Technical brake caliper swap

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Technical brake caliper swap


New member
Dec 21, 2005
what i want to know is if theres a differace in size between the front and rear calipers (i asume the fronts are lager) if so is it posible to put a new set of fronts on the rear? also how difficult would this be and what advantages or disadvantages would this swap pose? any advice is very much appriciated(y)
front caliper is 48mm piston, rear caliper on X19 is 34mm piston... simple hydraulics tells you that you will have a lot more rear brake bias with a 48mm piston... will this suit the motor sport you have in mind?

biggest problem is loosing your handbrake.

not a usual swap over unless your circuit racing and have larger front caliper pistons than the standard.

thanks steve you come to the rescuue again.i just picked up a 79 yester day that ive been looking at for some time,not a perfect car but a really good driver,so thats why ive been looking for tech help so franticly lately, i have a vision of what i want,just dont have the knowlege i had an 83 some years ago and every thing was bad,then i got suckered into an 81? 82? which didnt run ,so i want to make my dream come true finally, so i really appriciate the help
The tried and tested tactic is to use similar capliers from the old 131 but I imagine they could be rather hard to find now. These give a slight increase in rear bias *and* retain the handbrake mechanism.

Personally I never found any need to increase rear bias when using the stock front blocks - upgrading to the more reliable Uno Turbo front calipers (same piston bore) made the situation much, much better but that too is becoming a hard thing to find (calipers are easy but the mounting frames are exceptionally hard to find).

Currently I have big Tarox brakes on the front and standard front brakes on the rear.
well i have 2 new front calipers and wanted to know if -a its a direct mount to the rear bracket & -b how it will affect the handleing doring hard brakeing in the turns. i live near the beach here in NC but i venture up to the mts on a regular basis and drive quite hard on the parkway ;) i just dont want the ass end coming out again
Close... it's actually the 132 and 125's that use the larger piston rear calipers, the piston size on these are 38mm, so yes it shifts the bias rearwards by a small amount... I have both my X19's set up like this as I also have larger front rotors/pads so it balances things out again.

I believe the Montecarlo/scopion also had the 38mm rear pistons, but I'm not sure if that's a S1 or S2, as we never had the Monte/scorp here in Australia.

I personally would think that putting front calipers on the rear for a street driven car would be quite foolish, bordering on stupid... no E brake and equal brake proportioning front to rear.... that's just not how it's done.

Usually when 48mm piston front calipers are fitted to the rear when circuit racing, some sort of bias regulator is installed in the rear brake circuit, or some sort of adjustment provided between the two master cylinders usually used... otherwise the rear will have too much braking force.

The other thing to consider is that you will be displacing considerably more fluid thru the master cylinder, resulting in an increase in pedal stroke.

ooh i guess that makes some sense i just thought that w even braking it would make it handle a bit better w/o having to mess w suspension and adding swaybars and such. im on an extreamly low buget and want some added performance in all areas but i dont know any of the basic tuning tips so common to these cars , as spending the last 14 years in an area were there wasnt a large X1/9 fan base:(So knowlegable fiat entusiest were few and far between. plus the only fiat mechanic around for 200 miles was more into the 124's and wasnt of much help so if theres any thing that you could fore see or just some common stuff like for instance (the only one i know ) intalling a togle switch for the fan, please share. by the way i was looking for that intake and i found a guy that had 4 DCNF manifold from sprint for X's $50ea US but the post was from 04 so i tried to email any way to see if he might still have one address was no more:( that really sucked i was so exited at the prospect. oh well i'll just have to keep looking thanks Steve
Sorry - typo on my part. Yes *132* not 131 as I managed to post earlier. (teach me to read through everything before I post it)

If it is shoestring tuning tips you are after then I can recommend a few sites. First of all is the xweb community (, second is the sporting fiats club ( Both of these are free to join but my last option requires membership: the X1/9 Owners Club ( which has a long, long history of such things but are not quite the organisation they used to be.

For full on racing tuning I would also suggest you check out the mirafiori site ( and look in the racer's forum (used to be called the X1/9 racers forum).
thanks for the links and suggestions, i just want to do what the faactory should have from the get go, X's are great cars and alot of fun, im onto my 3rd now and its time to really have some fun but i certainly dont want to Afro-engineer it ,just some low cost stuff for someone w/o alot of know how can do
FOR NOW! that is thanks again
There are two evolutions of the X1/9 you need to know about then - the first is how it started.

The X1/9 was originally penned to take the twin-cam engine but Fiat insisted it should be a smaller engine. I've never really understood the logic here but I suspect it has something to do with cost. The X1/9 never really made a profit for Fiat as it was (at the time) one of the most complex vehicles they had ever constructed.

The second evolution you need to know about is the last version of the X1/9 that Fiat built that was never sold to the public. The Uno turbo engine was intended as a powerplant for the American market to replace the asthmatic 1500. It all fell apart because Fiat pulled out of the USA before it was finished.

The important thing about both evolutions is that in the first instance the car was designed to fit the twin-cam engine and in the second the engine was designed to fit the car. Both provide "cheap" upgrades - my preference is the turbo engine as it doesn't upset the weight balance of the car. The X1/9 turbo prototype had some engine bay modifications but everything on the Uno (MkI) fits in the space available.

If you can get your hands on an early MkI Uno Turbo lump and gearbox (with ancillaries) you have an instant power upgrade to 105 bhp in stock form. The best bit is that the engine was designed to run at 1bar boost, not 0.6bar as it did in the Uno. A few *very* minor alterations and you have about 120bhp (rolling road session recommended to ensure correct fuelling). If you can do the work yourself and are not afraid to tackle the wiring (that is the hard bit) you can easily do the install for under £1000 - possibly even half that depending on the cost of the donor parts.

If you just want a minor power hike you can take the oddball route and just fit the Uno Turbo head to the X1/9 1500 (you need a late engine though) and this gives you fuel injection with scope for all kinds of modifications on the normally aspirated route. Federal spec engines use the same head already but had a lower compression ratio and all sorts of emissions control systems strangling the power output. With a mild cam I would be very surprised if you couldn't get a good 100bhp but the cost is likely to be nearing that for a full turbo conversion. A different twist on this is that the same turbo setup can be bolted straight onto a federal spec engine and run in a low boost configuration thanks to the same lower compression setup.

Converting to the twin-cam engine is ironically the most expensive option although you can get a good 130bhp from the Abarth version of the 2.0 twink. You need to use IDF downdraught carburettors though and not DCOE as the X1/9 engine bay is not quite large enough. The manifolds are still available and the carbs can be sourced from the MG Maestro (if you can find one). The difficulty is you need a sub-frame to mount the engine (Avanti used to sell their own design) and you would need to upgrade the suspension to tackle the extra weight.

In all cases a suspension upgrade would be ideal anyway for handling purposes as stock suspension would be pretty much shot anyway by now.

Brakes have already been mentioned and I think you get the idea. Just remember to fit braided brake lines and get the caliper sliders working cleanly.
cool it all sounds promising but a little over my abillities im afraid:(besides i dont think i could come across an uno motor to easily here in the states, but i have heard that putting a 1300 head off an early X or a Yugo would bump the compresion up. but what all is intailed in this type procedure, bec if its as simple as ubolt one put the other on then hell i know where i could get a 1300 Yugo head tomorrow for like 25-30 US at the junk yard down the street.(i think i would perfer somthing along this route) but what kind of gains could i expect and is it worth the trouble? you mentioned mild cams i have an article from Grassroots motorsports that talks about cams for fiats (the 128 family)and lists cam profiles,but i dont know understand them,for example 30/70/70/30 they say this spec is greatfor mild street cars and yields impressive power would this speec work for me? and agaain what couuld i expect? i forgot, i must add i plan on useing headers at some point in the future and diching the cat soon. thanks again
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Being in the states does put a damper on the Uno Turbo route (it has been done though - as has just shipping the turbo parts out and fitting to a standard FI engine).

On the subject of cam timings I suggest you take a read of this: very informative and a good reference.

For mild road use you want a camshaft with good duration and lift but you don't want to go mad on overlap. Overlap is great for serious on-track performance but tends to kill driveability. The faza cams are very highly regarded and certainly very well proven.

Sadly a camshaft by itself will not give you the kind of power increase you imagine, you need to look at the cylinder head as well (the Yugo head is a good swap for a stock cam). Ideally larger inlet valves and some porting plus balancing the flow and cc of the combustion chamber. One thing worth noting is that if you do have the FI engine I think you'll find that the Yugo head does not come with the pockets cut out of the manifold face, if you are on the carb setup it isn't an issue.

You need to ditch the emissions control setup and raise the compression ratio slightly. If you can find one the european version of the engine has everything you need in it - higher compression pistons and an improved cam profile compared with the Federal spec version (not as good as the Faza cams though). I shipped a camshaft out to a friend a couple of years back but I don't know what happened to it after that.

You really need proper length headers to take advantage of the other modifications suggested and the same goes for the induction system - the stock carburettor is a good item but you can't get much more from it. An electric fuel pump is a good investment at the same time to bypass other "issues" that the car tends to have.

If you read Grassroots then I'm guessing that you are at least aware of most of this as the X1/9 has a long, long tradition associated with the magazine and the personalities that drive tend to be more than helpful in getting others on the right track (figuratively that is). Autocross would seem to be the ideal place to look but not all regions have X1/9s running in them anymore.
man that link is really really helpful im gonna have to read it a couple times to fully understand but thanks:) oh by the way i an running a carby and i have a DCNF i would like to use but finding the right manifold for a single is proving kinda difficult i have another thread up about that Steve C was really helpful, but if you want to check it out and add anything, its on the first page of this site. abbout headers for best alround would you recomend 4-2-1 or 4-1 ? i likee to send the tach high bec cause i love the sound of italian engines so i figure a 4-1 would help in that aspect, but then again around town, or on twisty mtn roads and up hills i figure a 4-2-1 would be best, whats your take? and in not botheerer w/ emmisson testing wheere i live,so i thought abouut stait heders, but figure id be too loud for the street, so should i just stip-out the cat,and run headers to a new muffler?, or, and lastly, would a "cherry bomb" sound good or would it slill be to loud
If you really want the engine to rev your main hurdle is not the header configuration. A 4-2-1 setup gives you a better spread while a 4-1 focuses the reverse pulse to get a specific peak.

If you want revs you need to do two things - first of all strip the engine down completely to a bare block and then cook it in a kiln. When it comes out measure the alignment of the bores. If spot-on then you have a real chance at building a screamer. If there is any misalignment you may as well not bother. Sadly this is a common fault on all of Fiats engines but it doesnt tend to show itself until the engine is thoroughly heated and you try to get big revs. The misalignment saps power and it gets worse with more revs.

The second thing you need to do is shed weight in the bottom end and get it properly balanced. The rods and pistons in the 1500 are pretty good stock (no substitute for forged pistons but we are on a budget so out of the question). A light flywheel and matched rods/pistons will give you scope for a lot more revs without risking the engine.

I've been lucky and all of my X1/9 engines have revved to just short of 9500 rpm stock but then again I had a nasty habit of blowing head gaskets...

I know stripping an engine down is a real pain but ultimately for the cost of a set of gaskets and core plugs it isn't an expensive operation - just time consuming. Get it right and all those other upgrades will be really worthwhile.
well s@#! i was typing a post but hit some thing an away it went but basicly i dont have acsess to a kiln, but this is what i had in mind a light weight (or macined stock ) flywheel, a single 36 DCNF w/ K&N on a 1300 head, w/ a 37/71 or a 35/75 spec cam, running a PBS 4-2-1 downpipes into a flowmaster(or comprable) w/o a cat what do ya think?
Re: engine build

wow like i knew.. you really got your s#@! together:) is there a book or article that really spells out what to do? i mean cams, heads, exaust, manufactures to use,sizes, profiles,ect... i mean really tells me what to do.keep in mind ive never raced or tuned any thing,so this is my first atempt and i want it right. thanks.....i still cant find a manifold!:(
The "bible" for such modifications used to be the "project X1/9" book from FAZA but it is heavily tailored towards developing an SCCA racer rather than something more general. On top of that much of the accepted wisdom in there is largely out-of-date and while it is not valid I doubt it would actually prove of much value to you - if you could find a copy that is!

The X1/9 owners club sell their accumulated wisdom (in the form of magazine articles compiled into a book) but it is fairly incoherent and does not distinguish good advice from just mediochre advice.

To a large degree the home enthusiast tuner (of X1/9s) has been left to fend for himself and work out the best options and how to perform the operations needed to get there. There are more than a few detailed guides on the internet that tell you what needs doing and to some degree how to do it but I've yet to see one that gives you a step by step set of instructions.

If you've never done anything like this before then you need to do some general reading first on what does and doesn't work and more importantly why. Guy Croft has recently published a book on the SOHC fiat engines that would cover (in great detail) much of what you would want to do to the engine. I don't have an ISBN number for it but Guy is contactable through this forum if you want to discuss it with him in person. Much of the research on the subject was done with the help of experienced X1/9 tuners so you can be sure that there is relevant material there for you.
thanks man!!! im not wanting to cheat the system or anything ijust dont want to tear s#!@ up and ruin a perfectly good car im really glad that guys like youu and others are so willing to help the novice ( wait im not even a novice yet) help out so much its real good of ya, im learning more & more every day thanks a load...Guy Coft....doesnt he have a web site,i think i cam across it on a fiat search.if you come across the link or chat w/him on here please ask him to get intouch w/me on this. thanks man
Re: x19 engine build

P.B.S. engineering (not FAZA) in the states still sell their book, it would be $10us well spent, but as Julian pointed out, it's written from a FP/GP class racing perspective... but that sort of suits you anyway, as these classes are limited to a single 36/40dcnf carb.

PBS in the USA know a fair bit about the sohc engine, you would be best contacting them, they sell cams etc.... but like just about everyone else, will mostly tell you what they can sell you.... and will only recommend what they stock, rather than what may be the best for the job...

gc is seriously bad for this, I doubt he could / will tell you much except that you should buy his bits....

FAZA (Al Cosentino) isn't in business per se any more....though he occasionally flogs parts (mostly way overpriced) on ebay from time to time. He was simply an importer / reseller of parts anyway, and from an engineers perspective, is quite weak on his knowledge of engine prep. This is pretty plain to see if you read his books, he used to buy finished race cars, and then have someone else do most of the work....

If you have limited finances though, most of this will be way over your budget anyway, apart from the "Project X19" book....

I thought my link to that older post pointed out what you should do.... I thought it spells it out quite clearly....I've only been building Fiat engines for 25 years, my dad has been fixing Fiats exclusively for nearly 50 years.

You can also get good results using a mix and match of off the shelf parts from the Fiat parts bin... but unfortunately in the USA your standard parts are not really up to the job, having been tailored to suit the USA market and generally are crap from a performance point of view.

A 1500 with 1300 type pistons to raise the CR, a euro 1500 cylinder head with standard valves and a PROPER valve seat job, a euro 1500 or 128 coupe/rally camshaft, a twin outlet exhaust manifold, a vernier adjustable cam gear, A single 36 or 40 dcnf and manifold to suit, electronic ignition, and a large bore custom exhaust system.... and you should be up close to 90rwhp without too much effort.... with an improved cam getting closer to 100rwhp.... which will be a noticeable jump from the 60 or so RWHP that your USA1500 has as standard... I build several engines like this a year for customers.

biggest bang for the buck is an exhaust manifold change.... nothing but this accounts for 9hp according to Fiat, your USA cars have a single outlet manifold and a convoluted exhaust system that strangles the engine.... do this first, it's the most effective singlechange you can make.

I have some new performance cams to sell, that I imported from Pittatore in Italy, Pittatore actually made the camshafts for Alquati to resell....

Alquati are now defunct, so this avenue for performance parts is drying up, though you still see the odd good piece come upon ebay...