understanding Lightened Flywheel combined with larger tires

General discussion about our beloved Tercel 4WD cars
Post Reply
The Professor
Top Notch Member
Posts: 310
Joined: Wed May 12, 2010 6:38 pm
My tercel:: 1987 Tercel SR5 4WD wagon
Location: Western Washington
Contact:

Re: understanding Lightened Flywheel combined with larger tires

Post by The Professor » Wed Dec 05, 2018 7:57 am

If you're putting on larger tires, just keep the stock flywheel. I have lightweight flywheels on my turbo wagon and WRX and while it does free up some existing horsepower that was previously accelerating the extra flywheel mass, there are tradeoffs with drivability, comfort, etc.
1975 Subaru SuperStar wagon
1984 Subaru Turbo-Traction wagon
1984 Subaru Turbo-Traction coupe
1987 Subaru RX coupe
1987 Toyota Tercel SR5 wagon
1987 Subaru RX Type-RA coupe
1999 Subaru Forester S
2002 Subaru WRX sedan

User avatar
Petros
Highest Ranking Member
Posts: 10596
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: understanding Lightened Flywheel combined with larger tires

Post by Petros » Wed Dec 05, 2018 5:18 pm

sounds like you are getting a lot of bogus speculations from those that do not know exactly what they are talking about. All 3a engines have the massive flywheel (heavier than any other Toyota engine at the time), it was designed to go into their entry level FWD car. Almost all of them went into 2wd cars, so whatever their merits for rock crawlers or off road use, that was NOT the motivation for Toyota with the 3a engine.

Lightening the flywheel does not give you more hp. It allows the engine to rev up faster which is important for performance shifting, be it on or off road. It will also reduce the weight of the installation overall, a benefit to pursue no matter what other benefits it offers.

for use in the Tercel model, their entry level cars, most likely bought by a beginner driver, it makes the engine more stall resistant from botched shifts or poor clutch/throttle skills. I think this is the motivation for toyota to put them in the tercel, rather than offering a higher hp engine, like Honda, Nissan and Mazda offered at the time for their entry level car. It was cheaper (less development investment) and easier to use a small lower hp engine with a heavier flywheel. Particularly since the ever increasing emissions restrictions, the heavier flywheel is a simple and attractive approach to getting easy shifting/drivablity without the complex wizardry that Honda used with their CVCC engine, or going to EFI like the others had done. Toyota was always more cautious and conservative than their competitors. So when a new driver goes to test drive a Honda or Nissan, but finds the Tercel results in less stalled engines (it is more forgiving of poor clutch technique), they are more likely to buy the Tercel. I suspect it was a marketing decision.

Although a heavier flywheel might be better for low speed rock crawling, I do not see any advantage to a heavy flywheel if you use proper clutch technique. The tercel4wd was never intended as an off road machine, their target market was bird watching according to their internal documents. In the tercel, once you have good clutch/throttle shifting skills, the extra weight just slows the throttle response and adds useless weight to the car. Tuning the engine to get a few more hp completely does away with the marginal amount of stall resistance the heavier flywheel offers.

There is one other benefit to heavy flywheels, it allows for less precision in the balancing of the engine parts, and mitigates the vibration it causes. but toyotas engine in my experience have highly balanced engines compared to the older crap that came out of Detroit. The heavy flywheel meant they did not have to reject as many parts that were out of tolerance in a big cast iron engine. Competition, regulations, and performance demands have eliminated that approach for manufacturers now. But that does not seem to be Toyota's motivation, particularly when all of their other, higher hp engines, had lighter flywheels.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

User avatar
Petros
Highest Ranking Member
Posts: 10596
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: understanding Lightened Flywheel combined with larger tires

Post by Petros » Thu Dec 06, 2018 1:42 am

I do not think there would be much difference with a lighter or heavier flywheel on larger heavier wheels and tires if you use proper clutch technique.

A heavy duty (more heat resistant) clutch will serve you well if you intend to do a lot of off roading. What you need to keep heavy wheels and tires moving from a dead stop is more power/torque. flywheel will not make a difference. the heavier flywheel only helps from a dead stop where once rolling the car keeps moving (on a smooth paved surface), I can not see this as your off road model. if the car is not moving after the initial clutch engagment the engine will stall. That is best accomplished with a smooth and steady clutch engagement, with a bit of slip to start out.

That being said, if you have the 4.11:1 final drive it should handle the larger tires well, without issues. certainly better than the earlier 3.73:1. Coaxing a bit more low end torque out of the engine will make a noticeable difference, more than a heavier flywheel.

what improvements to the engine/exhaust have you made, or are planning?
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

User avatar
Petros
Highest Ranking Member
Posts: 10596
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: understanding Lightened Flywheel combined with larger tires

Post by Petros » Thu Dec 06, 2018 5:49 pm

the 4ac low end will help, more displacement. when you rebuild it you can also mill the head to raise the compression ratio a bit as well to add a bit of power, but do not go too much. And you can overbore the cylinders to get a bit more displacment, this will require oversized pistions (if you were going to replace the pistons anyway, this is a good thing to do). you may have to switch to premium fuel or you will have head gasket problems with the higher compression.

You can install a Delta Cams street performance reground cam shaft. it is a fairly easy installation, and I think they are about $59. (exchange price) last time I checked. Delta Cams is in Tacoma WA

Along with the advanced timing, these will give you the extra low end power you will need for the larger tires and wheels. with the 4.11:1 final drive ratio it will work fine, and neither of these are too costly. And from the outside of the engine, both of these will pass the visual inspection and still pass the emissions test as well.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

User avatar
Petros
Highest Ranking Member
Posts: 10596
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: understanding Lightened Flywheel combined with larger tires

Post by Petros » Fri Dec 07, 2018 3:10 am

as I recall the Schneider cams are new billet and fairly costly. Forum member Synth used a Schneider on his rebuild with a weber carb, but went back to the factory cam as it was way too much cam for a street engine. though I do not know what grind it was, if they offer a more mild grind they may be okay (if it was not for the price).

Delta has the 3ac/4ac grind in their inventory but you may have to call them to order it. they will send you the cam and charge you a core charge. you get refunded the core charge when you return to them a good usable core cam shaft.
'87 Tercel 4wd SR5 (current engine swap project)
'84 Tercel 4wd (daily driver, with on going mods)
'92 Mazda MPV 4wd (wife's daily driver)
'85 Tercel 4wd DLX auto(daughter's daily driver)
'01 Honda Civic (other daughter's daily driver)

The Professor
Top Notch Member
Posts: 310
Joined: Wed May 12, 2010 6:38 pm
My tercel:: 1987 Tercel SR5 4WD wagon
Location: Western Washington
Contact:

Re: understanding Lightened Flywheel combined with larger tires

Post by The Professor » Fri Dec 07, 2018 7:40 am

You have to call Delta Cams to learn the options for your application, their website hasn't changed in at least 15 years. They are affordable, reliable and trusted in the old school Subaru world. They can also do custom grinds outside of what they normally offer.
1975 Subaru SuperStar wagon
1984 Subaru Turbo-Traction wagon
1984 Subaru Turbo-Traction coupe
1987 Subaru RX coupe
1987 Toyota Tercel SR5 wagon
1987 Subaru RX Type-RA coupe
1999 Subaru Forester S
2002 Subaru WRX sedan

Post Reply