Intake manifold modifications

[NoDOHC]

Ok, Vex has me thinking about this intake manifold thing now.

I have always been told that the RE Intake manifolds flowed the best. Not having access to a RE manifold, but having access to many Turbo II manifolds, I decided that i would make do with what I had.

After increasing the runner cross-sectional area from 2.32 in2 to 3.20 in2 (a lot of die grinding), giving the engine a mild street port (more die grinding), polishing the runners to 400 grit where dry and 80 grit where wet, measuring the entire runner length to maintain a uniform cross-sectional area in the manifold (don't ask how many times I broke through), modifying the plenum to fill all irregularities and smooth the air path, and porting and polishing the throttle bodies, I have encounted some odd engine characteristics.

(I polished the rotor faces to 1000 grit, but I doubt that had any effect on the power.) I am using stock S4 8.5:1 rotors (ground down to about 8.2:1)

I have yet to get on a real dyno, so I will not post numbers here except for AFR and VE (which I can compute) and relative torque (from the g-tech).

The VE for this engine is above 100% from 3000 rpm to 8500 rpm (9000 rpm rev limiter). I promised myself that I would stop at 8500rpm, but I couldn't cut an engine off that was pulling that hard. Unfortunately, my peak VE (108% at 6500rpm) is disappointing for me (I had hoped for 112% at 7000rpm).

The rev limiter is very annoying at 9,000 rpm because it is still pulling strong. (My legs are too important to me to rev it higher, my clutch is rated for 9500).

At 13.2:1 AFR, I can't keep my Bridgestone HP50s hooked up above 3500 rpm in first gear (with a gentle launch).

My first question: Would anyone find it beneficial if I strapped a stock TII manifold on the engine to see how much it kills the VE?

My second question: Why does my G-tech show the peak acceleration at 7500 rpm when the peak VE is at 6500 rpm? (Is there something I am missing, shouldn't peak torque and peak VE coincide?)

Is this a transient issue? Maybe the g-tech assumes a road load that is incorrect.

VE curve (based on injected quantity, injector size, fuel pressure and AFR as measured on the wideband):
rpm 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000 7500 8000 8500 9000
VE 67% 75% 78% 85% 95% 100%103% 103% 103% 104% 106% 106% 108% 107% 104% 101% 100% 94%
Torque curve: (Please do not set store by this, g-tech numbers assuming 3000 pound car weight, up to 10% high)
rpm 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000
lb-ft 130, 135, 145, 148, 152, 155, 156, 158, 158, 160, 163, 165, 160, 152, 140

For comparison:
NA 6-port, sleeves opened at 5000rpm, Stock intake manifold, secondary throttle plate mod.
rpm 500, 1000, 2000, 3000, 4000, 5000, 6000, 7000, 7500
VE 75%, 80%, 83%, 89%, 91%, 95%, 93%, 89%, 82%
lb-ft 120, 123, 125, 128, 132, 135, 135, 128, 120
(made about 155 WHp with 196,000 miles)

I really need to make a real dyno run (I am actually excited because I think I can break 200 WHp.)

Also: What AFR do you guys typically run on a NA rotary? This thing LOVES fuel. Seems to make peak torque at 12.2:1 (my 6-port, 9.4:1 engine made peak torque at 13.5:1 AFR).

I have heard 26 degrees is optimal ignition timing, is this true for NA? I get best torque at 44 degrees BTDC at 9000.

Any thoughts are welcome.

[vex]

For your second question it sounds like the G-Tech has the incorrect numbers as you believe. It's a rough estimation based off G-Forces that the accelerometers measure when you accelerate. (If I'm assuming function correctly) If this is the case the formulation would work out that their assumed constants are incorrect and as such would need to be altered to match the more accurate reading of the dyno pull. However this also depends on your VE and how accurate that measurement is.

Your G-Tech by all means could be accurate and your reading of the VE could be off. As it stands your VE and your Max Torque reading are pretty close together. What you need to find out is how accurate your measuring tools are. Is your G-Tech able to measure max acceleration +/-500 RPM? Remember, 500RPM isn't that big of a discrepancy as we already miss 250 when our engines are off (aka our tach isn't reading anything below 500rpm)

Making any sense? I would first quantify the accuracy of the gauges/measurements independently and see if you can rectify any inconsistencies between them. Then, and only then would it become beneficial to measure the differences in VE, Torque, and RPM between the two manifolds.

[NoDOHC]

So basically, a dyno is really the only good option to optain this information (which unfortunately means that it will cost me $75 to find out).

I will have to postpone the dyno run until later as it seems that I have ruined my 4th transmission (I can't decide if it is torque or revs that keeps killing them). I still hope to get in there by the end of the summer.

I know engine RPM from the data logs for the ECU. I know Air fuel ratio and injection duration which should give me a good VE curve (this is all data logged). I would trust the VE curve ahead of the g-tech.

I don't believe the g-tech torque numbers. 150 wlb-ft will make me very happy. The relationship between the numbers is what I find odd.

[vex]

For torque, yes. Unfortunately that doese not resolve the inaccuracies present in the dyno itself. You may be off as much as +/-5% maybe even more. If the shop has it available, see the last time it was calibrated (if they even have it calibrated beyond first install). I'm going to do some digging on this and see which dyno actually gets calibrated.

Yeah, there are services that calibrate dyno's:
http://www.taylordyno.com/oth/oth.ht...FRwpawodOwR-_A

[NoDOHC]

Update:

Decided to do dyno run on junk transmission as the entire test would be done in fourth gear (direct - no torque is transmitted through countershaft - doesn't need good countershaft bearings).

Unfortunately, when told that the engine turned 9,000 rpm and that the rear tires would be going 180ish MPH in fourth gear the dyno guy told me that a third gear run would be all I would get.

I was worried if the tranny would take it, but I figured we could always tow it home, so I let him run it in third.

I was very dissapointed with the output (186.9 WHP at 7200 rpm). I have a lot of tuning to do.

I learned that my gut feeling for ignition timing was not accurate as I started with 62 degrees BTDC at 9,000 with 13.8:1 AFR (gave 169 WHP at 8200).

Retarding the timing to 52 degrees BTDC at 9,000 gave me 182 WHP at 7100 rpm

Adding fuel to 13.2:1 gave 186 at 7200 rpm.

I think peak torque can be found at a more retarded ignition angle (as I was still increasing torque by retarding). I think peak torque is somewhere between 13.8 and 13.2AFR, but I will still try going a little richer. Peak torque (172 Wlb-ft) was made at 4800 rpm and it was running a little fat there (12.2:1).

Still hoping for 200 WHP as my high end is currently wasting fuel (>100% VE) and making no power. My spark plugs are filthy (too much premix) and will be replaced before the next dyno run.

More dyno runs later (the transmission is still alive!!)

On a side note, this is a Mustang Dyno and it has steady state loading, so I can actually tune real time (although I should get an electric fan to keep the engine cool during a steady state run at 8,000 rpm).

Comments/suggestions welcome (I will be renting the dyno for several hours this coming weekend, so I can try about anything).

[vex]

Rule of thumb 12:1.

[RotaryProphet]

Originally Posted by NoDOHC

Update:

I learned that my gut feeling for ignition timing was not accurate as I started with 62 degrees BTDC at 9,000 with 13.8:1 AFR (gave 169 WHP at 8200).

Retarding the timing to 52 degrees BTDC at 9,000 gave me 182 WHP at 7100 rpm

It's also really -really- far advanced from what I've heard of anyone running, even up at the redline. If you got 13WHP from retarding 10 degrees, I'd say you're way advanced. On an NA 13b, while on an engine dyno, I've never had to advance past 40, and that was a motor that was already on the down-slope of the VE curve. I seem to make pretty good power on most port configurations around 30+/-5 degrees BTDC.

Something to remember is that as you increase airflow to the chamber, you need less spark advance, not more. Retard your timing out towards the stock numbers, and you probably will hit 200whp

[NoDOHC]

If I really wanted 200 WHp, I would take my mechanical fan off. I think that it is single-handedly hurting my high end. You should hear it scream on the dyno, sounds like a jet liner. If I could get this mark IV fan to fit I'd have it made.

Thanks for the advice guys, I will give it a go on Saturday.

[RotaryProphet]

Originally Posted by NoDOHC

If I really wanted 200 WHp, I would take my mechanical fan off. I think that it is single-handedly hurting my high end. You should hear it scream on the dyno, sounds like a jet liner. If I could get this mark IV fan to fit I'd have it made.

Thanks for the advice guys, I will give it a go on Saturday.

In that case, also check your fan clutch. =cP

[drewski86]

Originally Posted by NoDOHC

(I polished the rotor faces to 1000 grit, but I doubt that had any effect on the power.) I am using stock S4 8.5:1 rotors (ground down to about 8.2:1)

Are you eventually going to turbo this motor?

Would anyone find it beneficial if I strapped a stock TII manifold on the engine to see how much it kills the VE?

It would be nice to know how much porting the manifolds really helped.

Why does my G-tech show the peak acceleration at 7500 rpm when the peak VE is at 6500 rpm? (Is there something I am missing, shouldn't peak torque and peak VE coincide?)

Peak acceleration should coincide with peak power.

Originally Posted by NoDOHC

186.9 WHP at 7200 rpm

See

I learned that my gut feeling for ignition timing was not accurate as I started with 62 degrees BTDC at 9,000 with 13.8:1 AFR (gave 169 WHP at 8200).

Retarding the timing to 52 degrees BTDC at 9,000 gave me 182 WHP at 7100 rpm

Something is wrong. You should be more around 25-30* BTDC. As far as you are advanced, you should be igniting on the compression stroke which will want to spin the motor backwards which is very bad. Hopefully your numbers are off somehow. I would make a pull at 25* and 13.1 AFR and see what happens. If you're way down on power than maybe your numbers are off but the motor is seeing the correct timing.

One more thing, you seem too focused on torque numbers. I don't know if this is because the g-tech only gives torque numbers but horsepower is what makes the car fast.

[NoDOHC]

Are you eventually going to turbo this motor?

I definately intend to put a turbo on the engine. In fact, it should be turboed right now, I was only going to run it 3,000 miles (breakin) and then add a turbo. I have over 5,000 miles on it and I still haven't found a good deal on a dual-disk turbo clutch (I refuse to deal with a 6-puck, I drive this car every day). I have a stock clutch in my garage, but I don't have the ambition to take the engine out twice and the stock clutch will never take 15psi boost (I have NA drivetrain in the car for now, will put the turbo drivetain in in one swoop).

If I was staying NA, I would have used 9.7:1 rotors (which I have been accumulating for years) and I would have given the engine more port overlap when I streetported it. I certainly would not have polished the rotors to the extent that I did, either.

Peak acceleration should coincide with peak power.

You are right, peak acceleration should coincide with peak torque. The G-tech measures acceleration, thus it displays torque. It is not that accurate however, as the dyno run would indicate.

It's also really -really- far advanced from what I've heard of anyone running, even up at the redline. If you got 13WHP from retarding 10 degrees, I'd say you're way advanced. On an NA 13b, while on an engine dyno, I've never had to advance past 40, and that was a motor that was already on the down-slope of the VE curve. I seem to make pretty good power on most port configurations around 30+/-5 degrees BTDC.

Something is wrong. You should be more around 25-30* BTDC. As far as you are advanced, you should be igniting on the compression stroke which will want to spin the motor backwards which is very bad. Hopefully your numbers are off somehow. I would make a pull at 25* and 13.1 AFR and see what happens. If you're way down on power than maybe your numbers are off but the motor is seeing the correct timing.

The timing is my fault, I knew that the rule of thumb was 26 degrees, but I thought that the engine seemed to pull harder at 60 degrees. I think that it must have made more noise and maybe shook a little more, which seemed like power to me. The dyno is definately informative and a great learning experience for me.

One more thing, you seem too focused on torque numbers. I don't know if this is because the g-tech only gives torque numbers but horsepower is what makes the car fast.

As to horsepower making a car fast... I will have to disagree on that one. My Rotary makes about 230 Hp, I have a friend with a 302 Ford in an RX7 that makes 230 Hp, that car is WAY faster than mine (the only difference is torque 210 lb-ft vs 360 lb-ft).

I like torque because it indicates the engine's Volumetric efficiency and combustion efficiency. You can always get more horsepower by porting more overlap and revving the engine higher, but you have to do careful tuning to get more torque.

Basically, my car makes 210 lb-ft of torque at the flywheel. Compare that to a stock 88 TII and you will see what I am talking about.

My goal is not to make a watchwinder, but rather to make a daily driver that has lots of low end, is very driveable and will still accelerate very quickly if it needs to (about 6 seconds 0-60). The total power number is not as important as what I learn and how pleasant the car is to drive.

Since I am stuck NA for a while, I figured I might as well benchmark it and see what it would do.

The timing that I am listing is definately right, I had a degree wheel on it.

In that case, also check your fan clutch. =cP

I know the fan clutch is bad, the car was referred to as the airplane at autoXs because all you could hear was the fan (I have the '91 for autoXs now, factory electric fans are awesome). I would take it off, but I think that is cheating, so I am leaving it (that and I don't want to overheat).

This may sound stupid, but I don't care what the number I put down is. It really isn't important, All that I care about is what kind of power it made NA so that I can baseline it against the turbo numbers. If I hadn't been seeing such increases last time at the dyno, I would have been happy with one $70 expense and called it 186 WHp.

[vex]

Originally Posted by drewski86

One more thing, you seem too focused on torque numbers. I don't know if this is because the g-tech only gives torque numbers but horsepower is what makes the car fast.

That is a negative. The true meaning of HP is the application of Torque over time. This means that 1 HP = 550Ft-Lbs/sec.

[C. Ludwig]

As has been pointed out your timing was advanced way too far. I would start at 25* and creep up from there. All of my NA experience is with 6-port 9.7:1 engines so your results may wary slightly. You would expect the lower compression ratio to want slightly more timing as well as a slightly fatter mixture with similar VE. If you can increase the VE a lot over what we can do with the 6-port and higher compression the timing could be very similar. At any rate, start low and work up until you stop gaining power. As you have seen already, in an NA form it's pretty much impossible to detonate one of these engines unless you have other problems.

The same goes for fuel. We've always found best power in the 13.5:1 area. Going fatter certainly has lost power. Whatever the conventional theoretical optimum a/f ratio is has not applied. Again, start fat and pull fuel until you reach a point you are comfortable balancing EGT and power.

What are you doing for exhaust?

It's probably moot but if you have a bad counter shaft bearing you're still spinning against that friction even in fourth gear. You might not be loading the counter shaft but the friction could be costing you several hp depending on how bad it is. And how big are your tires? No way you're doing 180 mph in 4th with a 4.10 rear gear. More like 130, maybe 140 with very tall tires.

Be extremely careful if you plan on doing full load, high rpm steady state tuning. The loading on the engine is quite dramatic. Something it will not see in real life. The heat build up is quite fast. You will literally get a couple seconds at full load to see what's going on and get an idea of what changes you need to make. You are not going to fully load the engine and sit there and make ignition adjustments and watch torque feedback in real time. You can do this at lower rpm but not at 8k regardless of what kind of fans you're using.

[drewski86]

Originally Posted by vex

That is a negative. The true meaning of HP is the application of Torque over time. This means that 1 HP = 550Ft-Lbs/sec.

You're right, horsepower is work(torque) over time, but that does not mean that horsepower is an irrelevant by product. Let's put NoDOHC's friends V8 RX7 vs an F1 car. The V8 makes 230hp and 360tq whereas the F1 car makes 800hp and only 200tq. Do you think the V8 will win because it makes 160 more foot pounds of torque? You would be wrong. Torque IS work, but horsepower DOES work. Here is a saying that puts it in perspective. "Horsepower is how fast you hit the wall. Torque is how far you take it with you."
You may want to check this site out.
http://www.vettenet.org/torquehp.html

Originally Posted by NoDOHC

You are right, peak acceleration should coincide with peak torque. The G-tech measures acceleration, thus it displays torque. It is not that accurate however, as the dyno run would indicate.

No it should coincide with peak horsepower, not torque. You said the G-tech showed peak acceleration at 7500 RPM and the dyno showed peak power at 7200 RPM. This is your own data that proves this as fact.

As to horsepower making a car fast... I will have to disagree on that one. My Rotary makes about 230 Hp, I have a friend with a 302 Ford in an RX7 that makes 230 Hp, that car is WAY faster than mine (the only difference is torque 210 lb-ft vs 360 lb-ft).

That's because the V8 has a much broader powerband. I'm sure if you compare dyno sheets you will see this as true. Peak numbers don't win races, area under the curve does.

[C. Ludwig]

Originally Posted by drewski86

You're right, horsepower is work(torque) over time, but that does not mean that horsepower is an irrelevant by product. Let's put NoDOHC's friends V8 RX7 vs an F1 car. The V8 makes 230hp and 360tq whereas the F1 car makes 800hp and only 200tq. Do you think the V8 will win because it makes 160 more foot pounds of torque? You would be wrong. Torque IS work, but horsepower DOES work. Here is a saying that puts it in perspective. "Horsepower is how fast you hit the wall. Torque is how far you take it with you."
You may want to check this site out.
http://www.vettenet.org/torquehp.html

You're ignoring gearing in your comparison. Gear the F1 car with the same gearing that would be optimal for the high torque engine and it will be a slug. What makes any car go is torque at the wheel. The F1 car needs a very short gear to extract it's power potential and allow it to use it's 20k revs to create torque at the wheel through gear reduction. Use the F1 correct gearing with the low hp/high torque V8 and, if traction is available, it will murder the F1 engine up to the point it runs out of revs which would happen very quickly.

Originally Posted by drewski86

No it should coincide with peak horsepower, not torque. You said the G-tech showed peak acceleration at 7500 RPM and the dyno showed peak power at 7200 RPM. This is your own data that proves this as fact.

Peak VE will always coincide with peak torque at the crankshaft. Peak VE is the point at which the engine is operating at it's peak efficiency and will create the most torque at the crankshaft. Peak horsepower is a product of torque and rpm. VE will fall past peak torque but if it's maintained at a high enough level the engine will continue to gain horsepower due to the multiplier of rpm. This is why most engines will have a torque peak at a lower rpm than their horsepower peak. You will see this in fuel curves, as NODOHC has mentioned, with fuel injector pulse width required to maintain a common a/f ratio rising up to the point of peak VE and then beginning to fall past peak VE as airflow falls.

Originally Posted by drewski86

That's because the V8 has a much broader powerband. I'm sure if you compare dyno sheets you will see this as true. Peak numbers don't win races, area under the curve does.

Broader than what? A stock 6-port engine will maintain 90% of it's torque for around 4500 rpm. Most stock V8s on the road hardly rev that high let alone maintain torque across that kind of rev range. One of the nice properties of the NA rotary (even boosted for that matter) is that they have nice flat, broad torque curves.

Stock S5 NA




Boosted semi-PP




Stock 2008 Mustang GT v. w/CAI