so that would be 4718...

 

The Precision Turbo Catalog call it GT4788 ( the bigger of the GT47s).
If the Garrett calls the GT42 with 102mm comp wheel a GT4202 and the GT 42 with 94mm wheel a GT4294, then a GT4708 and GT4718 means 108 and 118 compressor major. I believe the GT4708 has a 80mm compressor inducer, and the GT4718 has a 88mm inducer.
So we are referring to the same turbo.

The engine is built make 1000whp and spin to 11000rpms safely.
My goal is 800rwhp at 35psi.

I also have a D series 20B that will use the same turbo.

 

K, I guess I'll have to explain this properly. What I meant to say is that with PP and BP'd turbo rotaries the exhaust/intake overlap hurts performance at higher boost, a percentage of the pressurized air will make it to the exhaust during the overlap causing it not to make anymore HP at a certain point. This is the main reason most pro drag racers with forced induction(Dee, Abel, Ari, etc.) are running street ports. Porting always helps BUT its gains lessen as the engine revs faster or whenever it makes more power. Guess what I should've said is that PP and BP'ing a motor with forced induction is useless at higher boost levels, the duration of the motor will hurt HP eventually.

 

What makes you think this?
First off abel is now running a bp. And he's making more power then before!

People who talk about it not working due to too much overlap usually have never tried it. this is what they read or have heard thru so and so like it's some sort of urban legend... Besides don't you think people who actually do build these motors don't try different port timings? You can control how much overlap you want by moving the ports any where you want...

We tested a pp motor and the more boost we feed it the more power it made.
Didn't seem to stop even at the higher boost levels. That is if you consider 52lbs high.

 

Yeah precision puts there own numbers on it. I hate that.
I always deal with garrett direct so i never use precision labeling system.

anyhow you building a 2 rotor or 3?
800hp at 35psi on a 2 rotor is not impossible but very hard. (so a good goal i guess)
At least i think so since i couldn't do it....lol
needed just a couple more lbs to do it......

 

YES, but you forgot to mention he's also running alot more boost then before! therefore he's making more power mainly from the addional boost.

You just can't move ports anywhere.......there's such a thing as porting limits.

Ofcourse....if you increase boost you will always make more power as long as the turbo is not at its limits...regardless of port.

 

Dude, he's always been running a shitload of boost.
Fact is new motor, new porting, new turbo, equaled more power!

Regardless the statement was a bp or pp can't take high boost as it would just waste it out the exhaust due to overlap. Well what i'm saying is guess what it works and works well. And no **** you can't put ports anywhere, what i was saying is you have control on where you drill your ports correct? So you can decide how much overlap you want.

Yes increasing boost will make more power. It's not rocket science.

It was stated earlier that porting wasn't necessary for high boost, and then stated that bp and pp can't run high boost due to excessive overlap and that they wouldn't make more power.

Well even BP and PP ports like high boost and will make more power.
That's the point i was trying to make.

 

you do get a point of diminishing returns w/ too much overlap on a boosted engine. that's why people don't run n/a cams on a turbo application. not saying alot of power can't be made w/ high boost and a bp or pp, just saying that there is a compromise between flow and combustion efficiency.

and abel would not be a good example of a successful bp. he goes through motors like they were crack, and when he doesn't blow his motor, that car can't even get out of it's own way.

 

not necessary true. I used to think the same way until we tested it.
years ago after speaking to some pro rally guys(toyota) and pro bike drag racers both told us to try turboing a motor with the most hp n/a. So we did. We took a 200hp n/a honda motor and ran 35psi of boost thru it. Worked just fine and made wicked amounts of power. This was with 12.5 to 1 compression and huge cams. Most people thought we were crazy. Today you'll find that most of the high hp honda's run wicked cams with high compression. Cam's you would never think could work on a turbo application make some serious power. 1200hp on a little 4cyl is pretty impressive...300per cyl!!! Believe me don't think because a cam has to much overlap it won't work or have dimishing returns because unless you try it you'll never know.

You'd be surprised to see what cams toyota used in there rally cars!!

 

I have both 13B RE and 20B. I am planning on going upto 40psi on the 13B ( full bridge), and 15-16psi on the 20B(stock ports - for now). Goal is 800rwhp on both...

 

Probably won't get 800rwhp on the 20b with stock ports at 15-16 psi.

-Destin

 

He's running more boost then he ever did in the past !!!

Any port could run as much as one pleases.......results obviously vary:-)

Excessive overlap will allow a loss of boost pressure thru the exhaust ports and a large increase in fuel consuption.
Since we generate exhaust backpressure to spool a turbo it is natural to have higher pressure at the exhaust side then on the intake side and again excessive overlap can create a reversion problem where your exhaust pressure will flow back into your intake diluting the intake charge.

In forced induction the idea is minimize overlap regardless of what experience you've had !!! It simply enhances combustion efficiency or other words more power.

Not saying a BP or PP cannot make power....I'm sure they will but the boost pressure will need to be higher and fuel consuption will be rediculous !!!

I speak from experience......Turbo-BP for about a year in a daily driver.

JD

 

BINGO !!!

 

Holy crap...not asking for much, eh...

Man, there's so much BS thrown around in here...yikes.


-Ted

 

whatever.. I'm done argueing it's a lost cause...

JD if your so confident that a bp or pp needs alot of boost to make power
i'll bet you anything you want that psi for psi i'll make more then you
with a PP turbo motor vs anything you got....

 

Enzo Enzo man I'm following you around these threads like a stalker. No use in arguing with people on here they will soon realize how wrong they are. It is all in time! More and more cars will be coming out with PPort turbo setups and soon enough it will be the bench mark for the "TOP" rotary dragracers. As the tuners get better and the efi systems continue to improve more power will be extracted out of these little engines. What cracks me up is people are arguing that a PPort turbo will not make as much power to a point because of overlap. Ok believe what you want. Trust me on this a PPort turbo will make more power than any other ported motor at any given boost sorry to say but it is true. Yes it is true!

 

Yeah Im done.. It's a waste of my time... Don't know why i even bothered.
I'm getting back to work....

 

15 years ago low compression and low overlap was mandatory for turbo power. Ask around now a days and you'll find that most of the big power cars are running very large durations and relatively high compression. There's 2 major reasons, compression is due to the improvements in fuel and engine management. The overlap is because people have found that in extreme builds, while you lose alot of fuel efficiency etc, the overlap actually allows the motors pressure peak to occur much later preventing detonation.

Another interesting thing I noticed recently, high reving 8s with long strokes and short rods. The Jegs engine masters challenge guys are running these setups because the piston speed is so high that by the time detonation occurs you're already crossing TDC and starting a combustion event anyways. This is also the principle that most top fuel cars run on, once they're rolling down track they very quickly cease to use spark plugs for ignition, the cylinder pressures keep the motor running. We've been consistently increasing cam sizes and compression on the turbo hondas that a good friend of mine has been building and racing for several years. We've gone from an era where we were eeking out 300 hp from a 1.8 to pushing over 500 from a 2.0 without any major increase in costs.

Basically we've reached a point where alot of the old hot rod mantras have been superceded by technology and research. Just look at how far turbochargers have come, the new GT stuff defies any logic from 15 years ago.

 

Bro, now you know how I feel

 

why do all the 600+hp threads turn this way??

 

To many different opinions. Only some have done actual studies on what would work best for any given setup. Some say pp, bp wont make the same hp as a street port motor would do at a higher boost of 30-50psi. Its a arguable subject and very touchy as we can all see..

 

Let's see how long this one last before it gets closed!

 

Too much of this........

 

Chrispeed, I have an LIM for you, let me know where to send it.

 

Ok, here's what I have:
T 67 or T70 (.96A/R) turbo
20psi on 93-94 oct pump gas (no alcohol)

Set up a P/P motor with same set up and we'll dyno together....

P/Ps are simply not tolerant of exhaust backpressure.
You need to keep this backpressure to a minumun to get a balance where the P-ports are starting to do their job, but also need to spool a turbo....this is the big dilemna !!!
Luckily @ higher rpms( ~9krpm+) this dilemna lessens.

If this is so easy as you claim then we should have tons of 2 rotors making 1000hp or more. Side ports have made 900rwh+ !!!!

Even the guys in PR been getting frustared tuning these PP-turbo cars to make more power.

I'm done here....
JD

Sorry Ralph !!!