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I haven't seen much on the forum on engine mods. I am an old school tinkerer and can't leave well enough alone. I have done the following mods: smooth out the rough edges inside the stock throttle body and grind off the protruding butterfly screws, increase the diameter of the exhaust ports by about 10 per cent of the radius (produces a 20 per cent increase in flow), modify the stock air box with three well placed 1/2 " holes at a right angle to the inflow for a true ram air setup (google on Bernoulli Principle), add a K&N drop in panel filter and insulate the stock Air intake duct with adhesive aluminum and butyl duct wrap from Lowes.

The results are astonishing. A little bit goes a long way in such a light chassis. I will post pics from my phone.

post-1201-0-46435300-1402913932_thumb.jp

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I have more pics but the upload is limited to only 500KB. The foil is just the outer covering for duct insulation available at Lowes/ HD/ etc. It is meant to keep the intake air shielded from the heat of the exhaust. The zip ties are needed because the adhesive looses its grip with heat.

FYI my first 50 mile commute since the exhaust porting yielded an honest 49 MPG. The higher temps on the afternoon commute home lowered the average to 47 MPG.

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Get a free photo bucket account then hover over each image, click on the little wheel that shows up, and use the get links option. Choose the one to embed in forums and click to copy to clip board, then past each link into a post.

Did you take the head off to port it or just do this in place? Normally you don't get that kind of increase from the stock headers because they are so short.

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I'll work on getting the photo bucket going.

I opened up the exhaust ports without removing the head by stuffing the ports with paper towels and using my shop vac frequently. I also stuffed the header ports with towels. The stock headers are about 23 mm in diameter. The gaskets about 25 mm. I was surprised to see the head port only 20 mm! I basically beveled the outer 3/4 inch with a carbide cutter on a dremel flex shaft (essential to use the flex shaft) then blended and polished it with 120 grit sanding drum at low speed. HIgh speed for the cutter, low speed for the sander. There was enough room to move the header and cat down and away by removing the cat support that attached to the lower block. I didn't have to undo the exhaust. When I pulled out the paper from port, I vacuumed first, pulled it out and vacuumed again.

You are right about the short headers being top end benefits. My next step will be to put a ceramic thermal coating on the header and cat to improve scavenging and further reduce the underhood temps.

MPG update: 46 MPG mostly highway with A/C on, top speed 55. 42 MPG with 75 MPH, A/C on and full throttle accel from the stop lights.

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  • 1 month later...

When you beveled out the last 3/4" of the exhaust port to 23mm, was there still a 20mm bottleneck further in? Or did this increase the diameter of the opening all the way into the head?

Edited by gitsum
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  • 2 weeks later...

OK, I think I'll give it a try. Nice job on experimenting and finding the bottleneck allowing the possibility of a free mod to increase performance.

Still a little concerned about getting metal particles down in the engine. Your picture is a bit small to see details.

So the stock exhaust port splits into two separate passages after 3/4" ?

Are the paper towels stuffed into each of the two inner passages past the split? Is there plenty of room for the dremel bit without too much risk of pulling or pushing the paper towels loose and dropping metal shavings into the head?

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I had another thought...

I started the original thread on the airbox mod just over a year ago. I could see the airbox snorkel was a definite bottle neck seeing how it was much smaller than the throttle body. I expected a slight improvement, but was surprised by the significant boost in performance compared to stock.

Looking at the size of the throttle body and stock exhaust manifold, they seem to be adequately if not generously sized for a 1.25 liter engine.

I'm wondering if the majority of the extra performance from your mods are from the airbox mod exclusively?

Did you get an opportunity to test them independently to see if the enlarged exhaust ports and tweaked throttle body contributed significantly to the overall performance increase?

I'm not dissing your mods, they make sound mechanical sense. Just trying to avoid a lot of extra work with the possibility of no extra gain.

Edited by gitsum
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OK, enough questions, time for action. Pulled off the throttle body which is about a 5 minute task, about two minutes the second time.

Removed the extra screw length from the back of both screws, dremeled off a little material from the front of the throttle body shaft between the two screw heads, polished everything with some 400-grit sandpaper. The two screws attaching the throttle plate/blade to the shaft didn't want to budge, so stopped there and put it back together.

A short test drive revealed a slight increase in power, mostly at WOT above 5000 rpm's, but still detectable in the low and midrange.

So back off with the throttle body and more work to do. Did a variation of the throttle body shaft removal. The screw holes on the throttle plate/blade or slightly oversized, and the stock screws are regular machine head, not beveled. I guess one could try to pick up some larger head screws that are beveled, and the use a slightly oversize bit to partial drill out the holes in the throttle plate/blade itself, beveling the holes so hopefully the new screws will center perfectly.

I didn't want to risk the throttle plate/blade binding because it wasn't exactly centered, so I cut off the upper shaft between the two screw holes. This got rid of more than half of the top part of the shaft, and I used the stock screws in the stock holes on the ends of the shaft.

The throttle plate/blade is like a thick coin with flat edges and 90 degree corners. I carefully beveled and rounded the leading and trailing edges making sure not to reduce the outer circumference. And yes, those damn screws were red locktited on there from the factory, used blue locktite when reinstalling

Put it back together again and it was definitely worth the effort. Same type of results as before, only more noticeable. I would guesstimate the improvement to be about half of the performance increase the airbox mod alone gave it. My manual Spark felt pretty peppy when accelerating hard to 65-70mph, then acceleration dropped off as it crept up to 95 or so, which is as fast as I ever pushed it. Now it pulls strong all the way to 75-80mph, top end is where you feel the biggest difference.

14o6gee.jpg

295frrl.jpg

Edited by gitsum
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Cutting that shaft could be a big problem down the road. On my motorcycle we have an issue where the shaft snaps in the middle and causes tps issues, you have effectively done the same. I can not recommend that other users do the same that you did. Even cutting the extra screw off the butterfly can be an issue because normally that extra is staked so it can not back out and get swallowed.

Wouldn't it be better to get a slightly larger TB and adapt it to the spark? Otherwise it looks like there is plenty of room to bore the TB out a few millimeters and have a new butterfly made.

Edited by Greg_E
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The shaft has two sides, the back has the threads for the two screws. The mod is called "half shafting" the throttle body. It's been around a long time and successfully used on many different vehicles without issues.

The back of the throttle plate/blade is stilled fastened directly to the rest of the shaft, nothing is "cut in half". You have just removed one side for more and cleaner air flow. The throttle plate/blade is still in the exact same position relative to the shaft, the TPS isn't going to know or do jack.

I tested the mod successfully and it works with no issues. Before not recommending the mod, perhaps googling " half shafting" and doing a little research might be pertinent.

It's a free mod, a larger throttle body (if you can find one) costs money and will have the same flow restrictions.

Boring out the throttle body will make it larger with air going into the smaller diameter intake manifold, not much help there. Better flow makes this mod work, removing a bottleneck instead of creating a new one (like a larger throttle body opening flowing into smaller intake manifold) makes the idea work.

Edited by gitsum
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Update! After a successful preliminary test drive of a few miles, during a second drive the check engine light came on.

Nothing that concerned me too much, I knew the car was running smoother and better than ever. Did an ECU reset procedure and the light stayed off and did not come back on.

What does this mean? It means the throttle body mod was working so well that the ECU compared the new operating parameters with the old and thought something was wrong. Resetting the parameters allowed the computer to "relearn" and the ECU happily adjusted with no problems.

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I'm sure this technique has been used successfully for decades, but I still don't think this is a good mod for anyone that isn't using this car for just racing purposes. Also a drill bit is a poor choice for cutting a counting sink, few screws have the same angle as most drill bits. I would suggest getting the correct countersink bit for the angle of the screw head. Cost is going to be about $5 to $10 unless you buy a carbide cutter and then it could be much more. http://www.use-enco.com has a good supply of these, and you can often find them on ebay for way less from some of the other machine tool discounters.

Did you read the code the ECU threw to see what it said? Could have been unrelated as a flow change like this shouldn't really cause to much grief with the system unless you exceeded the flow rate of the injectors (which I doubt you could if all the injectors are working properly).

On the Fiestas the rubber "boot" that connects the air filter housing to the TB has been shown to be a restriction of some kind. Fitting a harder and smooth boot has shown some gain, just wondering if some form of more rigid and smooth "conduit" between the airbox and the TB might give a benefit on the Spark.

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The car has gone 32,000 miles with no check engine light. I don't think it's a coincidence that after modifying the throttle body it came on. 30 second ECU reset and problem solved. No need to make it more complicated.

However, we did check the codes when my son's Spark that started hesitating, having hard starting and lacking performance. The codes indicated a misfire in one of the cylinders. This is very similar to a problem someone else was having in another thread.

No dealer visit necessary. The simplest reason for a misfire is a screwed up spark plug. Cleaned and regapped the plugs, engine runs fine now.

Always check the simplest things first, one can save themselves a lot of extra work and aggravation.

Replacing the accordion rubber intake boot with a smooth rigid solution sounds like a good idea, I'll look around the hardware store for something that might work.

Edited by gitsum
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I forgot to ask, why is this mod only good for "racing purposes"?

The screws are using the same amount of threads as stock. If the stock screws were backing out the extra threads would serve no purpose except to extend the length of time until the screw actually falls out. I don't know of anyone or any dealership that checks those on a regular basis.

I applied locktite and put some paint marks on the two screws. It takes less than a minute to remove the rubber intake at the throttle body and eyeball the paint marks. I'll check them after a few hundred miles and then again after a few thousand. This is way safer than never checking the stock throttle body screws ever.

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Your assuming the mechanic would need to remove the throttle body, and if he did he would recognize it was modified. It still looks close to stock and was polished up with fine grit sandpaper.

Don't make the mistake of thinking a certified factory mechanic knows anything other than what a computer diagnostic code or a tech manual tells them the next step should be. Good ole common sense and mechanical aptitude aren't a requirement for the job anymore.

Edited by gitsum
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Trust me, I know. I work at a college and we teach an automotive diagnostic and repair degree... They are never in the shop with hands on the cars! I think they do about 2 weeks work on basic mechanicals, all the rest is sitting at a bench with pegboards and electronics set up to run simulations. Our newest cars are CNG Hondas, most of the rest of the shop cars are 10 years old or older (obsolete in the north east due to rust). And the CNG cars haven't been in the shop in over a year, guess we aren't teaching alternative fuels anymore. But I have a lovely CNG pump on my end of the building, it's also one of the places where people go to smoke illegally. That pump could never leak or anything. Since the pump went in, it has never been used, that was more than 2 years ago.

But back to the TB, my dealers would go looking for a reason to stop a warranty claim, they get paid more for non-warranty work. And if they needed to do some engine warranty, that boot might be something that comes off, and it's pretty plain to see your mod. That said, warranty is only as good as your dealerships, so you might be fixing your car anyway. You certainly couldn't do a worse job than some dealers, too bad it is so hard to get some of the special tools and impossible to get firmware updates, might be able to make good money if an independent service place could make warranty repairs!

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Just FYI, if your car falls into the 14110 pcv program replacement, you may be screwed. Part of the procedure is to clean the throttle and manifold. If you car starts consuming oil, you may want to just go buy a new pcv and see if that fixes it.

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  • 7 months later...

Other than a custom Turbo and complete sensor replacement/recalibration ($$$$), there is no way to get 100hp from this engine. There was this one guy who was into racing and replaced his engine and drivetrain with a small V8. That of course is a complete drivetrain rebuild/replace and really not relevant or practical if you get my drift.

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I haven't seen much on the forum on engine mods. I am an old school tinkerer and can't leave well enough alone. I have done the following mods: smooth out the rough edges inside the stock throttle body and grind off the protruding butterfly screws, increase the diameter of the exhaust ports by about 10 per cent of the radius (produces a 20 per cent increase in flow), modify the stock air box with three well placed 1/2 " holes at a right angle to the inflow for a true ram air setup (google on Bernoulli Principle), add a K&N drop in panel filter and insulate the stock Air intake duct with adhesive aluminum and butyl duct wrap from Lowes.

The results are astonishing. A little bit goes a long way in such a light chassis. I will post pics from my phone.

Hey I also have done a port job but I removed the head and done intake and exhaust ports you can check out my head pictures in the gallery it has changed the car totally

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