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GT2EvoGuy 11-26-2009 09:09 AM

8000rpm bottom end rebuild - what do I need to do?
I want some qualified advice on what I will need to build my 930 bottom end to withstand 8000rpm bursts. Im thinking about having my local builder dig into the engine this winter but before I plunk down any money I really want to get advice from some fellow forum members who are successfully spinning their motors this high.

The engine right now is a 3.4L stroker 930 engine laying down 585whp at 1.2 bar with Motec EFI. The car is still street driven currently, but I ultimately intend to retire it from street service and run it in PCA racing. Id like to build the motor to a higher spec in 2 stages. First stage would be to bulletproof the bottom end and have the heads reworked a bit while retaining my 3.6 plastic intake setup and streetable GT2 Evo cams. The second stage would be to go to ITBs with much larger ports in the head and custom racing cams. In this second stage Id be looking to rev the motor to 8k.

Here are the specs of the bottom end currently:
3.3L 930 case stroked to 3.4L via a 964 crank
Stock rods shot peened and prepped with ARP bolts
964 oil pump
Stock 3.3 P&Cs
Shuffle pinned

This setup with my current heads, cams, intake have been fine for a 7000 redline but obviously above 7000 things have to be changed considerably.

My builder (Auto Associates) is recommending:

*Have the 964 crank race prepped with oiling and other mods (does anyone know what must be done specifically to live at high revs?)
*Motorsport bearings - maybe the ones sold by Smart Racing?
*Carillo rods (is there a specific rod length I should go with?)
*Custom 98mm CP pistons 7.5:1 - the motor will be boosted up to 1.4bar
*Have the OEM cylinders bored and re-Nicked to accept the larger pistons
*Upgrade from 964 to GT3R oil pump

Are there any other things that should be considered re the bottom end of the motor? Looking to get this done right the second time around and be done with it once and for all. Wasted a lot of money by having to go into it a second time :(

onboost 11-26-2009 09:42 AM

Hmmmm, not sure how much more you want or really need. Sounds like a nice motor already though you may find that you'll enjoy it better with a cam change. The GT2 EVO cams tend to make power up top similar to the old Gruppe-B grind.

You have a quality/qualified builder in Auto Associates as I've dealt with them over the years and they tend to be both straight forward and knowledgeable. Their work is very tidy and clean. Some of the best prepped cars in the Northeast come out of that shop.

My only thought is you may want a race prepped GT3 crank and Titanium rod$.. but hey, what the hell do I know?

Good luck and keep us posted!


GT2EvoGuy 11-26-2009 10:09 AM

Yes they are the best shop I have ever dealt with in terms of their knowledge and the quality of the work they do. Im just trying to understand for myself what needs to be done and why.

They did bring up the possibility of going to a GT3R crank - same stroke as the 964 but Im guessing its the best choice because its a factory motorsport crank to begin with. They said the 964 crank could be brought up to the task but will a GT3R crank still be the best choice? Im assuming the crank mods would run me $1k+ and a good used 964 crank is worth some money so maybe net net its just better to source a GT3R crank? How much do those go for new/used?

TI rods would be nice but are they strictly necessary?

JFairman 11-26-2009 10:10 AM

Sounds like you know what you're doing.
If you don't already have or use fully finned 3.3 cylinders with all that horsepower than I think you'll need them for the motor to last a long time.

Post over on the engine rebuilding forum if you havn't already, lots of experienced and talented folks there.

9dreizig 11-26-2009 10:56 AM

wow I was just looking at your garage.. all that under a 1977 ?? what does that beast weigh?? Just curious but what is the weak link at 8000 rpm and what's the HP going to be ?

GT2EvoGuy 11-26-2009 11:26 AM

Hi 9Dreizig,

Yes, building the car off an early chassis for less weight was my primary goal. The car scales at 2200lbs now with back half caged, doorbars and half tank of gas. For full race use I would extend the cage forward and replace the steel doors with carbon to get it down to maybe 2100. If I had to do it over again I would have started with a late 60s 912 chassis like my shop did with their 935 replica.

The motor right now is making 585whp and my goal with the higher spec build would be 700whp+. To get there with a 3.4L motor its going to need to be able to make power above 7000.

BURN-BROS 11-26-2009 11:28 AM

What I would build per your requirements:

R&R billet H-beam rods from LN engineering with custom aged bolts(SC/dimensions)
The new pistons from JE that are box-in-box construction(much lighter)(alter comp height for the longer rod)
Sell the 964 crank and buy a GT3 crank and mod #4 for oiling.
Turbo or GT3 oil pump

Shuffle pin your case! I have seen a great deal of cracks in the case on high rpm high output turbos.

964 cranks are poo...

A better, more reliable build would be:

R&R billet H-beam rods from LN engineering with custom aged bolts(SC/dimensions)
SC crank modded on #4
The new pistons from JE that are box-in-box construction(much lighter)(22mm wristpin)
GT-3 oil pump
Shuffle pinned case

Less rod ratio issues for the rpm
better ring land support @ the piston
Less overall money as SC cranks are much cheaper than the 3.6 stuff.

98mm would be max with 3.2 barrels, 100 or 102 with a set of Nickies from LN would be possible.

GT2EvoGuy 11-26-2009 11:49 AM

What are the differences between the GT3 and 964 crank? What center to center rod length would work best with a GT3 crank for 8000rpm?

BURN-BROS 11-26-2009 12:24 PM

GT3 cranks are fully counterweighted,are 76.4 stroke, have an SC rod journal dia. and width.
Longest rod available is 130mm. They are made by Pankl and are Titanium. This would be about the best you could do.

Running a 130mm rod would require the piston to only have 1 compression ring and a small oil control ring(if a ring that thin is available in that dia).

Crankcase vacuum is necessary with this set-up so your options are limited running that rod with that stroke. So you would have to run a 127mm rod or 127.8 max.

GT2EvoGuy 11-26-2009 12:35 PM

Sounds like I should go with the gt3 crank and a 127mm rod. I will have to discuss the TI vs steel rod issue with my builder. Besides the cost I wonder how that affects the racing hours between teardowns.

BURN-BROS 11-26-2009 01:08 PM


Originally Posted by GT2EvoGuy (Post 5033674)
Besides the cost I wonder how that affects the racing hours between teardowns.

Bearing load at the rod will be much higher without the lighter pistons/pin/rod package

Pankl has made shorter rods for the GT3, but they are Extremely expensive IF they are even available.

Why run so much stroke/rpm on a turbo? If possible I would opt for a bigger bore and shorter stroke to get some longevity and lower some of the cost.

On 3.8 turbos that have seen high rpms and high boost experience cracks at the main webs. They form at the thin sides of the case thru bolt holes and run from the centerline of the case all the way up to the head stud bosses. #7 main on the #123 side has experienced cracks as well. Longevity is definitely not a term I would use with this particular build.

I'm not trying to scare you. I am trying to hint that there are better alternatives. Besides, if you are short on displacement, why not crank up the boost a bit?

GT2EvoGuy 11-27-2009 08:11 AM

Thanks Aaron for your insightful advice.

I hear what you are saying about going with a shorter stroke and bigger bore but I kind of like the idea of having that longer stroke to help spool the turbo and get me off the corners a bit faster. My engine runs a large single GT4094r.

Maybe my thoughts about where the engine would peak on HP are way off. If I go with ITBs, huge ports and wilder cams the horsepower would peak probably well short of 8000 anyway so really no need to rev so high.

I was just doing some simple math on the weight reduction needed to safely rev higher. Right now my redline is set to 6800 with the stock prepped rods (ARP bolts) and OEM pistons. From the Powerhaus website they say the stock piston assembly on a 3.3 Turbo weighs 622 grams (including rings and wristpins). If I set my redline target short of 8000 - say 7700, the goal becomes much more doable. If I take 7700/6800 and then square the resut you get 1.282. If I then divide the stock piston assembly weight by 1.282 that comes out to 485 grams.

If I were to go with those new JE pistons you suggested (those FSR pistons look very trick) and then factor in some savings on forged rods a 7700rpm redline is probably doable right?

BURN-BROS 11-27-2009 09:36 AM

On a 3.8 993 RSR I set the redline @ 7500 with the aftermarket rods and custom aged bolts for reliability(it actually saw a few overrevs of over 8000 rpm without failure). I personally would choose a cam that would peak at approx 7300. With a lighter reciprocating package I could increase that rpm limit. That engine ran a GT3 crank and SC dimensions for the R&R A-beam rods.

The above build will give you pretty good longevity.

smokintr6 11-27-2009 10:44 AM

Out of curiosity, how much effect on required overall ignition advance (if any) do you guys see with relation to longer rods, and lower piston piston acceleration rates? Any more or less tendancy for detonation?

BURN-BROS 11-27-2009 11:50 AM


Originally Posted by smokintr6 (Post 5034599)
Out of curiosity, how much effect on required overall ignition advance (if any) do you guys see with relation to longer rods, and lower piston piston acceleration rates? Any more or less tendancy for detonation?

The theory is that longer rods increase detonation. In reality, it has not been an issue. I have not looked into timing changes corresponding with rod length, but my guess is it would be very small.

beepbeep 11-27-2009 01:43 PM

Why such stratospheric revs? It all gets very expensive above 7500 RPM. If you need more power, you could try following combination:

6.5:1 C/R
Light JE pistons
H-beam rods
Cams that peak ~7000 RPM
GT3 crank/pump
Bigger turbo, more boost
Headwork,optimal headers

Yes, you would loose some off-boost toque but as long as you can keep it on boil, it will be fast.

Rod forces go up with square of RPM, so those last 500 RPM's demand very tricky parts. If power is needed, I would rather compensate with more boost and lowered C/R (to keep effective compression within reasonable levels).

It's usually TDC piston turn that loads the rods most, not the boost.

911st 11-28-2009 10:16 AM

Great, great info!

I would think that a turbo and cam that supports HP to 8K would not be as friendly when it comes to the lower rpm drive-ability.

Further, if the gears are not also then matched to the new power band the gain might be less than the bump in HP might suggest.

Such gears then might then be uncomfortably close for street driving with shift points every couple hundered rpm and / or require a very steep first gear to work.

Just a thought.

911st 11-28-2009 10:28 AM


Originally Posted by beepbeep (Post 5034822)
It's usually TDC piston turn that loads the rods most, not the boost.

I wonder why this is?

My best guess would have to be that the rod design is typically at it's weakest point at that angle with the bolts seeing its highest stress of 100% of the centrifical fource at TDC?


GT2EvoGuy 11-28-2009 12:38 PM

I've thought about the low compression ratio high boost approach but I don't think that will work so well in conjunction with a big single turbo. It would be a very tricky car to drive even on the track I'd think. Aarons advice has me rethinking the approach I will take. A little less revs and a cam that peaks at say 7300. Even for a race only engine that seems like the way to go

Lukesportsman 11-30-2009 07:36 PM

I think you'll likely be happier with Aarons ideas also. I'd really be concerned with the rpm spread and peak rpms without consideration for your tranny ratios. If your peak power goes up in rpm there is always some give at the bottom of your power curve also. You will likely find areas of the track where your waiting on boost later than before. I like the bump in compression idea, but the larger cam may negate this. Just keep in mind that the stock gear spread is for a rather mild broad torque curve. Yours is not mild and likely a narrower band of power than OEM. The farther from this, the more disharmony that will exist.

Just another thought:
Extreme heads
Custom Cam
L&N cylinders and JE
What is your exhaust situation?

I'm thinking about increasing efficiency both VE and heat dissapation. This would result in better compression both static and dynamic. Better surface area and thermal stability. More torque both off boost and throttle tip in. Power under curve is going to be easier to drive on RC....peak is for top end pulls. At 2200lbs, your still 300lbs over the tube chassis cars and are you willing to spend another 5+grand on tranny and give up all streatbility?

Saying this, I've raced for years but your ahead of me on actually putting down power with my turbo build up. Just my .02 for thought and devil's advocate. Not a disagreement to your plan, but an alternative thought pattern. 2.1 turbos ran well on a track!

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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