Saabscene Saab Forum - Saab Technical Information Resource banner
1 - 11 of 11 Posts

·
Registered
Joined
·
1,448 Posts
Discussion Starter · #1 ·
A number of people have pointed out that T7 heads will outflow even reasonably well ported T5 heads, which in turn outflow 2.1L/2.3L heads and so forth. It has been theorized that this may be at least in part due to the thinner valve stems on the T7 heads.

Because of the thinner stems, the T7 valve guides, and retainers must be used. It's possible you may also have to use some other T7 valvetrain parts as well, but the springs, lifters and cams should be cross compatible. Of course, for a performance application you'll probably want to stay away from T7 springs and cams. The springs are softer, and the cams have less lift and duration.

Here's the pertinent data:

The following is information comparing the T5 "shortblock" valves to the T7 valves. The T5 valves are cross compatible with all older Saab 16V heads according to the EPC.

1 = Valve Stem Diameter
2 = Valve Guide Length
3 = Valve Guide Bore Diameter
4 = Intake / Exhaust Valve Cut Angle
5 = Intake / Exhaust Valve Diameter
6 = Intake / Exhaust Valve Cut Width

T5

1: 6.9565 - 6.980 mm

2: 42.5 mm

3: 12.000 - 12.018 mm

4: 45.25 / 45.25 degrees

5: 33 mm / 29 mm

6: 1.0 - 1.5 / 1.0 - 1.5 mm

T7

1: 4.9725 (Nimonic, slightly smaller for stainless)

2: 42.5 mm

3: 12.000 - 12.018 mm

4: 45.25 / 44.50 mm

5: 33 / 29 mm

6: 1.0 - 1.5 / 1.5 - 2.0 mm


As you can see, while you should be able to use T7's intake valves in a T5 head (and thus in any other Saab 16V head theoretically) if you also swap guides, retainers cones etc (lifters shouldn't need to be changed, or springs), you cannot use T7's Nimonic exhaust valves in any head except a T7 head ... unless you get a custom seat grind for the T7 exhaust valves.

The considerably thinner intake valves might very well be quite usefull if you're trying to get your non-T7 head to flow better. If you can get all the other required valvegear to do the swap for cheap enough it might be practical. But if you're starting from scratch, it would be cheaper to get a T7 head and adapt it, than to have your other head ported/polished and to buy the T7 valvegear. (Saab Reccomended Retail price for T7 head with Nimonic exhaust valves = ~ $1,000 + $450 core.)

Just some food for thought.

Dubbya~
 

·
Registered
Joined
·
4,215 Posts
so
to get the best flow

t7 valves for the inlet
and bigger standard exhaust valves for the outlet ?
but..
My view was that being forced induction the inlet side is not so important
outlet more so for spool up and VE
or do I have this wrong?
Also as you lower the port resistance and effectively slow the flow as you open up the ports then the valve timing becomes more important to ensure least amount of cross mixing when both inlet and exhaust valves are open...
 

·
Registered
Joined
·
1,448 Posts
Discussion Starter · #3 ·
Originally posted by ylee coyote:
[qb]so
to get the best flow

t7 valves for the inlet
and bigger standard exhaust valves for the outlet ?
but..
My view was that being forced induction the inlet side is not so important
outlet more so for spool up and VE
or do I have this wrong?
Also as you lower the port resistance and effectively slow the flow as you open up the ports then the valve timing becomes more important to ensure least amount of cross mixing when both inlet and exhaust valves are open... [/qb][/b]
The T7 valves could be used on inlet and outlet if you also were going to get a custom 3 angle valve grind. Just make sure that the machinist knows that the T7 exhaust valves are Nimonic.

The Nimonic exhaust valves might be advantageous. They would extend the peak EGT from 1600 to about 1800 when done correctly with an Inconel/Nimonic turbine. But in most applications it probably wouldn't be worth it.

On the intake side, porting on a turbo car does two things:

1. Lowers overall pressure ratio of the turbo individually on each side (high pressure part divided by low pressure part, as opposed to intake pressure to exhaust backpressure ratio), which cuts down on heat of compression and overal strain. You don't need as much pressure to get the same power, which means you don't need as much intercooling. It can also reduce boost lag if done properly as you don't have to boost as high.

2. Porting lowers exhaust backpressure by reducing the intake pressure. Since turbochargers operate at an overal pressure ratio (exhaust pressure to intake pressure, usually between 2-3:1 on a stock engine) ... by reducing the pressure ratio the turbocharger's exhaust housing can be opened up, etc. All of that eventually can put the pressure ratio between intake pressure and exhaust backpressure as good as 1:1 or better. That also reduces the percentage of hot exhaust gasses left in the cyllinder, so the engine is more knock resillient. Once you reach near 1:1 power making takes on whole new dimensions as the intake gasses actually push the exhaust gasses out of the combustion space allowing for better than 100% Volumetric Efficiency.

Generally though, porting has little effect on a near stock car. When it becomes worthwhile is when you're using a turbocharger that flows far more air than the stock one. Then without porting you have to raise the boost to absurd levels to get the power. With proper flow the engine "feels bigger" to the turbo, and flows the air without requiring as much boost.

Just my thoughts on it anyhow.

Dubbya~
 

·
Registered
Joined
·
1,219 Posts
 Generally though, porting has little effect on a near stock car.[/b]
On Landrover/Range Rover 4.0 and 4.6 V8's, if you port the heads, then you get an extra 40bhp or more (around 40-45 bhp on the 4.0), because the flow is so cruddy on those engines... which is about a Stage 1 ECU for a fraction of the cost. but then on smaller, less cylinder engines, it may not make as much as a difference
 

·
Registered
Joined
·
1,448 Posts
Discussion Starter · #5 ·
On turbo engines, the only real downside to a slightly poor-er flowing head is that you have to turn the boost up a bit in the higher rev-bands.

Also, the "shortblock" newer Saab engines have about as much flow as anyone could hope for. They flow very very well. The only major improvements to a 94-98 T5 head are going to be in valve guide grinding, surface smoothing, and thinner valves. The size of the port is quite large.

Dubbya~
 

·
Registered
Joined
·
281 Posts
So will the T7 head go on a c900 block. I guess so. I've already bought my 2.3 head though so I'm sticking with that for the moment. What do people reckon on getting the 2.3 head ported and polished?
 

·
Registered
Joined
·
1,448 Posts
Discussion Starter · #7 ·
Originally posted by ejenner:
[qb]So will the T7 head go on a c900 block. I guess so. I've already bought my 2.3 head though so I'm sticking with that for the moment. What do people reckon on getting the 2.3 head ported and polished? [/qb][/b]
Yes, but not easily. Several brakets and plates need to be fabricated to adapt it. Someone could make some good money if they showed T7 head flow figures and marketed a kit to adapt it I think.

Otherwise ask Eric Van Spelde! He has one on his C900.

Dubbya~
 

·
Registered
Joined
·
11 Posts
Hi Gentlemen,
Would anyone have any knowledge on the advantages of having a stainless steel tubular exhaust manifold installed in placed of the stock cast 'log' style unit.
Any theories and educated experience is greatly appreciated. I look forward to all your kind response.
Cheers
 

·
Registered
Joined
·
4,215 Posts
welcome avantissimo

the advantage is less restrictive exhaust flow
(theory make the engine more efficient = more power)
speeds up exhaust flow = less lag on turbo spool up
equal length exhaust pulses on the turbo = quicker spool up

good thing to do but they are usually expensive
and while in theory easy to fit you have the prospect of the exhaust studs to contend with

If I do anything else to my car this will be it ...
 

·
Registered
Joined
·
1,448 Posts
Discussion Starter · #10 ·
If you're considering buying stainless headers make sure that they are 321 stainless and not 304.

Also, to do some research go here: http://www.burnsstainless.com/TechArticles/techarticles.html

That site is very very useful. I would suggest reading all pertinent tech articles they have. (Not too horribly long.)

The benefits from headers in theory are two fold:

1. The get the time between exhaust pulses down because they are evenly spaced. That increases spool up to some degree.

2. They decrease backpressure to the engine by keeping the flow of exhaust gasses in the form of velocity pressure which has a velocity vector pointing away from the exhaust port. Any sharp bends will quickly convert that velocity pressure into static pressure, which has pressure vectors in all directions, including back towards the engine in the form of backpressure.

Don't let that information stop you from going to Burn's Stainless and reading the tech articles though! They're well worth it!

Dubbya~
 

·
Registered
Joined
·
11 Posts
Many thanks for the affirmation ylee and Adrian.
I have recently installed a Stainless Steel header from ChipCenter on my 9-5 with great results as you have accurately indicated. Would anyone have any knowledge and confirm if CC power makes their extractors in 321 stainless? My EGT gauge has shown a tremendously sensitivity to the deviation in temperatures. What would be the estimated increase in Volumetric Efficiency as a result of this mod?
I appreciate all your kind and informative responses.
Cheers
 
1 - 11 of 11 Posts
Top