Building the ultimate 3.5l motor

[1meansc]

I am in the process of getting my thoughts in line for a 3.5 l motor build. My 3.2 comes early next year, and want to start sourcing parts. My base ideas as follows:
3.2l motor - case boat tailed
100 mm sleeves
JE pistons - flat top
Keep 3.2 heads basically standard
ITB with with high butterfly injection - 45mm
Crank trigger ignition - twin spark - with individual coils

There are a few points that need to be added here.
The vehicle will spend most of its time at 6000 feet above see level, but will also need to run at sea level.
We will use 98 octane fuel
Car is a dedicated track car.

I need some ideas on compression ratio, was thinking about 12:1, ideas on camshaft selection - like the characteristics of the 993 super cup cams.

The reason for the engine change, is that I currently run a monster 3.2l SS, with super cup cams, and ITB. This motor makes good HP but has peak torque at about 5500 rpm and peak HP at 6700 rpm. I compete against 993 super cups and 964 RS cup cars, and battle out of a corner. I would like to get more go low down.

Ideally I would like to have a motor that has peak torque at about 4500 to 5200 and peak HP at about 6000 rpm. This would allow a motor that is tractable.

The car will eventually be 2200 lbs.

Thanks for the input.

[Facey]

i have just finished building and breaking in a 3.5L

using: 100mm Mahle P&C's (74mm crank)
3.3L euro 930 case
46mm weber IDA's
matched intake manifolds
46/44mm ports
big valves
lots of custom machine work on heads
1 3/4" B&B headers
M&K muffler
twin plugged
electromotive crank fire ignition, w/individual coils and controable advance....


i made 278 (corrected to SAE) rwhp, (~320 crank) and there is at least another 20-25 on the table, that can be had with cam timing (which is presently a stock s-cam, @ stock timing) running a little rich

its hp peaked @ 6100rpm, torque was low ~5500rpm.
to say that it is tractable is an understatement, it pulls from 2000rpm hard to 4000, and from 4000-upper 6000'd better be reaching for the next gear.

as a pure race car u would obviosuly use ALOT more cam, as even i need mroe, basically i'm not using my avaible air flow.....
unbeknownst to me my mech decided to double up on head gasket spacing , making it between 9-10:1cr...i had planned on 12:1 , and with that according to bruce anderson it should be 330hp with stock cam and weber settings....

keep us updated on your build

[YTNUKLR]

Talk to John Dougherty (drcamshafts.com) about cams. 12:1 seems hard to do with Carrera heads, I guess it will depend on your planned deck height. I would probably run about 10.8:1, any cam like the Supercup, DC20, etc., build pretty high dynamic compression ratios.

Is your ITB setup 45mm at the head port?

Keep in mind the displacement increase will make the cam seem a bit milder because the 3.5L engine is moving more air overall at a given RPM (vs. 3.2L S.S.). Not to mention, the 3.2L 74.4mm-stroke crankshaft will lend itself better to low-end torque production.

Sounds like fun.

-Scott

[1meansc]

The 45mm ITB is at the butterfly. This will taper down to the 41mm at the head.

I will be using Georges headers (European racing) as we are not able to get proper equal length headers here. They will be the 38mm ID ones.

Where would you guys expect the peak HP and torque rpms to be.

What would the expected flywheel HP to be.

I am also looking at running full sequential fuel injection, from the new Wolf V500 ecu.

[boxermania]

1meansc.....

I'm not well versed regarding cam combinations for your engine, however, but based on your desire, I do know that to get more torque down low you need to increase displacement as much as possible and decrease the cam overlap.

Has any one tried a turbo cam on a large displacement engine and dynoed the combo?

I also agree with one of the other contributors, 12:1 compression is a bit high if your ultimate quest is to have a reliable torque monster.

I know that the following statement will get me in trouble, nevertheless, HP rules the straights, torque the corners, the rest is gearing.

Just my .02 cents.

[JeremyD]

I think if that high a compression motor if your goal- you better be looking at JE's with deep valve pockets.

[WydRyd]

You could use a crank from a 3.6L, for even more low down torque

[1meansc]

I was going to go for the 3.6 crank with my existing 98mm sleeves.

From what I have heard on this board, there are not a lot of supporters for the 3.6 crank, especially without the harmonic balancer and dual mass flywheel.

So I decided to make a 3.5 with a 3.2 as a base.

[YTNUKLR]

Just don't use the 964 crank...PM me if you want details on other options for a 3.6 crank.

[Jeff Alton]

Originally posted by YTNUKLR
Just don't use the 964 crank...PM me if you want details on other options for a 3.6 crank.

Share your wisdom....

Cheers

[1meansc]

With regards to cam selection, I have seen on other posts that people suggest a Mod-s cam for similar builds. Anyone with ideas on this.

[Facey]

if by mod-s u mean a slightly modified s-cam, and i believe the 'mod' is mroe duration, no change in lift, then thats actualyl what i am using, however i have been told for timing purposes it is bascially an s-cam. and if this is the case, in a race car i would defintly want the cam to come alive at higher rpms.

[1meansc]

My reason for wanting to keep RPM down, is durability. I don't want a low hour motor. I am prepared to do a top end rebuild every year or two, but budget does not allow full overhaul every year.

I have run my very quick 3.2 SS for two years now. Pulls like a steam train all the way up to 7200 redline. I have only reconditioned heads and replaced rings at the beginning of this season. Motor still sounds better than most, and possibly one of the quietest 930 based Porsches that I have heard. This with JE pistons.

I also want to try to design the peak RPM low, to allow for the possibility that the actual peak torque and HP are a little higher, at least the motor will be able to run there.

I will be using Johns racing springs & retainers, with his recommended cam. The rest of the motor will be made to run to 8000 rpm if necessary.

Thanks for the ideas and comments guys.

P.S. Scotts ideas are great, but budget would not allow the crank options.

[911crazy]

you have a pm.

[DW SD]

Originally posted by YTNUKLR
Just don't use the 964 crank...PM me if you want details on other options for a 3.6 crank.

Scott,
What's your info on the 964 crank?

[1meansc]

Well, this build has started. There is a year of dreaming, 6 months of design and 6 weeks waiting for parts.

The first of the parts arrived on Saturday.

The build is as follows:
3.2 carrera case and crank
Pauter rods
100 mm JE high comp pistons
Re sleeved 100 mm cylinders
GT3 Oil pump - man this thing is huge
Johns cams & racing spring & retainer kit
3.2 ported heads, twin spark - just cleaned up, not made any larger

The custom throttle body intake will be ready in one week.

Ignition & fuel will be controlled via Wolf V500, running sequential fuel injection, and wasted spark ignition.

Build will be documented on this site.

[Henry Schmidt]

Another approach.
3.5 MFI 369 RWHP 352 F/lb 112 octane fuel
Functional RPM range 4500-7800
Mahle 100s
RSR sprint cams
930 crank 74.4 mm stroke with 3.0 rod lournals
3.0 SC rods with ARP bolts
930 oil pump
50 mm Silver Line intake valve
42mm Silver Line exhaust valve
41 mm intake ports
41 mm throttle housings
54 mm intake stacks custom build @ Supertec
RSR MFI pump conversion
Supertec Valve springs
Aasco ty retainers
Custom Distributor MSD AL6 with Blaster SS coil
European Racing headers

[1meansc]

Henry, that looks great.

What compression ratio are you running on that motor?

How often will you have to rebuild it?

I am prepared to open mine at the end of every season for a check. My idea is to strip top end every season and split the case every other season.

I am hoping for a little less Bling with my motor, but should be close.

[1meansc]

Well, as promised i will post a couple of pics of the new motor.

I started with a 3.2 "long block", but this was covered in another thread.

The case was cleaned and a "small" GT3 oil pump fitted. Note modified centre main bearing.

100 mm JEs fitted to reconditioned 964 sleeves. Plenty of heartache here to get everything to fit. People tend to leave out a couple of points when they describe their work.

Then assemble the rest of the long block in an anti-bling fashion. Note: Old motor had a red fan & shroud, black fan housing and looked like a Christmas tree. A nice Christmas tree none the less.


Not bad for one months work, from dirty incomplete long block, to what I have now. Hopefully the remainder of the induction will be fitted today, and the custom HT leads will arrive. I hope to have the motor in the car and started today.
I have also realised that sleep is not important in the quest for Pure Porsche Power.

[Facey]

wow!!!!!! simply amazing