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C20 Let In Cav Saloon (Advice)


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hi i am looking for advice on converting my cav to c20let power will i hav to seam welded it for starters?? and what axle,brakes,mounts im basically looking a shopping list so i can get everything i need. any help will be much appreciated a full project thread will follow shortly when i work out how to upload pics . cheers chris

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You'll need a Manta 1800 sump (RetroPower are having these made very soon) and gearbox (or Carlton box if you want to rig up a non-cable speedo drive), exhaust manifold for RWD, engine mounts etc

Standard axle will take it, front brakes will want upgrading but the choice is yours on that one, lots of options available. Use the search on here.

As for photos, use photobucket.com, upload the images then hover over the images in your album and copy the text that starts %7Boption%7D into your reply on here

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Carlton GSI box has a different bolt pattern so won't fit the turbo lump. Gear Box wise you want either a 1.8s Manta Box as this will bolt straight up but might no last long. Carlton Mk3 2ltr box but you might have to make the trans tunnel a bit wider to take the bigger bellhousing. and play with the prop.

Omeaga 2ltr or V6 box is also an option, you will have the same problems as the Carlton box with the added bonus that the Omega box doesn't have a speedo drive so you'll need to knock up an electric speedo & pickup.

Another option is the Ford Type 9 box with an XE bellhousing, box is a bit longer i think so you may have to move the hole in the tunnel for the shifter.

As already said you'll need a big wing sump, mega bucks for an orgnial, if RP are having some made they should be alot cheaper and be a good fit.

Exhaust, being a turbo you may need the front section made as a one off and you may need a one off engine mount on that side as well, Intercooler will be required plus all the pipe work.

There is alot of parts to either buy or have made. Might be an idea to read Mickappy bulid thread




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The whole job rather depends on your target horsepower.

We tend to suggest spending more money upfront and building it very strong as you WILL want more power, and these engines can make a hell of a lot if you want it (500+ hp is no problem with the right mods)

Starting at the rear and working forwards, if you are happy with stock power and roughly stock boost, then a standard axle IN PERFECT CONDITION, will do the job, just! BUT you'll prob want an LSD in it, and pretty much all standard axles need rebuilding. The bearing, seal and shim kit is £250 excluding the halfshaft bearings, cheapest I can get these at the mo is around £80 each, and the labour to rebuild is usually around the £200 mark, so its over £500 before you add the diff, at around £800. You can just fit a stock axle, but the pinion bearings are weak, and prone to giving problems. Also if you fit an LSD, you'll have to get the diff set up, and then if it needs rebuilding, get it set up again, paying twice for the same job.

There are a number of alternative axles, though none that fit without some body shell modification. If big power is ever going to be on the cards, then we tend to use the salisbury 4HA unit, usually from a reliant scimitar GTE, post 1976. Jaguar lsd units fit into these with a couple of small mods. The stock axle is very cheap at around the £100 mark, the correct width, and a suitable, good, used jaguar diff of the correct fitment and ratio is circa £200 (pm or call retropower for info on this, too much to go into here!) They will all need rebuilding due to age, and you will need to add a rear disc setup, but then you would with the stock axle too. You will need to add mounts to the shell (we use an escort mk2 4 link setup usually) and there is a bit of work in stripping the axle down, building it back up, welding on mounts etc etc.

Moving forward, if you change the axle, you'll need a suitable propshaft!

Forwards again, I'd suggest forgetting the manta 1800 gearbox. They are on their limits with 200hp, and they are not even cheap now. I have no idea why people always suggest ford type 9 gearboxes. In standard form they are WEAKER than the standard manta 5 speed. The only reason to use one is if you want to go for a competition gearbox, as the ford unit is the mainstay of rwd competition gearboxes, that said, even the heavy duty "pro" quaife gearkit (straight cut, new mainshaft, deffo not for road use) is only rated to 275hp.

For road use, I would suggest a Vauxhall Omega gearbox. The ones from 2.0 and 2.2 omegas will take 350hp with no problems, and over 400 as long as you are not drag racing (this is from experience, not guessed). These are the boxes marked R25-R28 on the casting near the bellhousing end. The box from the later 2.2 dti (diesel, vauxhall 4 cyl not bmw 6 cyl ones) supposedly has the stronger R30 gearkit inside (still marked R25-R28 on the outside), as do the 3.2v6 ones, but we tried a 2.2 diesel box and it exploded (drag racing with 550hp) just the same as the previous 2.0 R25 one did!

Whatever though, these are MUCH stronger than the manta 1800 or ford boxes, and you can pick them up for £50 to £100. As lon as you don't get the 2.5 diesel variant (which used the bmw engine) then all the manual boxes bolt to the LET engine. You'll need a spacer for the clutch slave cylinder setup, but we supply those off the shelf (£45 delivered) and you'll need some sort of speedo drive as these cars drove the speedo off the abs system. We fit a magnetic pickup on the gearbox mount picking up off the gearbox output flange and use it to operate an electronic speedo, either hidden behind the stock dash so it looks standard or not, depending on preference.

Clutch wise, an uprated "fast road" LET unit will be fine to around 300hp, then a paddle version still with stock type uprated cover will go up to 425hp or so. We've used techniclutch and got on fine with them. You can use the stock LET pot type flywheel but they are heavy, We tend to use the flat type earlier xe flywheel, and if you do you will need the friction plate to be a normal LET type and the cover to be a non turbo, early, flat type one. if you call techniclutch and explain they know what you need, we've had a fair few from them. The standard omega release bearing is fine with all the above.

On the engine itself, I'd STRONGLY recommend going for a top mount turbo. It makes the whole setup much easier to work on, and stops it coooking everything in the engine bay. Its possible to use a nissan 200sx S14 top mount manifold, with the flange cut off, bent slightly, then rewelded to a vauxhall xe flange, but beware some of the chinese ones are a bit thin! We tend to use a bottom mount stainless manifold from autosprint, cut the flange off and invert it. Either that or fabricate one from scratch.

There's lots more, but I have to go!

Edited by Retro Power
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PS yes we will be doing big wing sumps (cast alloy, identical to original manta 1800 items but with very slightly thicker mounting flange for extra strength) we have the first off casting in the workshop now, production items should be in stock in March.

thanks for that much more clued up now al give u a shout around that time then for the sump im going to go 4 the omega box so will need the spacer aswell

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If you look through this project thread on our website you'll see the same conversion done on a chevette.


It's identical to the manta/cavalier job really, only easier in a manta/cavalier as there's more room!

The transmission tunnel does NOT need modifying in a cavalier for the omega box other than the need to cut out a little for the gearlever, same as if you were putting the 5 speed manta box in. You need to cut a couple of lugs off the side of the gearbox. There are 4 of them iirc, they are only used for mounting it to jigs in the factory, and the front ones can be chopped off, this gives clearance on the mounts in the tunnel.

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