Max rpm std valvesprings

[Homegrown]

I have a 75-2.7 K-jet with sc cams.Intake and exhaustports are the small 32mm.
Now Itīs peaking at 5500rpm but carries on to 6500rpm without protest.
This winter I hopefully gets my tumb out and disassembly the engine.There is no blowby or smoke so I will only make a portjob on the heads.
36mm inlet and 35mm exhaust.Retain SC cams.That will be topped by 42mm trottlebodies from bikeengine on homemade inlets.
Managemented by Haltech or MS (both on my shelf) not decided.
If everything works out the way I want it, the engine will pull strong too (todays) redline 6500rpm.
So the questions.
Whatīs maximum rpms without valvefloat with std valvetrain and springs?
Whatīs max rpms on std conrods with std bolts?
Port sizes?

Best regards/Stefan

[Eagledriver]

To start with, I assume the engine has been apart before and has case savers or time certs for the headstuds. If not I wouldn't remove the heads unless you are willing to have the bottom end done (very expensive for a 2.7). With stock springs the RPM limit depends on the cam. With SC cams (a good choice by the way), I would use the SC limit (about 6500). Con rods for that motor are good to 7500 with stock rod bolts.

Since you are opening up the ports, and you'll have a much better intake system, you'll want a higher RPM limit to get full power. I think you'll find the peak power at about 6200 RPM and a good pull to 7k. I'd get siffer valve springs and/or titanium retainers.

-Andy

[Eagledriver]

I'd use 36mm ports (like the RS).

[Homegrown]

Thanks for input!

Engine was rebuilt by a known builder here in Sweden some year ago, after chain tensioner failure.
So it was totally restored with new C and P it should be 93mm Mahles (I belive it when I see it). new valves and so on.
Engine is really greate but i use my car for autoX have a close ratio gearbox and the traktor power engine (just tourq )isnīt suited. I hope too up hp alot and trottle respons etc.I want a stronger and rewier engine to match the gearbox.
Exhaust is allredy SSI backdated.
So there will be portjob inlets trottlebodies and management system and no more(Maybe springs/retainers).

What differenses are there in the valvetrain
2.7 std 6500rpm
turbo 6800rpm
early S 7200? rpm

[lvporschepilot]

I believe with your valve size and rotating mass weight per valve I would want at least 75lbs on the seat and 200lbs open pressure @ 10mm. I found stock Ferrari motors with similar valve sizes to yours were floating at over 6000rpm with 65lbs seat pressure and 190lbs open. The spring locator and retainer showed a good amount of wear. Changed to 90lbs seat and 210lbs @ 10mm and there was a good difference from 6-8k. Hope this helps.

[Eagledriver]

The 911S cams have shallower ramps so the valves don't float at 7200 RPM. They might also use a higher seat pressure, but I'm not sure about that.

-Andy

[HawgRyder]

I would really look into lightweight retainers (Titanium) and possibly lighter valves.
The heavier the valve train the lower the rev limit before floating.
Just replacing the retainers (with good quality new springs) will increase your red line up into the 7000 area.
Make sure the lock angles are the same as the retainer angles.
Sodium filled valves are also a possibility ($$$).
Good luck
Bob

[lvporschepilot]

Ti valves are neat but the seats have to be replaced as well. Alum or Ti retainers with slightly better springs is probably best. The thing that kills the stock 911 springs are their lack of seat pressure, which unfortunately is the downfall for many stock springs. Open pressure is fine IMO.

[Homegrown]

This build will be on a low budget so all fancy titanium and similar is banned

Back to the question

How high rpm will the stock parts cope?

Seams like the valvetrain is identical on the 2.7 as the 3.0.The 3.0l has 3mm larger intakevalve and 2.5 mm exhaust whitch should be heavyer then 2.7 stock 46/39 valves.

Someone has the knowledge. plaese share.

[Eagledriver]

If you insist on stock valve springs and retainers, then don't port the heads. With SC cams I would limit my RPM to 6500. If you port the heads you'll lose power below 5000RPM and have to shift at 6500 RPM. I see titanium retainers on EBS website for 225 dollars. There are also aftermarket valve springs for around 200 dollars. With SC cams and big ports and an open intake system (not CIS) your peak power will be around 6200 RPM.

-Andy

[Homegrown]

Iīm not concernd that i will lose a lot of low rpm tourqe with the port job since I have the smallest ports 32/32 150hp version .
Other 2.7 have 35/35 and the bigport 3.0 cis got 39/35 other 3.0 34/35 all these engins are just tourqe the all have bad pockets that needs to be fixed.

Reason i want to up the rpms are this
241.708km/h Fasteast 911 on ice

Last year I set the record speed record on ice for all 2wd cars and all porsches at the toppspeed contestIts all about traction, its sideways from start to finish
This year i can go up with the 930and make a similar speed, or come with an other 911 drive in an other (class 2wd over 2.0liter engine before 1980)and hopefulle take that record too.
I got a rally close ratio gearbo with zf diff that limits topspeed to208km/h (130mph)at 6500rpm and that isent enough.
7300rpm makes 234km/h (146mph) thats ok.
So question in not tourqe or hp.

What is the rpm limit for the stock 2.7 valvetrain before valvefloat and other bad things happends

[safe]

My stock 3.2 carrera spinns to 7000 and make peak power there too. Don't know if they float, but I guess I would loose power sooner if they did?

[Walt Fricke]

I used to run my 2.7 race motor (10.3/1 CR, 38mm ports, Elgin 315 cam, Weber 46s, twin plug) up to 8,000 rpm before upshifting routinely. Stock valves and springs, but titanium retainers.

There was no hint of valve float when driving, nor of valve seat pounding or other evidence of things not working right. I think the stock valve springs are pretty decent.

Then I switched to race springs. Just in time - a missed shift showed 9,500 rpm on the telltale, but no valves were bent or rockers broken. I surmised the stock springs would not have yielded such a providential result.

But the race springs, after a couple of years, had the bad habit of breaking. I found that either the inner or the outer alone (with the broken part inside or outside still helping dampen harmonics, I suppose) were good for about 7,600, above which the motor acted as if a rev limiter had kicked ini. I took this to be float, but it didn't cause anything to hit anything.

But dynoing the motor, and using the torque curve and gear rations, showed me that I should be upshifting that motor at 7,600, and I was giving up something by spinning it up higher. I don't think running an SC up to 7,500 rpm is going to hurt the motor (its valves are a bit heavier than the 2.7s), it is just that at that RPM the motor won't breath at all well

If a motor is running out of breath at 7,000, running it up to 8,000 isn't likely to do much good. You'd be better off with slightly taller gears. Or maybe taller tires, or a taller ring and pinion, if you are running out of RPMs in 5th gear.

[HawgRyder]

The problem with almost all springs is fatigue.
Eventually they go "soft".
In the race cars...the term "going off tune" is often heard (valve springs go soft and the engine loses power at the top end).
The answer...not cheap...is Vasco-Jet springs.
They stay hard...and gain about 10-15% in strength in time...and then stay there for ages until they finally break.
The cost is relevant...use regular springs (lowest cost)...or race springs (higher cost and perhaps less running time)...or go for the gold and use Vasco-Jet (highest cost and longest life)...speed costs money...how fast do you want to go?
Bob

[Homegrown]

Finally 7500rpms safe with stock valve train

IF SOMEONE DISAGREE SPEEK UP!!!!!!

I put the limiter at 7500rpm for sure less power then 6800rpm but still safe revving on to 7500 without engine damage.

If I use this car at the top speed contest I think power is limiting the rpm to around 7000rpm 224km/h / 140mph (studed tyres making up a lot of resistan) but if rpms still climbing I can keep foot down just concentrate on maintaine car stable along the track.

I havenīt decided what car to use yet, fee is paid and accomodation is sorted.
Options is:
240km/h+ 911 turbo same as last year , been there done that

200-225km/h 911 discribed abow, most parts on shelf but need the tumb out

180-200km/h LADA Niva rushian 4wd car that really is skilled in climbing in difficult terrain(4wd Hi Lo centerdiff independent front suspension and raised 6") .Std 0-60 23 sek topspeed 82mph this is the car im preparing right now still sorting rust etc, but turbo kit allredy built 160-200hp is the goal.Gearing is the problem too revvy

240km/h+ Toyota Corolla-72 with +500hp BMW M10 turbo engine gearbox and volvo rear axle.Have all parts but a lot of work is needed.Propably best suited
Byt if I commit on the Toyota my 911 will lack power and rews next year

My best freind says that i should stick to one preject but that isenīt mee

[Homegrown]

safe

If I get tumb out I may have some quetions about the MFI an TBI


Ps Autocross course at the final was really nice sadly i got gearbox problems but
Drugge and Stockholm section copied your layout in a extra slalom event in Oktober and everyone liked it Ds

Best regards Stefan

[safe]

Originally Posted by Homegrown

safe

If I get tumb out I may have some quetions about the MFI an TBI


Ps Autocross course at the final was really nice sadly i got gearbox problems but
Drugge and Stockholm section copied your layout in a extra slalom event in Oktober and everyone liked it Ds

Best regards Stefan

Feel free to contact me if you like, email or cellphone, I'm not at home very often.

Glad you (and others) liked the course, it's a fun design that utilizes the width of the runway for a compact course, incorporating two types of 180 degree turns and get a few longer turns with higher speeds through the "church".

[afterburn 549]

If you "shim to SC Height it will give you a edge ..least that what I did..have had many a trip
to 7 G (By mistake) As a rule i try to stay in low 6 area

[Flieger]

Hmm. Springs should not go soft. They are designed to operate within their linear elastic region so it would take higher heat or more strain than they were designed for in order to plastically deform them. Valve springs would coil bind before being over-strained I would think. If the springs were not properly heat treated or the steel had a manufacturing defect they could plastically deform but that would happen within the first few minutes of operation. This must be creep deformation due to elevated cylinder head temperatures.

[tadd]

It's really all down to the cam you run. Porsche wanted rpms on their small motors and didn't have the greatest spring alloys, so the put really gentle ramps on the 906 cam. Typically a 906 is shifted at 8500 (on stock springs) to avoid dropping into the mid rpm hole due to the large 38 mm ports and giant 46 webers.

Most folks poo poo the 906 grind as 'old' and say to step up to the 2.8 RSR. That said, I do know that a lot of the 906/911R mid range unpleasantness was due to port size as the 'trick in the day' for a rally car was to swap the 906 heads for 69S and the 36 mm ports (keeping everything else). It is a transformation to say the least on a 2L from coughing and spitting, to being able to deal with DC/NoVA traffic.

So if you want lots of revs and stock springs, that's factory .

I have a set in reserve for my 2.8 build if I don't like my 'experiment' of 3.8 RSR On 102 LC.

t