After years of waffling and waiting, the time has come. I am going to build it up.

4 years ago I bought two cars:
88 Coupe with almost everything removed. Rustproofed and sound deadening installed in interior.
87 GT, badly repaired in front after a frame-bending wreck. Got me most of the panels needed as well as wiring, etc.
The rings were shot on the 2.8 and the getrag was grinding multiple gears.

Basically what this gave me was a complete 88 GT minus motor, trans and rear swaybar. Then it sat for four years waiting for me to finish school. Got married and had two kids since. No time to work on it.

Next semester is my last. I plan to work 40+ miles away.

We used to have a Cavalier with an Ecotec, the thing got 37-40 highway. Too small for our needs, and the Cavalier doesn't go the places our Trailblazer can go. I liked that little car, but getting something similar will cost about what building the Fiero with an Ecotec will cost...so why pay the same for an inferior car? The Fiero is lighter, so I should get more mileage with it.

The plan:
2.2L Ecotec, Getrag F23 5 speed
Building my own mounts, will probably have to mod the cradle a bit
Tsudo 4-2-1 Header, WCF Flowmaster 40 series, similar to stock exhaust tips
Megasquirt II mounted in stock ECM location, relay board mounted where battery goes
Older GM wasted spark ICM to ignite the A/F mixture
Wideband O2 sensor
Battery relocated to front (I already have the custom box in hand)
WCF Coilovers rear, WCF performance springs front, KYB's all around, GT rear sway bar
Kumho Ecsta SPT Tires, 225/45-17 in front, 245/40-17 in back, Konig Incident 17X7 wheels

One guy who did the swap with megasquirt, good intake, same headers got 47 MPG! Look at it this way, the EPA estimates the 2008 Prius at 45 MPG highway, 48 city, 46 average. I know the Prius will get way better mileage in city than the Ecotec Fiero will, but almost all of my driving will be highway. Pretty good considering the Prius costs in excess of $20,000...and calling the thing dog-ugly wouldn't be a nice thing to do to my dog. I love my dog.

With the wideband sensor I should be able to lean it out enough on the highway at cruising speed and vacuum to pass the 50 MPG mark under the right conditions. If not, high 40's is still pretty good.

Plus I can tune it to really burn gas and go fast at WOT when I feel like it. The thing should give me over 150 HP and around 160 ft/lbs...these are slightly higher numbers than the 2.8 I had in my 86 GT back in high school. Plus that thing was old and tired mated to the 3 speed auto...

With the manual trans, lighter weight of the ecotec and a fairly fresh motor I should have a car that outperforms my old GT in terms of power and performance while really beating it at the pump (it was getting high 20's on the highway if I kept it around 70).

More to come...

Looking at gathering most of the parts mid to end of January '09.

Edit:
After the topic of wheel/tire choice and transmission final drive kept coming up, I decided to start a new thread on this car build.

https://www.fiero.nl/forum/Forum2/HTML/097165.html

I realize that the 50 MPG goal may be attainable, but I am personally unwilling to make the sacrifices necessary to meet it. I would like to have a 3.8ish final drive and some good, sticky tires. I want good torque and acceleration and I don't feel safe on 185 tires, there are too many idiots out there to dodge on the road.

[This message has been edited by DustoneGT (edited 12-23-2008).]

build the fiero for speed and handling.. get a geo metro for fuel economy lol :P Good luck on your project

quote Originally posted by kawana: build the fiero for speed and handling.. get a geo metro for fuel economy lol :P Good luck on your project

That'll come later (the power, not the geo metro ) In the future at some point I will buy a second Ecotec and tougher trans, put in better pistons for some boost! Should be able to achieve in excess of 300 HP. Too poor for all that right now.

quote Originally posted by DustoneGT: Next semester is my last. I plan to work 40+ miles away.

To El Paso by any chance? We're dying to see it when it's done. You can laugh at all us V8 swappers here when gas hits $5 a gallon again LOL. Any chance we can see the work in progress on our next cruise up to Mesilla? You can join us for lunch. We try to get together every few months or so.

And if we can be of any assistance along the way, drop us a note. I'm sure Katatak will be stopping by this thread shortly.

Yep. El Paso. I am studying to teach HS History and Texas pays $12,000 more a year. I'd be a fool to teach in New Mexico.

I'll get in touch when there's actually something to see...it's just a muttly looking half-built wreck right now. Let me know when the next cruise is. I'll definitely stop by and check out your cars.

quote Originally posted by DustoneGT: Yep. El Paso. I am studying to teach HS History and Texas pays $12,000 more a year. I'd be a fool to teach in New Mexico.

Sounds great. Just remember that you still owe NM state income tax even though you're working in Texas....and employers in TX do not deduct it from your pay. Remember to put it aside monthly so there's no surprise at the end of the year. Ask me how I learned that

quote Originally posted by DustoneGT: I'll get in touch when there's actually something to see...it's just a muttly looking half-built wreck right now. Let me know when the next cruise is. I'll definitely stop by and check out your cars.

Sounds great. I'm sure it will be after the beginning of the year. We usually come up highway 28 and have lunch at LaPosta. Look for a row of Fieros with Tx plates





I'll drop you a note when we get together next time

quote Originally posted by DustoneGT: Kumho Ecsta SPT Tires, 225/45-17 in front, 245/40-17 in back, Konig Incident 17X7 wheels

I don't think you're going to achieve your goal on that wheel/tire combo. I switched my Pontiac 6000 SE AWD (3 speed auto) from 195/70-14's to 245/50-16's front and 205/60-16's rear and lost 1.5 out of 24 mpg. The rolling resistance of a wide, sticky tire is significant. You'd better plan for a rock-hard tire (something with a mileage guarantee) in the 185 range to hit your fuel economy goal, then go softer and wider to experiment.

[This message has been edited by Will (edited 12-10-2008).]

I am down by Houston. I get 39 MPG most of the time with the AC off. I have an 86 2.5 5 spd. I have about 10K miles now on a fresh overhaul. I have 15"lace GT wheels. I have been thinking about some smaller 14" wheels again with the correct size tires mounted and inflated to 40 PSI. The footprint would be about 1/2 of what it is now. Less resistance, more MPG. I thing 44 is a real possability I was suprised by the road noise created by these larger tires running 40 PSI. I am also thinking of advancing the timing 3-4*. Should be good for a few extra MPG.

Your Texas Neighbor
Joe Crawford
Texas

You guys are right up my alley. I just bought my 88 Duke with the idea of making a great (read fun) high mileage commuter. I make many trips between Chicago and Cleveland, it's 800 miles round trip. I think this car will be great for that task.

I initially had a deposit on a smart car. But spending 15 grand to save fuel. Well, it doesn't add up. So I bought my car for $700 and have thrown another $700 at it in parts, paint, sound system, etc. Now I'm spending $1400 to save some fuel. When fuel shoots back up, the payback should be relatively quick.

And I love the car.

Keep us posted on your progress!

------------------
Spent my days with a woman unkind Smoked my stuff and drank all my wine...

Lowering it some and swapping in a camshaft for economy oriented driving might help also. Not sure if the GT panels will help or add more drag.

Before long we may all be driving ECOTECs, look at the video attached to the story, and I believe the ECOTEC is already strong enough to handle 300 hp from what I have read.


http://tunersource.gmblogs.com/

The thing is... to make 300 HP, an Ecotec needs boost. Boost requires low compression. Fuel mileage benefits from high compression. The two goals are at odds. You can't maximize both.

At ~$4.00 per gallon for regular and $4.30 for premium, the improved gas mileage of a high compression engine requiring premium fuel will give it a lower cost per mile than a low compression engine that can operate on 87 octane.

At fuel costs below this, the low compression engine is cheaper to operate. At costs above this, the high compression engine is cheaper to operate.

Building a low compression engine that requires premium fuel (turbocharged) drives cost per mile up considerably.

Lesson: You can have moderate power and moderate economy, but you still can't maximize both (Which is something we've always known to be true).

quote Originally posted by Will: The thing is... to make 300 HP, an Ecotec needs boost. Boost requires low compression. Fuel mileage benefits from high compression. The two goals are at odds. You can't maximize both. At ~$4.00 per gallon for regular and $4.30 for premium, the improved gas mileage of a high compression engine requiring premium fuel will give it a lower cost per mile than a low compression engine that can operate on 87 octane. At fuel costs below this, the low compression engine is cheaper to operate. At costs above this, the high compression engine is cheaper to operate. Building a low compression engine that requires premium fuel (turbocharged) drives cost per mile up considerably. Lesson: You can have moderate power and moderate economy, but you still can't maximize both (Which is something we've always known to be true).

I agree but specifics are needed as to the compression ratio and boost level you are referring to. Technology has come a long way since the "you have to lower compression for boost" days. I believe all of GMs boosted engines as far as I have read are at least 9:1 compression, improved efficiency and direct injection ups the margin even more and is why the 3.6 DOHC has 87 octane as the recommended fuel although it has a 10.2:1 compression ratio and that's impressive. If you can cool the charge you can run moderate boost on a high compression engine. I've run a steady 7 psi with 9.8:1 compression and no intake charge cooling on about 89 octane in my 3900 swap and I'm certain the ECOTEC is more efficient than the V6. I believe it can be done although carefully and well planned.

This is the most intense I've seen to date; http://www.da-motorsport.co...jeler/mz3/mz3_en.htm

Scary. I agree with Will on this one. with a slight caveat. when I rebuilt my 2.8, I put in the higher 9.5:1 pistons, as I am not a great lover of boost or trying to plumb it in a tight compartment. on highway runs with the engine at temp, it consistently gets 34 mpg, not bad for old tech motor. The higher comp runs fine on 87, but I do have the option to boost it lightly (max 4-6 psi) if I wanted, but that will increase the octane requirement, and will by virtue of the increased power output lower the mpg on a highway cruise, which as Will says, you can't have both.
Ideally, a moderate compression increase for regular driving with a switchable boost for performance would be the holy grail. BUT the added exhaust restriction of a bypassed turbo won;t add mpg, so that is not going to help, and even a belt driven sc has loss just spinning a pulley even if it is disengaged from the load so you pay for the performance in reserve either way. (not to mention the change in fuel requirements when boosted etc)
So you just have to decide. longer trips between fuel, or more WOW factor. can't have both

Kind of ironic....the Fiero was originally intended as a high mileage commuter during times of high fuel cost. We've spent two decades modifying them for performance.....and now we're modifying them back to their original purpose. Everything really does come full circle.

Back in 1986, I bought my first Fiero new. A 2M4 coupe with a 5 speed. It regularly got 38-40 mpg on the highway if the air was off and the cruise was set close to the (then mandated) 55 mph speed limit. There was a nasty tempered peace keeper that patrolled the 90 mile span from home to college that was affectionately known as "The Lightless Bastard"....due to the fact that his patrol car didn't have the gumballs on the roof...only in the grill....and he was very hard to spot. He pretty much ensured compliance with the speed limit, as he had a penchant for handing out expensive tickets to college students. But in part thanks to his efforts, the Fiero got great mileage.

All of which got me to thinking a couple of years ago what could be done to make the Fiero hit the magic 50 MPG mark, just like Dustone is thinking. Gas will eventually go back up to the stratosphere....and the answer to saving gas money may have been sitting under our noses the whole time.

quote Originally posted by tjm4fun: Ideally, a moderate compression increase for regular driving with a switchable boost for performance would be the holy grail.

Nitrous

------------------
1987 Pontiac Fiero GT
418ci 'Mini-Rat' motor
dual stage nitrous injected
built 5-speed getrag

quote Originally posted by Will: I don't think you're going to achieve your goal on that wheel/tire combo. I switched my Pontiac 6000 SE AWD (3 speed auto) from 195/70-14's to 245/50-16's front and 205/60-16's rear and lost 1.5 out of 24 mpg. The rolling resistance of a wide, sticky tire is significant. You'd better plan for a rock-hard tire (something with a mileage guarantee) in the 185 range to hit your fuel economy goal, then go softer and wider to experiment.

Good point, I failed to think about the rolling resistance. I guess that's yet another area where I will have to trade off between performance and economy. I will probably go ahead with performance on that.

I don't think saving just a tad in mileage will be enough to get me to like the 185 tires...

i run a minimum 8 psi boost into my stock ecotec 2.2 .water/meth injection , air to air intercooler , and premium gas usually .no premium if i am not pushing it hard .i also have HP tuners .i use the GM electronics that the motor came from the factory with .i have seen 40 mpg(us gallon) on the freeway .mixed driving gets 30-36 mpg .no compression reduction and i have run 12 psi without damage .modern design motors with their amazing factory computers have changed the rules .

quote Originally posted by Frizlefrak: To El Paso by any chance? We're dying to see it when it's done. You can laugh at all us V8 swappers here when gas hits $5 a gallon again LOL. Any chance we can see the work in progress on our next cruise up to Mesilla? You can join us for lunch. We try to get together every few months or so. And if we can be of any assistance along the way, drop us a note. I'm sure Katatak will be stopping by this thread shortly.

You know me too well.

If you need any help, let me/us know. Would be more than happy to lend a hand.... 45 plus MPG in a Fiero would be nice and I think you can build some decent power with the Ecotec as well - I guess for the right amount of dollars, you can build power in just about anything. I'm all for a Hi MPG gettin commuter that is based on a Fiero. If you are like most of us, you won't have just one anyway. Have one for economy and one for - FUN oh and one for parts........lol. Keep us posted.

Hey Dan,

I now the holidays are near but I am feelin another run! Should have Ole Yeller together by the weekend.....Just cooking the ceramic paint on my exhaust right now. Had to do it while the wife was at work.... She'll kill me if she catches car parts in the oven..... Got the enngine/trans/cradle all together. Just got to get the wiring and a few odds and ends finished up. Talk to you soon.

Pat

How many v8 Fieros are there in EP?

Never driven a v8 Fiero before, would like to try it out sometime...

3 that I know of... Could be more! At least one more is planned. A guy can never have too many Fiero's. Meet us in Mesilia on our next run. I am sure that one of the V8's will let you go for a spin. Keep us posted on your progress and let us know if you need any help.

Pat

A pic from the last run to Mesilia. There is one V8 in this pic - red on the left!

quote Originally posted by DustoneGT: How many v8 Fieros are there in EP? Never driven a v8 Fiero before, would like to try it out sometime...

There just so happens to be one sitting in my driveway at the moment. Any time you feel like it, come on down and you can grab the pilot's seat. It's a 4.9 / 4T60E, so don't expect a 12 second quarter mile or anything, but it scoots down the road pretty good. The Honda boys never see it coming. They do, however, see it going And its getting around 20 mpg around town, so I can't complain too loudly. The only issue we have in El Paso is getting around the smog nazis....but there are ways around that too.

I need to get under the decklid on it this weekend...it's developed a squeaking drive belt. Only does it cold....squeak goes away after about 5 minutes of driving it, but it's annoying me. I may have to adjust how my tensioner is mounted....or the belt may just be getting old and glazed. At any rate, here is one of them.....mine in the center, flanked by Pat's Formula on the left and Jan's on the right on TransMountain Road



The only hint to what lurks beneath.....



....and the obligatory motor shot....



Pat....I'm ready for another cruise in the very near future. I can start sending out the feelers to see who's available to go. Dustone, we'll drop you a note just as soon as we get something planned so you can join us.

I just love the V8 look in a Fiero engine bay........ Next Falls project.......

Dan,

I am ready whenever..... Let me know!

You post this right after gas prices drop... just rely on the duke and call it good.

Gonna have to get the HD video cam out....been itchin' to make a nice Fiero video...

I'm sure we can make something more fun than this was with some nice mid-engined cars:

http://www.vimeo.com/2246749

Or This:
http://www.vimeo.com/1444829

[This message has been edited by DustoneGT (edited 12-10-2008).]

Man, the Bronco thing looked fun. I love those first generation Broncos....my dad had one, they were nearly indestructible. Very competent off road, and easy to work on. Some good looking rigs in the bunch.

Tuned @ 17.5AFR or so (only for cruising), I achieved 47mpg with my ecotec swap with the isuzi 5speed. 213 miles on 4.7 or 4.5 gallons.

Fosgate! Just the guy I was looking for!

I looked all over your threads both here and at Ecotec Forums and had some questions about your setup:

With the megasquirt, how do you get signal to the gauges? Does a wire go to the ECM and then to the gauge, or do you split the wire at some point between the ECM and the sensor so the signal can also go to the gauge?

How do you run the fan? Does the megasquirt kick on a fan relay, or is there an independent system that looks for the temperature and turns the fan on?

Any particular reason you chose to keep the Isuzu trans instead of one that came in an Ecotec car? It is my understanding that the Isuzu axles will slide right into an f23 getrag. Am I wrong?

Where's your O2 sensor? Can't see it in any of the pics of your exhaust. Do you have one?

Did you get rid of the vapor can (Right side between body panel and stock battery location) and charcoal thing (near stock v6 intake)? Does the fuel go directly from pump to fuel rail?

What ICM are you using? Were the blown ringlands caused by too much advance because you failed to correct for a 10 degree default advance that the ICM does?

quote Originally posted by Fosgatecavy98: Tuned @ 17.5AFR or so (only for cruising), I achieved 47mpg with my ecotec swap with the isuzi 5speed. 213 miles on 4.7 or 4.5 gallons.

The Ecotec bolts to the Izusu 5 spd?

quote Originally posted by DustoneGT: Fosgate! Just the guy I was looking for! I looked all over your threads both here and at Ecotec Forums and had some questions about your setup: With the megasquirt, how do you get signal to the gauges? Does a wire go to the ECM and then to the gauge, or do you split the wire at some point between the ECM and the sensor so the signal can also go to the gauge? How do you run the fan? Does the megasquirt kick on a fan relay, or is there an independent system that looks for the temperature and turns the fan on? Any particular reason you chose to keep the Isuzu trans instead of one that came in an Ecotec car? It is my understanding that the Isuzu axles will slide right into an f23 getrag. Am I wrong? Where's your O2 sensor? Can't see it in any of the pics of your exhaust. Do you have one? Did you get rid of the vapor can (Right side between body panel and stock battery location) and charcoal thing (near stock v6 intake)? Does the fuel go directly from pump to fuel rail? What ICM are you using? Were the blown ringlands caused by too much advance because you failed to correct for a 10 degree default advance that the ICM does?

Hey, I believe you emailed me? Sorry I never got back to you, I usually get about 2-3 emails a week from people interested and I lose track one once in a while. sorry!

Gauges: Speedo, runs off the transmission. I used the stock fiero transmission, nothing changed there. Water Temp, needs a second Coolant Sensor, wired same as stock. MS gets angry if you splice and try and share one CTS sigal. RPM, my original setup used a 94 Cavalier OBD1* (very important its OBD1 not OBD2) that had a tach signal wire, wired that up to the RPM gauge and I believe it read correctly. My new setup I havent got that far yet, and have just been using MegaTunix on my Laptop for the Tach. Fuel gauge, nothing changed as I just use a High Pressure Pump (ecotec is happy @58psi and a bit more)

Fan, I just use the A/C button to turn the fan on lol. I run straight water and drain in the winter. It runs happily at 182F, unless im sitting for 10+ minutes, but I when you hit the A/C button on it will kick the fan on. MS can be hooked up to a relay to control the fan, but I didnt bother.

The transmission is were most people ask the questions. NO the stock fiero transmissiosn do not bolt up, Bates Engineering build adapter plates for using an Generic GM Auto transmission, I used that adapter plate to make the Ecotec a "standard GM bell housing pattern" I then made an spacer and I use a stock ecotec flexplate-spacer- and a modifed Fidanza Quad 4 2.3L Aluminum Flywheel and a 9 5/8ths Ceramic Clutch. It sounds complex but I was researching some other stuff at the same time and made sense to test it on the ecotecfiero, very happy with the fiero transmission.

Another reason I used the fiero transmission is gearing. The F23 is good transmission, but more costly if I blow it up. The gearing isnt as high as the Isuzi either. I raised the Redline of the ecotec to 6900rpms. This allows me to do 0-60 in 2 gears (2nd goes to 70+mph) and the motor seems more happy then the cavaliers and such I drove with the F23 transmission, I believe it will benefit me for the racing I plan on doing.

I am using a Innovate Wideband 02, I havent posted any new pictures in a few months, most likely why no 02 sensor was in. I purchased the car with a swapped 1987 3.8v6 installed, most of the stock vapor/emissions stuff was long gone.

The ICM was a 1994 OBD1 ICM from a cavalier 4 cylinder. I am now using the "Direct Ignition Control" thru megasquirt. This is because I now have the "gen 2 ecotec block" which uses a 58x crank wheel instead of the earlier L61 7x which was readable with the OBD1 ICM (that ICM cannot read 58x thus I had to change the ignition)

Yes the ringlands gave out because I was unaware of the default 10 degrees advance. They took a beating before blowing tho!

Hopefully I got all ur questions!

The 3.35 final in the Fiero Isuzu is probably responsible for a large part of your high mileage numbers.

Interesting control system combo.

There's a 3 wire coolant temp sensor that GM uses now. It includes the two terminals that an ECM needs to sense temperature, plus a 12V ground to housing style sender for a gauge. It replaces the original CTS in almost everything and ensures that the ECM and the gauge see the same temp. Whether the gauge reads it accurately is another matter...

[This message has been edited by Will (edited 12-11-2008).]

quote Originally posted by Fosgatecavy98: I am now using the "Direct Ignition Control" thru megasquirt. This is because I now have the "gen 2 ecotec block" which uses a 58x crank wheel instead of the earlier L61 7x which was readable with the OBD1 ICM (that ICM cannot read 58x thus I had to change the ignition)

What is a "gen 2 ecotoec block"? Do you have a link to a breakdown of gen 1 vs gen 2? Is it any 2.4 or is it any displacement from a certain model year on?

Thanks,
Bob

all stock manual tranny axles fit right in to the f23 5 speed transaxle .i made my own mounts but roger thelin sells a kit that gives you mounts , tranny cable adapters and fiero to f23 hydraulic adapter .i run a redline of 6900 and that takes me to around 65mph in second gear .probably if i was running stock size tires that might be lower than 60 but i run245/50/16's in the back .these motors pull very strong in the higher rev range .i shift when i see the tach hit 6500 and when i look at my scan it shows i actually hit 6800 .thats the only way i can avoid the rev limiter in first and second .for me , i like having a nearly new tranny .

quote Originally posted by cerulean: What is a "gen 2 ecotoec block"? Do you have a link to a breakdown of gen 1 vs gen 2? Is it any 2.4 or is it any displacement from a certain model year on? Thanks, Bob

The 2.4 (LE5) uses the second gen block, but beware there are now some 2.2L motors out there using second gen.
More info here:
http://en.wikipedia.org/wik...ily_II_engine#Ecotec

The wikipedia entry has good information.

quote Originally posted by wftb: all stock manual tranny axles fit right in to the f23 5 speed transaxle .i made my own mounts but roger thelin sells a kit that gives you mounts , tranny cable adapters and fiero to f23 hydraulic adapter .i run a redline of 6900 and that takes me to around 65mph in second gear .probably if i was running stock size tires that might be lower than 60 but i run245/50/16's in the back .these motors pull very strong in the higher rev range .i shift when i see the tach hit 6500 and when i look at my scan it shows i actually hit 6800 .thats the only way i can avoid the rev limiter in first and second .for me , i like having a nearly new tranny .

Yeah my tranny I believe has about 150k on her, and has seen more than 4 motors (atleast 3 completely different ones not counting the different ecotecs) so why change it out? lol

20 psi of boost in a factory stock motor .i did not think that would ever happen .great info there thanks for the link .shows that my compression ratio is 9.5 ,my engine being out of a 2003 cavalier .

quote Originally posted by DustoneGT: The 2.4 (LE5) uses the second gen block, but beware there are now some 2.2L motors out there using second gen. More info here: http://en.wikipedia.org/wik...ily_II_engine#Ecotec The wikipedia entry has good information.

Thanks. I had read that page before, but I was focused in on the 2.4. It says that the 2.4 uses the gen 2 block, but it doesn't mention the 58x crank wheel in that section (just for the 2.2).

I'd like to replace the Duke with an LE5 with an F23 in my 84SE someday. Nearly double the horsepower and similar mpg.

quote Originally posted by cerulean: Thanks. I had read that page before, but I was focused in on the 2.4. It says that the 2.4 uses the gen 2 block, but it doesn't mention the 58x crank wheel in that section (just for the 2.2). I'd like to replace the Duke with an LE5 with an F23 in my 84SE someday. Nearly double the horsepower and similar mpg.

I have the LE5 in mine but I am using a non-VVT head with it. There is alot to still be gained with the LE5 bottom end tho.

quote Originally posted by Fosgatecavy98: I have the LE5 in mine but I am using a non-VVT head with it. There is alot to still be gained with the LE5 bottom end tho.

When you say non-VVT head, does that mean a 2.2 head on your 2.4?

Couldn't your Megasquirt also control the VVT if you wanted to go with a VVT head?

If you wanted to build the engine, VVT is a potential BOON to gas mileage. Think about what changing the phasing of the intake cam does... it changes the IVC angle... which alters dynamic compression.

You could build an engine with 13:1 static compression, and advance the intake cam at low throttle to keep dynamic compression in the 10-11+ range. You map the VVT such that when you nail the throttle the intake cam retards and reduces dynamic compression down to the 9.0 range so the engine doesn't knock. You'd make intake cam position your knock tuning variable more than spark timing. That ensures that you're always using optimal spark timing and the highest compression you can use at that manifold pressure without knock.