No mind-reading, just years of gobbling up everything I can get on the subject.

Intake systems: so much potential. Pressure-wave resonance along the runner length, resevoir plenums, focus ovals, the diameter balance of capacity vs velocity, soft-head swirl, deliberate port mis-matching to induce turbulence and reduce wall-wetting with lips and steps, full-radius valve seats, etc. All this trickiness just to set some dino juice and air on fire.

I love the ITB design, it makes so much sense (IMO) to feed each cylinder with identical straight paths, especially for NA builds.

Next step: sliding variable-length runners that are always at the optimal resonance length for the current RPM (ala the Mazda 787B's trumpets or the new BMW snail-shell design).

- Josh

 

Ok. Got it. Thanks.

 

For some reason, ive had no issues with mixture at low and high rpms, and the pressure is up around 73psi. 68psi with vacuum attached, 73psi at WOT or after idle. why wouldnt it idle, as it does, based on the fact that in closed loop mode, maybe the O2 sensor just fights the fuel pressure to make things fairly decent in the ratio department. i certainly dont see any idling issues, off throttle power, or smoothness. the only think i think is a problem, is on start up, i do get a quick high rev when the engine starts.

in my old Ljet, each 1/2 turn of the rrfr would change the fuel curve and shift it up a noticable and repeatable amount. it was super easy to change the curve. I remember, starting out at 13.5:1 and each half turn of the rrfr, brought it down by .5:1. Got it down to 12:1, and then brought it back up to 12.5:1 and left it there.

The new LHJet of the S4, doesnt seem to work as smoothly, but it does work. the one thing i did notice is that now at the high rpms the fuel goes richer, where the Ljet, the fuel would start to go leaner.

mk

 

I love intake technology. I've ported heads & intakes for 30 years & it's almost like you can get the engine to serve whatever power band you wish by tinkering with intake & port design, even aside from camshaft limitations. There's an awful lot of hp & torque available in ram tuning. Especially if you do coordinate it with a cam upgrade which is what I've done.
I originally thought of making longer runners crossing the engine to get a better resonance wave but that would direct most of the flow to the short side radius & try to seperate the air/fuel on the entrance bend. It would also deteriorate the shock wave to a degree because the 928 port is so vertical & the valve angle is so shallow. After a lot of thought I decided the way I'm going about it is the best compromise for what I'm trying to do.

Hammer

 

I'm running a stock EZK and LH w/sharktuned chips on my stroker... 30# injectors. works great. also did a dual map switch that lets me use different timing maps for 100octane/timing cranked up and retarded 91 oct. street fuel. I'd guess a supermaf would be in order as a minimum for your monster

biggest advantage of the sharktuning was getting the timing pulled back for street gas so it didn't ping anymore w/11.3:1 compression (static), tuning the fueling perfectly so it'll pass smog and still have plenty of fuel at WOT, etc... made it run much smoother and gave it more power overall.

 

Rob,
My static worked out to 10.82 to 1. Probably because I flycut the pistons for the 968 valves plus a little so I could use higher lift cams without disassembling the engine again.
Do you own a Shark Tuner?

Hammer

 

used mark a's unit at greg browns shop. iirc, dave roberts / 928 specialists will rent them out sometimes...

 

Thanks.

 

Hi,

I've got a recent 6.5 liter installation (running around 45 days) on stock Brains + authority chipset and stock 24lb injectors on my 86.5 and it runs fine. The heads have been modified with larger valves, stronger springs and stock cams


Brian
6.5 liters

 

any dyno results?????

mk

 

Mark,

I have not dynoed the car yet ,but it feels very strong (tire shredding) from idle to redline (Greg Brown built). I think people underestimate the early 32 v engines and once modified their ability to breath through that big pipe organ intake.

Brian
6.5 liters

 

doc brown builds a mean motor for sure. he did mine too. on the race motors, they use at least 30#, iirc, but they idle like crap too... not a big deal for race cars though. I suspect your top end will be maxing the 24# out at WOT, so I suspect 30#ers and shark tuning will make a noticable diff, at least it did on mine... I'd send you my maps, but I've got a blackbird intake, big headers & modified GT cams so I think they'd be a tad too fat for your setup as is.

long live NA thumpers!! yeehaaa!

 

Ive always thought the 85 intake has some big potetial.
you mentioned larger valves, did you use S4 heads or actually carve out all 32 holes and put in something larger than S4 valves? (like 968)

the nice thing about the 85-86's is that the cams are already there (at the sacrafice of small valves)

mk

 

Mark /928 ss

My Intention was never to have a track motor , I just wanted a little more pep for around town (the car is an auto). The engine heads were modified with a clean of obstructions multi angle valve job ( S-4 valves). In addition I also purchased Devek level 2 headers and rising rate fuel reg. ,replaced the air pump w/ euro idler assembly (no cats) x-pipe and a Magna Flow exhaust (dual 2 1/2"). Greg Brown also installed one of his oil control systems ( pan spacer/ baffle/screen- I'm not sure about a scraper). I always thought 86.5 as a transition car (I guess I have envy of 87+) and have had fun making these and the body and suspension modifications.

By the way 928 SS you have a Great Car ! - a good role model !

Brian
6.5 liters

 

Errika,
I did some math and Engine Analyzer Pro work this morning to see how fuel pressure and injectors sizes would work out for a 6.5L with GT/S3 cams, improved exhaust, S4 style intake, and 11:1 compression.

With S4 size valves, 24 lb injectors will work with the stock S4 fuel pressure (3.8 bar). The duty cycle would be about 85%. The engine should make about 400 hp at 5000 rpm. If you go to 968 size valves, then 30 lb injectors should be used to keep to less than 85% duty cycle and the power would be about 425 hp. If someone is determined to use the 19# injectors, expect to need 100 psi fuel pressure or have the injectors open all the time. Other unknown variables will change these numbers, but should be in the ballpark.

Volumetric efficiency come in to play a lot when selecting injector size. With the engine with S4 intake valves, I get 94% at 4500 (torque peak) and 75% at 6000 rpm. Using 968 intake valves moves VE up to 97% at 4500 and 78% at 6000. The low VE at 6000 shows the engine is gasping for air at the upper RPMs. Different cams and intake can help the upper VE. With B1 cams and ITB intake, the VE max is 117% at 5250 (tq peak) and still 111% at 6000. That's the effect of intake resonance giving an over pressure (boost).

Here are some formulas that can help figure this out manually.
First determine how muchair the engine will use at a certain RPM. These are in British units, but can be converted to metric to make it easier . The 6.5L engine is about 394 cu in. I'll figure it for 6000 rpm using the engine with 968 intake valves (VE 78%).

1728 cu in. in one cu ft. of air. 394 cu in. is 394/1728 = 0.228 cu ft.
Since teh engine intakes air once every 2 revolutions, and the test RPM is 6000, multiply 0.228 * 3000 = 684 cu ft. per minute. Now, multiply 684 by 0.78 (the VE) to get 533.5 cu ft. per minute.

One cubic foot of air weighs 0.076 lbs at standard temperature and pressure. Forced induction engines will use a different number because the intake air is more dense.

Multiply the air flow in cu ft per minute by 0.076 to get the mass of air flow per minute. 533.5 * 0.076 = 40.5 lb per minute mass air flow.

That is for all 8 cylinders so divide by 8 to get each cylinders use of air.
40.5/8 = 5.0625 lbs of air per minute.

Assume I wanted an Air Fuel Ratio of 13.5:1. That's 13.5 times the weight of air to the amount of fuel. Divide 5.0625 by 13.5.
5.0625/13.5 = .375 lbs of fuel per minute.

Assume I was intending to use Bosch 30 lb injectors. That's 30 lbs per hour at 43.5 psi pressure. The standard S4 fuel pressure is 3.8 bar or about 55 psi. The 30 lb injectors at 55 psi will deliver 30 times the sq root of the pressure ratio.

55/43.5 = 1.264
1.264 ^.5 = 1.12
1.12 * 30 = 33.6

The 30 lb (at 43.5 psi) injectors will deliver 33.6 lbs per hour at 55 psi.

The delivery per minute is 33.6/60 = 0.56 lbs per minute

We determined earlier that the engine needed 0.375 lbs of fuel per minute per cylinder.

divide 0.375 by 0.56 = 0.69. The injector will have to flow 69% of it's capacity.

Almost done now.

An engine turning 6000 rpm is 100 revs per second. That is one revolution every 10 milleseconds. The LH uses batch injection with one injection cycle every revolution except above 5300 RPM. That RPM can be changed with the Sharktuner. Above 5300 the LH injects every other revolution, or every 20 ms at 6000 rpm. Out of the total time we have (20 ms) we need to turn on the injector for 69% of the time. It's generally considered that the duty cycle be less than 80%, maybe 85% max.

20ms * 0.69 = 13.8 ms.

Injectors don't begin spraying fuel immediately when the pulse begins. There is a short time called "dead time" sometimes it's called "latency". This is sort of a hard time to determine and it isn't often published. It's usually between 0.75 and 1.0 ms. In other words the pulse length that is sent to the injector has to be 0.75 to 1.0 ms longer than the fuel delivery requires. For a fuel delivery pulse of 13.8 ms we could need a pulse sent to the injector of up to 14.8 ms

We'll be using 14.8 ms of our 20 ms time period between injection cycles or


14.8/20 = 74% That's well within the spec.

Remember that for AFR richer than 13.5, you'd have to refigure the pulse width required with the new AFR. The duty cycle would increase.

Even though your engine will make more power than the theoretical one in this example, 30# injectors may still work with the pressure bumped up. I can't quite remember the max recommended pressure for Boschinjectors, but seems like around 70 or 80 psi. I know people use a lot more than that, but whether higher pressure will give consistent fuel delivery depends a lot on the system voltage, injector driver, wiring, and plug contact resistance. The injector solenoid has to raise the pintle under both the closing spring pressure and the fuel pressure. Sometime with excessive pressure, the injector won't close properly, or not at all. Worse, some may close and others not, or the "dead time" be different for different injectors.

I made a spreadsheet I use to help with tuning fuel AFR/Lambda and changes with fuel pressure. It may be useful for someone. It's here for downloading.
http://members.rennlist.com/louie928...%20Ver%202.xls