Noahs944

Based on what logic or physics?

Noahs944

Sure, but you can anticipate and pre-check before running the engine.

Regarding the tire & maf and muffler, I won't argue, but there's plenty of other threads that discuss those matters, mate. This threads about valve train only.

OPINIONS WELCOME

944CS

Based on my testing, experience, and the fact that a stock 944 engine has so many other hinderances to airflow - additional lift is the last thing it needs.

I realize you are looking for "free" horsepower, but it just isn't there in this motor.

If you want more power, you are going to have to change components. Air flow meter is the #1 start. Then Muffler. If you want to play with your powerband, you can mess with the cam, but the stock cam has a great street /daily driver profile.

When I first read your thread title, I thought you were going to talk about machining the cam box for a solid lifter conversion. This will allow a more aggressive ramp profile to the cam, which will help airflow.

Remember, peak lift will help high rpm breathing, but, this is a 2 valve head. High rpm and breathing physically aren't possible due to space constraints, when compared to a 4 valve head.

If you are thinking high rpm in relative terms(for example, if you want the engine to make power to 6500) this is possible with just a cam and exhaust change (recommended to replace air flow meter for maximum gains).

Noahs944

Thank you for your input. I always like to read from mechanically inclined racers because they have credibility.

I agree with the 8 v stock bumpstick being great for daily driving. It's my impression that a "stage one" cam has more duration and a stage 2+ has more lift with (possibly more duration).

odonnell

What about getting bigger intake valves? They're relatively cheap, $120 last I looked, but machine work is a few hundo.

Otto Mechanic

It's hard to believe this site is so cheap to join.

V2Rocket

No real point, IMO.
The stock 944 head flows 190-200cfm at 28", enough to get ~200hp if you really built up the engine and had a CAM to get there.

IMO the only reason the 2.7L had such huge valves/ports was to get around the fact it had a very mild cam and still had the AFM to breathe through...and the power numbers reflect the mildness of the cam.

Duration, duration, duration....

Noahs944

Hahaha... that is a fair assessment Spencer.

Michael,
John Milledge recommends bigger valves for some of the bigger cams (starting with the last cam I bought from him, though I ignored the recommendation - he did mention 2.7 valves, although heavier, would improve the breathing), my answer to that was to undercut the valves so they allow gas to slip through at less lift... well at all phases of lift.

I think larger intake valves would be helpful.

----

Spencer,

You kill me when you defend the cfm of the head and the stock exhaust brother. I know it's good, but if nothing changes then nothing changes

Otto Mechanic

It's my understanding that the sodium filled Turbo (49mm) exhaust valves are the solution for that head?

V2Rocket

The intake and exhaust systems (including the head ports) are just pipes to carry air toward and away from the engine. They are sufficient in size and flow capacity. Yes, you can improve them and find gains but head work tends to be expensive and specialized.

The camshaft is the main thing that determines how much air goes in and out, and when that happens (RPM range), and is the easiest to change in the search for power (especially in a 944, it is dead nuts simple to swap out a 944 cam).

Stock 944 cams make peak power at 5500-5800rpm and are made to put a good flat torque curve peaking at 3000-4000 rpm. Street manners, emissions, economy, all in one. We don't necessarily care about economy or emissions when modifying the car for power so the cam design perimeters can be changed "hotter".

Someone once pointed out that the 944 cam profile (and the profiles of most all the AFM equipped cars of any make) are very pointy, fast ramp rates and very short "nose time" in order to make sufficient vacuum to keep the AFM flapper open. Not sure how accurate that is, but I could definitely see it being a factor.

Think about other engines maybe you have experience with...what are the top 4 things people change for power?
Intake, exhaust, cam, and tune.
Typically a K&N filter, different mufflers/cat delete for the first two, to not much result but fun noise. But they are all shocked when a bigger cam goes in...

Look at the old SBC LT1 vs LT4...the LT4 was essentially the same engine, but they put a slightly hotter camshaft in (with different rocker arms...for slightly more lift/duration ) and it picked up 30hp in the same car (Corvette).



turbo for all years has 45mm/40mm intake/exhaust just like 944NA.

Otto Mechanic

Typo, bad memory, who knows anymore...

My question was whether the larger Turbo exhaust valves played a significant role in increasing HP with the 2.7L head?

Otto Mechanic

Maybe I should clarify.

I've been looking at turbocharging a 3.0L block using a stock 2.7L head. From what I've learned so far, the 2.7L head is compatible (bolt on) with the 3.0L block and also the 2.5L Turbo hardware. I've been told (understand so far) the 2.7L head requires the Turbo exhaust valves in that configuration, I was only looking for confirmation.

Noahs944

This makes a lot of sense! The lobes certainly are pointy.

Noahs944

Hey, it's taken me 23 hours but I finally realized...

YES you guys are right: Maximum extension is maximum extension. I completely agree, no benefit to shaving the cam housing or top of head.

Per vers

When i put in a 280* duration cam. It really woke up the engine.

I had to retard the cam 3* to make the best power(Max rpm. 6500 on std. ecu)

The engine feels the same from 1000 - 3000 (only small gain in power ~ 5-10 hp)
From 3000 - 4500 the engine starts to pull harder. (+10-15 hp)
4500 - 6500 things really starts to happen. The power really kiks in, and the rear wheel distrubute gravel big time