Thoughts on some different engine configurations

[Walko]

I've just spent teh better part of half an hour reading all the old posts .

I would have thought that if you wanted to build a big bore motor lets say a 3.5 on MFI then the smart way to go about it would be
to use a 3.6 case with 102mm pistons and a 3.0 crank therefore you keep the strength in the barrels and teh case no machining and you get a better rod angle.

Okay I expect that you will have to machine the heads for the MFI and modify the left hand side cam for the MFI belt but surely this would be the most bullet proof way of keeping a high reving hig HP motor together.

Any thoughts.

Michael

[CEO]

I am building a 3.45L motor from a 3.0 case. Here are the specs.
3.0 Case Boat tailed
102mm P's and C's half mooned w/ JE pistons 10:5:1 compression from LN engineering.
Cams’ I have the 964s but I think that they will be too mild.
Ported heads, 5 angle valve job.
Ceramic coated pistons, combustion chambers and exhaust ports.
All internals are going to be balanced to within .02 Oz
Aluminum Flywheel
Stock rods Balanced up to 8200 RPM
And I want to use the Jenvey setup but am on the fence about if I want to use the 48 taper or go larger.

Kenneth

[Walko]

Excuse my ignorance but what is a jenvey setup??


Michael

[CEO]

www.jenvey.co.uk

[Walko]

Great looking motor the color coding looks awesome

I am aware what Jenvey is now.

I hope Henry or someone will chime in on my 3.6 case question.

Michael

[350HP930]

Originally posted by CEO
I am building a 3.45L motor from a 3.0 case. Here are the specs.
3.0 Case Boat tailed
102mm P's and C's half mooned w/ JE pistons 10:5:1 compression from LN engineering.
Cams’ I have the 964s but I think that they will be too mild.
Ported heads, 5 angle valve job.
Ceramic coated pistons, combustion chambers and exhaust ports.
All internals are going to be balanced to within .02 Oz
Aluminum Flywheel
Stock rods Balanced up to 8200 RPM
And I want to use the Jenvey setup but am on the fence about if I want to use the 48 taper or go larger.

Kenneth

Speaking of balancing, you have you seen the recent thread on the subject?

930 Engine Balancing Results

[KobaltBlau]

Are there any major advantages/disadvantages between Jenvey and the TWM 3006 setup?

[Brother]

As a person with a newly discovered leaky CIS intake boot... CIS sucks the big one. Just my unwanted two cents.

The question for the pros: I eventually want to build the SS3.2 with SSI's and PMO's. Can I put the 46 mm PMO's on my 3.0 in the meantime until I get around to the rebuild?

[Walko]

Does anybody know teh answer to whether you can use a 3.6 case barrels and pistons with a 3.0 or 3.2 crank and MFI


Michael

[Shuie]

I the stud spacing on the 3.6 stuff is going to be different, but I think they can be modified to work. I thought someone had documented this, but I cant find the thread. You can use a 3.6 crank (76.4mm) in a 3.0 or 3.2 case.

[Walko]

I was going to use the 3.6 heads and cam boxes and just have them machined to accept the injector or use ITB with the mechanical injector mounted up high.

Michael

[Shuie]

I don't think you can use the heads. I think the cylinders can be machined to use the smaller stud spacing of the earlier cases, but I cant imagine how the heads could be modified to work. Even if you did make them fit, you would then have the challenge of mating MFI throttle bodies up to the 3.6 intake studs. There is a thread somewhere that talks about all of this stuff. I'll keep looking for it.

[Walko]

Sherman,

I think you missed what I wanted to do.

I was going to use a 3.6 case 3.6 Heads 3.6 or 3.6 BArrels and Pistons with a 3.0 or 3.2 crank

My logic was that I could then have a bulletproff bottom end that would be rev happy but on mechanical injection.

I know that when I converted my 3.0 SC motor to MFI it cost me $200 to have the heads welded up where the CIS went in and machined to accept the MFI Injectors

The only reason for using a 3.6 cas eis you are not maching the spigot bores therefore the case retains it strength.

Michael

[Shuie]

sorry, I thought you were asking about using the 3.6 stuff on a 3.0 case

You are definitely going to need some kind of adapter to get the MFI throttle bodies to bolt up to 3.6 heads. The linkage, pump mount, and the oil lines from the breather to the pump could be a challenge on the 3.6 case also.

Good luck! This sounds like a lot of fun

[Walko]

Sherman.

I would think that mounting the pump shouldnt be that difficult and I agree that some type of adapter will be needed but then I do have teh other option of using ITBs and having them modified to accept the MFI Injector.

Hey it is another project but i must do my homework first.

Wife says the loong hoods need to be finished first.

I am selling toys at the moment to purchase my next daily driver
914/6 with MFI 3.5 I hope.

I think it will be a good sleeper.

Michael

[Shuie]

ITBs modified for the MFI injectors sounds interesting Its probably cheaper than enlarging and rebuilding old MFI throttle bodies and the finding adapters for them also. You wouldnt have to dork around with the linkage either. You would need custom fuel lines, but that shouldnt be too difficult. Im starting to like the sound of this motor

[Walko]

Me to


Michael

[kenikh]

Originally posted by Wayne at Pelican Parts


Short stroke 3.0 – 98mm x 66mm stroke Type 930/02 early turbo or euro Carrera case and an early 66mm crank with 98mm P&Cs. I’ve never heard this mentioned here and I don’t even know if it’s even possible. Seems like it should work the same way a short stroke 2.8 would. Any thoughts or opinions on this one?

Yes, it should work fine, providing you have the proper pistons - I'm sure JE could make you a set. This engine would have big barrels and a very small stroke. I don't know of anyone running this engine, but I would guess with a high-lift cam, it would be very difficult to drive on the street.[b]

What about with a more moderate cam? Is it the larger cylinders that exacerbate the problem?

[KobaltBlau]

With a 911 motor you only have one cam profile, unlike some of the modern motors (VTEC, VarioCam _Plus_ (not basic), whatever the ferrari sliding cam system is called, etc). you will have to tune your cam to a specific RPM range. specifically, your cam will affect your torque levels at various RPM.

To the point, if you are going to drive the engine on the street at all, IMHO a 70.4x95 or 70.4x98 is going to make more sense than a 66x95 or 66x98, partially because the parts are easier to find, and the stroke will not limit your max RPM, any sensible street cam will be out of juice anyway. Note something John said earlier in the thread:

Originally posted by jluetjen
Andy, it's not clear to me that there is any sort of a stroke versus rpm trade-off on 911 motors. As you mentioned, in general terms 911 motors have shorter strokes then most comparable engines. The reduced stresses on the bottom end I believe has contributed to Porsche's legendary toughness in endurance racing.

Near as I can tell it's usually a top end failure that results from overrev'ing. Specifically some sort of valve/piston interference issue. This becomes a bigger issue as the valves get bigger (and heavier) with the increased bore size and capacity, and when more radical cams are used, or a combination of both of these. These problems are not insurmountable, but then you're talking about stronger valve springs which have the knock-on affect of increasing rocker and cam wear.

There are other subtler combustion related issues that could occur with big bores and short strokes, but they may only show up as you try to extract the very last HP out of a given sized engine or pass emissions testing.

I am particularly interested in where the RPM vs stroke trade-off lies. I posted earlier in the thread:

Originally posted by KobaltBlau
Note that the 3.0RSR made peak power at 8000rpm, with max. engine speed slightly above that.

The question is, do you want your power peak higher than 8000 on a street engine? If so, where do you think your torque is going to end up? Of course the 3.0RSR engine would get more service than a street engine, but you get my point. Keep in mind that although there are some street engines with rev limits like this now, they invariably have multiple cam profiles. For reference, the Ferrari 360 Modena engine has a power peak at 8500rpm, with a rev limiter at 9000, with 85x79 B&S. Now, don't get me wrong, the weight of the rods, crank, and pistons are all factors in the rpm capability of the bottom end, and they are definitely not the same between the ferrari and the motors we are talking about.

Now, if you are building the engine for a specific racing class, such as something with a 3.0 limit and free intake, exhaust and cams, would the 66x98 give you an extra edge over the 70.4x95 guys? It just might, and therefore be worth it.

Please people (Henry esp), feel free to argue with me as many of you have lots more experience than I.

[kenikh]

After reading your post, I have to say "duh" on my part. Must have brain farted on the correlation between needing a high lift cam to make top end HP. Why have a short stroke if you don't have a cam that allows you to use it without the motor becoming completely asthmatic. Unless you force air down the motor's throat w/ postive manifold pressure...