z8cw

What are you saying??? Overlap makes more power at higher RPMs?? Overlap hurts lower RPMs power?? Boosted, non boosted, is it all the same, up to what PSI? In any case the discussion hasn't been conclusive, has it? Does overlap hurt higher boost applications? Maybe it is just great up to 30 PSI and than suffers??? Maybe 20PSi is the magic number. I was trying to get away from the extremes that were discussed in this threat. I thought people on this board might be interested in a more "for us folks" discussion rather than discussing what one drag racer's succes is over one others spending more on an engine than we would ever spent on our homes. Even if we knew their secrets we couldn't afford to build a race car that could compete.

As a side note, PPs seem to be able to spool big turbos very fast. This is certainly an advantage for a car with a big turbo. Since this is where a lot of people trying to go that might be a set-up to consider even without reving to 10k or boosting 50PSI. Looking at Ernies GT42r set-up, it looks like he is making 140hp at 4k and 8 psi, 200hp at 4.5k and 10psi, 300 HP at 5k and 17psi and 500HP at 5.5k and 31psi (as far as I can make out on his posted graph and assuming my calculations are correct). A pport making 9 psi at 3k rpm with a similar turbo seems attractive. Obviousely there is lots of reason for results to be very different and I only repeat what has been said on this board.

Fire extinguisher at hand....

CW

BoostedRex

My one question to the guys who know PP and BP setups best is this. Other than huge A/R turbine housings and large diameter piping for your exhaust manifold, how would you go about lowering the back pressure in the exhaust manifold? I have already taken into accoutn that the largest possible DP/MP/exhaust setup is going to be used.

Zach

Zero R

iTrader: (1)

Size of turbine wheel, size of exducer on turbine wheel, number of blades on turbine wheel, angle of blades on turbine wheel. Are just a few things that can make a difference.

BoostedRex

From what it sounds like any of those choices will hurt your spool up time quite a bit. Am I right in assuming that? Not that it really matters since it seems people are more worried about huge power up top over a nice looking broad power band.

BDC

Having the major overlap is definitely not a bad thing when it comes to both power and powerband. I can personally attest to that.

B

BoostedRex

It just seems that you would lose almost all of your low end ability. Granted you would gain a TON of top end. But what does an overlap setup do to the midrange of the car's powerband? Take into account that I am a noob as far as porting engines and making all of my own setups. I'm just trying to learn here.

Zach

z8cw

The dynamics of what size turbo to pick are the same, with all ports. It might be harder to find the right balance with a PP or large BP since there is very little data out there.

peejay

Increased overlap brings the powerband LOWER in the RPM range. This is not a shocking new development or the rantings of a lunatic, it's been proven time and again.

Given that the intake closing is what defines more or less where peak power is, and port open time determines more or less how much power you can have, it stands to reason that to maximize midrange and even low-end you have biiig ports that close as early as possible, this means you're going to have a lot of overlap.

Of course there are downsides... you kill idle vacuum, and the engine becomes *very* sensitive to intake tuning and exhaust tuning, and it becomes more of an on/off switch at lower speeds. These are just things that need to be dealt with! And the process of dealing with them hurts things in other ways. People don't build J-bridge engines and use bone stock intake manifolds and exhaust systems and expect to magically make huge power... it's all part of a system. Likewise you can't espect to smoothly putt around town in a low gear basically idling the car at 2000rpm...

Nihilanthic

Overlap is generally not a good thing for boosted engines... this is common knowledge. I fail to see why you cant place the ports to eliminate or minimize the overlap. And uhhh... everywhere else I see overlap it tends to raise the rev range - but then again it depends on scavenging to work, I dont see how youd get scavenging with a turbo setup unless you have that mythical backpressureless turbo setup.

Also, I have an idea: why not just compute the VE% of the side, bridge, J, and preipherial ports and look at the graphs of them over the rpm range, then factor in overlap, and then scientifically predict it?

z8cw

That is basically what I did when I came up with the HP numbers a couple of post back. Not sure what you mean by factoring in overlap? VE number is all inclusive.

Nihilanthic

If it is, then it is, lol. But you dont get scavenging from overlap with a turbo stuck on th exhaust manifold :-p

Boostn7

Yes, I agree. Just saying he has the best PP-engine builder at his side.
Hehehe...Yes, Siguel tuned the ECU he knows best and left the engine builder pissed since they had spent countless hours dialing in the motor with the Motec.
What did happen to Major League ? he has been MIA since those record runs.
And again, Denis (the menace) has an identical set up in his now green FD and has yet to get a full pass with it in years !!!! Tons of money and still has engine issues !!!
I don't think the PP-turbo is at its infancy....Rotaries have been turbocharged since early 80's, PPorts go further back and Racing Beat had a triple turbo/PP/3 rotor engine over 10 years ago.
But I do have great respect for those that continue to devote time and money to find more ways to generate more hp with releability regardless of port.

Boostn7

Not true....sizing the proper turbo for a PP/BP motor is very critical.
A turbo that will work well on a SP motor may make less hp when bolted to a BP/PP motor !

Nihilanthic

It woudlnt make less so much as just be maxed out. Progressively more 'wild' porting with a rotary is analogous to aggressively camming/porting the cyl heads of a piston engine.

When youre running in a higher rpm range and at a high VE in those rpm ranges, youre going to be moving more air.. classic engine design theory. So, youd need a bigger Turbo. Also, youll be able to move more air at lower boost ratios, so you need to pick a compressor map accordingly.

enzo250

His problems were not engine related.. He had issues with electronics which were recently fixed and the motor has made numerous pulls on an engine dyno without failure...

Boostn7

YES, the car did have engine related failures in the past...and yes he also has had electronic issues as well.....Tunning the motor was also another issue.
If its fixed I hope to see it in 2006 making some noise at the track. That car is a work of art all around !

I still remember Dennis wrecking his backhalved Starlet "Cecilia" @ Atco years ago.
He then started building a beautiful FD which has been in the works for years, even before Abel's Rx7.
His bright yellow single turbo/PP/3rotor-FD was unvailed in early 2000 at Spring Nationals @Englishtown Raceway, NJ aiming to be the fastest Import in the world.
Pro cars were running mid 7's and 170+mph back then before the 2JZ motor became the motor of choice.
Unfortunately the car has yet to run any impressive numbers and it now sports a new paint job(green w/gold) and a triple turbo/PP/3rotor set up.

http://www.evotuners.com/gallery/dm_rx7

Here's a link to City Performance which show pics/videos of this car in the last ~5 years.

http://www.cityperformancecentre.com...s/dmarquis.htm

The effort and money placed on this car has been almost with out limits...

I sure hope to see this car put down some serious #'s and pick up sponsors.

JD

RETed

Where's the proof?

Same thing to BDC...where's the proof?

A while ago I plotted 87GTR's BP 499hp run versus my measely 253hp SP.
I made more power up to 4kRPM.

Where's the low-end advantage?
All I heard was excuses and subjective comments about it-feels-faster-so-it-makes-more-power-lower BS.
Dyno graphs don't lie.


-Ted

BDC

The proof has existed for quite a long time now yet you refuse to acquiesce to it. I remember seeing those graphs and what I do recall is that you fudged the figures in favour of your argument. Even so, you were unfair in how you made the comparison, not taking into account the size difference between the turbos amongst other things, all the while asserting that you'd "win the race to 4krpm". Give me a break, man!

B

RX794

The proof I wanna see is at the track, BOTTOM LINE! What are the fastest forced induction 2 or 3 rotors out in competition that can actually stay together long enough to win events? Last time I checked they were STREET PORT motors!

RETed

Dude, you're basically calling me a liar.
This is why arguments with you is a waste of time.
I got my DynoJet graph.
You got your DynoJet graph.
How can you )(#@)(%&)#@ "fudge" the numbers?

Why don't YOU plot them in Excel yourself and see what the graphs look like?

I can't believe you would stoop so low to call me a flat out liar.
What little respect you had just went all down the drain.

Still arguing about turbo size?
Well...let's see...then that means YOU fucked up on the turbo sizing?
How about we take this one further?
How about your tuning sucks to be making that low power at low RPM?
We're talking about a rechipped STOCK ECU here in my car.

"Win the race to 4kRPM"?
I thought we're talking about low-end power here?
Why you trying to twist things around?
Who said anything about racing up to an artificial low redline?
I put my proof up, and all you can do is blast it as a lie and whine and bitch about how I twisted the number?

Dyno graphs don't lie.
Go complain to DynoJet about how the graphs are "wrong".


-Ted

BDC

I'll post this one more time and hopefully you'll come to your senses on it: I was against the idea of doing this overlap bit on turbo motors because I thought it wouldn't work. I thought it would be detrimental. Guess what? I was wrong. My good 9 months or so of stubbordness was proven to be nothing more than ignorance on my part. It worked so surprisingly well on Tony's car that I stayed with it. Had it not worked, I wouldn't have promoted it at all. You'd do well to heed the moral of this story, Ted. You can take it or leave it, but that's the truth. If you don't like it, tough. I'm not changing a thing to suit your selfish and unreasonable needs so you'd might as well get used to it.

B

BDC

Oh, and one more thing while I'm thinking about it ... going back to the age-old question I've poised at you time and again -- have you actually gotten any real-world, personal experience in any of this? You exert so much vocally about this subject yet I've not seen you once with your own experiment, be it a good one or bad one. All you've said is, " oh, it's coming", as if that were meant to be some sort of ominous and threatening visage resting just over the horizon. I'd really and truly love to see you shut your loud mouth for just 5 minutes and actually try some of this stuff on your own before you go trigger-happy in slamming others that are doing the work, have the guts to spend the money, and are taking the time to see what does and doesn't work.

B

Boostn7

Just as Ted replied, those numbers are bit unrealistic.
But if you are looking at all 3 options for a street car then turbo-PP setup will be last choice for sure. It will have the worst idle and fuel consuption and the most wear on apex seals due higher rpms and 2 openings on the rotor housing to go over.
Bridge-ports could be made to last like Street ports but idle and fuel consuption are also affected.
I know Ari(rx7.com) also experimented with a bridge-port to find the same results as Steve did. I understand the issue being on the exhaust side and going to a bigger A/R or turbine wheel will also result in a peaky powerband.
The only way this would benefit is if you had a tranny that would keep the engine on its happy spot, like I few Steve mentioned earlier.

z8cw

Don't know..why are these numbers optimistic?

The benefits of an overlapped motor in a turbo charged application seemed twofold...quick spool up and high torque peak. So if I see this right you have good mid range due to the fast spooling turbo and great top end due to the breathing capability at higher RPMs. The tricky part is finding the right turbo specs.

I am just wondering why so many on this board still chase the ultimate turbo for the 15 pounds of boost on a street port looking for some extra hp or spool rather than explore other porting options....

CW

Boostn7

In our engines bigger ports(intake & exhaust) is what increases overlap and anytime you increase your port size it results in less low rpm power, torque and also affecting fuel consuption as well as your steady idle like you mentioned.
So, how does increased overlap bring the powerband lower in the rpm ???