I saw this post and was trying to figure why a GX motor would only rev to 6800..............I've used to different GX heads (stock GX springs) and they revved to 7500 or better.....then 1200Rallycar's post reminded me that we installed an electronic distributor from the get go.

Fro the record the A12GX I run now finally floats the valves at 8150; mods are 14lb flywheel, extractors/header, ported head & velocity stacks. I only see 6100ish in top gear as I run out of track.............no idea what it will pull in top gear before ye olde Aero-Limit kicks in.

Tom

Hi Tom, The GX engine is factory redlined at 6800. Yes, I agree they will go higher because many club members have reported their GX engine goes above this.

With new springs, properly set up I'm not suprised you get more. Others here report valve float at various speeds over 7000.

My point is that if you want a certain RPM, buy springs accordingly, and don't expect a used set of GX dual springs to pull in extra-high RPMs. I realize you know this and you buy the good stuff. But before someone goes on eBay buying "dual valve springs" they should understand the potential tolerances. A14 heads have heavier valves and heavier pushrods and won't rev quite as high given the same springs (compared to an A12 GX engine).



Interesting that this redline may have more to do with the points limitation than the valve springs.

racetech : No,the engine is not struggling to reach 6800rpm,last weekend i tried,it can make to 7000rpm,but no point because there's no 'power' above 6800rpm.is it valve bounce?

forgot to mention that i'm still using a stock distributor and a stock H89 head except for the dual springs.

i agree with what ddgonzal have stated..

thanks.

What is the points limitation?

TJ-Flames : what do u mean by points limitation?


**sorry, my english is not very good.

bituten your english is better than our er Malay (that is the language correct??)..........point limit is like valves.......the points are sprung and at a certain RPM they will physically bounce and naturally no longer deliver the spark correctly.

Dave I made comments because I was just surprised at RPM limit...... a classic case of "I'm the Center of the Universe" I just figured everyones car behaved exactly as mine :)

Now on a different but related note, since I installed the close ratio 4 speed I no longer "need" to rev the car to 7800 to cover the 3000 RPM drop between 2nd and 3rd. I find myself using a few hundred RPM's less.

Tom

Been reading all the max rev stuff. Well back 30 years ago I was running a A10 motor to 9000Rpm on standard Datsun 120Y variable rate valve springs with not a hint of valve bounce, I was running a 268Deg Waggott Cam twin 40mm Webers and a 12 pound flywheel. The only problem I had was the oil pump supply. I ended up shearing the thrust faces off the centre main bearings and the A10 only had three. This was after about 20,000Kms of hard driving including normal road use Gymkanas and Hillclimbs.

so...conclusion?? can L16 valve spring be use in A-series

any info??

I seem to recall somewhere folks using L series valve train stuff but I also remember it was modified..........might be cheaper to just buy the items designed for A series.

Now with all engines the Max RPM can only be determined as follows: floor the car in a lower gear and then wiat..............note what RPM's the rods flew out the block then set the redline 100 RPM's just below that............it's a time honored racer traditon.

I think the realistic Rev limit for an A series street motor is 7200-7500. Race motors will go 9500 BUT one way or another you'll have the engine out in short order..........either replacing parts before the liberate themselves or replacing all the busted parts.

Tom

Back in the early 1980's I had a 1971 1200 coupe that I built for local club rally's. The engine was fully balanced, but stock pistons , rods etc. I had a rally cam (cant remember the make or grind) and ported and polished the head myself. Ran a single 45mm weber dual throat carby choked to 32mm and jetted to suit a lynx crossover manifold. At the time we rebuilt the motor my mate was working as a mechanic in a servo and had just pulled down a blown motor out of a toyota dyna truck, we found that the inner valve springs on the dyna fitted perfectly inside the stock valve springs so we gave them a try. After running the engine in it would rev to 8000rpm no worries and continued to do so for quite a few years. Not long after the rebuild I had to fit a race clutch as the original disintegrated when changing from 1st to 2nd at 8000 revs one day. Finally I totalled it by taking 3 pine trees out of the ground at around 80mph in a club rally. The old Datto was amazing the punishment it took, one day I hope to get another and rebuild.