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

[jmz]

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

[BURN-BROS]

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.

[jmz]

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...

[BURN-BROS]

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.

[jmz]

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

[Laneco]

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!

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

angela

[jmz]

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.

[jluetjen]

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.

[Laneco]

Originally Posted by jmz

Thanks Angela.

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

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

[joetiii]

Originally Posted by jluetjen

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.

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.

[jluetjen]

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.

[jpnovak]

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.

[Jeff Alton]

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

[joetiii]

Originally Posted by jpnovak

I did a quick model of your engine type using Desktop dyno.

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

[jpnovak]

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.

[joetiii]

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.

[911 tweaks]

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

[jpnovak]

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


Torque


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?

[jluetjen]

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.

[911 tweaks]

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