Project: 1939 Jaguar SS100 Replica Classic Roadsters, LTD. "Duke"

[Bruce Nunnally]

Thanks Jim. i went first thing and got new bolts and a m8-125 tap. I was able to get the 5th bolt firmly inserted and have a good header to head seal. I will post a video of sound.

Still sorting the exhaust. I might can creep down to muffler shop Monday or Tuesday. They are not open Sunday.

The steering bracket is 1cm off the header. If it turns out to be an issue I will scallop the bracket to give more clearance.

So exhaust pipe disconnected and hanging on bungie cord, and no exhaust piping in the flow.

[Texas Jim]

Glad you got all the bolts in.

Too bad you can't go make a run in the morning with the header open and see what it does... LOL

[Bruce Nunnally]

 

Header install video (for sound).  What we don't hear is the explosive sound of a exhaust header leak.  What we do hear is the muffler is not attached yet.

[Bruce Nunnally]

Temporary jury-rigged flow path has some flow coming out the muffler.

The Air fuel is reading max high at idle. I am unclear if the internet says this is due to exhaust leaks the AFR is not reliable, or if the AFR is high, or if it need calibration. It seems to me that with exhaust leaks the AFR would still be representative, but perhaps the non-oxygen gases escape early first chance or similar? When I rev the engine the AFR goes down from 22.4 (max) to 16-17.

My strategy is to get the exhaust sealed well enough myself to test and to quiet it down for the trip to the muffler shop. It is quiet enough now, but the AFR reading gives me pause. Any suppositions?

I would prefer not to spend a lot of time getting 100% seal to the exhaust, but I would like it to be sealed well enough to be representative for testing.

Tomorrow I will get some Permatex Ultra Copper High Temp RTV silicone sealant and see if that will do well enough for a temporary fix.

[Cadillac Jim]

If the AFR is reading high but the engine runs, then the pressure pulsations are pulling air *into* the exhaust and some of this air is getting to the oxygen sensor. You're going to have to get a good seal to get the AFR readings back.

[Bruce Nunnally]

Tonight I closed the exhaust up as best I could and took the Roadster out to test the Header. Temp 78F, baro 30.01.

It still has an exhaust leak, and can't use the AFR, although it is better than it was. My thinking is I got it 'good enough'

to test and decide whether to keep the headers on, and get the exhaust fixed at a shop, or swap them back off.

The previous low was a 13 sec 0-60 mph before the airhorn tests. I still have the airhorn on the carb. The best

with airhorn was 13.5 sec 0-60.

Today's run:

Run num Speed(mph) Time(s) Dist(f) Graph run Description
2 0.00 0 0.00 Speed Start
2 10.00 1.10 8.35 Speed Line
2 20.00 2.58 41.58 Speed Line
2 30.00 4.41 108.79 Speed Line
2 40.00 6.41 212.02 Speed Line
2 50.00 8.99 382.91 Speed Line
2 60.00 12.77 688.82 Speed End

3 0.00 0 0.00 Speed Start
3 10.00 1.07 8.30 Speed Line
3 20.00 2.54 41.08 Speed Line
3 30.00 4.35 107.69 Speed Line
3 40.00 6.36 211.52 Speed Line
3 50.00 8.93 381.34 Speed Line
3 60.00 12.58 677.02 Speed End

Previous run before header install with airhorn:

Run num Speed(mph) Time(s) Dist(f) Graph run Description

2 0.00 0 0.00 Speed Start
2 10.00 1.11 8.74 Speed Line
2 20.00 2.62 42.62 Speed Line
2 30.00 4.53 112.74 Speed Line
2 40.00 6.63 220.86 Speed Line
2 50.00 9.45 408.16 Speed Line
2 60.00 13.70 752.78 Speed End

best with airhorn was a 13.5 but that was this one that had the odd trough in the middle:

Run num Speed(mph) Time(s) Dist(f) Graph run Description

2 0.00 0 0.00 Speed Start
2 10.00 1.18 8.69 Speed Line
2 20.00 2.69 42.54 Speed Line
2 30.00 4.58 112.03 Speed Line
2 40.00 6.66 219.07 Speed Line
2 50.00 9.46 405.14 Speed Line
2 60.00 13.50 730.44 Speed End

So time, temperature, header, different day, and 13.5 down to 12.6.

3TC Virtual Dyno plot:

This plot shows the 2 test runs with the header in. The red was the 12.8 sec run, the blue was the 12.6 sec run. On the red run I fumbled the shift at 6000 rpm and shifted to D instead of 2, but should have little impact on the dyno -- just on the time.

Comparison of red/blue with headers and carb air horn to green/yellow without headers with carb air horn.

Average with headers: 67.5 whp. Average without headers: 62 whp

Average with headers; 125 lb-ft of torque; Average without headers: 120.5 lb ft of torque

Improvement in 0-60 time: Average before 13.5 sec average after 12.7 sec.

Side by side comparison of Run 1 with Header (12.8 sec) to Run with Air horn pre-headers (13.7)

[Texas Jim]

A 1 second improvement is a pretty big gain...

With the header, looks like it is pulling all the way to 5000 before starting to drop off, instead of going flat at 4000 then dropping off after 5000...

[Bruce Nunnally]

After examining the 4-2-1 stock exhaust manifold I was concerned that the header would not be an improvement. My interpretation of the results is that it is an improvement of 5-6 whp. It comes at the expense of some ground clearance, and I'll have to see if we can mitigate that in restoring the exhaust flow. Once the rear springs are repaired that will add some clearance in the back end and help somewhat. The header can't really be bent or altered and the collector hangs low and angles down.

Hard to visualize from the photo but I am hoping we can come off the header collector to an S pipe that would curve back toward the driver side and allow the midpipe and muffler to sit higher. That won't change the header collector height but it would keep the rest of the system from sitting low.

There are other header vendors and I could look to see if there is a selection with a shorter manifold to collector distance, but I am hoping properly pinned up I can get up the drive without scraping. another option would be to take the stock manifold as a model and replace all the piping with one size larger.

I like the sound of the headers and the science, but loss of ground clearance for ~6 whp is a hard trade.

I suppose we will continue to see some relatively large changes in 0-60 time for small changes in top-end hp as long as the top end is off the curve low. If you look at the delta trend in 0-60 for the 13.5 sec run, the car struggles from 40-60. 0-10 1.2 sec 10-20 1.5 sec 20-30 1.8 sec 30-40 2 sec 40-50 2.8 sec (now 2.5) 50-60 4 sec (now 3.5). A proper trend would be 1.1/1.5/1.8/2.1/2.5/2.9 or similar for 11.9 sec. So that last 40-50 and 50-60 can show rapid improvement with small changes in hp between 4000-6000 rpm.

Another way to look at it is that the car should be doing 12 sec flat 0-60 and is not properly tuned yet to do so.

[Cadillac Jim]

The stock header looked like it was designed for performance, with constant cross-section, gentle bends, and 4-to-2-to-1, so I didn't expect this much difference. This is *major* and shows that the stock exhaust manifold does restrict at high RPM; perhaps the stock manifold was designed for a power band below 5000 RPM.

The weld in the stock setup may have been for a dual cat at the 4-to-2 level, which would have acted as a pressure relief point for resonances. Keeping a constant cross section through that point as the weld did (and your flex pipe does) would remove the resonance that the port-to-relief distance would generate, and a new resonance would be introduced at a much lower RPM. The point is, perhaps you can move the ultra-low-RPM torque peak up into a better range by using that ten inches for a resonator or a straight-through "muffler". It's a bit too close to the ports for fiberglas, so watch out for that. What you really want is a resonator, not a muffler.

Note that most 4-to-2-to-1 and 4-to-1 high performance exhaust systems end at a collector, which acts as a resonator at the 2-to-1 point. The collector extends for a few inches, then necks down to the exhaust pipe, cat, or muffler pipe size. This allows the system between the exhaust ports and the collector to provide a resonance for mid-band torque enhancement. If you add a resonator where your ten inch gap is now, that will do this for your system. Note that the size and shape of the resonator moves the resonance around, and broadens it, so this is yet another degree of freedom in the tuning.

You can test this idea by removing the flex pipe and doing a test run with the manifold open and see what it does to the torque curve. Don't do it for more than one run, because cold air is getting to the AFR from there, and if it gets to the valves and ports it could be bad for the engine over any period of time. The torque curve this provides is approached by a very large resonator; smaller resonators will provide a compromise between this torque curve and the no-resonator torque curve.

Another variable is the offy intake manifold. With the stock manifold, the neck-down in the adapter to the stock carburetor venturi sizes is effectively a throttle plate that makes the flow capacity of the Weber not much more than the stock carburetor. You removed a poorly done gasket that was effectively an even smaller throttle plate to some effect. The Offy intake will allow the Weber to deliver its full capacity to the intake ports.

Both the stock intake and the Weber intake ports show near constant-length runners to the ports. The runners to cylinders 2-3 are an inch or so shorter than the runners to cylinders 1-4. This will give two intake resonances at high RPM that will give a broad horsepower peak. But the Offy intake should flow much better than the stock intake. This, combined with your headers, should wake up the engine as much as you can without cam and possibly head work.

[Bruce Nunnally]

Nice points, Jim. I need to research where the stock catalytic converter was located, and why the stock manifold has those mid-pipe welds. The replacement cats I see for 1980 Corolla are simple 1-pipe in/out affairs that would have been located after the collector in the manifold, not at mid-pipe as I suggested earlier. The length of those pipes doesn't make sense for the targeted RPM bands.

The offy manifold hopefully will also add another 5+ whp and take another .5-.8 sec off the 0-60 time. I do have the intake manifold and am ready to start that install once we get the header tests completed.

I am also tempted to do a without air horn with header before offy test.

[Texas Jim]

The offy manifold hopefully will also add another 5+ whp and take another .5-.8 sec off the 0-60 time. I do have the intake manifold and am ready to start that install once we get the header tests completed.

I am also tempted to do a without air horn with header before offy test.

I think that would be an EXCELLENT idea...

For some reason, I don't like that air horn.

[Bruce Nunnally]

Over to muffler shop next, then will retest with muffler welded and no air horn. Also want to do another 6200 rpm all 1st gear run.

After that as I get time can get started on intake install.

[Cadillac Jim]

The welds in the photo of the stock manifold and exhaust seem to be ordinary assembly welds and may be there simply to make fabrication of the sections simpler by limiting the total number of bends or keeping each section in one plane, with the cat after the collector as it is in most cars. But the welds are relatively fresh. Perhaps they were simply un-done to move the rear section when the car was lowered. If that is so, then putting in a resonator at the current ten-inch gap would simply restore the tuning lengths for the stock system by putting in a pressure relief at about the same place where the stock collector and cat were. But just a resonator would provide the pressure relief without obstruction, as the stock cat probably did to some degree.

[Texas Jim]

Some of those type engines had the Cat attached to the actual exhaust manifold... the welds may be where the CAT was cut off of the pipes.

[Bruce Nunnally]

The parts diagram shows 2 midpipe options, one with two tubes as mine has and one with a pup cat. Both run into a single cat.

Read more: http://www.villagetoyotaparts.com/showAssembly.aspx?ukey_assembly=332029&ukey_make=1021&modelYear=1982&ukey_model=14407

I am still unclear why the oem setup doesn't flow well past 4000 rpm. Could be some damage or obstruction / clog inside my oem piping? Regardless, the header improves the 5000 rpm flow at no loss of low rpm. Cadillac Jim may be onpoint that replacing the cat with straight piping actually acted to effectively extend the header pipe length and lower rpm range supported? Re-engineering the oem to perform is beyond my skillset or budget, so I will try to mitigate the ground clearance loss and work with the header.

[Texas Jim]

back in the old days.... we used headers with equal length pipes and long collectors for low and mid range TORQUE.... short collectors for high RPM horsepower.

[Bruce Nunnally]

Yes. Since the stock engine was designed to red-line at 6000 rpm and peak hp at 5000 rpm I am still confused as to why the seemingly stock exhaust manifold won't support that. But, I am glad to see some improvement in the shape with the header.

[Cadillac Jim]

The stock exhaust manifold in your car had the cat replaced with the constant-cross-section pipe to the muffler in the rear. Your header setup is similar. Thus the main resonance is probably the volume resonance of the entire set-up from the head to the muffler, because the RPM corresponding to the length is probably too low to benefit the motor. We estimated that ten inches corresponds to 5000 RPM, so ten feet corresponds to 5000/12 = 420 RPM; that won't map exactly because the speed of sound in hot exhaust is different from cool intake air.

There are two reasons that short runners into the collector are used. In "shorty" exhaust manifolds, the idea is to provide a volume resonance off-idle or mid-range RPM to improve throttle response in normal driving, which is very important for driveability in moderately aggressive performance camshafts for street cars. Production cars often use this idea to allow higher performance camshafts for daily drivers. The other is to provide a resonance at high RPM to enhance or broaden the horsepower peak in conjunction with other resonances (in the intake), a technique which is rarely used on street cars but is seen in rally cars (such as the DOHC variants of the 3T engine; notice that the collector is labeled "Pipe" and not "Cat" and thus there seems to be no catalytic converter in that configuration) and other off-road uses. Also, note that this production configuration uses a Y-pipe from the manifold to the collector, whereas the configuration on your stock setup uses two pipes bent to allow clearances on the way to another pair of bent pipes that connect to the final Y-pipe that has the cat flange.

I'm a bit puzzled as to why the new headers flow so much better than the stock setup too. The only things that I can think of are a straighter pipe right out of the exhaust ports and a gentler first bend, or a significant difference in diameter of the header compared to the stock exhaust.

[Bruce Nunnally]

finally found a pic of an unmodified corolla exhaust pipe, and it does not have these midpipe cuts -- the pipes were all one pipe each.

So I think what happened is previous owner shortened the Corolla exhaust to fit the height of the roadster exhaust manifold to tailpipe.

The header is just 3-4" too low, so I assume they took 2-4" out of these pipes on each side. That part is probably not a disaster,

but I am guessing based on the flow restriction that the welds on these mid-pipe connecting joints impinge on the 1.5" inner diameter

of the pipes.

I am thinking of cutting each pipe, using a rotary tool to port and polish the inside of the joint, then patching them back together.

Other ideas?

[Cadillac Jim]

Yes, cleaning up the existing setup will probably give you a better ground clearance than a "new" front collector pipe from a recycling yard and the difference in length is not likely an issue. But, if you can keep your new header pipe, the old pipe is moot. I would look into a resonator at the Y pipe for either or both of them that may move up the torque peak and help give you your high RPM torque. If it turns out that one loooong constant cross-section exhaust pipe has been giving you the stump-puller torque curve, then that and adding your Offy intake manifold to let your Weber truly commune with the nature of the 3T might just give you the optimum tune that you are looking for.

[Bruce Nunnally]

The header collector sits too low by 3" or so. Either I would need to modify it or get the modified oem "unclogged"; I think the latter more likely. So I am thinking cut open, port the inside to open it back out, and repatch

[Cadillac Jim]

Have you thought about asking a muffler shop if they can do some subtle bends in the new system?

[Bruce Nunnally]

My experience has been that anything out of the easy/quick/normal is not preferred. I plan to take the oem exhaust pipes and see if they can re-patch them and put them back on.

Then I can take the headers another day and see if they can bend or squeeze them to not have so much vertical offset.

[Bruce Nunnally]

Had new exhaust manifold piping connection patches where the pipes were shortened done this morning. A previous owner installed the 3TC engine and this oem exhaust piping.

When that was done they have to remove several inches of pipe to reduce the vertical offset. When they did that I believe they also reduced the flow through the pipes.

I am hoping this re-do of their patch and welds will flow better.

Next I plan to replace the header with this and retest, then if needed work on how to reduced the vertical offset of the header by 3-4"

[Bruce Nunnally]

Today I removed the Headers and re-installed the modified stock exhaust manifold. I took extra comparison pictures along the way.

Side by side the header and the stock exhaust manifold appear to have a similar vertical offset.

here one can see there is a difference of a couple of inches.

Stock exhaust manifold back in place, shield not added back yet.

here is the real advantage -- the shaping of the modified stock exhaust manifold leaves all the ground clearance, while the header sits lower and is angles downward.

comparison shot of the header in place (previously)