Twin Turbo 535 RA-V Build
 

Making some progress on the heads!

Looking good ED. Waiting to here some thunder

VERY IMPRESSIVE

Looking forward to watching a dyno test at some point.

Tom Vaught

Thats going to be a great combo!

Very good Mr.Ed!

A great build takes time.

Very Cool! Best of luck with it.

Are you planning on leaving the deck wet or plug the holes? Have you looked at the possiblity of adding the extra bolt holes in that head? Just curious if the layout allows it?

What size turbo's?

We did the newly designed header flanges yesterday and put them on the heads. Now we can do the exhaust. These heads have the alternate valve spacing for the 4.350 bore. This head will have 2.30 intake valve.

This will be our standard CNC program for the stock head castings.

We’re going with Turbonetics 88mm turbos.

Plan ahead for back pressure issues -

Anything specific we should watch out for?

On my 525 - it starts to get into back pressure "issues" at about 22 to 24 psi - we had the tubine housings modified and it helpped but is still there - I have been told the only way to fix it is 91s or 94s -- and those things are huge -

cg did you dyno this engine? Normally aspirated and then with boost?

I would like to hear more about these issues at 24 psi of manifold pressure in the intake. What is the pressure in the Turbines at the same boost levels?

Tom Vaught

OK CG you got the ears of the "big dog" boostman listening. I have the explanation from my engineering student son, but students are silent when the professor is ready to chime. :hail::hail:

Did they go into specifics on why those would fix the problem? Better/bigger turbine housings than the 88s? just curious :)

I have never run the car on the dyno with no booste - but I know it will run mid to high 9s with out the turbos working - dont ask how I know - the back pressure starts to creap up into the 2 to 1 range when it goes over 24- to 25 psi - and yes - the bigger turbos seam to have a better - more efficient turbine housing - but the whole turbo is so big it would take a major rework to make them fit -

Couldn't you bypass some of that backpressure through the wastegates? Back in the day,turbo drag racers used to use small turbine housings for quick boost response and then run a lot of the exhaust gases through the 'gates.

So If I read your reply correctly, you are saying that you have 24 psi of boost pressure in the Intake and 50 psi of exhaust pressure in the turbine housing inlet. Correct?
So how are you reading that pressure? A 3 BAR sensor can only read accurately to 43.5 PSI (1 bar is atmosphere - 2 additional BAR would be 43.5 psi. So how is that 2 to 1?

Last time I looked 24-25 psi at 2 to 1 was 48-50 psi of pressure.

Need a lot more actual info/ data. How you read the numbers, what instrumentation, etc.

That trick is still being done today Taff, except that the exhaust pressure acting on the turbine wheel(s) need to be high enough to support the horsepower required to drive the compressor wheel(s) at max boost.

A Guy named Danny Jones, who was the Indy Car Turbo Guy for Ford many years ago, told me you would like to be close on the intake and exhaust pressures at max boost with the waste gates open. You confirm this with pressure taps/ gages on the compressor and turbine flow paths.

Tom Vaught

Tom - Im reading the back presure with a unit that racepak makes to tie into the data recorder - and yes - I have seen over 70lb of backpressure at 30lb of boost ( by mistake) I just checked - its a 0-75 pressure sensor -