How worthwhile are exhaust mods?

General discussion about our beloved Tercel 4WD cars
Post Reply
Fudd
Newbie
Posts: 13
Joined: Sun Feb 18, 2018 10:01 pm
My tercel:: 87 4wd wagon

How worthwhile are exhaust mods?

Post by Fudd » Sun Feb 18, 2018 10:22 pm

I just picked up an 87 4wd wagon with a 6 speed. Body and interior are very good. The motor runs and seems to have strong acceleration,(considering what it is), and the trans shifts smoothly through all gears.

Unfortunately, that’s about the extent of whats good. The idle is erratic and way too high, the exhaust is rattly, the brakes grind worse than any I’ve ever heard, the front and rear ring gears are mismatched, the heater gives out no heat, etc... I got it cheap, but it’s gonna be a project and I’m prepared to spend $2000 or so building up the car I want.

My initial plans were to put on a Weber 32/36 carb, a header and a 2” exhaust. It seems however that headers are largely a custom job, and spending $800 for a custom header on an engine not noted for performance is probably not in the cards.

So I’m wondering what kind of performance gains could I reasonably expect with a larger manifold back exhaust and how big should I go?

User avatar
LowBuckCanuck
Top Notch Member
Posts: 350
Joined: Sun Apr 02, 2017 12:32 am
My tercel:: 1986 DLX 4wd Wagon "Jenny"

Re: How worthwhile are exhaust mods?

Post by LowBuckCanuck » Sun Feb 18, 2018 10:39 pm

I put a $30 cherry bomb on mine, and I think it feels faster. Might be just a placebo effect though. :wink:

Fudd
Newbie
Posts: 13
Joined: Sun Feb 18, 2018 10:01 pm
My tercel:: 87 4wd wagon

Re: How worthwhile are exhaust mods?

Post by Fudd » Mon Feb 19, 2018 7:53 pm

I had a glasspack on a 4Runner I used to own. It sounded good, but I’ll probably keep this one quiet. So long as I’m spending money fixing it up, I just want to pick all the low hanging fruit I can. If there’s no real benefit however, then I won’t bother.

User avatar
LowBuckCanuck
Top Notch Member
Posts: 350
Joined: Sun Apr 02, 2017 12:32 am
My tercel:: 1986 DLX 4wd Wagon "Jenny"

Re: How worthwhile are exhaust mods?

Post by LowBuckCanuck » Mon Feb 19, 2018 8:02 pm

Fudd wrote:
Mon Feb 19, 2018 7:53 pm
I had a glasspack on a 4Runner I used to own. It sounded good, but I’ll probably keep this one quiet. So long as I’m spending money fixing it up, I just want to pick all the low hanging fruit I can. If there’s no real benefit however, then I won’t bother.
Usually the general consensus is that with the amount of money you spend on performance farkles, you can just buy a Toyota 4a-c motor that bolts straight in. The motors are fairly cheap if you find one. They are about 7 to 10 more horsepower, a notable difference on a car that makes 60-something horsepower. The 4a-c was the stock motor in the famous AE-86 corolla, so they are constantly being swapped out for much more powerful versions. Hope this helps!

Jarf
Top Notch Member
Posts: 343
Joined: Sat Jun 21, 2008 9:20 pm
My tercel:: Currently without
Location: Borden, Ontario

Re: How worthwhile are exhaust mods?

Post by Jarf » Tue Feb 20, 2018 8:44 am

Engine design is all about balance.
Factory engineers work to produce the best balance of torque to HP across the widest usable RPM range suitable.
Can you get more HP out of an engine by opening the exhaust, yes, maybe, as long as you maintain sufficient back pressure to create effective scavenging of exhaust gases from the combustion chamber. That said, the power increase is going to come at the top end and at the expense of lower end torque.

Petros has outlined just about all you can do with a 3A, or upgrade to the 4A or go crazy with a 4AGE

But do understand that changing how much and where the power occurs is just as important, maybe more so, than how much you have.
200hp at 7000 doesn't help when you need grunt torque to get up and going.

Webers (et al) became popular at the track, changing weather conditions can affect things like air/fuel ratios, being able to dial that variable in by swapping out jets can be the difference between win and lose. On a street car, its a pita. Because it isn't as adaptable to varying conditions (like real life) it ends up running perfect twice a year, the rest of the time is a balance between nursing it along and changing out jets.
The power increase they provide comes in the upper rpm ranges and they tend to be peaky.

So it all depends on what you want and what you're willing to trade off, to get it.

User avatar
Petros
Highest Ranking Member
Posts: 11399
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: How worthwhile are exhaust mods?

Post by Petros » Tue Feb 20, 2018 9:08 pm

welcome to the forum!

where do you live Fudd?

I have owned and driven many miles on both the factory carb and the weber. I do not find the weber produces significanly more power, and performance at extreme weather events it does not perform as well (very hot or very cold). Although all of the vac operated equipment on the stock carb might look intimidating, but the Service manual walks you through each system. Each one is realatively simple and easy to test/check, you just take it one system at a time.

Sounds like you have a bad vacuum leak, you must find and fix that first (you might be more than one leak, one project Tercel I found had six vac leaks, and several misrouted vac lines, that also acted like a vac leak, ran great after about 5 min of correcting the vac lines! Previous owner thought the carb needed rebuilding and did not want to do it). You might spend a lot of money replacing the carb with a webber, and find you still have a vac leak and it still runs like crap.

First rule of auto repair (and most other repairs too):
ALWAYS DIAGNOSE THE PROBLEM BEFORE YOU TRY AND FIX IT!!!!!

If you rush into "fixes", you will waste time, money, replaced good parts and get very frustrated.

Brakes are an easy fix, cheap too especially if you buy parts from Rockauto.com. If you are going to replace all of the brakes, you should consider doing the brake up grade I outline over in Repair guides section, all of the parts are from other Toyota models, you can order them on line, or get them from a wrecking yard. There is no point in replacing the stock brakes, the front one are too small and will over heat and warp, turn blue and get full of heat cracks. go for the bigger ones. only costs a small bit more, but saves you money since they will last longer.

As far as engine performance: you can not push this under-powered and obsolete engine too far, it will become unreliable. If you intend to rebuild it, than do not waste your time and money, get a 4ac engine core and and rebuilt that for your Tercel. It iwll be more power and much more reliable, and all the external parts swap right over from the Tercel 3a to the 4a no problem.

that being said, if you just want to get a bit more performance out your stock engine: first thing you do is getting running good, tune up (check spark plug wires, dist cap, spark plugs), fix all vac leaks, verify all vac operated devices are working properly, clean out the carb if necessary (or complete rebuilt, the remanufactred carbs are not recommended, they are not a good value and too many are junk). Set the spark timing at 10 to 12 deg BTDC (rather than the factory 5 deg), that improves performance and econmy. Than see how it performs, if still unsatisfied there are a few other items to try.

You might also consider a SeaFoam engine treatment, many have good luck with it. I replaced my whole exhaust system from the manifold back, but not worth it until yours rusts away (like mine did). it has a straight pipe to a single rear muffler (A stainless performance muffler I pulled off a lowered Civic in the wrecking yard and bought for $6). I think the local muffler shop did that for me for about $160 as I recall.

Delta Cams in Tacoma WA sells a street performance cam which is a good deal, about $60 exchange as I recall. easy to install without removing anything more than the valve cover, timing belt and a few other things. This may affect your fuel economy a little if you do a lot of stop and go driving. I doubt it affects long distance trip economy.

Do not be tempted to strip out all of the emissions equipement, most do not effect economy nor power, and a few actualy improve the economy. The carb was designed to run with all of this stuff in operation, if you strip it all out it will never run correctly. Than you would be forced to up grade to the weber.

Short of replacing the engine, anything else you might do is a waste of money, or the cost is not worth the tiny gain. do not fall for the after market devices that claim to improve power or economy. If it was that easy all of the manufactures would have already installed that stuff.

Good luck.
'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)

Fudd
Newbie
Posts: 13
Joined: Sun Feb 18, 2018 10:01 pm
My tercel:: 87 4wd wagon

Re: How worthwhile are exhaust mods?

Post by Fudd » Tue Feb 20, 2018 11:00 pm

Thanks for all the advise, and I live in Tacoma BTW. It appears that there isn’t much to be gained with any engine mods, so I guess I’ll just leave it stock for the time being.

One thing I’m going to have to do in the future is get the front and rear ring gears matched up. I’ve got 4.10’s in the rear and 3.73’s in the front. The guy I bought it from threw in a spare differential with a 4.10 ring gear on it. He told me it was an easy matter to install. Made it sound like it was just a bolt on. Having owned a few 4x4’s over the years though, I’ve never heard of that being the case. I’ve always understood that swapping ring gears requires special tools and is best left to a pro.

My own thought was to buy an early model corolla, swap the rear axles and then resell it. That just seems like the simplest and cheapest method to me, plus I’d rather have the 3.73 gears.

Lastly, and this is kind of off the wall, I’m wondering about the feasibility of manual hubs on the rear axle. I’m sure if it were easy then someone would have already done it, but It seems to me that constantly having to accelerate both the rear axle and the driveshaft, (at 4x’s the rpms of the wheels), and then deal with the drag of both is just very inefficient. I’d think there’d be some major efficiency gains to be made there.

User avatar
Petros
Highest Ranking Member
Posts: 11399
Joined: Sun Jan 28, 2007 6:31 pm
My tercel:: '84 Tercel4wd w/extensive mods
Location: Arlington WA USA

Re: How worthwhile are exhaust mods?

Post by Petros » Tue Feb 20, 2018 11:23 pm

I do not know about "major" efficiency gains, but perhaps a bit. not sure it is worth it. there is a two solid half shafts, one on each side, with a single bearing in the end of the housing (the inner end is supported in the diff that has its own bearings), so not sure how you can add hubs, it would be a major retrofit, and add a lot of weight (also not good for economy).

Swappig out the diff assembly is easy, swapping out just the ring gear is not, and I would advise against it. the rear diff has an assembly that contains the bearings, carrier and ring and pinion all set up, you remove the two half axles (from the brake backer plates), and than remove the drive shaft (4 ten mm bolts) and than you remove about 14 twelve mm bolts from the housing and the whole assembly comes out. It can be changed out in about an hour, perhaps a bit more for time to refill the gear oil. you can buy the whole 3.37 rear diff assembly from a wrecking yard, out of any model 4wd Tecel '83 and84 model years. the rear assembly is way easier to swap out than the front...unless you have to remove the trans axle assembly for some other reason, than the front is not too bad to swap.

DO NOT use the 4wd until you have matching front and rear diff ratios. It will put a lot of stress on the drive train and you will either tash the transmission, or trash one of the diffs. I have seen it happen.

too many idiot autoparts listings for interchangeablity show all models Tercel4wd trans are interchangeable. Not true, only the gear box, or only if you swap out the two diffs together, if you have a different ratio from the one in the wrecking yard.
'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)

Post Reply