loved all your posts jmac. you should write a book :)

I do hear what you're saying Jmac. But I also like driving around corners too. It it develops tramp issues, I'm just going to make some caltrac style bars for the rear. There is a brief overveiw of how to do it at the hotrods and hemis website.
Plus once there's no danger of the caliper touching the body, I'll be able to drop a leaf or two (And definately the overload springs) and get a little bit of "squat" to help put the power down to the road. Worst case I could alway pull out the blocks and change back to the current caliper plates before a drag meeting.
As it is I'm having a real hard time getting my 60ft times under two point two seconds. Except when I ran a less powerfull variation of my current engine.

If that is the case then you probably don't want to go with softer rear springs. there's a difference between the weight transferring to the rear and the body moving back (vs the wheels at least) It is no doubt a balancing act, but softening the rear too much (I'd speculate that the factory springs are softer than ideal, since they are specced for ride comfort etc as well, over-rider/overload leaves ignored for the moment).

It's a hard one to put into words (and I didn't do mechanical engineering, so I don't know the right terms, or even the specific math involved, but I can visualise and understand the various competing forces in my head clearly enough) but if the rear is soft it can delay the rear wheel downforce, instead of cushioning it and allowing it to maximise (obviously it is a balancing act between the two - too sloppy and no grip, to harsh, and it can shock and lose traction).;

Based on the current 60ft times (and to be fair they aren't exactly 'dreadful' and this isn't a 600bhp ultralight car on slicks) i'd actually suggest it is evidence that raising the front spring pivot point is going to help things out..

Essentially you have to come up with ways to increase the rear grip (which more or less means more downforce on the tyres) without it also adding weight to the car in proportion to the increase in downforce. In other words, if you increased grip by 10%, but did it in a way that there is now 10% more mass to accelerate there'll be no improvement in launch, and overall it'll now have worse power:weight and run slower again.

One trick therefore is to add weight to the rear, but to add it as far back as you pssibly can. Believe it or not I got this idea (*it makes perfect sense and no doubt others would have come up with it too) from an article about early super stock racing in teh US. They basically ran production/showroom spec cars with narrow mods allowed. At the time, winning races = big sales so the factorys got behind various racers to help. Winning meant everything, and obviously winning cars were heavily scrutinised, so they couldn't cheat - but they did anyway. What they did was to also secretly sponsor other cars run by privateers, but build them illegally, bigger motor, etc etc, and this faster than legal car would hopefully knock off the main competitions in the elinimations/semi finals, then they'd deliberately red-light or otherwise lose, so the cheat car never got scrutinised, and the official factory backed cars went through to the finals without as much competition.

Anyway - what they did among many other things was to custom make new rear bumpers that were full of lead (couldn't be seen from the outside, and never got stripped down after) or other weight (obviously well secured/integrated) Being right at the rear tip of the car, every kg of extra weight had considerable leverage, so it translated into 5-10 times that amount of extra downforce on the rear tyres. Nice gain, when you think about it that much extra grip for only a few kg extra weight (I forget how much they allegedly ran, something like 20+kg.

Obviously this would make for less optimal handling, as it puts weight so far back from teh centre of gravity and rear axle centreline that it would promote oversteer if cornering near the limit. But you could always just run the weight (strategeically placed, and using a spare bumper might even be the cheapest way) naturally none of the dattos has the sort of rear 'overhang' as US musclecars from that era had, so the potential gains/improvements are lessened, but hey, why not. I suppose other stuff like a relocated battery. could be tried too. Perhaps even the totally dodgy idea - like getting a 'stuffed' spare wheel and tyre, and filling it with water (and a little bit of air just to keep the valve from seeping any water) and fitting it in the rear as if it were a normal spare. dunno if that would be far enough to totally outweigh the costs of extra mass to accelerate. Might make for an interesting experiment.

I wouldn't trust another 20kg hanging off the two bumper bar bolt holes Jmac, the heavy spare seems like an easier option to try first. I was looking at my sedan yesterday after reading your thoughts on the matter and was thoroughly annoyed when I notice I can't move the front mount up >_<

Sadly, the front mount can't be raised, as Aiden said. Although on most of the vals I've owned I've inverted the front hanger to lose a bit of rear ride height, and corrected the pinion angle with wedges. But I never ran any of them down the quarter anyway.
Another thing which isn't so ideal is that my front suspention has been lowered, so I'm quite sure that I'm losing some potential weight transfer there. Although I'd be running the risk of worsening my rear end geometry by lowering the rear, at least if the car sat level there may be a whisker more weight transfer.

I raced again on saturday just been, and still couldn't get under two point two (numeral keys one to five are broken on this computer)in the 60ft. The difference this time was I was running some stickier compound tyres. but to no avail.
Also slightly OT but I'd read at FABO that every some many tenths in the 60ft, were worth so many tenths at the other end of the track. Although my times seemed to only differ by the differential of my 60ft.
I'm going to remove the spring loaded locker, and fit a lower ratio locked diff for the next meeting. as well as fitting a pair of two four fives if I can find a pair of rims wide enough for them.

That cuts hard Bart....it's Aidan man, that Dattoholic with a heart of gold :P

What cuts hard? sorry, I'm a bit slow atm.
If it was calling you "the last poster" rather than knowing who you were, My apoligies. I was typing flat out, and didn't want to stop to go back and see who had added that factoid to the discussion. (edited now )

is all good, I was just practicing for if I end up in a "*textuation" where I need to say "that cuts hard"

*word I made up but is probly already made up and will soon be overused in everyday speech thanks to teenie boppers and society in general.

Moving on...what size diffs are you running that spring locker in?

I'm rocking a spring loaded locker in an H one six five. In all fairness, it's a great wee invention, but it's just not up to the task for drag racing. see footage of me racing, I could see it open up during my staging burnout, but for fanging around the hills, it gives a pleasant two wheel push without the horrid-ness of a locky.
I began my H one six five locky today. The welded up spool I have had smaller bolts than the crownwheel. So I resized the holes to suit, and I'll slap it together tommorrow.

I've decided to get my 60ft as refined as possible before I hook up the nitrous oxide bottle. Theres no point in wasting it (given the price of the stuff) untill I have perfected the launch.

Another suggestion or two - both relate. If you can't relocate the front leaf pivot/bolt higher, then would there be room to do a dodgy and relocate the diff about 1-2 inches forward, by shifting where it locates on the leaves? might not be possible at all, esp with large tyres.

In the US in the 60s they did a similar thing, well technically they relocated the whole leaf pack forward a few inches. Essentially gives more overhang and higher %age of load/weight n the rears. naturally one has to measure things up - even if the wheels fit ok, the tailshaft length might be to the extent it will bind when you shift the diff forward at all.

By the same concept, they also relocatd the front wheels forward a similar amount (doing it by itself means a little mre weight on the rears, but combined with rear relocation doubles the effect potentially).

Obviously it'd be way limited on the rear of a datto 1200 (they cut wheel tubs, relocated the guard openings so they almost looked 'stock' - as much as possible (but obvious to anyone looking for it)) but even 1 inch could help. On the front there's obviously dramas wth the front lower lip of the wheel arch hitting the wheel with larger than std front wheels. Hypothetically if you alrady cut the guards to clear the tyres, if you went back to stock front ones, then you could move the front forward via adjustable caster bars. By the time you get 1-2 inches forward movement you'd start to push the inner lower control arm bush into therange it'd tear (or risk damaging the bolt, given long enough time, if it was a urethane style bush with even less deflection/compliance) - so it couldn't be done long term for a streeter, but hypothetically if you only adjusted it like that for racing (simply counting how many turns of the caster bar nuts to go back to std etc) it'd help with a touch more rear weight distribution even when standing still). Ironically, it'd also temporarily have a few degrees (about 1 degree for every inch forward you can shift the stub axle centreline) increase in positive caster, which would make it more stable in a straight line - nice for drag racing.

Last little tid bit that I found helped a bunch of cars at launch (and it will even work with a locked diff, though its benefits are more pronounced on an open/std diff. - basically the leaves on the right hand rear will sag a little more over the years - from the axle always tryng to lift the right rear under acceleration. If they raise the right, they push down on the left, which should mean iwth a locked diff, the overall grip would be the same, but for some reason it seems slightly better in practice, evne iwth locked diff, if the tyre downforce is evened out.

Anyway, the right sags, so swapping left and right leaf packs (on any car that is possible on, or coils on others etc) works wonders. That slight sag is reversed, so there is (whilst sitting still) more downforce/load on the right rear. When you add the right rear lift under heavy acceleration, that slight bias ends up evening out at the most crucial point - off the line. So that it is more even stevens. I'd actually go for that in distinct preference to new leaves both sides, which means static downforce is equal, but right rear lift throws it out of whack under launch conditions (not as bad as a sagged rear would, but still not as good as a sagged leaf swapped to the left would achieve).

On those cars where springs aren't interchangeable left to right, often one can 'cheat' and simply run a lowering block on the left rear (make the block as long as practical, so it contacts more of the leaves and helps prevent axle tramp/windup more than most el-cheapo one size fits all lowering blocks ). If spare time (a bit chunk of it) permits, the way to optimise it is fairly simple. Fit a single spinner/open diff temporarily, find somewhere safe and practice launches, then add a small thickness lowering block (choose the initial added lowering block test thickness to level out the rear for the first test). do another bunch of launch tests, then go 5-10mm per time with thicker blocks.

Basically you keep going and it'll get to a point where even with an open diff, it no longer just lights up the right rear, it'll get to the point that both of them try to spin (or even just the left rear).; Find that point and go back just a touch (2-3mm) and re-fit the locked or LSD centre. Another option is to run (if you can find one to suit) an air shocker on the right rear, and inflating it to maybe as little as 5-10psi at a time, till it did the same job of preventing the right raar losing traction at launch.