Fiat Sohc 1.9L stroker head gasket question

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Re: Fiat Sohc 1.9L stroker head gasket question

Post by Guy Croft » Thu Sep 10, 2015 1:24 pm

34mm venturis, might give more power, I would do a back-to-back and see what happens..

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Re: Fiat Sohc 1.9L stroker head gasket question

Post by tmvolumex » Thu Sep 10, 2015 5:50 pm

Elderair,
You wrote: "Ignition set to 10 degrees btdc. and a computronix ignition system giving me 28 degrees total timing above 3800rpm."

Total timing, by definition is: static advance, plus any additional advance such as: centrifugal (RPM) , vacuum, black box etc.

That would make it 10 degrees plus 28 degrees = 38 degrees total.
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by Guy Croft » Thu Sep 10, 2015 8:12 pm

no, Tom

the total adv with that Compu unit is 28 deg..

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Re: Fiat Sohc 1.9L stroker head gasket question

Post by tmvolumex » Thu Sep 10, 2015 11:55 pm

Guy,
I am not sure how the computronic is programmed ie if it has a static programmable setting and a programmable advance setting based on RPM.
If static advance can be programmed in, then engine total would be what ever is programmed in for static plus the RPM advance that was also programmed in.
I was thinking the computronic started with a static advance that was crank sensor position based (physically 10 degrees advanced) not programmed.
An actual engine total advance of only 28 degrees seemed a little low to me, thus I assumed the 10 degrees of static had not been included. I dont know the engine and I don't know how much advance it likes. On the other hand, based on the detonation damage just breaking it in, something seems wrong.
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by elderair » Fri Sep 11, 2015 3:37 am

Tom, the computronix unit is an 18 degree advance piece of magic (as shipped) that takes the place of the distributor and triggers a coil pack . You may then play with the static or base timing. You are correct that there was indeed something wrong with the initial setup. I was drawing hot X1/9 engine bay air into the open style K&N type elements and with close to 11:1 compression and too low octane fuel, and the wrong plugs I hammered it slightly one time and I then saw a puff of white smoke out the tail pipe. No major injury to any components and I got by with a fairly inexpensive learning experience.

So, now with the installation of the airbox the whole mess was horribly rich. I wound up switching down to a 50 idle with the same 130 mains and went to a 210 a/c. Good acceleration past 4,000 rpm so I installed a set of F30 emulsion tubes I had and it is back to running sweet! Just need to verify with the wide band digital a/f ratio gauge when I get it hooked up. Running Sonoco 110 right now.

Any bad side effects that anyone can see to using the F30's. I have F22's and the stock 24's but as stated I was still horrible in transition. I could drop to a 125 main and go back to the F22's or 24's. Seems great though. The airbox sure does make a difference. Can't wait to get it to the dyno. Any recommendations as to how much break in before the dyno trip?
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by Guy Croft » Fri Sep 11, 2015 8:41 am

Tom the SOHC has a faster burn rate than the TC - hence 28 deg total


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Re: Fiat Sohc 1.9L stroker head gasket question

Post by tmvolumex » Fri Sep 11, 2015 4:30 pm

elderair and Guy,
Thanks for the replies, this has been a informative exchange of information. Your ducting turned out well in both performance and appearance. Break in will depend on ring type, Guy can answer that question better than I can. What type of air filter is under the housing? Is the housing a off the shelf part? I may have an application for one, depending on the size.
Good luck in your tuning adventure.
tom
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by Guy Croft » Fri Sep 11, 2015 7:37 pm

please call me about jetting, you are welcome to publish what I tell you,

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Re: Fiat Sohc 1.9L stroker head gasket question

Post by elderair » Sat Sep 19, 2015 1:11 am

Tom, the plenum is a "bit of italy" BOI performance part available from them and I guess you could bolt it to any base plate that it would cover. I am using a 6.5" cone filter on the end of a 4" duct sitting in the left side vent area.
Thanks Guy, I will give you a call at your convenience and get the recommendation for jetting. I am currently installing the 34 Venturis' so that will be the setup I will be jetting for. As for accelerator pump cams, I'm not sure if too much is available and there is no pump bleed hole like in the IDF if I am not mistaken? That would leave pump nozzle size to adjust the amount of fuel delivered from the pump? Thanks.
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by Guy Croft » Thu Sep 24, 2015 5:31 pm

I think Kent's short primary pipes on his 4-1 header may to be blame here, often the case when all the jetting efforts bring no benefit ...

there is little in his setups with jets that stands out as being likely cause..

we talked by phone earlier this week,

more from Kent soon I hope..

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Re: Fiat Sohc 1.9L stroker head gasket question

Post by elderair » Sun Sep 27, 2015 2:32 am

Guy, just wanted to let the forum know what I discovered today in my allotted Fiat X1/9 work time. I was running the engine with my air box off and noticed fuel puddling in the carburetor for the 1 and 2 cylinders. Upon removal of the carb top I found the brass float partially full of fuel which explained me chasing the jetting all over the place! Better late than never but I feel like a clod for not noticing that a bit ago.

I went ahead and swapped out the Italian Webers with a new set of Spanish webers I had on hand with the plastic ish floats which I really didn't want to do but for lack of a brass float. I jetted as follows; Venturis' 34; Mains 145; A/C's 200; Idles 50; aux 4.5. ET's F24. Spark Plugs NGK B8EGV Computronix ignition with 10 degrees base timing. Sunoco 110 leaded fuel. Allison Ceramic header with a hush power muffler. BOI airbox and 4" duct to the left wheel side vent with a Spectre 6" dual cone filter.

Went for a road test and took it up to 110mph at 7,000rpm with a bit of a bog at 4,000rpm.
Second run swapped out the 145 main jets for 150's and 195 A/C's.
Ran 120mph at 7500rpm and pulled hard past 7500rpm in every gear with no indication of stopping at 120. I just ran out of good road. I would say that this motor likes the 34 Venturis for sure. Light brown plugs and may need just a tad of richening on the mid range. Ever so slight. Maybe a 190 A/C. Still need to get my wide band A/F hooked up and do some comparisons with my plug colors. Have a Dyno session set up for one week from Monday so I will be sure to post the results as soon as I get them! Thanks for your time and thoughts on this Guy. I still think the exhaust can be optimized for this motor with the longer tube header and less back pressure but the dyno will show the weak areas.
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by Guy Croft » Tue Sep 29, 2015 11:21 am

MODEL POST!

Great work and good report, thanks Kent!

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Re: Fiat Sohc 1.9L stroker head gasket question

Post by elderair » Wed Sep 30, 2015 2:58 am

I was able to get in to run my dyno run today and here is what I found out! Now I can hopefully get some step by step analysis and correct any issues one by one. Firstly, I ran the dyno with the 150 mains, 34 venturi, 185 a/c, 55 idles. Went back to the Italian webers with this jet combo due to imbalance between cylinders on the Spanish webers. The throttle plates and or shafts need a bit of tweeking due to flow imbalance. As the dyno shows the A/F is below the 12:1 line so a good bit rich. I plan to correct this first and run again. Then I will be needing next step advice. Thanks.
https://youtu.be/2_1_M5hp7NE
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Re: Fiat Sohc 1.9L stroker head gasket question

Post by Guy Croft » Wed Sep 30, 2015 4:20 pm

well done Kent, thanks for the vid!

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Re: Fiat Sohc 1.9L stroker head gasket question

Post by elderair » Thu Oct 01, 2015 1:20 am

Guy, thanks for your valuable input to my project. Once I get another dyno pull in I will post results.
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