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Cheap-a$$ long rod + stroker + high CR pistons?
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ideola  



Joined: 01 Oct 2004
Posts: 15506
Location: Woodstock IL

PostPosted: Thu Mar 29, 2012 11:48 am    Post subject: Reply with quote

Picked up the crank today. Also received my pistons and rods. Bought a 12" digital caliper so I could accurately measure my deck height, and will be taking block in tomorrow for cleaning and prep work.

First for the pix:




This pic shows how much smaller the big end is on the Manley rod as compared to our stock rod:


Comparison of pistons. From left to right: OEM NA; OEM turbo; Diamond Euro-spec 931 replica; Wiseco off-the-shelf piston.


OK, now for the numbers. Bear in mind, this is specifically for using a 931 head on a NA application in order to achieve a D-Prod-like build. There are many additional configurations that can work depending on whether you want to use a 931 or NA head, and whether you intend to run forced induction or NA.
  • My deck height measured 231.15mm. I am going to have my machinist remove .025" (.635mm) to bring the deck height down to 230.515.
  • The pistons are 88mm bore (also available in 87mm and 87.5mm bores). I decided to go big or go home.
  • The piston should end up about 1.3mm down from the deck. Not 100% ideal for quench, but this particular piston had the highest compression height I could find, and consequently the lowest quench available, which is why I opted for the Wiseco pistons even though they were $150-$200 more than some of the other alternatives.
  • Wrist pins are 22mm floating. The rods are available in the correct width for either 21mm or 22mm pins. I chose the 22mm pin because of other piston selection criteria, most notably CR, compression height, and minimal quench.
  • The total additional stroke on my crank ended up being 2.8mm over stock, bring total stroke to 87.2mm.
  • Rod length = 150mm
  • I am going to run a standard .051" Cometic gasket.
  • Calculated CR comes out to 10.7:1
  • Calculated displacement comes out to 2122cc


I am hoping to receive the rod bearings next week, and also that the block will be done early in the week. As soon as I have bearings and block, I will do a quick assembly on everything to verify that there is no rod-to-wall interference with the additional stroke. As you can see from the pix, the Manley rod is quite a bit smaller on the big end, so I do not anticipate any issues there.

The crank work ended up costing more than expected even though he again confirmed that nitriding was not necessary. Apparently, our cranks have what are called "rolled radius" journals, which is a hardening process where the journal meets the lobes on the crankshaft. It is impossible to tell if the radiuses have been rolled (resulting in signficant hardness and strength) or simply machined (less durable but easier to work with) until the machinist starts the grinding process. Well, our cranks have rolled radiuses. According to my machinist, no one else in this city will touch a rolled-radius crank for this kind of work. He claims that while working the rolled radius, the crank will bend slightly as each journal is worked, and requires re-straightening after each journal is completed. A tedious process. So no need to nitride because the crank is pretty beefy to begin with; but a little more than we had originally anticipated for labor.

Here are the dollar figures:

Crank work = $400
Rods = $350
Pistons = $600 (off-the-shelf with side skirt coating, no teflon tops)*
Total = $1350
* there are cheaper options available but with less desirable quench distance...

By comparison, here are the numbers for the weld-and-regrind approach:
Crank work = $650
Rods = $870 (custom Crowers)
Pistons = $880 (custom slugs with skirt coatings AND teflon tops)
Total = $2400

Frankly, I have not been able to find an ideal piston configuration, particularly as it relates to the quench distance. Using off-the-shelf pistons means you have to take what you can get for compression height, and NONE of the hundreds of configurations I've evaluated have sufficient compression height to bring the piston flush with the deck. However, for a high compression NA application, the quench area with this particular setup is still significantly better than stock (which is over 6mm), although it of course results in being an interference design. Based on the numbers, I don't see any way to achieve increase stroke AND increased CR while retaining a non-interference motor.

It's also worth noting that at $600 for the off-the-shelf pistons, it may be worthwhile to just spec out custom Diamond slugs for only $100 more in order to eliminate the valve pockets, while also achieving the precise quench distance and CR desired. Just another option.

I hope to report back next week with an update on the rotating assembly.
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ideola  



Joined: 01 Oct 2004
Posts: 15506
Location: Woodstock IL

PostPosted: Thu Mar 29, 2012 11:55 am    Post subject: Reply with quote

Forgot to post weights:
Manley rod = 544g
Wiseco piston = 365g
Wiseco wrist pin = 112g

I don't seem to have a record of the weight of OEM slugs or wrist pins, but the tech specs booklet indicates the rods are between 815g and 927g, so up to a whopping ~1500g of weight savings is possible on the rods alone.
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924RACR  



Joined: 29 Jul 2001
Posts: 8334
Location: Royal Oak, MI, USA

PostPosted: Thu Mar 29, 2012 10:15 pm    Post subject: Reply with quote

Conveniently I just weighed my stock (S2 '82 931) rods, as I just balanced them out. Without substantial weight removal from the big end, I got them all balanced at about 851g. Not too bad. That's for the Series 2; the Series 1 rod I swapped in (due to the original damage that necessitated the rebuild) was 4g heavier. Which meant more grinding to balance.

The Series 1 piston is, likewise, the same 4g or so lighter than the S2 piston. So the rotating mass would work out the same... though of course in my case I just reused the stock, still perfectly good S2 piston, so needed to balance the rod.

I was impressed by how well it was all balanced from the factory; definitely much better than I recall the 924 NA stuff (from the race motor build).
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RC  



Joined: 25 Mar 2007
Posts: 2634
Location: Australia

PostPosted: Thu May 17, 2012 9:39 am    Post subject: Reply with quote

FYI its not too difficult to shave up to 50 gms off the big end cap alone. This set, balanced individually and end for end came in at an even 200gms on the caps.






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BionicBalls  



Joined: 05 Jan 2009
Posts: 642
Location: Charlotte, NC

PostPosted: Sun Aug 05, 2012 8:28 am    Post subject: Reply with quote

Any updates on this thread?
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ideola  



Joined: 01 Oct 2004
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Location: Woodstock IL

PostPosted: Sun Aug 05, 2012 10:24 am    Post subject: Reply with quote

The head was completed last week, and the dual DCOEs arrived this week. I'll be assembling the motor in September, and it'll go in the silver D-Prod-bodied car I just brought back from Florida. That car will get paint before the motor goes in, so it will all depend how long my body man takes on prep and spraying.
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AFRICA DEE  



Joined: 16 May 2006
Posts: 48
Location: JOHANNESBURG, SOUTH AFRICA

PostPosted: Tue Aug 07, 2012 6:02 pm    Post subject: Reply with quote

My stroker conversion... long winded with other stuff I am doing....

I started with a 931 totally original and painted in Guards Red, 93 000km’s. Some photo’s and development/progress work are on the forum.
Three years ago I reconditioned the engine with new standard bearings; rings, a fairly proper F/M intercooler and the boost turned up to 1 bar it was used as a track day toy. A bucket seat, smaller steering, half roll cage and a 4-point harness went in, with a local aftermarket coil over suspension. The front discs were upgraded to cross drilled items, better pads went in and Goodridge braided hoses. But with 3 head gasket failures, piston destroyed due to detonation and one turbo failure (1 bar Boost, maximum 98 octane, CIS and standard radiator etc with an average day temperature in summer of 30+degrees C in South Africa do not go well together …) So I have decided to convert it to a narrow body ‘light weight” normal aspirated RHD “street legal” track day car. This is what I have done and/or acquired to date:
RHD steering box went in with all the standard steering gear.
Brake booster has been deleted in favour of a 3 Pedal Box with separate master cylinders for clutch and back/front Willwood master cylinders.
Boxster 16 inch rims with 225 and 205 tires respectively
GTS headlight conversion, ex GT Racing
Interior has been totally stripped including dash and gauges except for door panels and roof lining.
Electric windows to go, side window glass to be replaced by Lexan , electric mirrors to go.
Aluminium fabricated dash with electronic DigiDash and Innovate MTX-L Wide band AFR system to go in.
Wiring harness is considerably lightened.
All interior sound deadening has been removed lots of no longer required brackets and spare wheel well and LHD battery box floor has been cut out and holes are covered in aluminium. Weight loss +20kg.
Total heater delete, only modified interior fan will be kept with directional outlets.
Bumpers lightened with some discreet holes cut in. Bumper fog light deletes with ducts for piping to brakes. Original head light areas and wheel arches has been modified to run cooling pipes
Fuel tank has been replaced by a 40l aluminium tank with a single h/p fuel pump and a small aluminium overflow tank.
Two OMP TRS bucket seats and 6 point harnesses
2.5 kg fire extinguisher
Light weight battery to be fitted, position still to be decided on.
Lightweight Toyota forklift alternator 1.2kg
BMC filter in ‘cold box’
Gotech Pro X Engine management system (ECU) (www.gotech.co.za)
Larger capacity aluminium radiator and twin fans controlled by ECU
Modified 931 intake manifold with VW VR6 throttle body
Fuel rail with Bosch 440cc injectors and head has been machined to lower injectors.
Big Valve Conversion with H/D Springs from Ideola. The 931 head has been gas flowed with reworked 280 degree stage 2 cam. ARP head studs to go in. Await “new” Cometic gasket.
Ideola lightweight lifters and lash caps bought and distributor gear cut off from rear of cam. Rear of head has now been blocked off.
Vernier cam wheel.
Due to heater delete could modify the rear water outlet on head to 32mm with 32mm pipe to water pump
Engine: Ideola stroker conversion bought with Wiseco pistons( 11:1 CR) and Manley Rods. I await the arrival from US of A….
Crank will be knife edged.
Baffled crank and scraper system to be made up.
931 Flywheel -2kg
New exhaust manifold to be manufactured, D-Prod like...will have to see about oil filter and oil cooler pipe modifications (Ex 931)
Development and work to continue…
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Khal  



Joined: 26 Sep 2003
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PostPosted: Thu Aug 09, 2012 5:54 pm    Post subject: Reply with quote

How's the toofah handle in that snow?!
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musicalannette  



Joined: 21 Feb 2012
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Location: UK

PostPosted: Mon Aug 27, 2012 11:14 pm    Post subject: Reply with quote

So the tab thats on the sump?, stopping it from being removed easily?, is that for this type of "blueprinting" you should be doing if you want to go racing? Or do they say something at scutineering if your going 20mph faster than everyone esle down the straights and say its because you only have one door mirror? made me chuckle. looks a good hidden mod if too expensive fo me though.
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CorsePerVita  



Joined: 25 Jul 2008
Posts: 1992
Location: Redmond, Oregon

PostPosted: Tue Aug 28, 2012 2:16 pm    Post subject: Reply with quote

Khal wrote:
How's the toofah handle in that snow?!


I've never had an issue with any of my Porsches in the snow. Good snow tires are a must, but they're a hoot to drive. The 924/944 cars are easy to drive, easy to correct and fun to get sideways if you desire. The 911 has a ton of grip but isn't quite as easy to recover if you eff up. The 914 even does well.
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itbracer85porky  



Joined: 02 Mar 2012
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PostPosted: Mon Dec 17, 2012 5:00 am    Post subject: engine Reply with quote

Hello all. Any updates on this motor build yet? I am very interested in this. I would like to know how successful it is/was, and how much to get one built. I would like to go this way with my 924 DP replica, as I found other uses for my spare "hot" engine.
I would gladly be a guinea pig for something like this, and let you all know how it works out. I have a few questions though:
1) what is an estimate on the HP of a 10:1 engine in this configuration?
2) how streetable would that be?
3) could a well tuned CIS handle an engine like this?

I just want to play around with the car a bunch more, and think this would keep my busy. Thanks in advance!
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the_mad_electrician  



Joined: 16 Nov 2009
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PostPosted: Mon Dec 17, 2012 10:27 am    Post subject: Reply with quote

I would be highly interested in this if I get another 2.0 car
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ideola  



Joined: 01 Oct 2004
Posts: 15506
Location: Woodstock IL

PostPosted: Tue Dec 18, 2012 2:05 am    Post subject: Re: engine Reply with quote

itbracer85porky wrote:
1) what is an estimate on the HP of a 10:1 engine in this configuration?
There are a ton of variables that will affect total power gain. Fixing the shortcomings of the NA head will have a big impact, but if you're going with a D-Prod style motor and using a 931 head, there should be some positive gains, even if you don't go with a big valve head. Stage 1 or Stage 2 cam will make a difference too without impacting streetability. All that said, and all else being equal, from this thread:
ideola wrote:
From this article (using the code tag to preserve the table spacing...):

Popular Hot-Rodding wrote:
CR Power Gains
The theoretical thermal efficiency (E) at any given CR can be predicted by the following formula:


Where E = the Otto cycle (thermal) efficiency, R the compression ratio and k the coefficient of adiabatic expansion for air, which is nominally 1.4. Rather than flogging through a lot of calculations, the quick reference chart (Figure 2) has been made up. To use this chart locate your original CR horizontally. Next, locate the new CR down the first column. Where the two intersect is the gains that can be expected. For instance if the CR is raised from 9:1 to 12:1 we find the two values intersect at the box with 7.7 in it. This is the percentage increase that can theoretically be had by raising the compression from a lower to a higher level.

Code:
     ORIGINAL CR
NEW    8:1   9:1   10:1   11:1   12:1   13:1   14:1   15:1
9:1    3.5                     
10:1   6.5    2.9                  
11:1   9.2    5.5    2.5               
12:1   11.5   7.7    4.7   2.1            
13:1   13.6   9.7    6.6   4.0   1.9         
14:1   15.4   11.5   8.3   5.7   3.5   1.6      
15:1   17.0   13.0   9.8   7.1   4.9   3.0   1.4   
16:1   18.6   14.5   11.3  8.6   6.4   4.4   2.8   1.4

Now anytime we use the word "theoretically," it usually implies that there is not much chance of achieving as much in practice. Here the good news is that because intake valves do not close at BDC, the gains computed in Figure 2 tend to be a little on the low side.


From this table, you can see that a full point of CR increase will yield about a 3% gain on our motors. 125 BHP (Euro-spec) x 3% = 3.75BHP. Pretty measly, eh?! You'll have to decide if half a point of compression is worthwhile to take a chance on losing the non-interference aspect of your engine.

For me, because the timing belt is so easy to do on our cars, I feel that the issue of interference is way over-rated. Most modern cars are interference design. To achieve the biggest possible HP gain, I'm going more radical, and going to 11:1 on my NA project (120 BHP [US-spec] x 5.5% = 6.6BHP). Of course, it also involves additional stroke, Stage 1 cam, Cometic gasket, big valve head, free-flowing header, etc. so I expect the gains to be multiplied. I'm also encouraged by the fact that the stock motors went from 120 BHP at 9:1 in US-spec to 125 BHP at 9.3:1 in ROW-spec. That's a 5 BHP gain, or ~4% increase from .3 increase in CR...



itbracer85porky wrote:
2) how streetable would that be?
Streetability will not be negatively impacted by the CR. In fact, the CR increase should improve torque response especially in the low RPM range.

itbracer85porky wrote:
3) could a well tuned CIS handle an engine like this?
Absolutely.

I've been traveling quite extensively during Q4 for my day job, and have had ZERO garage time. This is as far as I've gotten prepping for the build:





Head is complete, carbs are prepped and ready, but I have machining to do on the intake and exhaust manifolds, which is holding me up at the moment.
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itbracer85porky  



Joined: 02 Mar 2012
Posts: 43
Location: New Hampshire

PostPosted: Fri Dec 21, 2012 3:24 am    Post subject: Reply with quote

Hello all. I just had a thought regarding using a 931 head on an NA motor such as this build.
Would it be possible to have the stud holes filled in/welded shut, and then re-tapped to accept the bolt pattern of the N/A headers? There would still need to be some match porting for sure, but would that work? Has it been tried?
It would require some aluminium welding skill (not hard at all), and some precise drilling tapping (again, no hard), but it could solve a lot of problems with putting a 931 head on an N/A motor...
thoughts?
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fiat22turbo  



Joined: 18 Jan 2006
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PostPosted: Fri Dec 21, 2012 4:10 am    Post subject: Reply with quote

I wonder if the NA head could be machined with the 931's combustion chamber (or something similar)? Would that be easier for use in a NA application? Just thinking out loud since the heads don't seem that much different other than the combustion chamber, the location of the ports and the spark plugs on the opposite side (hey maybe put a set on either side and run dual plugs!)
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