The good old days ?

The offset IS about 15 on the even sprocket , tooth and a bit over half on 38 teeth so should be fine I think ....



Going to fire this lump up pretty soon .Making up a test bed so I can at least hear them run and check a few tings before plonking in a car ..
Got a shite old frame ,ECU ,bellhousing ,enough of a loom and a jerry can

The offset IS about 15 on the even sprocket , tooth and a bit over half on 38 teeth so should be fine I think ....



Going to fire this lump up pretty soon .Making up a test bed so I can at least hear them run and check a few tings before plonking in a car ..
Got a shite old frame ,ECU ,bellhousing ,enough of a loom and a jerry can

And a big extinguisher

si21

Si, Stunned has given you some good advice on a reasonable atmo build with the parts you have available. Everything is a compromise, and bang for buck that is a combo.

You have 24V pistons, they will do the job, and even with the 280 cams shouldn’t give you any clearance issue - the crown is 0.7mm lower at the point of interest between the 3ltr n/a piston and the 24V. I have the figures and valve lift measurements digitised for all OE cams (even and odd fire), so could easily check anyway. They will give you a higher CR than the 3ltr even-fire piston. The 24V piston does carry a 4mm longer gudgeon pin so a little heavier than the 3ltr n/a, but if you really wanted to save the 5g - yes I have measured it- you could by running spacers.

The 24v piston and 3ltr even-fire piston has the same casting mould for the inside of the piston. The rings on the 24V are pushed up, so for a snappy atmo / n/a engine a better choice over the 3ltr slugs. Both carry the same rings.

BTW the crown is not 2mm - I can post a pic with one cut in half... yes I have done that on all OE pistons to know what can be machined out of them. The 3ltr n/a is more like 7mm at a guess from memory, anyway far from 2mm...

The even-fire and odd fire cams blanks and basic machining detail are identical, and have been successfully swapped between engines, more often 280 cams into 28E/F odd-fire units to get the better spec cams.

The 280 cams as Stunned has suggested saves you having to change to more expensive valve springs, and will also encourage you to keep to a more realistic rev limit – piston speed, valve bounce, and think engine life…

The other thing you want to focus is hp doesn’t accelerate you up the hill, but torque does; hp is simply how quickly you can deliver than torque effectively. So you need to think of the aggregate torque / power put down on the circuit over the duration of the race, not just the peak hp number, as you will more than likely be accelerating out of slow corners somewhat off max hp… so you need strong mid-range, and a good spread between peak torque and peak power – the band of maximum effort. The UN1 restricts you as the std cogs are pretty disadvantageously spaced for hill climb, and if I wanted to be a real serious contender, I would opt for a good spec motor and the best gearbox I could afford i.e. put your money into a close ratio set of gears spec’d for the power and torque curve of your engine – then go race…. I would not make the engine the principle focus if my budget was 2-3k, and you can spend that in a blink on an engine rebuild… HP numbers get the glamour – the gearbox is your torque multiplier, may it be chosen well…

400ft/lb... I wouldn't get drawn to silly numbers, you want to finish races to have a chance of winning, or getting up the leader board, so think more in terms of good power and good reliability. You also want to do it with a least a season or two racing on the engine to make it economic racing and fun. You would soon tire of rebuilding your engine after each season.

The 3ltr heads are pretty good out of the box, and if you take the sensible route and keep the OE manifold – you have one already, then the gains are not going to be huge if you start modifying them. There are gains, but put in terms of changing the final drive ratio from 3.44:1 std to the R25 3.89:1 you can have a 13% increase in real torque put down on the tarmac throughout the rev range from changing the final drive ratio…so what would I do… I think that’s pretty obvious…

Thanks guys that's all really useful information. Mr faulks that's definately my way of thinking. Tbh i had not thought of gearbox mods due to the costs involved. My box needs looking at and i was seriously considering pulling it apart during the winter......your right the Le mans will never get finished maybe i should sell it and build a quick lump with a pucker box tbh i am hooked on the motor sport thing and really love ghe idea of seeing how well i.can venture up against later more poweful machinery.

I have,a diff out of a 21 turbo i beleive is a fraction lower than a 25 diff, just csnt think right now what the ratio is, used to know who do you approach for aset of gears i think the likes of quaife and hewland and gt engineering would have me sat in an early coffin

Any ideas on anyone else or advise on cost? I know the 25 turbo boxes are rarer than hens teeth now:roll:

Si21

Fit smaller rear wheels.....

21T diff is 4.1:1 IIRC

UN1s can be found in Espace's also and I believe with the 3.89:1 ratio

21T 9x31 3.44
25 9x35 3.88
D500 9x31
D501 9x31
Blindee thing 9x37 4.11

See it's not all about engines Andy001 we can get very anal about the box as well

[mettersl]

Lee are you sure,
I though the 21T and the GTA Turbo/D501 (D502 and D503) shared the same final drive ratio? and the atmo was shorter?

( other) Lee

Yep ,I have UN book B.V.UN

4th and 5th ratios different
D500 27x28 , 39x32
D501 28x27 , 41x31

It's here on the site as well ...

http://www.renaultalpineownersclub.com/ ... manual.htm

fair enough mr clee, when you fire that engine up don't forget your ear plugs.
gear ratios in a way im as bad as you lot i can still remember all the 90s colour codes
389 white
719 red
455 midnight blue
640 iceberg silver
777 pearl red
608 tungstone

[mettersl]

Ah well I'll have to start reading the Un1 book at bedtime until I am number perfect!
Only joking....., really joking.....where did you get it

From a mate who used to work for Renault .He gave me that and also ones for engine + both electronic and jetronic injection
He had loads but had never looked at them

BTW the crown is not 2mm - I can post a pic with one cut in half... yes I have done that on all OE pistons to know what can be machined out of them. The 3ltr n/a is more like 7mm at a guess from memory, anyway far from 2mm...

Correction - 8mm, I just measured it again for another purpose...

Just adding to the retentive category...

I remember where the figure of 2mm came from - it's what you end up with if you try to make an A610 piston from an NA one

Lee are you sure,
I though the 21T and the GTA Turbo/D501 (D502 and D503) shared the same final drive ratio? and the atmo was shorter?

( other) Lee

The 21T has exactly the same ratios as the Atmo box although I am not sure about the diff ratio; had better read the thread again to check and see.

I know the price of new parts for the UN1 are extortionate as I enquired when having parts rebuilt back into my Le Mans turbo box. in the end I used a doner box with good internals, well the parts I needed were anyway, which was why I was asking about a the 21 Turbo diff?

I was thinking that If I were to spend money on a limited slip with a lower ratio, this would give the benefit of better traction and power delivery to the road, becoming more predictable to drive and possibly help the engine overlook the slighly long gear spacing. Are the crown wheels and pinions custom made and available in different ratios, or are they are are they modified originals?

I was thinking that as a cheap alternative by lowering the gearing, the fact that the slightly long gear spacing would become less evident, not optimum but a big improvement for a reasonable outlay, as I can't imagine gear sets are going to be cheap If a grand gets me this and improves torque this may be an option for me. Apparently Quaife do or did a limited slip for the UN1.

Anyone fill in the massive blanks of knowledge I have regarding this

Actually I have just remebered that someone I know looked into a 6 speed UN1 so I guess this would have have had to have newly spaced gear ratios' not unless this was like an over drive 6th to give a taller gear for cruising, but I distinctly remember the cost being £6,000 some 4 - 5 years 4 ago

Anyone looked into a limited slip? Clee surely with the sort of power you will be chucking out this must be an essential for your Jil

Si21