Jetting for a turbocharged 1500 SOHC Fiat engine?

[turbofiat]

I've been desperetly searching for this information for 7 years now.

What would be an appropriate size primary jet for a turbocharged 1500 SOHC Fiat engine?

My 32/32 DFTA was jetted for a 55 BHP 1100cc engine but is now on a 75 BHP 1500cc engine. It currently has a 100 primary jet with a 250 air corrector.

I need to know if this jet is too small for this displacement. I've found bits and pieces on the web and seem to believe a 120 primary jet would be more appropriate. At least what I've read when it comes to DCOE 40, IDF40s and 34 DMTRs. Would the same hold true for a 32/32 DFTA?

[Guy Croft]

James, 7 years???!!

I suppose that may well be the case. I will have a go if you like but I want some photos of the carb and I need to know the choke sizes.

The X19 1500 is some 85bhp on a Weber 34 DATR. Why is yours 75bhp? Because of the small carb? Some idea of the engine spec would help me.

G

[turbofiat]

James, 7 years???!!

I suppose that may well be the case. I will have a go if you like but I want some photos of the carb and I need to know the choke sizes.

The X19 1500 is some 85bhp on a Weber 34 DATR. Why is yours 75bhp? Because of the small carb? Some idea of the engine spec would help me.

G

I'll have to dig that information up. Hopefully it's in the Weber Haynes manual. This 32/32 DFTA maybe US spec only. It was used on 76 to 80 US spec Fiestas, 90s US version Escorts and the Yugo 1.1 liter.

As far as 75 BHP versus 85 BHP:

1500 US fuel injected versions had 8.5:1 C/R and milder cam profiles which resulted in 10 less HP than the UK versions.
1500 US carbed versions in 79 and 80 had 28/30 DHTA carbs and allot of pollution control devices that resulted in even less. Something like 60 to 65 BHP.

[Guy Croft]

I'm a bit confused, since you have a couple of rather similar threads going on - you have two engines of 1500cc but this particular one is atmo and the other is turbocharged?

Please clarify if you'd be so kind. It would be a good idea to state 'turbo' or 'atmo' as appropriate in the subject line. You can alter it with the edit function.

G

[turbofiat]

I'm a bit confused, since you have a couple of rather similar threads going on - you have two engines of 1500cc but this particular one is atmo and the other is turbocharged?

Please clarify if you'd be so kind. It would be a good idea to state 'turbo' or 'atmo' as appropriate in the subject line. You can alter it with the edit function.

G

Sorry for the late reply. I thought I reported an update on this problem. No it's the same 1500 engine I'm talking about.

I stepped up from a 100 to a 120 main and noticed a HUGE difference in how the car runs. It runs so much smoother now and it even builds up boost quicker.

I can now drive this car at temperatures below freezing and it runs as well as it does at 95F to 100F. By all accounts this car would be struggling to run at 32F. At freezing the misfiring would start to happen under boost. I believe the backfiring was related to the misfiring.

I've got a 115 I may try when the temperature dips down below freezing and see how that does. As of right now, this is the best this car has ever ran at these temperatures so I'm afraid to start messing with the jetting anymore.

[Guy Croft]

OK turbocharged. Now I would like some photos please, get a clearer idea of the installation.

G

[robert kenney]

I would keep going richer not back down. You were clearly lean at 100, now @ 120 it runs well but I doubt you're there yet.....

On a side note the main jet increase reccomendation was given 3 months ago....

[Joff]

Many years ago, a guy on one of the Yugo forums was building a turbo yugo and was having trouble getting the fuel right with a blow through carb. He eventually switched to megasquirt programable fuel injection and was very happy with it. I've been using MS 10 years or so, and I'm never going back..... Hmmm that might mean I have some jets for you!

[Guy Croft]

"trouble getting the fuel right with a blow through carb..."

yes, I am hoping to get the kind of information I need to be helpful here but struggling as - sorry - the information re engine setup/installation is insufficient for me to comment.

To offer diagnostic one needs to know almost everything (in concise list layout) about the engine and inlet/ex system.

Turbofiat - your kind attention please!

G

[turbofiat]

"trouble getting the fuel right with a blow through carb..."

yes, I am hoping to get the kind of information I need to be helpful here but struggling as - sorry - the information re engine setup/installation is insufficient for me to comment.

To offer diagnostic one needs to know almost everything (in concise list layout) about the engine and inlet/ex system.

Turbofiat - your kind attention please!

G

Sorry for the lagtime between posts. My job does not permit me to be at the computer everyday.

Here are some specs:

Engine:

Stock 1500cc , 8.5:1 C/R (US spec), I'm not sure about the cam profiles but they are milder than non-US spec 1500s. Based on what I've read lower compression ratios and milder cams work toward the advantage of turbocharging. Some may beg to differ.

Clutch:

Yugo 4 speed transmission, 4 speed ring gear mounted on 1500 flywheel, stock 1500 clutch.

Fuel system:

Weber 32/32 DFTA , 50 idle jet, Main 120, Secondary 150. 250 air correctors (both mains).
Fuel pump: GM T.B.I. (20 PSI dead head pressure) used on 1980s GM cars, Now used on the Lada Niva?
Fuel pressure regulator: Malpassi 1:1 sourced from a 1985 Maserati Bi-turbo.
Fuel vent bowl connected to carb bonnet to equalize pressure across jets.

Turbo : T25 sourced from 1991 Saab 9000.

Ignition system:

All stock Bosch except for GM HEI 5 pin control module (78 to 81 V8 GM vehicles) for 5 degrees boost retard.
Magnecor plug wires, NGK plugs.

Here's the photos you requested. Not the best example of a carb bonnet I realize but the other alternative was to cut a hole in the hood/bonnet and build a buldge around it.

Also some photos may contain bits and pieces of the L-jet fuel injection system. I was thinking about going Megasquirt but changed my mind.

Yugo.JPG (72.48 KiB) Viewed 1416 times

Yugo (1).JPG (62.93 KiB) Viewed 1416 times

[Joff]

I didn't see mention of you raising your fuel pressure. I don't have the stock specs handy but think it's only a few psi. Having the proper jet size will not help you when your boost pressure is higher than your fuel pressure! Why did you decide against the Megasquirt? You'd have plenty o fuel pressure with the regulator giving you more as your boost pressure goes up.

[turbofiat]

I didn't see mention of you raising your fuel pressure. I don't have the stock specs handy but think it's only a few psi. Having the proper jet size will not help you when your boost pressure is higher than your fuel pressure! Why did you decide against the Megasquirt? You'd have plenty o fuel pressure with the regulator giving you more as your boost pressure goes up.

The static fuel pressure is set at 3 PSI and the fuel pressure regulator raises the fuel pressure 1 lb accordingly to every pound of boost.

I know I have enough fuel pressure because I rigged up a pressure guage to my windshield and monitored the pressure. So around 7 PSI of boost my fuel pressure guage reads 10 PSI.

One problem I had was trying to find a fuel pump that would work. The original pump I tried used created too much flow so the regulator couldn't dump the fuel back to the tank quick enough. The result was fuel pressure spikes when the turbo kicked in. Based on memory this pump produced around 150 US gallons per hour.

Maserati (what this regualtor was sourced from) actually used a fuel pump from a fuel injection system (~50 to 60 PSI) and somehow managed to get it to work with a Weber carb. I have no idea how this regualtor would reduce the fuel pressure down from 60 PSI to 3 PSI.

I finally found a pump for a GM T.B.I. system (also listed in the book as a Diesel pusher pump) that created around 130 US gallons per hour. When tested it deadheaded at 20 PSI.

I still had to connect my fuel return line to the 5/16" fuel vapor line which originally went to the charcoal canister. The orginal 1/4" return line was too small.

So I have 8mm going in and 8mm going out.

As far as Megasquirt goes. I just didn't feel like building an ECU and trying to get it to work and all. Expense. I turbocharged my 1980 Fiat Spider and it has L-jet and works well so it's not like I am against fuel injection or anything.

I guess more of a personal challange because allot of people said it was impossible to turbocharge a carbed engine.

[Guy Croft]

To be brutally honest I think you need to change to a different cam which has absolutely the right characteristics for turbocharging.

G

[Joff]

US spec Fiat 1500 SOHC cams are 12 52 52 12 Same as my supercharged yugo.

[turbofiat]

To be brutally honest I think you need to change to a different cam which has absolutely the right characteristics for turbocharging.

G

So a cam from an UNO turbo mk1 or mk2 might be more suitable?