reno: I trust that you mean the maximum on a 944 N/A is 2.5 inches. I know of Periperal Ported rotary engines that need larger than that.

 

Solo i wasnt reffering to a Rotary engine but thanks for the info i didnt know that.

 

They are indeed, but the Renault & Brabham Alfa were not and they had tiny tubes. If somebody would like to explain the benefit of a 4" tube for driving between 3000-5500rpm my ears are open

 

I think we are getting of the intake subject guys. We can start another thread for that if you would like but I think its been beat to death.

 

I'm building one in 3 months. I will have a before and after Dyno sheet. EVERYTHING will be the same - apples to apples comparison. - 18psi. 60-1 turbo. Before and after. Only manifold and throttle body will be different. (70mm) I'll let you guys know if it made ANY power. It will be based on JG's intake manifold for the Honda's. It has clearly made more power than any of the others (On 300+ hp cars. any lower and not much or nothing at all was realized) I Had the luxury of dyno testing many cars upgrading from numerous styles of intakes and only intakes.

This is not one for sale. or the like. Just going to let you guys finally know if it's worth it or not.
If any one wants to let me borrow any aftermarket one to test, I will be happy to swap out and compare that day. (beginning of May.) Lindsey, Extrudehoned. whatever. You WILL get it back. I don't want them!

If someone wants to do this earlier. GREAT! I won't have to. But my quest for knowledge is too stong. I have to know. But it won't be until then.

 

That would be incredibly complex for little to no reason, and in the end that 1.5" you'd add to an already well designed manifold would vastly change the harmonics in the manifold. The plenum volume has much less of an effect on overall manifold performance than the runners.

Runners provide the acceleration, the resonance, and dictate the powerband of the manifold. The plenum volume is more or less a steady state available volume to the engine. If it is undersized then typically it will provide slightly increased velocity that may benefit the low end via an inertial supercharging effect. However this will come at the cost of the top end power.

After looking at Lindsey's manifold it is somewhat near what I would construct for a 944 Turbo engine by just looking at the pictures. However because of the broad scope of usage you get in a turbo engine they seemed to have opted for a middle of the road design.

I'm not 100% sure of the head inlet diameter but that can be ported to some degree. Here's what I'd aim to use on a high output 951 motor.

46mm Non Tapered Runners
195mm Runner Length
2500cc Plenum Volume
70-80mm Throttle Body

You'd probably lose low end (sub-3000 RPM) but once the turbo started to come online around the 3500 - 4000 RPM point you'd see a positive increase in power over the Lindsey manifold. With that above setup you'd start to see marked torque loss after 7000 RPM. This is more as a result of the head beginning to choke due to airflow velocity.

On a lower powered car you'd probably want to use a 210mm or possibly longer runner to maximize the powerband you have to work with.

If you want to actually see what I am saying about the cylinder head choking you only have to look at Special Tool's car. The reason he hasn't broken the 600whp mark isn't necessarily the turbo sizing but the fact that he has a choked condition in more than one point of his intake tract. This condition will create reverberations in the local pressure which then leads to turbulence. In order to create more mass flow he is having to run quite a bit more boost pressure. He is actually overaccelerating the airflow; creating unstable velocities and their resulting inlet Mach #s. Because he has such a reduced upper volumetric efficiency he must resort to high cylinder pressure (read: boost / torque) in order to try and make the numbers he wants. This is creating another problem; head lift.

For comparison sakes a modern Japanese 4-cylinder head is capable of flows of 340 - 360 CFM on the intake side and about 250 - 270 CFM on the exhaust side. These are at 0.500" lift @ 28" H20. That is why they can make such large HP numbers on relatively less boost pressure. The mass flow is roughly the same, just they require less pressure to overcome flow losses.

I personally feel that you really need to introduce a bell mouth entrance at the top of the velocity stack otherwise you will need to overcome rather large friction losses. Lindsey doesn't have a picture of their inlet manifold so I'm not sure if they are integrating this into their design.

Some people have also created a radiused floor entry in the design. I'm not certain how they compare to each other, but I would imagine the floor entry would create some sort of negative affect because of the shorter radius taper height. I'd imagine it wouldn't allow sufficient development time in the flow.

So many people want to discredit me for not having a 944, but I assure you I enjoy learning and modding just the same as you all. I'm not trying to make this into a "x engine is better than yours thread" I am just trying to illuminate what I see is the problem in the upper power range and see if we can come to some degree of solution.

Discuss.

 

I agree with this point as its the one I was making. Chris is dealing with companies from all over the world to get the best stuff - the intake design won't be "perfect" i'm sure but will be very close. The point being is that it will be leaps and bounds above the stock design and even better than most other 951 designs.

The plenum that Jon Milledge went with looks an aweful lot like the honda one you showed earlier, and I garuntee that this intake will be extremely more effective at delivering equal quantities of air at an increased flow rate. But simply hacking up a honda intake and doing some trial and error on a motor to me is more wasteful than doing the mathematical calculations and creating something from scratch that will work. This is the approach Chris is taking as its the best for the car and not something 'adapted' to work on my car. No shortcuts but at the same time its not costing as much as many think. Expensive? Yes...drastically and uncalled for expenditures? No. I can justify the cost in terms of drivability and new characteristics given to the motor along with the increased output.

Respectfully of course

 

Nice post Drifto. What's your take on the inlet to the plenum on the Lindsey Racing intake? From an intuitive fluids standpoint, it seems like having the intake come in directly into the center of the plenum and perpendicular to the plenum would cause friction loss issues for the #1 and #4 cylinders.

 

I have to agree with drifto, on a couple points but, I don't want to get off the "intake" theme.

If anyone here has taking the time to flow these intakes, aftermarket, stock/moddified stock, you would know that most, if not all, out flow the 951 head.

Even big valve heads can't flow big numbers. You are limited to the ceramic ports on the exhaust side. I have increased exhaust valves and did the most I could with the valve seats/bowls etc.. and a modded/stock intake still out flows it.

I don't care if you have 1 - 70-80mm t-body or 4 ITB's you are limited by the head.

Drifto(even though you don't have a 944,lol) is right Japanese motors with 350/200+ cfm heads are far better.

At a .450 stock lift the exhaust valve flows a terrible 181cfm. There is a huge difference in just 20cfm and thats hard to get!

 

How does the int/exh flow of an S or S2 head compare to the typical Japanese head?

With the flow of the 8V head being the limiting factor, do you guys think a 2.5L has reached it's limit at the +/- 500 whp/tq with whatever intake and/or modified head that is used? I'm gathering that at this power, "superior" intake design is only going to shift the delivery of power and not so much add to it.

I completely agree with Dave's perspective on cylinder head flow as I have had a chance to test stock and modified cylinder head flow numbers on a flow bench. So, if a stock or modified stock intake can outflow the most tricked out 8V cylinder head, what's the point in designing a new one? Do you guys think that the flow increase of a custom intake will justify the expense? If you're shooting for the highest numbers possible, I guess every little bit helps.

 

I heard figures og 300+ cfm for stock 16v head and 440cfm from a modified 968 head. Both figures are from intake ports. Though I can't verify that information. But, if you look at the 16v head, it's one of the best stock designs to have and so said my machinist who have extensive experience in 16v heads.

When fabricating an intake, one has to tune the runners according to intake resonance frequency. In ideal circumstances, it would be best to set them to 1st wave, but that leads to extensively long runners (length in meters not mm's) and usual practice is to use 4th wave. It has it's losses but the benefits outweigh the losses that come out of the very long runners restriction.

And bellmouth/trumpet, whatever you call it, is A MUST!

 

Yes , maybe , but you could also go backwards with this change if not executed correctly .. as your 1 st assumption is that there is something amiss with the stock intake ..it is better than you think ..

 

Ok, but the F1 renault engine had 2 , 2inch tail pipes.. , most if not all turbo cars with a single exit will benifit from a 3 inch pipe., IT IS ALL ABOUT WHAT LEVEL OF HP. 530 BHP FROM A STOCK 951 intake is doable , it has been done , need's a 3 inch exhaust min. , a larger exhaust on a turbo engine wil not cost T/q , this is controlled by the turbo exhaust housing , too big a rear housing will cost you T/q , as well as too small will kill your HP. It is all about Horses for courses'. where would you like to go and what do you want to do .

 

Dave could you give us the total info on the flow numbers , 181 flow rate at what inchs of merc. this way we can compare..

BMW and Honda heads , flow better than any other stock head tested , 300 Plus cfm from a stock 968 16 v head is hard to believe , 260-270 is more likely. the honda and BMWs' give the most specific output /litre that i have seen from Factory Street n/a/ motors . When built . 160 bhp /Liter is possible with the Honda 4 cylinder engines in road race trim , a BMW M engine is slightly behind.
In stock trim at there best power outputs the BMW M 3 L engine is a good 50 bhp stronger than the 968 . it does not flow 300 cfm in stock form...

 

Sure, Test Pressure @ 28”, Barometric Pressure 29.89 steady, Air Temp 60.00F, Air Density 0.0762

Port Velocity measured at Port Center at Valve Stem Centerline below Guide Boss.

And YES! 300+cfm intake side is true on a 968 head.