Tubo charged T4 for a 1966 Porsche 912 - need advise

[Rickster]

Hello everyone!
I have been cruzing this forum and thesamba for awhile in preparation for building an engine for a 1966 Porsche 912 my uncle gave me to restore. The 912 was parked in his backyard for many years and had a tree growing over the top of it when I first saw it. I asked him about it and he offered it to me to restore. I plan to start this summer as my Factory Five project will be complete.

I have built several Ford Windsor motors, but this is my first foray into the VW world. I think I'm at a place now where I have figured out the differences between the dizzying array of motor types, body types, cooling options and have been preparing a type4 build list. The 912 has no motor in it to rebuild and after looking at the different options I settled on the type 4 for a few reasons.

* Real Porsche engines are prohibitively expensive to build
* The 1976 912 had a 912 E model that actually used a 2.0L type 4 engine, so I know it fits
* The type4 bolts right up to the existing transaxle
* The type4's bottom end is supposedly bullet proof
* Going to a larger displacement appears to be relatively well supported
* From an originality perspective, the T4 isn't too far out of line considering the 912E

I picked up what appears to be a 1.8L type 4 from a friend for a very reasonable price. I have not removed the heads or split the case yet to see if it is actually a 1.8, or what changes may have already been made in the past.

I have also never built a turbo motor before, and I would really like to give this a shot. I have experience using Megasquirt ECU’s, and used a highly modified version to build the Ford 306 ITB motor that I used for my FactoryFive AC Cobra replica. I also converted my wifes 1969 Camaro to EFI using megasquirt.

Looking over the engine kit manufactures it looks like I can purchase a kit to bring the 1.8L to 2257cc without extra machining. Also, I am not sure the turbo would play as nice with a stroke longer than 78mm, and I really don’t think I need a bigger bore because the HP/torque should be way more than enough for me. I considered keeping it at 1800cc, but I could not find any forged piston 1.8L kits.

I was hoping that the more versed members in this forum might be able to look over my build plan and make sure that I have not missed anything, and that my plan is sound. I am definitely open to suggestions! My goal is to build a turbo motor that will see street use only. I want it to be reliable, but fun to drive. I know I will need to upgrade the gear set in the 601 transaxle as well to accommodate the new motor. I have only done enough research in this area to know that it can be done and that the parts are available.

So, here is my initial build list:

* 1.8L engine case
* Engine cleaned, and bore align checked (European Motorworks? HAM?)
* 2257cc forged engine kit from AA Pistons (Part#: EK 004 2257 JE) (cast iron not biral cylinders?) 96mm bore x 78mm stroke with forged JE pistons
* Dynamic balancing performed by AA Pistons – in addition to kit package
* Scat 20088 (c45 grind .507 lift, 298, 262 duration) cam – or Webcam 119
* Solid lifters (Scat or WebCam)
* Heads – Assuming the 1.8L heads I have can be rebuilt (by European Motorworks? HAM?):
** Larger valves – 36mm x 48mm? (need advice here!)
** Dual springs
** New valve guides
** Full port & polish
** 3 angle valve job
** Swivel valve adjuster kit (EMPI 4061)
** Solid rocker arm spacers to replace spring tensioner

Turbo’s I am considering (I plan to run 15PSI max):
* T28 (AKA “disco potato”) - sr20det
* TD05H – from Mitsubishi EVO9
* T04B – twinscroll option available and oil cooled only (my first choice ATM)
* GT3076R

As I mentioned above, I am a turbo novice so any recommendations here would be most helpful!

Notes:
* Max RPM 6500ish is plenty for me…I really don’t know how the type 4 revs?
* My research shows that a 914 flywheel, clutch and clutch plate should bolt right up?
* I will need to fabricate a motor mount
* I will fabricate my own exhaust and intake plumbing
* What compression ratio should I strive for? VW engines in general seem to run much lower compression ratios than I am used to on Ford V8’s?
* I will be running a DubShop hidden crank wheel for the crank VSS
* I will be running a DubShop mini cam sync for the cam VSS
* I will be running an intercooler
* Original pancake style cooling (more room for turbo plumbing and intercooler) I will need to do some fabrication here.
* Is the standard oil pump OK?
* Turbo headers will be equal length

I think my biggest concern is how this combo will work together. The cam selection is also not my forte, so please speak up if you have better options

I appreciate your time, and feedback!

Rick Johnston
Cedar Ridge, CA

[Piledriver]

Your gonna fit right in.

Welcome to the STF!

If you are looking at boost and considering a stroker and want the thickest possible cylinder bores, note that 93mm is 1mm overbore for a 2.0 or 2.2L suby, and there are at least a couple choices of forged pistons out there with different pin heights/dishes etc.
There are probably factory oversize pistons as well.

The only thing you'd need to use them is have the rods set up for 23mm pins, which would basically be free with a rod rebuild with good Carrillo bolts from RIMCO if reworking stock 1.8 rods.

Note the stock 1.8 rods are only 127mm long, so the stroker crank set it actually can work with is pretty limited.

Mind, we (STF hive-mind we) usually suggest your first T4 should be of the "stock+" variety, as it basically goes together as stock, with none of the possible issues of building a stroker with custom pistons etc.


But... as this isn't really your first engine build, I won't discourage you from thinking outside the box.

DO read the stickies, tons of good info and a LOT of weird ideas have been covered.

One thing to consider is if you want 912E style T4 pancake cooling, or an upright fan housing, like a std 912 or 356 or T1.

[Rickster]

I like the way you think!

OK, so let's take it another step. As I alluded to in the original post, I would not be opposed (actually I would prefer) to stay with the stock 1800cc. The turbo should MORE than make up for any lost displacement. The whole reason I initially decided on the stroker was because it was the smallest displacement I could find with forged pistons. Thicker cylinders would be another nice benefit as you pointed out.

so everything is readily available except I need to find a Subaru (2002-2005 Impreza WRX EJ205) forged pistons with the correct pin height. Next step would be to do some math and see if I can locate some.

To do this I will need to know:
Stock deck height - distance from the crank center line to top of cylinder (my understanding is that this can be increased with shims?)
Rod Length (need to find this)
Stroke (already known - 66mm)
Compression ratio for a boosted type 4 application (what should I shoot for?)

When I have this done I will check back in for a sanity check if thats OK...

Thanks!
Rick

[Piledriver]

Stock deck is 202.5mm
Stroke is 66mm

1.7/1.8 stock rod is 127mm
Pin height is 42mm
With no spacers/gaskets the piston is ~.5mm in the hole.

Sadly most of the Subaru pistons have a short compression height and would be more amenable to a longer T1 rod or stroker crank;
2.0 Subaru is 92x75mm with 130,5mm rods, and ~32.5mm compression height.

That piston on a stock length T1 SCAT Ibeam has a deck of: 202.5mm.
(infers a stock crank with some welding for t1 rod journals or piston aligned rods)

If you went with T4 2L 131mm rods and 78mm crank, with same pistons, deck is: 202.5mm.
Rod ratios a bit short, but given the thick bores and if you keep the revs down should make some good tq, and Rimco sells "2L super rods" with Carrillo bolts, and could easily make them 23mm pins at the same time, likely for no more $.


Another route would be the Chevy/buick 2" journal/Porsche lenght (5.325") on a 76-78mm crank with a stroker 2.2L Subaru piston.

You could of course shim the cyliders etc, but its easiest if you plan it so you don't have to.
...the ideal length for a rod is so that the piston ends up in the right place...

[Rickster]

OK, I cheated a bit after looking for rod lengths and dimensions between the T4 and Subaru engines, I realized all I really needed to compare were the compression heights between the pistons. This is the distance between the pin center line and the piston top.

AA Performance lists their 1.8L pistons between 41.3 and 42mm CH. The average CH I found for the Subaru pistons was 33mm.

This leaves the Subaru piston sitting about 8-9mm lower at TDC than a stock 1.8L T4. I assume that I will want to lower my static compression somewhat for the turbo, but I think that is way too much. Is there a way to mitigate the difference when assembling the engine? shortening the cylinders perhaps?

I also assume that since the 1.7 and 1.8 use the same rods that there is no longer rod available for this application?

Another thought would be to use a 76mm stroke 2.0L crank, that would bring me closer (1-2mm over stock). Then I could add cylinder shims as needed for compression ratio. that would get me to 2064cc, and I would have a nice thick cylinder wall for the turbo. The down side is that the longer stroke (rod ratio) may not be suitable for the higher revs like the shorter stroke? I was planning to have the rev limiter set at 6500 RPM.

Do you see any issue reving this combo to 6500RPM?
76mm stroke x 93mm bore
ARP grade bolts

Thanks,
Rick

[Piledriver]

Any of the above proposed combos would do 6500-7K just fine with good bolts.
The 78 w/2L journals is an off-the shelf combo both in Chinese parts and from DPR.
The 2L super rods with Carrillo bolts are done by RIMCO, who could easily set them up for 23mm pins.
Also available clearanced for stroker.

Strokers beyond ~69mm won't work out with the 5" 1.8L rods as the pins won't clear the crank with a piston on them.

You cannot just slap in a set of upgraded bolts. Go with the RIMCO setup. Better bolts anyway.

Not all of the T1ish rods can be set up for larger pins safely, the "stock replacement" Hbeams from EMW etc have scary thin small ends with 24mm pins.
The SCAT Ibeams are an exception....

...But the "easy" combo is 2L rods w/23mm pins/78 stroke/Suby pistons.

You could even stick with the factory turbo-use hypereutetic Subaru pistons if they can be had in 93mm.
Will last 10X longer vs, the typical 2xxx alloy JEs etc unless you have knock issues, then they won't.

4xxx series forged pistons exist as well, they last about like stock and are pretty tough.

[Rickster]

Looks like you replied while I was typing

Still digesting all this, but while I was poking around Google I found that Ford Sierra/Cosworth/Escort pistons may look promising?

93mm bore
24mm pin (like the 2.0l rods)
40.75mm compression height (very close to the stock 1.8l pistons 42mm)

I assume you could probably get away with a 24mm pin on a 1.8L rod?

Here is the link to JE Pistons:
https://www.jepistons.com/Catalogs/Spor ... worth.aspx

And some by Wossner (never heard of them)
http://www.jemo-motorsport.de/Woessner- ... 925mm/93mm

Thanks again!
Rick

[Piledriver]

All T4s had 24mm pins from the factory.
You'd have to shorten the cylinders. Not as easy as shimming them out.

I've heard of Woessner, popular in some racing circles.(Porsche)

Those have pretty big dishes, a tight deck helps a lot but can't fix a 5:1 compression ratio.

If you are looking at $1K custom pistons anyway, just have them made as you want.
Ross has the best prices for custom IIRC. Any piston MFR can also make them in 4xxx alloy that holds up past 10K miles...
Probably for half that or less.

If you are looking for cheap, just get the 1.8L bus pistons and keep the boost down.

[Piledriver]

Toyota 22RE,(C)(T) pistons are also contendas, with useful dish sizes and available in 93mm and larger oversizes. 22mm and various compression heights, 1.355-1.526 nominal. range stock.

I believe there was also a 94mm version shown used in a series by DB&HVWs awhile back for T1 use.

[Rickster]

So after digesting all this new info and doing more research last night, I found something interesting over at AA performance. They offer longer T4 rods with 22mm rod ends. They are also avaliable with 2 types of ARP bolts. When I plugged this all into a spread sheet to come up with final deck heights, I found that the Subaru pistons fit the bill very well indeed!

The standard rod they sell is actually 0.699mm longer than stock:
http://aapistons.com/collections/type-4 ... am-rod-set

And they also offer longer rods as well:
http://aapistons.com/collections/type-4 ... l-22mm-pin

Using these and info I found in the Wossner catalog, I come up with 2 interesting combos that can be further massaged with the piston compression values they offer.

2063cc (76x93)
Deck Height: 202.5 mm
Stroke: 76mm AA Performance #004 4376
Rod Length: 131.699mm AA Performance #004 5158H
Compression Height: 32.7 mm Wossner #K9403D100
Rod Ratio: 1.733 to 1 Higher is better (1.75 is ideal outside of NASCAR)
Deck Clearance: 0.101 mm 0.004 in

1792cc short stroke (66x73)
Deck Height : 202.5 mm
Stroke: 66mm Keep the stock crank
Rod Length: 135.225mm AA Performance #004 5325H
Compression Height: 33.4mm Wossner #K9432D100
Rod Ratio: 2.0489 to 1
Deck Clearance: 0.875 mm 0.0344 in

The rod ratio is much better than I initially thought it was for the 76x93 kit and I don't have a hangup any longer reving this to 6500RPM. I think I am now leaning toward this combo instead of the shorter stroke 66x93 as it will give more displacement and still have the nice thick cylinders for the turbo.

So in summary:
Crank: 76mm stroke - AA Performance #004 4376
Rods: 131.699mm - AA Performance #004 5158H - small ends re-bored to 23mm - ARP2000 bolts
Pistons: 31.5mm CH - Forged 4032 alloy - Wossner #K9403D100
Cylinders: 93mm bore - AA Performance cylinder kit #VW9300T4L

Piledriver, thank you so much for all the valuable guidance!

The next step seems to be to get my compression ratio figured out so I can make sure that I can select the final piston to use. There are many slightly different CH and cc volumes offered by Wossner to get this dialed in.

What compression ratio would you recommend for this combo using 15PSI max boost?
Any Cam recommendations? I know they kind of go hand in hand with compression ratios.

One last thing naggin me in the back of my head. Does anyone know if there are rod to piston clearance issues with these pistons?

And a link to my Factory Five Racing AC Cobra build for those interested:
http://www.ffcars.com/forums/17-factory ... -back.html

Thanks again,
Rick

[Piledriver]

No idea, but with a 76 stroke I wouldn't expect it.
Those pistons chamber dish shape and volume is less than ideal, and they are hideously expensive.
I'd keep looking for other options and crunch some more numbers...
Those HBeams may not like 24mm pins.

Stock 2L rods are good for >7K with the good bolts.

[Rickster]

Here is the Wossner catalog I found for reference:
http://www.wossnerpistons.com/images/si ... atalog.pdf

Page 73-76 is the Subaru section.

"No idea, but with a 76 stroke I wouldn't expect it."
Right on, I will probably see if I can find a stock piston (used) just to check the clearance. Cheap insurance IMHO.

"Those pistons chamber dish shape and volume is less than ideal, and they are hideously expensive."
Not sure where you saw the pricing, but I find them selling for about $550 for a set of 4 including rings, pins and locks?

I will be searching to find catalogs for JE, Ross and others as well to see what else is out there in the 4032 alloy.

"Those HBeams may not like 24mm pins."
23mm pins right? Only 1mm over the 22mm pin size as sold...doesn't seem like a stretch to me? Agreed?

My research shows that 8:1 to 8.5:1 CR is good for 15psi of boost. That is on a water cooled engine though. Any insight on this?

Thanks!
Rick

[Piledriver]

The factory 2L pistons long skirts need a lot of work to use on even a 76mm stroker, but most of the alternative pistons we looked at have pretty short skirts due to the long strokes used in the original use, the T4s large bore/short stroke boxer is the outlier.

The 2.2 suby had a 75mm stroke for example.

If the rods you select have 5/16" bolts, you should have little to no worries past 80mm stroke as far as thee rods go.

If 9mm or 3/8" bolts you can start running into things at 76, the "super" rods are available clearanced for this reason.

I'd bet there's a stroker Toyota 22REC or T piston out there with a much better dish size and shape for T4 use than the 4 valves.
Toyota 20R/22Rs were used in ~everything they made for decades, and hot rodded to the hilt, its sort of the Japanese Small Block Chevy.

The Woessners I saw were ~600 UK Pounds, which is pushing US $1k with shipping.

An 8:1ish CR and a reasonable cam will give you decent off boost manners and a decent spool.
You have plenty of room for an intercooler and related plumbing in a 911 engine bay.

[Rickster]

I guess another option would be to have Mahle custom make a set based on the Subaru piston with a flat top and a specified compression height? Who knows, I might even be able to get to drill the pin hole at 22mm? It sounds like you have some experience with the overall piston height and how it relates to the stroker cranks. Any idea what the ideal overall piston height should be?

Summit has them listed as about $100 each custom ordered.
http://www.summitracing.com/search/prod ... ly-pistons

Thanks again,
Rick

[Piledriver]

My turbo engines still reside mostly in boxes (put away post mockup until I actually have time and a shop to finish it properly)
... but I have crunched the numbers a hundred different ways over the years and have a pretty good idea what works.

I still maintain that for your spec'd use, the RIMCO "Super Rods", stock 2L rods, prepped, clearanced , with upgraded bolts & 23mm bushed...would be ~ideal for a 6500 RPM redlined turbo motor.
(Unless you spend several thousand $$$ on heads there's not much point spinning it higher)
.
They are going to be much stronger than H beams in compression, less expensive, and don't suffer from paper thin small ends.
Hbeams get you nothing under ~7500 RPM other than looking pretty.

That combo works with off the shelf pistons, but the Subaru dish may be more CCs than ideal and not optimal for the chambers.
That would essentially bolt together like stock at 2130cc with a 78mm crank.

If you want to do custom pistons,(may take awhile via JE, Ross or Venolia are much faster) get pistons with 24mm pins to match the std T4 rods.
OEMS tend to use larger pins rather than smaller on turbo motors for some reason.

The Toyota 22REC or RET dishes are going to be a lot closer to what you want with T4 heads, get them in whatever dish size, pin size and compression height you desire. Keep a ~13mm squish band around the edge, and you do NOT want the Toyota valve reliefs.