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 Post subject: FastKid's 260
PostPosted: Mon Oct 31, 2016 11:06 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 13270
Location: CT
Andy,

I'm trying to remember what I saw you do to your front SU at the picnic. When you raised the piston with your finger, did something stick out the top of the carb? If I recall correctly, you had the damper piston out (unscrewed the black finger knob on the top) and when you raised the internal piston with your finger, it....what?....fell back?...stuck up?....let a needle stick out the top of the carb?

Sorry for not remembering but somebody called me across the lawn and was walking away and you had several experts there with you and more walking toward you. I knew you'd be ok but I never got back to you while you were playing with it. Long minutes afterwards I asked myself, "Wait ~ what did I just see?" but you were gone from the car by then.

Nothing is supposed to stick out the top of the carb when you raise that piston with your finger. If anything IS sticking out, it might be your metering rod (altho I've never heard of that happening). The rod is supposed to be securely screwed into the BOTTOM of the piston, so it can enter the jet and meter the fuel flow. Please tell me I didn't see something sticking out the top of your SU?

Here's a diagram of what your Hitachi SU should look like inside.
Top "H" diagram (HJG-46-W) applies to you. Locate and study the jet needle and the jet, and reassure me that's not sticking out the TOP of your carb? Tell me I don't remember seeing that, please?

http://sucarb.co.uk/technical-h-type-ca ... er-diagram

Frank

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 Post subject: Re: FastKid's 260
PostPosted: Tue Nov 01, 2016 8:23 am 
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Posts: 36
If I am remembering correctly it binded at the top of its travel. I believe he put an additional washer on top of the piston to prevent it from travelling all the way up, thus avoiding whatever sticky spot was at the end of the travel.


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 Post subject: Re: FastKid's 260
PostPosted: Tue Nov 01, 2016 11:28 am 
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Posts: 25
Yup Dave has it right, however I noticed that sometimes but not all the time if it was raised slightly, let's say half way, it will stay stuck up but the slightest tap of the finger and it will fall back down. Also I'm sure this has to do with tuning the carbs but during all the roadside trouble shooting I had to perform I noticed if I raised the rear carb piston the car will start to sputter and die, but if I did the same to the front piston, not much would happen. I just want to apologize if I don't use the right automobile jargon when describing things, I'm coming from mostly just oil changes and once and a great while changing starters so I'm trying to learn as I go so thanks for all the patience everyone!


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 Post subject: Re: FastKid's 260
PostPosted: Wed Nov 02, 2016 11:29 am 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 13270
Location: CT
No apologies needed Andy. We all learn something new about these cars each time we have a problem. Within a year you'll have learned enough to help someone else because you've been there, done that. In a perverse sort of way, the more problems we encounter with our cars, the better off we are (wait ~ did I just say that? :? ) Well, you know what I mean.

Describing the basics sometimes offends people because they already knew what you talked about. If you already know the stuff I'm covering, please don't take offense. It isn't meant as a put-down at all. It's just better not to assume you know something and remind you of it, than to continue discussing something you're unfamiliar with.
And many Z lovers of different capabilities read these Forums, so somebody, somewhere, will benefit from learning the basics.

BASICS #1>
The internal combustion gasoline engine needs 4 simple things to start and stay running:
1. Intake of the proper air/fuel mixture for what the engine's trying to do at the moment;
2. Proper compression of that air/fuel mixture;
3. Proper ignition of that compressed air/fuel mixture AT THE RIGHT TIME (called ignition timing) and
4. Proper exhaust of the spent vapors when we're done using them.

There are also provisions for lubrication, cooling and electrical generation. Each of these needs has a (sometimes) complex mechanism to make it happen correctly and on time. The carburetor(s) obviously have the job of supplying the PROPER mixture of air and fuel as the engine needs it for whatever it's trying to do at the moment (start, idle, accelerate, decelerate, high speed, low speed, etc).

In my humble opinion, our SU (Skinner's Union) carbs are one of the simplest, most-accurate and reliable automotive creations of our days. This top diagram shows what your carbs look like inside:

http://sucarb.co.uk/technical-h-type-ca ... er-diagram

The basis of the SU is a "floating" piston moving btwn vacuum and spring pressure, which raises or lowers a metering rod into and out of a metering jet as the engine demands more or less fuel.

For a Fred Flintstone picture of a metering rod and jet, please picture an upside down highway traffic cone (the metering rod) inserted into a big donut hole (the metering jet). Picture liquid (in this case gasoline) trying to flow upward thru the donut hole. When the "cone" is lowered completely into the "donut", no fuel can rise thru the hole. As you gently lift the cone, more and more fuel can sneak past it out of the hole. If you raise the cone completely, the maximum flow of fuel can come up out of the hole.

VENTURI
A venturi is a restriction in an otherwise open air passageway, thru which air must speed up in order to keep up with the flow ahead of and behind it. You can imagine a wide river flowing downstream at a leisurely rate, then being channelized into a much narrower strait, creating rapids. The water speeds up and rushes thru the narrows, then slows back down to the previous rate downstream of the rapids. So we have slow water upstream and downstream of the rapids, but fast water racing thru the narrows. I also like to picture cattle being moved from one corral to another thru a narrow gate; the cows ahead and behind are moving casually; the cows in the gate are running to keep up. Or you can picture two funnels, taped together like a dog bone. Big air comes in and goes out, but small fast air races thru the neck of the funnels.

That's exactly what a venturi does to air flowing thru a carburetor, and every carburetor has a venturi (some have more than one). Because air is composed of molecules, they "stretch" farther apart when the air speeds up thru the venturi. That causes a lowering of air pressure in the stretched air column.

*[Please note: in absolutely technical scientific terms, there is no such thing as a "vacuum" and flowing air cannot "suck" fuel up thru the metering jet. Correctly, there is only a "difference in air pressure" btwn two locations, and the higher air pressure pushes air (or fuel) into the lower-air-pressure area in an attempt to fill that "vacuum". I have used these terms only because they are commonplace mistakes which everyone uses, but I admit they're wrong. My AutoMech shop teacher would roll in his grave if I led you to believe there was any such thing as "suction" or "vacuum" anywhere in your engine. It's only normal 14 lbs of atmospheric pressure pushing against lower pressure air].

As the air rushes thru the venturi, it causes a difference in air pressure which we (inaccurately) call a vacuum. While atmospheric pressure is about 14 lbs per square inch, the pressure in the venturi is much lower. "Nature abhors a vacuum", so if we place a metering jet into this venturi, 14psi atmospheric pressure will force fuel thru it to the low-pressure 9psi airstream flowing thru the carb, trying to fill that 'vacuum' with fuel. The low pressure air wants to 'suck' fuel up thru the metering jet. The greater the airflow thru the venturi, the faster the rapids, and the stronger the 'vacuum' gets.

We route some of this low venturi pressure ('vacuum') to the top of the moveable piston (the part which sometimes sticks on your car) inside the "bell" vacuum chamber or "dome" at the top of your SU. Don't confuse this big piston with the tiny oil-filled piston you take out with the thumbscrew at the top of your carb; we're discussing the largest moving part of your SU, inside the dome. The small oil piston is a damper to make the big piston move smoothly; think of it as a small shock absorber for the big piston.

So the big piston is pushed downward by a large weak spring wrapped around it. The metering rod (the traffic cone) sticks out the bottom of the piston and is inserted into the metering jet (donut hole) beneath it. Both the rod and the jet are in the low-pressure venturi, which tries to "suck" as much fuel up thru the jet as the rod will allow when air rushes thru the venturi. Thus, the higher up the piston is lifted by vacuum, the higher it lifts the metering rod, letting more fuel flow thru the metering jet into the engine. When the vacuum drops, the spring returns the piston to it's lowest position, and the "cone" shuts off the fuel flow thru the 'donut'.

When you step on the gas, the ONLY thing you do is open the throttle butterfly plate which blocks the carburetor air passage. Picture that plate as a manhole cover tipping open to allow air to flow around it into the manhole. The cover stays in the hole, but it tips open and closed to control airflow around it. The more air you let into the carb, the faster the flow is thru the venturi, and the higher the "vacuum" becomes. The stronger the vacuum, the higher the piston gets lifted, and the more fuel is released thru the metering jet into your engine.

CONT'd in BASICS #2>

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1970 240Z


Last edited by Frank T on Fri Nov 11, 2016 2:18 pm, edited 12 times in total.

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 Post subject: Re: FastKid's 260
PostPosted: Wed Nov 02, 2016 11:37 am 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 13270
Location: CT
BASICS #2>

So, what's happening to your car?

If the piston doesn't move freely on your front carb, it is essentially working against the rear carb. Regardless of the engine's changing need for fuel/air, the stuck piston will continue giving a set amount to the engine. Like a stopped clock, it will eventually be correct occasionally, but most of the time it will be supplying a wrong fuel volume and mixture.

At an idle, when you lift the rear piston from outside the carb, the car dies? That indicates the front piston is stuck in a 'wrong' position and can't respond to the engine's needs for proper fuel/air mixture. It's apparently just on the verge of being OK for an idle, but as soon as you introduce even a little more fuel from the rear carb venturi by lifting the piston manually, you load ("flood") the engine with too much fuel and stall it. That would explain your blackened spark plugs. Bearing in mind that each carb feeds 3 cylinders, you might see 3 blackened plugs from the 'broken' carb and 3 normal plugs from the 'good' carb.
But not always, since they share a balance tube.

The SU carbs are hand-adjustable for richer or leaner operation. A thumbscrew at the bottom of each carb physically raises or lowers the stationary metering jet. That of course has the same effect as lifting or lowering the metering rod, so you get richer or leaner fuel flow. In fact, when you pull the choke ON at the console, all you're actually doing is lowering the metering jets a tad ("lowering the donut away from the cone"), which allows more fuel to flow into your cold engine, making it (somewhat) easier to start. Our SUs don't use a choke plate like old American cars did.

It's essential that your metering jets ("donuts") are adjusted to the same height. The only way to determine this is to turn both adjustment knobs fully closed (raised), then lower them the exact same number of turns (usually 2.5 turns to begin with, and adjust from there). The biggest problem with this is determining which direction to turn the knobs.

If you were laying on your back under the car, looking up at the carbs from beneath, you would want to turn the jets CLOCKWISE to close them (raise them). It's up to you to picture how to do that from above; you would turn them COUNTER-clockwise to close them from above. All the hand adjusting knobs I've encountered have had 4 little raised nubs around them to help me determine each 1/4 turn. Some people have said they had no such nubs, others claimed 2 or 3 nubs. Go figure. If possible, COUNT the number of turns it takes to fully close (raise) each jet and compare that with the other carb. That will tell you how well tuned or how far different your carbs were before you began. If they were both opened the same number of turns but you felt they were too rich or lean, you could estimate how many fewer or more turns your car will be happy with. Make adjustments only 1/4 turn at a time.

The initial hand-adjustments of the metering jets must be made with the choke FULLY OFF. The best way to ensure that is to disconnect the choke cables completely. Be very careful not to lose the tiny (tiny) screws which secure the cables in place. :cry:

So, what's to be done about your car?
1. Remove the vacuum dome of each carb and remove the pistons. Compare the metering rods. Make sure neither is bent and that they are both seated with the shoulder (square part) absolutely flush against the bottom of the piston. I would loosen the screw and remove them just to compare the number stamped on them. Because you're working with carbs new to you, there could be a chance they each had a different rod (many rod options are available);
2. Check both pistons for any burrs which might cause them to drag against the interior walls of the vacuum chamber. It is absolutely essential that the pistons be free to move fully up and down within the chamber without any interference. Fix as necessary with fine sandpaper;
3. Check the inside of both bells for any dings or rough spots which might interfere with free piston travel. Fix or replace the bell as necessary. (Get rid of that washer. It doesn't belong in there);
4. With the choke OFF (technically you should disconnect both cables), turn both metering jets closed (up), one carb at a time. Record how many turns it takes to seat each one so you can compare how well sync'd they were before you began;
5. Re-open (lower) your jets (one carb at a time) the same distance. Start with 2.5 turns to begin with and judge from there how happy your engine is with that. Make adjustments 1/4 turn at a time as needed;
6. Re-connect your choke cables, adjusted so both chokes move the same distance when you pull the lever. With the console choke lever fully forward ("off"), the jets should remain in the position you set them to. Pulling the choke lever backward ("on") should make them both drop slightly. Some guys have a choke cable hooked to one carb only;
7. Clean or replace your fouled spark plugs with the proper heat range plugs. Use only NGK or Bosch plugs in the heat range your 260 engine requires (they are different for each engine and I don't know what the 260 is happiest with). Avoid Champion or AC plugs like the plague;
8. Check for vacuum leaks by carefully spraying carb starting fluid around your (cold) idling engine. If the rpm increases, examine that area for any hose or gasket which is causing a vacuum leak and sucking the starting fluid into the manifold;
9. Get some kind of velocity stacks (air horns) on your carbs. The backing plate of a standard "breadbox" air cleaner does very well. Any replacement should be the exact duplicate of the original air horns. These are important on the SU to get the proper air column moving before it enters the venturi.

Your carb problems should be solved, so you can drive the car to Vinny to get the cam bearing (or whatever is clunking) changed. :D

I understand you spent the final hours of Sat night replacing those flattop carbs with your new round tops just to get the car to the picnic. You did a fine job and your success (the car MADE IT!) shows you have good potential as a 'wrench'. Now you have all winter to work on the details to make the car run smoothly and reliably. We're here to help as you might need us. Many of us have spare parts laying around which you might need. We can't drive the cars during the winter, but talking about them helps keep (many of) us sane until the Zeason starts again.


Here are some very valuable notes about SUs (altho bear in mind there are many models of SU and not 100% of this will apply to ours):

http://www.zparts.com/zptech/articles/m ... 11601d.htm

_________________
1970 240Z


Last edited by Frank T on Sat Nov 05, 2016 2:12 pm, edited 1 time in total.

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 Post subject: Re: FastKid's 260
PostPosted: Wed Nov 02, 2016 9:04 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 13270
Location: CT
PS Andy ~ do you have electronic ignition yet or are you still using breaker points?

Frank

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1970 240Z


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 Post subject: Re: FastKid's 260
PostPosted: Thu Nov 03, 2016 1:51 pm 
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Joined: Sun Oct 02, 2016 4:12 pm
Posts: 25
Frank it's electric, I have read your previous 2 posts once already but Im going to need to read them over again as well as your links. You give some great visuals and I can't wait to sit down after work and try to soak up all the knowledge you have given so far.


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 Post subject: Re: FastKid's 260
PostPosted: Thu Nov 03, 2016 3:45 pm 
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Joined: Wed Apr 09, 2008 5:53 pm
Posts: 13270
Location: CT
Cool.
The only criticism I have about the second reference link is that under the diagram of the "Variable Choke Carburetor" they cite #4 as vacuum routed to the top of the SU piston coming from "manifold vacuum", which is completely wrong. As I explained, that vacuum is routed from the carburetor venturi. It wouldn't work at all if it was tapped off the manifold vacuum.
Take your time.
You have all winter.
8)

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 Post subject: Re: FastKid's 260
PostPosted: Mon Mar 06, 2017 9:52 pm 
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Joined: Sun Oct 02, 2016 4:12 pm
Posts: 25
During the few beautiful days we had the other week I dropped the gas tank and refinished the inside and out, installed a new oem electric fuel pump and an old oem mechanical fuel pump as well as replaced all the ventilation hoses and fuel filter. I'm proud to say that one of those things fixed the sputtering and eventual dying going uphill or at highway speeds!
As for the carbs, they seem to be functioning after reading and adjusting them as Frank so kindly posted about earlier but am very sure that they are nowhere near their full potential.
I was reading "orange peels" thread and didnt want to hijack it but this question is directly for Frank. I have found the same header made by Clifford from a facebook group and while I'm waiting for it to arive I am trying to figure out the the rest of the exhaust. The header has been modified so it now has a single 2.5 inch collector so Im planning on having a glasspack in the middle of the exhaust but am trying to find tips or a muffler, I love the abarth muffler with the over under style vertical tips but
At 395 euros plus shipping its a bit to much right now. I saw that you said the exhaust warehouse still had some ansa tips and im just wondering if that was just the chrome tips or an actual muffler? Also you have quad ferrari ansa tips?? That sounds very cool I would love to see what they look like :mrgreen:


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 Post subject: Re: FastKid's 260
PostPosted: Tue Mar 07, 2017 10:45 am 
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Posts: 13270
Location: CT
AHA! Clifford's Performance Exhaust, out of Ontario! I should have known, and it makes sense that a pair of their headers found its short trip across the border to Rochester. Clifford makes only competition grade intake and exhausts for many many cars, is capable of one-off custom work and I have plans for them in the near future 8) Thanks, Kid. :thumbs_up: John probably doesn't yet realiZee that he has a very expensive header on his project car.

The early dealer-option ANSA exhaust system sounded great. It was made in California by a small shop who contracted to Datsun exclusively for that purpose: it was all the shop did for about 5 years, and they could hardly meet demands. They all got rich and the owner finally called it quits and retired happily. I spoke by phone to two of the old employees (in California) and they both told me the same basic story; They were the only people in the industry with mandrels small enough to custom-bend 1.5" Inside diameter pipes and they ALWAYS had an "IN" box full of work. In fact, the day the shop closed and retired, the IN box was full or orders.

I've never heard a 260 with ANSAs, but my free flowing ANSA system allowed my little 2.4L to wind up very quickly. Yours might have a slightly deeper voice due to your longer stroke and larger cubes. I would recommend studying your idea about placing mufflers anywhere but back by the fuel tank. The Z has enough ground clearance problems as it is and my own ANSAs were the lowest point of the car (after the wheels) all the time I had it. I can't count how many times I had to have them welded back on after hitting a steep driveway. If I had stuck any sort of muffler or resonator along the pipe, it would have compounded my problem.

ALSO, the big cargo deck offers itself as a "drumhead" for road noise and muffler vibrations, which can drive you craZy. I'm sure that's why Datsun choZe to place the mufflers so far rearward. Even mine had an annoying resonance right at 66mph, which is why I drove 70 when nobody cared. I could actually tell when I hit 66mph without looking at the speedo.

Mine had twin pipes (off a factory stock exhaust manifold) running from the engine back to the bumper. The stock manifold is a 6-into-2, and mine continued that way, side by side, the length of the car. Just at the end, on the driver's side of the fuel tank, the pipes went vertical (Over/Under) into dual CHERRY BOMB glass pack "mufflers" (haha!), then 2 very short exhaust pipes poked out thru the 'mouse hole' where they were tipped with dual chrome ANSA tips to the exact edge of the rear bumper. The result was thrilling each time I started the car and added to my complete satisfaction with the Datsun 240Z.

I will dig those Ferrari exhaust out of the garage and take a picture for you, maybe today.
Did you ever meet JP260z from Pennsylvania? He's putting a nice 260 on the road now and you two might share some common tears. A bunch of us are planning to drive down to Scranton on Fathers Day weekend to attend a large car show there, meet Jay and park our Zs together for the show. You might be interested in that!

Frank

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 Post subject: Re: FastKid's 260
PostPosted: Tue Mar 07, 2017 1:37 pm 
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Sorry, I didn't answer your direct question about the exhaust tips. They were added onto the twin CHERRY BOMB glass packs, on the short pipes which stuck out the back of the mufflers. I think they were tack-welded if I remember correctly.

The Cherry Bombs were connected to each other and sold as a side-by-side unit. I could look thru the two of them together like a pair of binoculars when they were off the car.

Here are a couple companies which sell Cherry Bombs ("Disturbing the peace since 1968"):

http://www.jegs.com/v/Cherry-Bomb/545

https://www.exhaustking.com/cherry-bomb

The glass packs you want for your car are the red cigar shaped $27 muffler on the left of the website header. I suppose you could run a single straight pipe back to the back of the car and use only one glass pack, but I have no idea what that would sound like.

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 Post subject: Re: FastKid's 260
PostPosted: Tue Mar 07, 2017 7:44 pm 
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I havn't met Jp260z yet, I doubt my Z will be up for a ride to PA quite yet, I still need to figure out the ticking cam noise and a few other things too. Maybe ill drive down to hang out though!

I'm guessing just a pipe to just a cherry bomb glass pack at the end woud be quite loud! Cant wait to hear it with out an exhaust leak and the new headers :lol:


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 Post subject: Re: FastKid's 260
PostPosted: Wed Mar 08, 2017 12:12 pm 
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It would be cool for you to just cruise down to Scranton with us regardless what you're driving. Heck, if you have an SUV in the driveway you might bring that along as a tow car in case anything falls off our Zs :lol: It's only a 3hr trip. I would go down there the previous day and sleep over, so I wouldn't have to get up at 0300 and drive hard to get there in time for the morning show.

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 Post subject: Re: FastKid's 260
PostPosted: Thu Mar 09, 2017 8:46 pm 
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Hi Andy!

Yes you should come to Scranton! It'll be a great time even if you can't take your Z, trust me.... Mine only made it once so far and I go every year. Also I'm looking forward to meeting Frank and the crew!

As for exhaust, last summer I installed a Magnaflow muffler (which is a straight through design similar to a glasspack) in the stock location, with 2.5" pipes and it is loud and resonates. I'm adding a glasspack in the mid pipe to mellow it out a bit, and hopefully knock out the resonance.

Good luck with your Z Andy, I hope I'll see you in Scranton!

Jay


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 Post subject: Re: FastKid's 260
PostPosted: Sat Mar 11, 2017 10:39 pm 
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Hey Jay!

Whats the date of the car show, Im going to look up the info about it. Your trips to the car show sounds like the one and only time I drove the Z a long distance to the ctzcc end of the year meet ending with a long tow truck ride home lol.

I talked to the guy in the netherlands whis sells abarth parts and I may save up to get an over under style nos abarth muffler and then do the same thing with the glasspack in the mid pipe, I cant wait to hear it!

Good luck with your Z too hope you make it this time :thumbs_up:

-Andy


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