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Hmm. Now that I'm collecting parts for a 78x90.5 or 78x96 engine, the turbo project seems like a good vision into the future.

Keeping small valves increases velocity, but also limits the ammount of air that goes into the engine. One way to overcome this, is to increase lift, but this also means that a reduced circle cam can only have so much lift with the 78mm stroke. I wonder if the best compromise is more boost.

E

Take a look at Jake/Lens head flow charts---

For a given engine size, more cam/ratio rocker arent going to really help much beyond .450" lift, even with the "big" flow heads.
How do you make more power?
A) Raise compression
B) Raise RPM
C) Pressurize.
D) Nitrous.

I suppose one could do E) all of the above

(A fellow at work is offering me his NICE NOS N2O setup super cheap after shoving the crank out the bottom on his V8, and it's giving me...
Really. Bad. Ideas, especially with the turbo already enroute and the intercooler already in hand.)

You DON'T want to blow on/juice KB 96s, or rev them too high.
Stock pistons can be better.
(KB==NA only, too brittle alloy, 7500 RPM, maybe less)
Mahle 90.5, 92s, 94s (or maybe, just maybe... 92/92.5/93mm 2.0 WRX slugs, 32.5mm pin height, 23mm pin, 12cc dish) would be a much better choice, AA forged T1 94 pistons would be the cheap+hot ticket IMHO.

(I've even found conflicting info on 4032 alloy pistons vs boost, the 95s I have might work fine since I'm not running 20+ PSI... Even the JEs/Arias WRX slugs are 4032, not 2813...)

The WRX slugs on T1 H-beams/71 T1 rod crank would only require ~3mm base shims... 93x71, 7.5:1 CR with 55cc heads, only 8.12 with the 78,4 crank, and require 1.5mm less shim than "Bs", ideal for BOOST or perhaps even Bays. 93mm will work fine in 1.7 OR 1.8 jugs...

A set of JEs run $441, for the 2.0s from Jegs.(about the same for the 99.5s...)

T1 rods on a T4/t1 rod 66 crank and those pistons will give you a bullet proof 9K+ bottom end, and with 50cc chambers 7.5:1 CR (.030 deck/92mm std pistons)... in 1700 or 2.0 register heads. (one would need a valvetrain to match) Magic number works out to or 202.5mm, need .5mm shim (or less) under jugs, stock cylinder base metal gaskets might be sufficient.
It would be very close to bolt-together.
(Yes, after researching this I'm looking for a set of stock WRX pistons for the 1700 jugs)

The 2.5L WRX pistons are 99.5mm... and a bigger dish... even shorter pin/ht.(30.2 stock, to 29.5 from JE, not sure of pin dia)
Hmmmmmmmmmmmmmmmm.

I thought I would provide an update as well as ask for some recommendations on my engine build.

My heads have been sent off to HAM for a rebuild and I have a parts order in at ACT for a cam and some other items.

The engine is staying a 71 x 94 and I have had the rods resized for the dodge 2.2 bearings and had ARP bolts installed. The crank/rods/FW/PP/bolts/pulley hub are being balanced and the cylinders honed for new rings. The stock pistons look great so I will be reusing them. I am loosing the head gaskets as well.

I have decided to upgrade to 48lb injectors, might be looking for 55lb injectors but I will see what is available.

I have the WRX TD04L-13T turbo which I am happy with but think I may be maxing it out as I had been running the car at 16 PSI when the intake seat loosened up.

I want to upgrade the turbo (want more CFM) to an IHI VF34 (one step up from the STI VF39) but can't find any information on if this turbo will be too big for my engine. The reason I chose this is that it has the same uppipe flange as my TD04L-13T, and from what I can tell online, is about the same physical size as the 13T.

The STI engine that uses the VF34 only a 2.0L (1991cc)

Any suggestions ? I have a friend with a 914-8 (Corvette engine) that took me for a ride ... I WANT SOME OF THAT !

Thanks for any input.

Sandeep

Sandeep wrote:
I have decided to upgrade to 48lb injectors, might be looking for 55lb injectors but I will see what is available.

Sandeep

Don't know about turbo's, but for the AFR and hp associated (and very possible) with your engine, I think the above is a very good call.

I am very curieus about what sort of cam you will wind up with. especially duration and LC would interest me.
You're staying with the stock (42x36) valves sizes? I probably would go 42x38 on your engine if I had the opportunity

Loosing the head rings will raise CR. Will you compensate this with larger combustion chambers from Len while they're there?

am very curieus about what sort of cam you will wind up with. especially duration and LC would interest me.
You're staying with the stock (42x36) valves sizes? I probably would go 42x38 on your engine if I had the opportunity

I will leave those details up to the experts

That is the great thing about programmable EFI .. if I want more power, just swap out the injectors for larger ones ... my fuel system is good for 4x680cc injectors ... don't think I'll be going there

I have decided to go with the VF34 - ball bearing turbo, I hope the 914 2.0 runners that I am using will not be a limiting factor.

Sandeep

Time for an update !

I have received the heads back from HAM ... 42x38mm with exhaust port work and 12mm spark plugs, dual springs.

The specs have changed on the engine build

1. 80mm chevy journal nitrided crank with 5.325 T1 rods from the Type4 Store.

2. 599cc injectors X 4, using MS hi res code to control them

3. IHI VF39 turbo, ported

I am looking for pistons now but all my searching seems to point to a custom piston. I am looking for a forged piston, most likely a JE 96mm with a 15cc dish to get my CR down to 8:1

I am planning to bore my 94mm cylinders to 96mm but am not sure how the 96mm cast iron barrel will like boost

Sandeep

Sick! just sick.


E

NICE

Consider this if you will...

1800cc jugs, 93mm Suby pistons, 12mm dish, 23mm pin, pin height 32.5mm. I believe the JEs are in a low expansion alloy, and 4 run ~$450 all the time.

Lose a tad in displacement, but thicker cylinder walls, and common off-the-shelf pistons.

Also, the HD Twincam pistons are very nice looking, the factory ones are ~$20 for 4 low or zero mile "pulls" on Ebay, 95,25mm bore, 32.66 pin height, .927" pin.

Even the JE and WISECOS are ~reasonable... And IIRC available dished for turbo apps.

Interesting suggestion.

Here is another one

I was on the wiseco site and saw a Nissan / Infinity G35 piston, 1st over @ 96mm with a 10cc dish and 22mm pin, compression height = 29.67 mm.

Running the #'s, with a 0.04 deck height, 80mm crank, 5.325" T1 rods, gives me 204.925mm total length = minimal shimmage inder the barrels.

Only issue is it puts my CR @ 8.58 ... still a little high but I wonder how much more the piston can be dished.

Or I could wait another year for the 100mm turbo nickies to be tested

Sandeep

A 1.8t with a decently built bototm end and a well designed turbo/EFI system sounds like an ideal setup for a light car like the VW based ones we use.

This is all really good stuff.

Pile, what other findings do you have on Suby pistons in combination with VW/914 jugs? this sounds like a cheap/sure route.


E

CR and cam choice are joined at the head.

Something on wide lobe centers or with a late int close event reduces the dynamic CR.

My static CR works out to 10.3:1.@1mm deck,

My intake close event is ~ 58ABDC...

Using (IIRC) Crane cams online dynamic CR calculator, plugging in the cam timing numbers, it worked out to ~7.6:1., or somewhere in that range, very nearly what the stock setup delivers in the same calculator.

Pile,

How thick are the walls on a 93mm jug ? Is it the same as a 94mm OD, just bored to 93mm instead of 94mm ?

My 94's have a wall thickness of ~ 0.213", boring them to 96mm gives a w/t of ~ 0.174"

I believe T1 94's have a W/T of ~0.14"

Based on this, I would think a 96 would hold boost atleast as well as a T1 94 ?

Sandeep

Sandeep wrote:Pile,

How thick are the walls on a 93mm jug ? Is it the same as a 94mm OD, just bored to 93mm instead of 94mm ?

My 94's have a wall thickness of ~ 0.213", boring them to 96mm gives a w/t of ~ 0.174"

I believe T1 94's have a W/T of ~0.14"

Based on this, I would think a 96 would hold boost atleast as well as a T1 94 ?

Sandeep

The 93s would be a 1/2mm thicker than 94s.

The G35 slugs look like an excellent choice, but IIRC Jake has suggested 96mm +turbo issues, or even against 96mm in a Bus app.

Ephry73 wrote:A 1.8t with a decently built bototm end and a well designed turbo/EFI system sounds like an ideal setup for a light car like the VW based ones we use.

This is all really good stuff.

Pile, what other findings do you have on Suby pistons in combination with VW/914 jugs? this sounds like a cheap/sure route.


E

I also like the suggestion Piledriver made ....but I think he's suggesting it for the 71mm crank, not the 66. From the numbers it would appear that the cylinders would require a fair amount of trimming to use the subi pistons on a 66 crank, or longer rods. Someone correct me here, I'm still getting my head around the piston pin height thing!

1.7 / 1.8 is the capacity I'd like to turbo for my 1302 Might be a number of years off yet though, as first baby has recently arrived.

Cheers
Jeremy