DOHC B6 Information

[bhearts]

Quoted from a discussion that started on the "high performance clutch test" thread.


"Think you could draw through the b3 vaf and have a fmu for a b6d with 8psi?"
- BHEARTS

The b3 VAF is practically identical to the b6ze miata vaf. In fact, Dragonhealer swapped a festiva VAF onto a miata on the dyno and made slightly more hp than the miata vaf. That was probably just a calibration difference, but it proved the point. The Festiva VAF isn't a restriction until somewhere around 140ft.lbs of tq.
In fact, the entire b3 fuel injection system is very similar to the 1.6L Miata system. The biggest difference is the ignition system. However, the festiva has sequential spark ignition, whilst the miata is wasted spark. Sequential spark is better for boost because there is less chance of burning exhaust valves under boost. With that said, in thoery the Festiva engine management system should be better suited to run boost than the miata system. The same tricks that they use to turbo the 1.6 miata will work on a Festiva.

That. ^ exactly what I was hoping to hear. I really want to clean up my engine bay though. I was thinking about stripping it down before I paint it and just putting my ms3 back in. But that scares me.

Sent from my SM-G900V using Tapatalk

[Advancedynamix]

Quoted from a discussion that started on the "high performance clutch test" thread.

Well, the positive side of this is that stock festiva fuel injection will make enough power to glaze a racing clutch. There ya have it! No need to do all the excessive wiring on these swaps guys, the stock electronics will fuel a b6d good enough to torch a spec clutch.

"Think you could draw through the b3 vaf and have a fmu for a b6d with 8psi?"
- BHEARTS

The b3 VAF is practically identical to the b6ze miata vaf. In fact, Dragonhealer swapped a festiva VAF onto a miata on the dyno and made slightly more hp than the miata vaf. That was probably just a calibration difference, but it proved the point. The Festiva VAF isn't a restriction until somewhere around 140ft.lbs of tq.
In fact, the entire b3 fuel injection system is very similar to the 1.6L Miata system. The biggest difference is the ignition system. However, the festiva has sequential spark ignition, whilst the miata is wasted spark. Sequential spark is better for boost because there is less chance of burning exhaust valves under boost. With that said, in thoery the Festiva engine management system should be better suited to run boost than the miata system. The same tricks that they use to turbo the 1.6 miata will work on a Festiva.

[Advancedynamix]

[Team Lightning]

Thanks Charlie. I use that route as a gas mileage loop, 1, it's a beautiful route, 2, I go by my moms. Normally driving to work, it's 32 miles with 29 of those on I-85. Traffic generally runs in the 70-80 mph range. At those speeds, I get 34mpg plus/minus 2. The B6D is a big improvement over the B3. I'm very happy with it.

[Advancedynamix]

Thanks for the details Jerry. I've been getting 32 city with mine, but it's been over 100 degrees out and I drive pretty aggressively. I got 40mpg average from Phoenix to San Diego, and we were traveling at 80+ mph the whole trip except the steep parts of the mountain just before S.D. where the stock B3 in front of me couldn't keep that pace. The b3 had to be shifted to 3rd in places, but the b6d could pull 5th no problem.
The amazing part is the b3 only got 32mpg on the trip, but to be fair that was with 2 people, a bunch of gear and the A/C was blasting. Haha. Pedro has the old hand crank style air conditioner that is way better on gas than that new style engine driven stuff.

[Team Lightning]

Yesterday I ran a gas mileage test on my 90L with a B6D.
Specs are as follows:
1990 Festiva L, 363,473 miles, E series Transmission, B6D with Approx 117,000 miles with the Capri wiring and ECU.
165-55-14 Federal Formosa FD1 tires, Miata Semi hollow spoke wheels (12 pounds)
Aspire swap with Rio KYB struts, and mounts on the front, Festiva KYB'on the rear with
full coilovers, lowered 3 or so inches. Also has an Aspire manual steering rack
Factory Rear spoiler.
Left Lavonia on highay 17 north.
Followed Highway 17 through Toccoa Bypass to highway 441 North
Followed 441 North to Cherokee NC.
US highway 19/74 from Cherokee,NC thru Bryson City,NC to Murphy,NC.
Highway 60 from Murphy,NC to Blue Ridge,GA
Highway 515 from Blue Ridge GA to Elijay,GA
HIghway 52 From Elijay,GA to Dahlonega,GA.
Highway 115 from the 52/115 Split to Highway 105 just outside of Clarksville,GA
Highway 105 to Racetrack fuel station.
Total miles driven 286.5, fuel used 6.48 gallons.
44.2 miles per gallon.
Test drive has speeds ranging from 25mph in town to 4 lanes at 65mph.
Both mountains and flat driving, both open road and heavy traffic.
I stayed within 5 mph of posted speed limit with the exception of going down long hills where it gained speed as a result of gravity.
At no time did I coast in neutral or with the clutch held in, drivers window was up for approx 1/2 of the drive. All other windows were fully closed.
No hyper miling or anything special to increase mileage other than no jackrabbit starts.
Temp was 64 degrees whenI left Lavonia,GA. In the 80's, i'm sure when I filled up at the Racetrack station.

The last time I ran this with the B3, which was low on compression,I got in the 38 mpg range.
I'm very pleased with this motor.

[Safety Guy]

Thanks Charlie!

Karl

[Advancedynamix]

The fuel line swap is pretty straightforward, but take lots of pictures of how the lines are routed on the donor car. They fit in there like a brain teaser game and can take hours to get right after you've forgotten which line went where (like I did).
You'll need the lines and all the brackets from the F.I. donor car because they are all different.
I would swap the tank. Brand new tanks are cheap for the F.I cars, and that gives piece of mind that the tank and all the lines are fresh. You can use a sender from a 2 door aspire because they fit right in and seem to be more plentiful at the salvage yards. For that matter, an aspire 2 door tank also fits in a Festiva. It is easy to upgrade the aspire sender with a high flow aftermarket pump.
If I were to convert another carby car, I'd go straight to megasquirt. On my car I used Capri fuel injection because I wanted to compare this version of L-jet to the miata version. After my experiments are finished I'll most likely sell this setup to a member and switch to megasquirt.

[Safety Guy]

Charlie, how important is it to replace the carby fuel and fuel return lines with larger diameter FI ones? At least that's what I recall from reading around here. And do you recommend an FI fuel tank or going with an exterior electric pump?

If I get another carbed Festiva I'll probably go older B6 with a Weber 2bbl. But I may also go FI with whatever else I may have on hand.

Karl

[Advancedynamix]

Can I use a Carb Intake and Carb on a B6 even though it was designed for EFI ?? I have a 88 with a carb

Like Karl said, the first generation (1985-1989 mazda 323, mercury tracer) SOHC B6 can fairly easily be used in place of your original engine. Though everything will swap over from engine to engine, the stock festiva carburetor can be troublesome and expensive to maintain. Probably the best carburetor setup to use would be Bravekozak's Twin Carb Conversion
That being said, this thread is dedicated to the DOHC B6 variants. These engine cannot be easily carbureted. There have been exotic carburetor conversions which have been done to these engines (mostly on the Miata roadster) but the cost of these setups is usually far more expensive than swapping a car to EFI.
If your 88 festiva is in good, solid condition, and you enjoy the car, I suggest swapping to an EFI DOHC B6. The fuel injection swap is more work than the actual engine swap, but I recently did this swap on my 88 and within 1 drive I was convinced my time was well spent. It can also be a fun little project, with people on this forum always willing to help out with advice and parts. The festiva makes a great project car.

[Safety Guy]

Salesguy, if you have an '88 Festiva and you want to install an older B6 engine ('86 to '89), I believe the Festiva B3 intake and exhaust should bolt up to the older engine. If you have a '90 to '94 B6, no dice.

Keep in mind your B3 manifolds won't maximize the B6's capabilities, but they should work okay and give you some more zoom.

Karl

[salesguy01]

Can I use a Carb Intake and Carb on a B6 even though it was designed for EFI ?? I have a 88 with a carb

[Advancedynamix]

^ The discussion above has been copied to Festiva Chassis Dynamics thread.

[Dragonhealer]

interesting. thanks for your input. the 100% was a "hypothetical" limit but mathematically impossible. just wondered how close to that would be ideal. my build goal will require the engine be moved forward as much as practical and my old school magazine thinking was that it would hurt handling so this is good news. now it brings up other questions. i wonder how much this affects the contribution of the rear brakes if the rear of the car is unloaded by the fulcrum?, effect of a heavy front end. do you use an adjustable proportioning valve? or as silly as it seems, if they don't contribute much, could the rear brakes and their unsprung weight be removed? not on a street legal car of course.

Excellent questions! And I'll leave it for Charlie to reply, but here is a datum point: stock Festiva on corner scales with the rear seat and rear hatch assembly removed has 70.7% of the weight on the front axle. I had hypothesized a 77%/23% as ideal, but that may fall short of the optimum, we are working to find out!

[Advancedynamix]

This is a great topic. It's good enough for it's own discussion, so I copied your post to a new thread in the wheels/suspension area. The new thread is titled Festiva chassis dynamics. We can discuss this in more detail there, so it's easier to locate when other people have the same question.