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 -

Sensors have a range where they are accurate, Typically in the middle/two thirds area.

Reading OVER 70 on a 75 range, says that you might be 80 or higher in reality.

All of the back-pressure is not helping the EGR EFFECT inside your engine diluting the next charge. So whose waste-gates are you presently running?

It appears that you have plenty of energy to spin the compressor wheels at a lot less turbine in pressure.

Tom Vaught

Running turbonetic nex gen gates - I dont plan on running 30lb of boost so if I keep it down the back pressure is going to work for me as it stand's now - on my car - the ratio is about 1.6 to one untill the boost starts working up over 25 lb -- then the back pressure seems to ramp up pretty fast

Curt, I'm curious what your rpm and boost level is at launch?

Seems to me you could run a much larger turbine wheel and greater A/R and still spool fast enough. Even 1.6 differential is alot for a drag car. (You are reading intake manifold pressure vs turbine inlet pressure correct?)

launch is 5200 and 10 lb -- with a quick ramp in and yes - back pressure to manifold pressure - we have up graded to a larger turbine wheel and modified housing - but it looks like it wants more - -damn

Time to make room for some BW sx 500's (T6 flange). 80-98 mm inducer available. Ratings from 1250 to 1850 hp each these have a 111mm turbine wheel and several a/r choices from .85 to 1.6.
There are some s400 series (t6) that support up to 1350 each along with customized BW s400's that support up to 1575 each. They use 83-96 mm turbine wheels 1.10-1.32 A/R's.

Just a thought anyway.

My apologies for jackin the thread.

We did up grade the Precision 88s on the turbine side to an 111 wheel and had the housing modified to match - its better - but is not perfect so Id say your on the right track - anyone got any money ??

Still think that you have plenty of energy, adding a second set of gates would remove some of the excess pressure (1.6 ratio) and still allow you to use your existing turbos.

25 psi and then the second set of gates open up using a co2 bottle, a control valve and a pressure switch.

Tom Vaught

Gee Tom I was thinking of more gate(s) myself. Maybe put a balance tube between turbines and mount gate(s) on the tube.

Balance tube would work if the entry for the balance tube was in the previous location of the wastegate. You must put the wastegate in a branch of a Y with the bottom leg of the Y feeding the two upper legs of the Y. Right leg of the Y goes to the turbo. Left leg of the Y goes to the wastegate or in your suggestion: balance tube/wastegates.

That would be the plumbing for one side of the engine.

Tom Vaught

As it is now - the gates are CO2 controlled and will control the boost level very effectivley - by adding more gates are you just not reducing flow to the turbine wheel and as a byproduct reducing backpressure??

Thats the theory. Once spooled it doesnt take as much energy to maintain boost as it did to get it there quickly. A larger AR allows more past the turbine thus reducing backpressure. However it does so at the expense of increasing spool time.

88mm turbos are in!

Nice...Christmas in July!:jumping:

The Turbonetics Turbos will work very well for you.

Tom Vaught

RA-V Heads are almost done!

I wanted to ask if you could stage twin turbos like that. Run a small turbo to get off the line that by passes at something like 10lbs into a larger turbo. I always thought it would over spin the small turbo though. Anyone know if it works, I think I have seen an import do something like this but not at the scale I'm talking about.

sorry to jack the thread I have been meaning to ask, and didn't want to make a whole post about it.

Thanks Shad

3rdgen I'm thinking appropriate sized turbine wheel for the compressor you are running but smallest A/R housing for it to get max response. Then two gates one to limit boost based on intake pressure the other gate referenced to exhaust back pressure to keep exhaust pressure at or below intake pressure. The exhaust pressure reference line would likely need to be a hard line and long enough to coil to let it flex and help disapate heat. I dont know if you could disapate enough heat to prevent damage to the extra gate. Seems like it could work but dont know if its ever been tried.

For what I'm building I dont want too much boost off the line and will just size my turbine(s) to favor mid thru top end.

I was thinking on an inline six, I have rode in a few 1000hp supras down here and the big problem I see is that they have no power on the bottom because they are running the very large T88-34D - GReddy turbo's. you may have seen some run like 11 in the 1/4 with a MPH of a 9 sec car. If they could run a small TD06 before the big turbo and it wouldn't burn up the small one it could fix some of the huge lag problems.

I don't want to do it on a supra but if I could make a ohc cammer stay together I would love to go play with the supras with a 40+ year old engine. I figure with drag coefficiency of the 3rd gen I might be able to topend a few bad supras around here with a bunch of junk. well thought out junk, but still junk.

A few more pics.

More Turbo Pics

Rods.
They were the only parts that would sit still during the the professional photo shoot.

I would not be doing the beer can on the compressor blades too many times. Even the slightest dings, scratches, etc on the blade fins will affect the final performance and balance of the units.

Tom Vaught

Those heads are definitely going to be moving some air for sure. I originally was going with twin 88's as well but got a good deal on the 106.

That will be an awesome ride when the project is done.

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similarities????
 

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Lynn- who designed the crank's eight counterweights?