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-   -   8000rpm bottom end rebuild - what do I need to do? (

GT2EvoGuy 11-30-2009 09:40 PM

Hi Luke,

Good ideas as well. My car actually has shorter 2-4 gears so it is already somewhat ready for more revs. I could always go to a stiffer ring and pinion gear to take further advantage of more power on the top end.

For the top end of the motor xtreme would be my choice for full race heads and then maybe get Elgin to grind a custom cam to match. The exhaust is already optimal- Mode full race headers :)

The car is staying on the street for now though so huge ports, wild cams and ITBs are really going to be on hold until the car gets relegated to track use.

Lukesportsman 12-02-2009 04:12 PM

I agree certainly on the ports and cams, but differ on the ITB's in regard to street use. May not be fully utilized without the cam, but don't think the ITB's would hurt you on street. Should give give you quicker throttle response and with boost (unlike a NA engine) partially eliminate the differential of a long runner intake.

Though saying that,I know that for a 'V' configuration engine it has been shown over and over on the chassis dyno to still make a difference in torque curve beyond theory. But you can only use so much low end torque on street. Now this is only a thought if your building it in stages since you already have a working setup....why rock the boat I guess.

Do you have any thoughts on CMW heads? In theory, they sound like the cat's meow for the $$, but I hate their fast tooling. Extreme seems the most sure fire and 9M sounded promising before the exchange rate with the dollar going to crap. (This hurts when your in the middle of restoring a XKE)

Have you priced boring and replating cylinders? When I last talked to US Chrome? , their prices made LN look more attractive when you include the selling of your old setup as P&C's.

I'm only running a 993 oil pump, but everyone points to the GT3 and if buying new does make sense.

Al and Ti parts all have a life cycle. I know that they are seemingly getting longer and more durable all the time, but CrMo doesn't. Sure it is heavier, but as an amateur racer.. i hate life cycles. I'd love Ti valves but they also 'need' to be clocked and replaced. The chrome moly rods and SS valves if kept within the ultimate fatigue limits will cycle indefinitely (within reason). I am NOT and engineer, but take these with blind faith. The nice thing about Al rods is that up till your engine explodes, she keeps getting faster :)

Gruppe B's are horrible for street and just OLD school cams like muscle car cams for a V8. But are you looking for more duration and or more lift than the Evo? I'd still love to see someone market a modern cam with good lift and proper overlap for boost with EFI.

Ceramic Bearings? Are you running water in the turbo? What kind of pressure drop are you running across I/C and across TB?

GT2EvoGuy 12-02-2009 05:42 PM

Hi Luke,

I just talked to my shop again and we kind of came to the conclusion that the cost benefit of diving into the bottom end is just not worth it until the car truely becomes a track only car that will be running at over 7k. The parts plus labor are well north of $10k :eek:

What we decided to do instead was to maximize what I already have for a bit more fun while the car remains on street duty. Not that 585whp at 1.25bar is shabby but I am looking for a bit more power and better pull up top (hopefully to 6600-6700 instead of 6200 peak now).

So, sticking with my current 3.6 plastic intake and single TB setup for now, but they will be reworking my heads for better port velocity and flow for a nice bump in performance. My conditioned stock rods with ARP bolts should be fine with a 7k redline, which is all I need for street use. Much more cost effective upgrade for now at about 1/3 the cost.

My heads currently are:

40mm intake ports (not sure on the exhaust side).
Twin plug
Stock 49mm and 41.5mm valves
Running a slightly bored out 71mm TB with the plastic intake.
Aase valve springs
GT2 Evo cams

The plan is to:
Stay with the 40mm port size
Stay with GT2 Evo cams for good compromise between midrange and top end
Replace stock intake valves with 51.5mm valves with thinner stems
Totally rework the ports for better flow and velocity
Full radius valve job
Make sure all surfaces are trued up and that the spring pressures are proper
Larger TB - maybe jump up to 75 or 80mm

Sure I plan to get into the bottom end eventually but we figure it just isnt very cost effective or noticable for street use right now. When I go to a race only motor, I will be looking to sell the heads, cams, intake, TB setup and go with some custom Xtreme heads starting from their own bare castings along with ITBs. I dont have any experience with CMW so I cant speak to those heads.

911st 12-02-2009 06:05 PM

Sounds like a good plan.

I belive 993TT has 43mm intake ports for what it is worth. Your intake manifold should support up to 41.5mm and might support up to 43mm.

GT2EvoGuy 12-02-2009 08:02 PM

Hmm for some reason I thought the ID of the plastic 3.6 intake was 40mm but if it turns out to be larger we would take the ports out as far as that intake will allow. :D

Peter Guldan 12-10-2009 08:44 AM


Don't need 8 grand to win if that's your ultimate objective. Here's the PWR 3.4 TT GT 1 winning PCA 's Oktoberfest . You'll note on the heads up it hard cuts at 7,500rpm. By limiting rev's to 7.5 and focusing on flexible usable power below that it can compete at a much lower $/hour at this level than it's competition (GTA-C) at 60 hours between builds, the largest parts replaced being the exhaust valves.

Only the 2.1tt out of the 2.6TT, 3.0TT and the 3.4TT is rev'd over 8 grand in competition.

A mod'd 3.4 Turbo in a 911/930 is likely to land you in GT 1 in PCA if you build anything adequate to convey that power (safely) to the track. Sadly, there're are less and less of our beloved old machines being campaigned, thus, your run groups will be predominantly the latest no-lift shift, traction c, abs equiped and sorted factory machinery up to 4 litres and rev'g over 9K. The key is handling/driveability.

juicersr 12-10-2009 09:31 AM

Peter, do you have a PM or email address?

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