Best twinchoke carb option for 1300cc X1/9

[GPW]

Firstly, Hello to everyone I am new to this forum and this is my first post.

I have just collected my first X1/9. 1978 Lido 1300. My long term plan is to upgrade the engine to fast road spec using well known combinations of,

Fast road cam
Big valve, ported head
CSC 4-2-1 exhaust manifold and custom Powerflow exhaust
electronic ignition

and so on.

However in the short term I need to concentrate on stopping the bodywork deteriorating but I still want a little bit more BHP so I am going to do the exhaust and hopefully get it to breath a bit better.

The question is what is the best Twinchoke upgrade to put on a stock 1300 engine? In my Vauxhall days the Nova 1.3 sr responded well to a weber 32/34 upgrade will the Fiat respond well in the same way? also if there is a easy, sutable twinchoke upgrade what would be the best jet sizes etc to use.

Any and all advice welcome

thank you

Guy Wilson

[Julian]

The "standard" carburettor upgrade uses a pair of Weber DHLA's taken from the early MG Maestro (before it swapped to fuel injection). The hard part is sourcing a suitable inlet manifold. I don't have any jet sizes I can recommend - I always suggest a visit to a traditional rolling road, a one hour session will see everything jetted up to suit your car rather a generic, off-the-shelf combination.

The 1300 engine responds very nicely to this kind of treatment without other modifications - it isn't so much a case of more power as a stronger response to the throttle and a bit more top-end. You really do need to look at the cam profile and the exhaust before you see much of a change and the cam profile is already quite aggressive (in road use terms). A fast-road cam for the european X1/9s is very aggressive, bordering on a moderate race profile. Just remember Fiat were getting a solid 75bhp from the engine when the likes of Ford and Rover struggled to get 45bhp from a similar capacity engine. 75bhp may not seem much be today's standards but it was significant in the mid-70s.

[James Bowen]

Hello,

I presume the car has the standard 32 DMTR carb fitted. As an alternative to Julians suggestion of fitting a pair of twin downdrafts, you could stay with the same inlet manifold. Then get the larger 34 DATR carb from the 1500 model. The choke sizes are (from memory) 25mm primary and 27mm secondary. I found a decent performance gain on my 1500 by boring the chokes to 27mm primary and 28mm secondary. I also got rid of the choke assembly that obstructs the primary slightly. A free flow air filter was fitted, then had it all re jetted on a rolling road.

The inlet manifold was smoothed and flowed, but not hogged out completely. An aftermarket exhaust system made a big difference to how high an rpm the engine produced power till... an extra 500 rpm at least. Though the exhaust was a CSC model, I have moved on from that. A look through all the posts on these topics, and other forum members projects for Fiat 128's X1/9's and other SOHC motors will give you most of the answers your looking for.

Regards, James

[GPW]

Many thanks for you replys

I will hope fully be going down the twin 40 downdraft route in time. For now however moving up to the carb from the 1500 sounds like a good short term solution. That and a good rolling road tune. I will contiue to read my way through the other members posts with interest.


Thanks again

Guy

[Guy Croft]

This conversion to twin carbs rather than a single twin-choke carb turns to a great extent on the availability of an inlet manifold, doesn't it?

Now I don't retail one and I don't know for sure whether anyone else does, although there have always been firms offering them who'll keep you waiting for months on a one-off order.

40 Sidedraft are way better than 40 downdraft, for the simple fact that there is no flow loss associated with a change in direction between port and carb. And - if you can't get a manifold readily (and I mean decent one that doesn't need 2 days of fettling to get it performing right) fabrication from alloy tube and plate is much easier for sidedraft.

The picture shows the kind of results that can be achieved using an inexpensive Sealey hydraulic pipe bender, hacksaw, files and a bit of 'elbow grease', plenty of cut-and-shut , and a competent welder of course. Final post-weld machining will tend to be needed of the mating flange (flanges in the case of your SOHC of course).

Now many will think, 'wow, I can't do that' (or perhaps 'can't be bothered) but look at it this way. Maybe you learn a new skill and when it's done you can say 'I MADE that'. Which is what this site is all about really, retaining the 'old' skills of making things.

Ah well, not many of us 'Meccano generation' left now..

GC

[GPW]

Hi Guy

Thanks for that. And yes I am very much of the meccano generation. That manifold is fantastic.

I appreciate the benefits of side draft carbs over downdraft, but as my car is a "Lido" I am unwilling to cut the bodywork to make them fit. I understand that PBS in America do a of the shelf downdraft manufold for the x1/9 but I have yet to contact them. I will let you know what I find out.

Regards

Guy

[robert kenney]

FYI, I have talked to PBS and can assure you they no longer deal in Fiat or other automotive products. Not even any old stock items.. Sorry..

I see a fabricated round section runner manifold is a good inexpensive way to go assuming the skills exist.

Robert

[Guy Croft]

Hullo Rob,

thanks for that helpful 'heads up' on PBS,

GC

[Julian]

The problem with a sidedraught setup on the X1/9 is that it doesn't fit without chopping up the firewall between the engine bay and rear luggage bay. You can *just* squeeze the carbs in but you are then left with no way to get trumpets or an airbox in which is a long, long way from ideal.

The option for downdraughts is the best compromise unless you are talking about a serious track conversion. Ironically I did see someone in NZ having downdraught manifolds being made (cast in aluminium) quite recently. He is still at the prototyping stage but does have the first castings back - one set for the inclined engine of an X1/9 and one set for the upright engine of a 128.

These are the manifolds he has so far:


I don't know the man behind this project, just read his posts on Fiat Forum but he does seem to be taking a thorough approach to the matter. I will ask him to post in reply to this thread but you can find his post on Fiat Forum here http://www.fiatforum.com/x1-9/153909-x-nz-3.html

[GPW]

Thanks for the helpfull posts everyone.

Regards

Guy

[ladaspeed]

Hi there - not sure if you are still interested in DCNF manifolds, but I now have some available..

The link is in the for sale/wanted section and on my profile.

Thanks
Dylan

[Guy Croft]

Well done for making that X19 type DCNF manifold set available Dylan!

GC

[ladaspeed]

Well it was driven by being the easiest way to get hold of some manifolds for my X...!

If I can fill a gap in the market at the same time then that cannot be a bad thing.

Thanks
Dylan