95mm to 98mm and one full point of compression H.P. Torque Increase questions
 

Hi Pelicans

I am on the quest for a bit more power.

Here's what I've got now:

3.0, (95mm)
Weber 40s
Elgin Mod S cams
9.3:1 c.r.
Head Work by Walt at CE w/ some performance port work done (not full race)
Heads twin plugged already but only running single spark ...again 9.3:1 now.
dyno 212 at the wheels

I'm thinking about adding displacement and building a 98mm 3.2 SS at around 10.3:1 and putting on a set of weber 46's that I have.

How much h.p. and torque should I anticipate

I would anticipate around 280 hp at the flywheel and 90% volumetric efficiency. That would be with a cam that is all done by at least 6500 rpm. Expect less with a milder cam. Expect more with a hotter one...They are a nice motor to build.

I have a pretty solid 3.0 now w/ Elgin MOD S cams. I think that should be enough cam even in a S.S. 3.2. ...wonder if it would make sense to consider doing it without splitting the case?

Now I just need to find a way to run a twin plug set up...

Got any suggestions Aaron?;)

I still have that Marelli Twin Plug dizzy that's in the 2.8 sitting in my garage...

I might :)

You should put that motor in something and enjoy it.

I would check with your favorite cam guy about the Mod S. You may need to step up to a DC60 or even a DC80.

Thanks Again Aaron.

As for the 2.8 twin plug, I am waiting for the right one to come along. ...keep hoping I'll find a rust free long hood in a barn/garage car lot somewhere for a song...

One can hope.

JZ

JMZ

I cannot tell you how much power your engine will make with the mods you suggest but it is very similar to our engine that we have in the spyder replica. SS 3.2 10.5 compression, twin plug, with 40 PMOs on it. I think the 40's might be a little under what this motor really wants... Okay let's be honest, a little under what I really want! :p

At any rate, this is a GREAT driving motor. Really zesty and surprisingly well mannered. You are going to LOVE IT!

angela

Thanks Angela.

That spyder must be crazy fast. What's it weigh?

I'm mostly curious how much of an increase the extra displacement and bump in C.R. would increase the h.p. of the engine as it is. ...sounds like somewhere around 40 h.p.

I'm willing to guess about 260 HP at 5900 RPM, and 217 lb-ft at 4525 RPM assuming that you don't change the porting or the cam. I'm not sure what the specs are for the Mod-S cam. If the lift is comparable to a factory S cam, you might find that you're leaving some high-RPM performance on the table compared to a cam with bigger lift. The flip-side is that the engine should be even more flexible then what you've got now assuming that you get the 46 mm carbs dialed in.

A hair over 1600 lbs with fluids. Quite zesty. But the best part is that this motor will drive in traffic, drive across the desert, up mountains, thru death valley and on one extremely memorable occasion in the snow...:(

I call this motor the "no drama mama". Run anywhere anytime, then at the flick of my right foot, hand out ass-whuppins or lollipops. And baby, we are flat outta lollipops.

angela

If the Elgin Mod S cam is anything like the DC40, I think the peak would come in higher than 5900. S cam lift is .455 and Camgrinders DC40 is .474 lift.

My assumption is that he's running about the same port sizes as he is now. The S's lift of .455 is a little marginal in a 2.7 with it's 46 mm valves. The 3.0 engines have 49 mm valves which should help some, but still I suspect you'd be in a situation where ports (at least on a "large port" head with the 39 mm intake ports) could flow more if you lifted the valve higher. Unfortunately I don't have any flow-bench data, which would be the determining factor.

I did a quick model of your engine type using Desktop dyno. I know the numbers are not completely correct but I find the program useful for comparing shapes of curves with different cam specs and compression ratios. I used a 3.0 with 9.5:1 and then enlarged the bore to 98mm and increased compression to 10.3:1. There is a healthy bump over most of the rev range.

What you will see is that the two engines have the same power curve shape. The exception is that the larger engine (3.2SS) seems to fall off faster as it gets choked off at higher rpms.

btw, the predicted peaks are right in line with John's suggestions.

http://forums.pelicanparts.com/uploa...1201062379.jpg

http://forums.pelicanparts.com/uploa...1201062388.jpg

For what it is worth.... I run a "MOD S" cam (dc44 108 centers) in my 3.4 with 48mm throttles and 10.5CR. I only have about 500miles on the motor (putting about 200 more on it tomorrow) but I like the cam so far. This is what John recommended when given the specs of my motor. I probably could have gotten away with something bigger, but it is nice and strong down low and pulls nice up top.

Heading to the dyno hopefully in the first week of Feb to do the final tuning to the ECU and then beta testing the Hargett throttles too. I am interested to see where the power will fall off with this cam.

Cheers

This looks like a cool program to play with, is it available to download on the net somewhere?

I found an old copy on the net. It works fine but does not have all the features enabled. You can download a trial from the manufacturer but it is VERY limited. I realize the limitations of modeling compared with real world numbers but I have found it very useful to compare outputs while changing one variable.

It is nice to see how specific changes influence the power output. For example, when I first ran the increase from 3.0 to 3.2 there was very little change. Most of the change comes from the bump in compression. I have used it to design my engine to isolate a cam that gives the broadest torque curve for a given duration and lift while operating with a specific rev limit.

Let's just say that they agree very nicely with John Dougherty's (camgrinder's) suggestions. :) Just shows that some people really do know what they are talking about.

Hey Jamie,

I've always wondered what a more beneficial upgrade would be.... twin plug a 3.0 or upgrade to 3.2 and stay with single plug. Both engines would run the DC40 cam with 39mm intakes, though the twin plug would run 10.5:1 and the 98mm would run 9.5:1. SmileWavy

I would really like to understand the difference in these 2 build directions also.
Jamie and or others... what are the trade-offs??
Thanks, Bob

Here are the predicted graphs for 4 engines:

3.0 with 9.5:1
3.2SS with 9.5:1
3.0 with 10.5:1
3.2SS with 9.5:1

HP
http://forums.pelicanparts.com/uploa...1201149367.jpg

Torque
http://forums.pelicanparts.com/uploa...1201149426.jpg

What I see is:

-the 3.2 builds more low rpm torque due to displacement, independent of CR.
-the higher compression maintains more VE at higher rpm. i.e. the power levels do not drop as fast as the lower compression versions.

Realistically, 98mm PCs will not like to be single plugged due to combustion chamber shape, piston dome and flame front propagation. It is likely that if you want to clear a Mod_S cam you will need a new PC set. Just buy the 98mm. Overall the cost difference is minimal by the time you price all the ignition components, etc.

Why not just build the high compression 3.2SS?

The models that I have done support what Jamie's charts show.

- Increasing the capacity will move the torque curve up and down the rev range a little bit. The curve will move up for obvious reasons due to the increased volume of mixture burned, but it will shift down the rev range because it will be drawing more air through the same intake track, so the air will reach maximum velocity at a lower RPM. This is the same affect as you'd get if there was an FIA style restrictor on the intake. The result is that the torque will increase, but the HP won't.
- Increasing the CR (and twin plugging) will basically move the torque curve vertically, increasing the torque and the HP. This change is not as affected by the intake design since the cylinder pressures are increased proportionately across-the-rev range, no matter what the air flow. The key is the twin-plugging. Without the second plug, the increase in the travel time of the flame front to the edges of the combustion chamber will negate much of the high-RPM benefit of the increased CR.

So, if it acurate to say that in comparing the 2 3.2 SS motors that the 10.5:1 gains you ~10 more hp & torque WITH the required cost of twin plug ignition and probably 46 carbs vs 40 on the single plug? If so, that means $3k+ for ingition for this very modest gain? Am I reading this correct?

If so, I would build the 9.5:1 motor in a heart beat... with one last question in my mind... what is the status on the 3.2L JE pistons that have a wrist pin? breaking issue... or is it only on the higher compression pistons from JE??

Great thread!!
Bob

Tweaks 911...... I know there was a Max Moritz short stroke w/ 98mm jugs that was done to 3.0s over in Europe where gas was ahigher octane. Possibly a 9.0:1 98mm would be safer than the 9.5:1??? There are those with more knowledge and experience than I.

Though I am weighing the same choice, twin plug is a bit more affordable since I already have an electromotive crank fire ignition that only needs 3 more coil packs and wires.

Interesting graphs. I would expect the h.p. increase when bumping the 3.0 to 3.2 high compression to be larger.

I'm hoping to add ~40 more h.p. and a nice bump in torque.

To be honest, to do that you'll most likely need to change the porting, and maybe the cams.

The heads have already had some port work done to them by Walt at C.E. He opened them up to a bit larger than the 78-79 heads and smoothed them to increase flow. I suppose that a step up from the Mod S. cam could be in order...

Could you measure the ID at the smallest part of the intake port? This will help me to quantity the impact a little bit better.

sure, I'll take a look at them sooner than later.

sign-up

Intake ports are a tad over 38mm. They have been ported by Walt at CE, the bump around the valve was smoothed as well as the entire port to an extent.

Looking at my numbers, your engine with 98 mm cylinders with 38 mm ports -- I'd be surprised if your HP peaks above 6200 RPM, so 260 HP looks about right. I'd expect your torque to be peaking at around 4300-4400 RPM.

For some reason the torque curve with carbs seems to be shifted quite abit higher than the port/valve/cam selection would indicate. I think it has to do with the intake runner length. We have found that the peak torque of a carbed SC motor with stock cams is around 5500 RPM and the peak power around 6500 RPM. There is alot of torque to be gained with the carb motors by running longer intake manifolds.

-Andy

I do run the PMO tall manifolds and have the booster venturis as well. For what that's worth.

I keep hearing that larger intake ports give up some power (torque) on the bottom end. How much is sacrificed if the intake port were to stay at 35mm? Does the motor give up performance, only on the top-end? To compare apples to apples; lets say both motors were equipped with 40mm carbs.

Yeah Jon; Using JMZ's short stroke 3.2 has an example, I would expect the peak HP with his 38 mm ports to be at about 6200 RPM. If you were to do nothing else but change the intake port diameter to 35 mm, I would expect the peak HP RPM to drop to about 5300 RPM. Above that point the HP will drop off. The flip side is that the engine should be stronger below 4000 RPM. Between about 4000 RPM and 5300 RPM, I would expect both engines to be pulling about the same.

To be honest, 35 mm intake ports would be too small for a 3.2, because a 911 motor should be capable of pulling way past 5300 RPM without giving away much in the 2000 to 4000 RPM range.

John, Thanks for the reply. I'm still trying to figure-out the direction for a 3.0 I've got on the floor. Increased displacement has been a consideration. I imagine the 3.2, being a larger pump, can certainly take advantage of more carb than the 3.0. I don't mean to divert the thread, but I was curious since some sharp minds were focused here. Thank you

One can build a pretty nice budget-wise engine out of a 3.0.

Port the heads a bit, add some J&E pistons with valve relief and higher compression matched to your current cylinders, cams, carbs exhaust and a distributor re-curve gives a fun engine with good power. ...much improved over stock.

or go big with the 3.2 and beyond!

Good Luck.

Interesting... my carbed 3.0 w/ SC cams peak HP at 5800 while torque comes in at 4700. These peaks are 300 rpm more than the stock. This engine has the smaller intakes. Shouldn't I be making power lower w/ carbs?

This setup does make more torque (214 @ FW) than HP (203 @ FW).

How does the taller manifolds raise torque? Same way that the smaller intake ports flow faster charge at lower rpms?

How to tell if my PMOs have them and where to get please;)

Personally I think that the removal of the air flow sensor plate from the intake track has a lot to do with the shift in the torque curve. As long as there is a pressure differential to move the sensor plate, the cylinders won't be getting a full charge. If the cylinders don't get a full charge, you won't get as much torque.

There are two different things that I think that you are referring to:
1) The taller intake manifolds that connect the carbs to the heads.
2) The tall secondary venturis which are inside the throats of the carbs.

1a) Taller intake manifolds generally help high-speed running by moving the point where the fuel is introduced to the air flow further up-stream, thus giving it a little more time to atomize prior to being sucked into the cylinders. The downside of tall intake manifolds is that at low RPM, the airflow may be so slow that the fuels drops out of suspension, which hurts low speed running in cold engines. The largely vertical intake tracks of a 911 I suspect are a little less sensitive to this as opposed to engines with horizontal intakes.

1b) Taller intake manifolds also change the acoustical properties of the intake path, just like a trombone player can lower the pitch of the instrument by pushing the slide out and making the length of the pipe longer. This is tied in with the shape (preferably conical) of the intake path. If your car has cams with a lot of overlap, it's possible at certain points in the rev range (generally just before the engine "comes on cam" with the throttles partly closed) to have higher pressures in the exhaust port and a partial vacuum down stream of the throttles, resulting in the intake charge being pushed back up intake -- aka: Reversion. By making the the intake an inch or two longer, it's possible to put that whole series a little out-of-tune, which can then suppress the reversion and improve part throttle running in the 4000-4500 RPM range. Cars with MFI or other independent throttle-body injection systems are less sensitive to the reversion BTW.

2) Tall secondary venturis inside of the carb. I'm pretty sure that these provide a stronger vacuum signal to the carb at high air flows, so that you get a more even fuel metering across the rev range. The standard secondaries in a weber carb are about 1 inch tall, the "Tall secondaries" are more like 2 1/2 inches tall if I remember correctly.

Being a 20 watt bulb in a package of 100 watts, please forgive my ignorance here but I have to ask....... I thought airflow sensors were only for electronic injected cars. Do AFS exist in carbs too?

If so, what other effect does the AFS plate have on driveability or fuel milage or what, I don't know. Again, I'm a 20 watter trying to understand.

Yes, CIS systems do have a metering plate. EFI systems have a flap that moves a rheostat, or else a heated wire that is cooled by the air flowing past it. I believe that in general both of the EFI metering systems constitute a smaller restriction on air-flow compared to metering plate in a CIS system. Here's a diagram of the CIS system from a BMW 320i, essentially the same as the CIS system in a 911.

http://www.lexam.net/peter/carnut/fi...-77-79-web.jpg

The metering plate is item 9, which is pulled up by the air-flow past it. It's connected by an arm/crank arrangement to a metering device, that increases the fuel flow in relation to how far the plate is displaced. So the throttle plate in a CIS system is always in the air-flow. If it is being displaced by the air flow, it must be taking energy out of the system and creating some sort of a partial vacuum down stream of it. I wish I had access to a car with CIS on it so that I could measure how much vacuum is being generated. I suspect that it's only a couple of %, so maybe .5 PSI, but that 3.4% would be equal to about 7HP at in a 200 HP engine at wide open throttle, or 6 lb-ft of torque!

The metering flap on an EFI system such as Bosch's L-Jetronic or LH-Jetronic on the other hand is pretty well pegged to the side of the intake track after about 4000 RPM at wide open throttle, at which point the EFI system switches over to a map of some sort. So past 4000 RPM, I doubt that a good EFI system is losing much HP over an open loop mapped system (ie - a system with no metering loop, but which runs only off of a map) assuming that both engines have the same level of tune.

Subscribing for information purposes. Hope I am not too late. This is a great thread.