RennBod

I know that neither the Tial38 or 46 wastegates fit the 944 turbo as they come.. But I have seen a company that makes some really cool replacement pre and post wastegate pipes and fitting kits for getting both Tials working well with a 944 turbo.

My question is... is there a point where a Tial38 will no longer be up to the job and a 46 tial will be needed?

Has anyone found that after they passed a certain BHP the tial38 was no longer able to cope?

TRP951

david floyd has a 35 on his car and he had a 2.8 with a vitesse stage 4. (the 35 was a older model they had)

Bustadouglass

Yeah I had the same question. The previous owner of my 951 had a 46mm Tial installed. What are the benafits from that over the 38mm? Or just the differences in performance/functionality?

Driftomagnifico

None, I've seen 38mm W/gs on Hondas making 500 - 600whp with perfect boost control.

Basically imagine you putting a 38mm diameter hole in your exhaust manifold. Do you think the turbo will spool? LOL.

The larger wastegate was intended for larger engines that get boost creep, like a turbo V6, or turbo V8.

Using a larger wastegate like the 46mm on a small engine like the 951's can cause less than ideal flow in the wastegate. The 46mm has 46% more area than the 38mm gate, so the amount of air it can flow would never be achieved by a 951.

So in short, I have no idea why you'd go and buy some monster wastegate for the car if it's not required.

Bustadouglass

Hmmmm, that could be why my car is so damn laggy!?

streckfu's

No. It won't cause your car to be more laggy.
The 46mm will scavenge more air more quickly than the 38mm but as Drifto mentioned, the advantage of the 46 cannot be realized on a 2.5 motor.

Driftomagnifico

If the valve is on an engine that is too small (ie. D16Z6 SOHC VTEC) it would create lag because the valve would scavenge too much air even being partially open. The effect would be the valve fluttering momentarily until the engine produced enough exhaust gas to support the turbo.

I doubt it would be large enough to affect the 951's engine, but if I were to buy a valve for the engine it would be a 38mm. If I was running a big HP 951, which with it's inefficient head design requires high pressure, I would look to run a larger valve, but not a 46mm lol.

streckfu's

If you have the WG configured as a DP, there is no reason for it to open before your set boost pressure.

Bustadouglass

Hahaaha, I guess I need to go back to Turbo101.

So there really is no disadvantage of having the 46mm wastegate? Short of the fact that it will never really reach its potential?

streckfu's

Correct. There is no need to spend the extra money on the 46mm. Save the difference and use it toward another part of the project.

azmi951

Ideally you want the smallest WG you can get without boost creep at high RPM. 38mm is fine for our cars.

WesM951

I see and hear alot of conficting ideals on what to go with on our cars. Can anyone produce a dyno chart with 38 vs 46 at high hp levels? I'm talking 400rwhp+.

Driftomagnifico

I run a 38mm W/G on my car producing 630whp, and it works fine.

Anyone that has problems with a 38mm W/G keeping boost regulated at a 400whp 4-cyl. needs to look at their placement and manifold design. It is not the W/G creating the problem.

The dyno will show very little if any difference. The volume of air exiting both valves is similar, but the 38mm will have a faster and more efficient flow profile than the larger 46mm in the 951's case due to the high amounts of boost pressure.

As I've said before the 46mm is used by much larger engines producing nearly twice the power.

TonyG

A bit of clarification....

First off, the 46mm actual valve material is far superior than that of the 38mm valve. The wastegate body is also designed to properly deal with sustained high thermoloading where the 38mm wastegate body is not. This issue is extremely important with respect to reliability of you run with any sort of sustained loads.

Second.. it's not about HP. It's about quantity of gas flow across the valve. HP is largely irrelevant.

Third, on the same engine at the same boost, the lower boost setting, the higher the quantity of exhaust gas that must be passed through the wastegate. The higher the boost setting (more power), the less gas the wastegate has to pass through it.

This is very much the opposite of what people here have implied in their arguments.

Fourth, the 38mm valve has to move substaintially farther off the valve seat to flow the same quantity of gas, as the 46mm valve. Thus at the same boost, on the same engine, the 38mm valve and valve spring are working far harder (moving further off the valve seat with more valve articulation) than the 46mm valve and valve spring to exhaust accurately, the same quantity of exhaust gas (in order to maintain the same boost level).

The more valve articulation required and the more valve lift required, the slower the wastegate response... the higher the propensity for boost control problems.

Bottom line: The 46mm is a far superior wastegate to the budget minded 38mm wastegate.

Apples to Oranges.


(think about what rides on the quality of the wastegate...)


And.... the 46mm will fit perfectly (albeit a tight fit) into a 951. SFR has a great kit that uses the 46mm Tial.


TonyG

badass951

Not to mention that most of the larger wastegates have more space between the diaphragm and the exhaust gases, increasing longevity.