Jetting for a turbocharged 1500 SOHC Fiat engine?

Road-race engines and ancillaries - general discussion
Guy Croft
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Re: Jetting for a turbocharged 1500 SOHC Fiat engine?

Post by Guy Croft » January 24th, 2012, 9:51 am

Yes, indeed. The characeristics of a suitable cam for a turbo engine are markedly & necessarily different from atmo units. I have dwelt on many of these critical aspects in my new book.

For the record: An OE Uno T cam (I suggest MkII as the ex lift was rightly reduced) could take a 1500 SOHC engine like yours - with gasflowed head - to well over 190bhp with as little as 12psi boost even on a blow-thru carb and standard turbo header.

A lot of the running problems you have will suddenly disappear...


G

turbofiat
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Re: Jetting for a turbocharged 1500 SOHC Fiat engine?

Post by turbofiat » January 24th, 2012, 5:52 pm

Guy Croft wrote:Yes, indeed. The characeristics of a suitable cam for a turbo engine are markedly & necessarily different from atmo units. I have dwelt on many of these critical aspects in my new book.

For the record: An OE Uno T cam (I suggest MkII as the ex lift was rightly reduced) could take a 1500 SOHC engine like yours - with gasflowed head - to well over 190bhp with as little as 12psi boost even on a blow-thru carb and standard turbo header.

A lot of the running problems you have will suddenly disappear...


G
Could the drivetrain withstand 190 BHP? This car also get's squirrely (torque steer) when the turbo kicks in. It's also a bit dangerous to drive in the rain because the tires spin out of control if the turbo is spooled up so I have to make sure not to kick the turbo in when it's raining. But my turbo Spider does the same thing.

I wanted to adapt an UNO split driveshaft and a guy in New Zealand offered to send me one for shipping but I couldn't figure out how to adapt the 4 speed CV joints to the 5 speed hubs. The other alternative would be to install a 5 speed transmission and hubs from a Ritmo or Yugo 1300 but those are hard to source over here.

One thing I've always pondered over with my L-jet turbo Spider is how much more boost could I run without breaking something. I've been running 7 lbs of boost, 123 HP dynoed at the rear wheels for 13 years and so far I've yet to actually break anything so I have been reluctant to run more boost. One time I turned the boost up to 9 lbs and the transmission tunnel started getting hotter than normal. I normally run about 5 degrees retard and had to back off the timing another 5 degrees or so to elminate detonation but the engine seemed handle the extra power and the stock clutch did not slip.

However I would imagine at 9 PSI the stock headgasket would evenually blow or I'd need to O-ring the block.

Also the dyno showed that the fuel mixture stayed constant throughout the RPM range until it hit around 4500 rpms and started to lean out a bit but the guy running the dyno said I was not in the danger zone. As I understand it on an L-jet system, the injector duty cycle is at it's limit at 4500 rpms. So 7 lbs of boost is about the limit with L-jet and a Malpassi rising rate fuel pressure regulator and stock injectors.

I met a guy at one of the Fiat club meetings who claims his turbo Spider is producing around 240 BHP. I think he is running a stock K-jet from a VW or Audi. If you goto YouTube you should be able to find his car. It's yellow. I asked him about drivetrain issues and he said he has went through 4 transmissions so far. Maybe he needs to upgrade to a T5 from a Mustang GT that you recommend.
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Guy Croft
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Re: Jetting for a turbocharged 1500 SOHC Fiat engine?

Post by Guy Croft » January 25th, 2012, 9:51 am

Certainly not saying you should head for 190bhp merely indicating that power of that kind is readily attainable with the cams I mentioned..

As for the head gasket I would need to see it to comment.

G

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Re: Jetting for a turbocharged 1500 SOHC Fiat engine?

Post by turbofiat » January 25th, 2012, 1:23 pm

Guy Croft wrote:Certainly not saying you should head for 190bhp merely indicating that power of that kind is readily attainable with the cams I mentioned..

As for the head gasket I would need to see it to comment.

G
Would an UNO turbo headgasket fit a 1500 engine and would it withstand 12 lbs of boost?

That DOHC headgasket I purchased from you about 10 years ago for my turbo Spider was impressive but the machine shop screwed up my cylinder head and was afraid to reuse it.
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Re: Jetting for a turbocharged 1500 SOHC Fiat engine?

Post by Guy Croft » January 25th, 2012, 2:45 pm

From memory I don't think the Uno head gasket marries up. Different bore sizes I think,

G

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Re: Jetting for a turbocharged 1500 SOHC Fiat engine?

Post by Joff » January 26th, 2012, 8:41 pm

The rising rate fuel pressure is a good start, but even with that, it's still like trying to find the right sized jet that will work at very high altitude and also at sea level, without having a altitude compensator. Carburetors are set up to flow more fuel as the velocity of air through them increases. I don’t see what is in place to increase the flow of fuel into the air as air pressure increases. I also don’t see how changing the cam will enrichen the mixture under boost. Is the plan to jet it for max boost and let it run even richer off boost? Intended max boost would be good to know if that is being considered.
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Re: Jetting for a turbocharged 1500 SOHC Fiat engine?

Post by PawelS » January 26th, 2012, 8:55 pm

Definitely from MkII Uno Turbo 1.4, cam from 1.3T has other characteristics, not as good for turbo application. You can also use camshaft from Punto GT (except 176B6.000 engine) but you need to make a groove for distributor.
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turbofiat
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Re: Jetting for a turbocharged 1500 SOHC Fiat engine?

Post by turbofiat » January 27th, 2012, 3:37 pm

Joff wrote:The rising rate fuel pressure is a good start, but even with that, it's still like trying to find the right sized jet that will work at very high altitude and also at sea level, without having a altitude compensator. Carburetors are set up to flow more fuel as the velocity of air through them increases. I don’t see what is in place to increase the flow of fuel into the air as air pressure increases. I also don’t see how changing the cam will enrichen the mixture under boost. Is the plan to jet it for max boost and let it run even richer off boost? Intended max boost would be good to know if that is being considered.
When blowing through carbs, everything is a balancing act. By connecting the fuel bowl vent to the bonnet befoer the throttle plate, equalizes pressure across the jets and makes the carb think it's still functioning under vacuum conditions. If the fuel bowl vent is vented to atomosphere, the engine will shut off immedietly as soon as the turbo produces boost.

Renault has had great success with blowing through carbs. Such as the R5 turbo. Sold in America as the gutless "LeCar".

One advantage with progressive carbs is the secondary can be jetted richer for boost. On my Yugo, the turbo doesn't spool up unless the secondary is open. So the purpose of the primary is to provide power during off boost conditions. However I did not take into consideration the importance of the primary jet otherwise. My engine doesn't ping but I was having issues where the engine didn't run well below 60F and would also misfire under boost at or below freezing. With the richer jet that problem seems to be a thing of the past and the turbo builds up boost quicker but there is still room for improvement. I'm not sure if the turbo is sized wrong or if swapping cams would help the turbo spool up quicker.

More power would be nice as long as the drivetrain could withstand it without having to make any serious upgrades like O-ringing the block. Also there is a limit as to how much power you can run through a front wheel drive before the wheels start spinning without a LSD.

I would like to get the turbo to spool up quicker. On my Spider which uses a T3 from a Volvo 240, boost is almost instant. My Yugo struggles to make full boost (7 pounds). I have to push it really hard. The turbo I have on my Yugo came from a Saab 2.1 liter. This was the smallest turbo I could find from an American junkyard. If I had to do it al over again I would have looked for a T25 sized for a 1500 engine through an internet auction site Europe.

Blowing through carbs is not ideal but it can be made to work so I don't see any reason to Megasquirt the engine just for the sake of modern technology. I always thought the purpose of fuel injection was it took care of itself. I'm sure connecting a laptop to the ECU is easier and cheaper than swapping out jets though.

One thing that does baffle me is if this engine has been running to lean for so long why is the gas mileage less than yours? I believe you said yours was getting 35 MPG (US). The best I've seen mine get is around 25 mpg (US). However I haven't measured the fuel comsumption since I advanced the timing 5 degrees and fixed the non functioning vacuum advance. That may make a huge difference.
Last edited by turbofiat on January 27th, 2012, 3:39 pm, edited 1 time in total.
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turbofiat
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Re: Jetting for a turbocharged 1500 SOHC Fiat engine?

Post by turbofiat » January 27th, 2012, 3:38 pm

PawelS wrote:Definitely from MkII Uno Turbo 1.4, cam from 1.3T has other characteristics, not as good for turbo application. You can also use camshaft from Punto GT (except 176B6.000 engine) but you need to make a groove for distributor.
My engine uses the block mounted distributor so the notch in the cam is of no concern.
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Guy Croft
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Re: Jetting for a turbocharged 1500 SOHC Fiat engine?

Post by Guy Croft » January 28th, 2012, 9:47 am

FWIW I made contact with a guy who has a Delta 1600 Turbo with blow-thru carb, he kindly offered to pull open the carb and let me known the settings,

G

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