhaust ports smaller than the centre ones, so going to even them up. Spent tonight working on the combustion chambers, just blending it all from the seat to the chamber itself - from the factory it has fairly large machining ridges so I've knocked them off with the dremel and will smooth and polish it all.

Then head to be checked / machined, and pull the bottom end out to be stripped down and check no busted rings, etc and just put it back together. If I can get a few more hp, and a few more revs out of it, and make it last for 2 hours around Mt Panorama, I'll be happy and will consider long term engine plans after that. Or I'll just keep driving it till it blows up again........

Outermost ridge to be blended into chamber :
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Preparing for some exploratory measurements:
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Takes the guesswork out of porting / working out where water passages are :
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Author:  RJB510 [ Tue Oct 15, 2019 7:52 am ]
Post subject:  Re: Dave's "track-spec" 1600
Hi Dave, i enjoyed reading the update. 1000k out of valve guides seems very low. Are the stem seals also busted?

Just wondering what carbies you're using to push through that big of a cam? I'm assuming Webers?
Author:  Dave [ Tue Oct 15, 2019 8:11 am ]
Post subject:  Re: Dave's "track-spec" 1600
Valve stem seals were new, and still looked fine. The guides I put in last time were some sort of steel ?? I've got new bronze guides for it this time. There was a good 2mm or so "rock" at the valve head. Only other thing was that I shortened the guides last time to see if that helped breathing, maybe this time I'll just turn a "cone" on the bit that sticks into the port but leave it full length.

Carbs will depend on time. If I've got enough time, I'll buy and fit webers. If not, same old 1 3/4" SU's. My (hopefully not flawed) logic is the SU's are same size bore as 45 webers (actually a bigger bore, if you consider webers are choked down), and engine is only on the intake stroke every 2nd revolution so can only "suck" thru the carbs one cylinder at a time which negates the "one choke per cylinder" thing for webers. I previously fully reconditioned and modified the SU's (trimmed down throttle shaft, bigger needle & seat and better / adjustable float) and had a great old school tuner get them spot on, although he has recently retired so I'll need to find another one....The Group S 240Z racers get great results from twin SU's on bigger 6 cylinder engines.

I'm sure webers would be the "best" option, hopefully SU's aren't too far off if I have to stick with them.

Only other "modification" I'm looking at this time is crank-triggered ignition, I've had a few issues over the years with dizzy's (both points type and electronic) but again will depend on time - I'd need to wire in an ecu and get it all tuned. Probably just end up fitting trigger wheel and sensor while engine is out of the car for future use.
Author:  RJB510 [ Tue Oct 15, 2019 9:03 am ]
Post subject:  Re: Dave's "track-spec" 1600
The only reason i asked re carbes was because i thought you had su's. I had a set of early round top Hitachi carbs that ran su jets and needles. They struggled with the positive pressure on a 72 cam and I've heard that on a 76, they aren't quite strong enough. You sound like you know what you're doing with the su's though!

I think that the ecu and cas option is the best way to go. But while you're at it, might as well go digital fuel injection too! That's always been my plan for my old L series.

The budget and time though... Haha
Author:  Coz22a [ Tue Oct 15, 2019 10:25 am ]
Post subject:  Re: Dave's "track-spec" 1600
Hi Dave
Great to hear you’re heading back to The Mountain. I wish I could be there too but, travelling Oz this year so I can’t complain.
I’m sure you’ll have no probs getting what you need from the SU’s but.... this sounds like a perfect opportunity to make a GBP purchase.
https://store.jenvey.co.uk/heritage-twi ... r-tdp40-48
I’ve not seen anyone using them but I like the idea of injection with the carby look.
Anyway good luck getting it sorted and have a great time up there Mate.
Mick
Author:  SR20Datsun [ Wed Oct 16, 2019 1:35 pm ]
Post subject:  Re: Dave's "track-spec" 1600
Hey Dave. Good to see an update and progress!
Author:  Lurch [ Thu Oct 17, 2019 10:36 am ]
Post subject:  Re: Dave's "track-spec" 1600
Great to hear your back onto it Dave.
However Twin Hitachi's/SU's wont flow enough for a 76 works style cam...

Oh, and S15 6-speed gearboxes aren't 'close ratio'.
Author:  Hatchman [ Thu Oct 17, 2019 3:00 pm ]
Post subject:  Re: Dave's "track-spec" 1600
Lurch wrote: *Thu Oct 17, 2019 10:36 am
Great to hear your back onto it Dave.
However Twin Hitachi's/SU's wont flow enough for a 76 works style cam...

Oh, and S15 6-speed gearboxes aren't 'close ratio'.
I have a 76 degree cam in an L20B using dual 45mm Webers and that seems to work well enough
Author:  Dave [ Thu Oct 17, 2019 4:58 pm ]
Post subject:  Re: Dave's "track-spec" 1600
Lurch wrote: *Thu Oct 17, 2019 10:36 am
Oh, and S15 6-speed gearboxes aren't 'close ratio'.
Closer ratio might be more accurate. Or a close ratio 4 speed with an additional really low gear for getting it on the trailer and a rediculously high overdrive gear for 6th.

2nd to 5th in the S15 are closer than 1st-4th in the Kameari "super close" gearset that a lot of guys seem to love. Not quite a close as most of the older comp boxes though. One day I'll see if I can fit the Lexus 6th gearset that;s been sitting in the shed for years to bring 6th back to being useable. Or perhaps build a decent engine that can pull higher speeds to need more gears.

s15 - 2.200/1.541/1.213/1.000
Kameari - 2.427/1.814/1.360/1.000
Author:  RJB510 [ Thu Oct 17, 2019 5:15 pm ]
Post subject:  Re: Dave's "track-spec" 1600
What diff ratio are you using with the s15 6spd box? I want sure about my mates s15 sylvia with it running a 3.7.

But... what that translates to in regards to expectations was, i expected a normal 1-5 gearset with an extra overdriven 6th. So i could run a short diff and still maintain low highway cruising rpm.
His seemed like the 6th gear was the same as a normal 5th.
Is that not the case?
Author:  Dave [ Thu Oct 17, 2019 6:03 pm ]
Post subject:  Re: Dave's "track-spec" 1600
I run a 4.44 diff.

6th in the S15 box is .767, 5th is 1:1. So 4th in a 5 speed = 5th in a 6 speed (ignoring diff ratios), and 6th is a little more overdriven than 5th in a 5 speed. My car is geared for 230k at 7000 rpm in 6th, which is just a little unachievable, even in 5th I run out of speed before I run out of revs.

I have basically the same box in my MX5 (slightly wider 2nd-5th ratios, and a better .843 6th) with a 3.6 diff. I use 4th gear around town, 5th gear once I'm up around 70 or so, and only get to 6th once I'm on the highway (a flat or downhill highway......). I've always thought it would be nicer with a shorter diff, but starting to modify the MX5 is a slippery slope I'm keeping well away from.......
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