Intake manifold modifications

[vex]

Originally Posted by drewski86

This is starting to make sense. For some reason, ever since I was a kid I looked at x amount of horsepower meaning x amount of horses available to work and more horses can obviously pull something faster. I wasn't taught this, it's just how it made sense to me as a kid.

An easy way to think about it is this. It takes Horsepower to accelerate a car to a specific speed. Depending on where you are in the RPM band you are applying a certain amount of torque at that instant to the ground.

If you've taken a dynamics class in college or have yet to (I highly recommend it, it's one of the most confusing, hard, and most rewarding I have taken thus far) you will learn that to accelerate a car from 0-60mph in a certain amount of time takes some amount of horsepower. Maintaining 60mph takes significantly less hp. Accelerating above 60mph takes much much more than it did to go to 60.

That's more however due to wind resistance then overpowers rolling resistance. But just something to remember.


Torque is only good if the object doesn't move. IE: The wheel applies 90ft-lbs of torque at some point in time. Proceed a little further in time and you may be applying 200ft-lbs.

For this reason dyno's are able to calculate both at the same time since they're both relative and related to each other as previously attested.

If you'd like I could write up a little dynamics example about a car if it will better illustrate the point.

[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.

[NoDOHC]

On my tired 6-port, I made peak power at 6200 (155 WHp) this was at 13.5:1

It made 140 Wlb-ft at 3200 rpm.

I am impressed with the 4-port power.

My 6-port experience was what led me to tune around the 13.5:1 region. However, I can believe that my polished intake runners, smoothed ports and polished rotors will require a little more fuel.

I appreciate the advice everyone, I certainly hope that the transmission holds together for this pull.

I should be able to get dyno plots this time. Last time the rpm trace blinked out at about 5200 rpm (I computed horsepower rpm from wheel speed).

Believe it or not, at 9,000 rpm in 4th gear, the rear wheels are actually going 180 mph - not that I have gone that fast, but the engine is running exactly 4,000 rpm at 80 mph (I have checked the speedometer and the rpm is from the Haltech).

The Dyno guy wouldn't run it in fourth.

I know I may lose something to bad bearings in fourth, but the friction must be higher when the bearing is experiencing a side load as the power is transferred through the input gears in 3rd gear (thus 4th gear would be better).

I did check the transmission temperature between runs and it was not touchable, but not smoking yet either.

[C. Ludwig]

Originally Posted by NoDOHC

On my tired 6-port, I made peak power at 6200 (155 WHp) this was at 13.5:1

It made 140 Wlb-ft at 3200 rpm.

I am impressed with the 4-port power.

My 6-port experience was what led me to tune around the 13.5:1 region. However, I can believe that my polished intake runners, smoothed ports and polished rotors will require a little more fuel.

Doesn't really work that way. You're trying to provide just enough fuel so that every oxygen molecule has something latch on to. You'll hit peak efficiency when you use all of the oxygen molecules without wasting a bunch of fuel. Stoichiometric is the theoretical mixture at which all of the oxygen available find a fuel molecule to work with and all the fuel is burned up. You usually find max torque in the real world at a mixture on the fat side of stoich because in a combustion chamber things aren't ideal. A good intake system and combustion chamber will allow for proper mixing (tumble and/or swirl of the charge) and proper quench to keep the charge more or less packed into a homogeneous mixture near the plug. A good combustion chamber will also promote good flame propagation which helps to ensure the entire mixture is burned. If you need a mixture that is fatter then you've lost efficiency somewhere. It's possible you're seeing peak torque at that mixture but if you are something has changed to the detriment of efficiency. You're still not making more power than has been made with completely stock components so if it's taking more fuel you've erred somewhere.

Originally Posted by NoDOHC

Believe it or not, at 9,000 rpm in 4th gear, the rear wheels are actually going 180 mph - not that I have gone that fast, but the engine is running exactly 4,000 rpm at 80 mph (I have checked the speedometer and the rpm is from the Haltech).

I absolutely don't believe it. I spent a number of year racing these car in SCCA Club Racing. I know how fast the thing goes in 4th with a 4.10 rear gear. Even a gear calculator will tell you that you're well short of 190 mph. Just ran through one and it gives 150 for a 23" tire and 163 for a 25" tire. That's higher than I said before. Guess I was thinking 8k max rpm which was typical at most tracks we ran at. Unless you have a 30" tire on there you aren't seeing 190. They don't call them dreamometers for nothing.

[NoDOHC]

C. Ludwig - You are my new hero. I think I can safely run in fourth gear. I ran the numbers and you are right. I guess my speedometer is wrong then (I timed it between milemarkers... I thought it was right). Maybe the curve will be more accurate in fourth, plus my transmission will not take as much of a beating.

Thanks for pointing that out. I should have done the math (especially since I looked at the VSS input to the Haltech and it indicates 55 mph at 3000 rpm, not 60 as I thought). I guess this is good, I don't need to worry about a speeding ticket...

With my new knowledge, my power numbers shifted.

It is now 186 WHp @ 7600 rpm
and 170 lb-ft @ 5100 rpm

(we had calibrated the dyno to the speedometer for rpm).

You are right about the efficiency too, I doubt that my highly polished rotors and runners do much for my fuel mix.

I did drive it hard a little today with a wideband on it and I found that it seems to pull just fine at 13.5:1 (Which is what I am currently tuned for). I am running lean of that between 5000 and 7500) just because the VE is higher in that range and I copied and pasted the fueling from 3500 rpm. The tune is identical to what I ran on the Dyno. I only got an average AFR from the dyno, as the rpm signal was wacky. Apparently I was running a bit rich down low (11:1 at 1200 rpm). Leaning the low end out helped with the load up issues at idle.

We will see tomorrow (assuming that my new-found vibration doesn't disqualify the car from the dyno).

[NoDOHC]

Update:

Right before the scheduled pull, I lost my leading plugs. I didn't have time to troubleshoot what had happened (corrupted something in Haltech trying to get a Tacho output working). I went anyway, as I was not willing to miss my appointment.

With no leading plugs, the car starts hard and has no low end (I didn't know why at the time).

Interestingly enough, the high end was fine.

First run of the day was 163 WHp and 123 lb-ft (13.8:1 11 degrees of timing (which I thought was 26, but I had the trailing plugs only)

Richened it up to 12.8:1, went to 181 WHp and 142 lb-ft

Gave it 10 degrees of timing (21 BTDC) went to 198 WHp 150 lb-ft

Richening to 12.2:1 and giving another 5 degrees (26 BTDC) gave 201.3 WHp and 150 Lb-ft

Made 3 runs at 12.2:1 and adjusted the timing around 3 degrees in either direction yielded 200.6 WHp and 203.2 WHp.

At this point, my clutch was starting to slip and I was running out of time, so I had to head home. It is really a pity that I had no leading plugs, as this would most likely have helped my low end torque.

Sadly, I probably won't dyno this car again until I get the turbo on it.

Dyno plots are yet to come.

[NoDOHC]

I finally got the dyno plots scanned in. I deleted the header (for obvious reasons).

I don't know why the dyno scaled the horsepower and torque to different levels. The last one I actually got them to drop air/fuel just so that I could see both scales.

[NoDOHC]

I must remove some misinformation.

Later analysis of my wiring on my car has proven to me that I had to have operational leading spark plugs for the dyno run. This indicates that I really was making peak power at 38 degrees BTDC (203 WHp run).

Looking at the curves, I think I should have run a little leaner for peak power too. If It didn't cost so much to go to the dyno, I would do another run to see if I could sneak another 10 WHp out of this build.

Maybe I will go back after I get my clutch fixed and I can run the stock manifold too.

Information Summary:

Polished rotors seem to require more ignition timing (38 BTDC)
Low compression (8.2:1) is probably another part of it.
Lack of swirl in intake manifold due to excessive polishing requires additional fuel (Probably 12.5 - 12.8:1).
Even so, 460cc/min injectors are PLENTY for 200 WHp (69% duty cycle at 7100 rpm).

I really want to thank everyone for their input. It helped me to get a sanity check. It also allowed me to get a feel for typical timing and fuel requirements so that I can estimate what effect the changes I made had on the engine operation.

After I blow this engine up with too much boost I have every intention of building a HOT 6-port (custom intake manifold) that will have much more radical port timing and 9.7:1 rotors.

I am puzzled about one thing - Why is my high end missing?
It can't be VE, here is my -5 kPA Injection time map (I run about -3.75 kPA at 2500 and -6.75 kPA at 9000. I have also included this data as an excel file (inside the .zip).
2500 4.53
3000 4.73 (rich spot on scan0005)
3500 4.53
4000 4.83
4500 4.93
5000 5.21
5500 5.31
6000 5.53
6500 5.72
7000 5.83
7500 5.83
8000 5.65
8500 5.41
9000 5.10

Running the numbers, I find that I should make a lot more power at 8500 than I do at 7500, why does it taper off?

Any input is appreciated, as I am surprised by the VE being 115% (giving me more torque than I expected) but I am disappointed with the engine's high rev performance.

Please review the attached spreadsheet for errors, but I don't understand why I am seeing this drop in combustion efficiency after 7000 rpm. I can only think ignition timing, but I did not have enough dyno time to do anything with it.

Any input is appreciated!

[C. Ludwig]

Good power!

The oversimplification is that the air flow is not there for high end power. Whether it's intake or exhaust the package as whole isn't flowing past 7500.

[NoDOHC]

I found some issues...

First, the ignition toggle output pin had come out of the Haltech the last time I had the plug apart. This caused my rear rotor to receive all of the ignition for the trailing plugs (which made the car start hard, it kept kicking back on the starter).

At 38 degrees BTDC, the apex seal is just crossing the leading spark plug. Thus I had very poor ignition on my front rotor without the trailing plug firing.

I lost the ignition driver for the leading plugs on the Haltech (by a stupid testing procedure on my part) and this allowed me to discover this problem. Imagine my worry when the engine only ran on one rotor.

A compression check yielded 120 psi on both rotors (5,300 miles on rebuild) so I knew that it wasn't a mechanical failure.

After fixing the ignition toggle output, the car idles smoothly enough at 700 rpm that I think you could balance an egg on the intake manifold and it would stay there (or at least close).

I didn't show the curve that high, but I was at 110 WHp at 9,000 rpm (which is REALLY low) I think now that I was only running on one rotor by that point, the fuel in the other rotor was getting lit during the expansion stroke (So the wideband was none the wiser).

Unfortunately, the other issue I found was that I need a turbo clutch. My NA clutch was slipping during the last dyno run and after I got out on the road (and got intake air temps below 40C) it wouldn't hold at all at full throttle.

I finished it off trying to keep up to my friend in his hopped-up Duramax.

I could barely get the car to move by the time I got home from the dyno.

I will keep you posted when I get the chance to run again. I am hoping that I can make better power.

[C. Ludwig]

I've run 300 whp through Miatas which have the same clutch disk as the NA RX-7. If you're upgrading to turbo components anyway then by all means do the swap. But a good small diameter clutch will hold well more than you're throwing at it.

[RotaryProphet]

I've used the NA style centerforce dual friction clutch to very good effect on a 240rwhp turbocharged 12a and a 230rwhp bridgeport NA, and it even managed to hold up to 315rwhp on a turbocharged bridgeport (although admittedly, I stopped streeting that setup after only a couple of weeks of driving it)... meanwhile, the clutch engagement is very smooth, and pedal pressure is near to stock.

[NoDOHC]

This was a cheap F1 racing clutch from eBay. The purpose was to hold until I went turbo, so I didn't figure it mattered. I think it would have been ok, but my master cylinder leaks off over time and sometimes the pedal will stick partway down with the clutch only about half engaged. I think this happened to one of my friends when he was driving the car, the pedal effort was significantly decreased when I drove it next (I think that the pressure plate got hot enough to partially anneal the engagement springs).

I intend to remove the engine soon (I can't drive the car anyway) and see what I can see.

I got the F1 racing clutch mostly for the rev rating (9500 rpm) which I figured was all my engine could safely do. Now that I have trailing ignition for both rotors I expect to need that rev rating.

If I had intended the car to end up as NA, I would have purchased a better clutch. I have a stage 3+ SPEC clutch (505 lb-ft rated) and a billet steel 10 lb flywheel for the turbo build.

If I ever get the time and ambition, I will install the turbo drivetrain in the car.

[NoDOHC]

Update:

Got the new clutch (It looked pretty neat, I may get some pictures up later).

Installed Turbo drivetrain in the car.

Pedal effort is a little high, but the engagment is very smooth (as long as you don't try to drive gently).

The new tranny is excellent (has synchros in all gears!!)

After I finished with the drive train swap, I decided to take the car to the dyno again (more money...)

Unfortunately, I had to give up my easy turning transmission, my ultra-lightweight flywheel, etc so I figured that I would lose a couple wheel horsepower.

I was happy as a clam when I put down 203 WHp and 152 Wlb-ft of torque on my first run (Identical numbers to last time). I then decided to adjust the ignition timing some more.

Here is a summary of what I found
Ignition Advance at 8000 (Degrees BTDC),Peak Power,Peak torque
38,203,152
43,198,154 (I think the torque was inaccurate)
33,198,148

So now I decided to try fueling.
AFR (Average),Horsepower,Torque
12.5,203,152
12.8,210,155
13.0,216,158
13.3,216,160
13.8,200,145

Going back to 13.3:1 I started adjusting trailing split
Trailing split (degrees),Horsepower,Torque
15,216,158
10,216,158
5,216,159
0,216,160
-5,212,157 (I swapped leading and trailing plug wires for this test).

So peak power was 216.4 WHp at 7575 rpm and 160.2 Wlb-ft at 6100 rpm w/ 38 BTDC timing, 13.3:1 AFR,0 degree split.

(The glitch in the air fuel chart was corrected later, but after the AFR was steady, we quit including it on the trace.)