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

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

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.

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.

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

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

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.

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...

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?

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.

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

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.

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 !

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.

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...

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

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

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

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!

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

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

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

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.

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

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 ???

Those are the two major benefits I've noticed in doing this, Claus -- the quick spool and the higher power band. From what I've seen even with just my small half-bridgeport stuff, the upper RPM limit doesn't seem to 'fall off' like it does on a similar, street-ported setup.

B

I have NEVER seen overlap push the powerband lower. Overlap effectively lowers dynamic comprression, but if its setup right with your exhaust header lengths and intake runner lengths you will get scavenging - and Ive never seen scavenging at low rpms, but I HAVE seen tuned runner lengths work.

I dont see how you can scavenge with a turbo, btw.

Regardless, when I see people playing with cams and timing they seem to want to dial out overlap with boost.. this make no sense. Any gain in the high end coincides with a loss in the low end unless you have VTEC or staged ports.

One thing I fail to realize is why you cant simply place PPs to not have a lot of overlap. Peripherial ports are the apex of trading flow for velocity, which turbos seem to like... and nobodys gonna build a rotary for low rpm torque anyway.

Again, has anyone found a VE curve of a SP, BP, and a PP yet?

In your above example, I don't think the psi difference is going to matter that much on the engine. Theoretically the internal combustion pressures and temperatures should be the same on all three of those engines to make that power regardless how much boost there is. The only thing I see different is how "efficiently" the air gets into the engine because of the ports. I mean you could slap on a humongous turbo and make that power at 15psi but would it really make a difference? Sure the cooler charge will be better but the small engine is still under a tremendous amount of stress. I'm no expert so please correct me if I'm wrong.

From what I've seen, people have done this, they're called semi-pp or combi ports, not the full size 2inch hole of a regular pport. I've read that the semi-pp makes great power (with a turbo, I can' remember). But it just doesn't seem right to me, not having the full sized port. I gotta get outta that mindset:-)

To answer your question, you can only move the 2inch hole up so far before you intersect the tension bolt hole. That's why people go with the semi-pp for less overlap.

What about angling the port at say, 45-degrees, instead of at horizontal? Does that have any effect on overlap?

Owen

Brian I seem to remember back when you first tried the half bridge you changed nothing else on the motor. Same turbo, intake, exhaust, intercooler, etc that was used on the streetported motor just now it was on a bridge. If I remember correctly you did find out that the turbo needed to be much larger to get the engine's full potential at higher rpm's. That was to be expected though. The thing that seemed to impress and dowright surprise you about the setup was that you only got 2 more peak hp with the same setup but over 70 more ft lbs of midrange torque in spots with a faster spool up time than the streetport! That was probably the single thing that convinced you of the validity of the setup back then. Later on you experimented with larger turbos. As everyone who knows anything about turbos knows, if you want to make more top end power efficiently, you sacrifice low end power somewhat and spool times due to the larger turbo. Of course Tony's chart you posted was with a much larger turbo than the turbo setup it was being compared against. The results are exactly as to be expected. I wish you could have posted your original dyno chart with the smaller turbo from the first setup you did and compared it to the other dyno chart. Low end would have been off the chart in comparison all across the board. Keep up the good work. It's obvious you know your stuff and everyone sees proof of it constantly with pictures, videos, and proof. I have yet to see a single bad thing said about you by anyone who has ever had work done by you.

I just chose to try and make the same HP and RPM to compare what boost level is needed to do so. I can give you another chart with the same boost. Lets pick 17PSI (possible on pump gas) and 7k rpm

street 429
bp 505
pp 550

You need to size the turbo right for the flow of the engine. Just slapping a large turbo on an engine and not running higher boost will make very little difference accept kill your low end. The numbers above are backed out of dyno charts and assume that the right turbo is used for the flow requirements. At 17 psi and 7k the side port flows 47lbs , the bp 55lbs and the pp 60lbs. These numbers are averages. Every ported port flows slightly different. On top of that you have to deal with different intakes and exhaust set-ups which will also effect flow through the engine. Still I believe these numbers are in the ball park and illustrate the difference in breathing capabilities.

Hey Fred,

Yep. The thing we noticed on that car was that TO4 got 'peaky' -- it came on real powerfully and built boost aggressively, but started to fall on its face in the higher RPM ranges. It made more power at less boost. At 12psi of boost on that setup, the car was running 11.70's in the 1/4 on slicks. It was a TO4E-57 trim if memory serves.

I wish we still had the original dyno charts. Ari originally got a hold of them and I believe that's one reason why he decided to try it out on his race car, but other than they aren't around anymore. The shop that had the latter graphs lost all of their data when switching to new software or some junk (we called them last year to see if they had them and that's what the dyno op guy told us).

Thanks for the vote of confidence.

B

AGREE! :)

Only the Renesis engine has no overlap. Our turbo Stock port 13B's already have some minor overlap and whenver we street port them we add to this overlap but nothing radical as a BP or PP.

Volumetric Efficiency :blue:
Again, the ratio between intake and exhaust pressure is very critical to the engine's VE.
Can't get a full chamber of fresh air if exhaust is being pushed back around in the rotor chamber during the overlap.

"Generally" is a disqualifier for use in situations like this :P most cams have SOME overlap to a certain degree anyway, it seems. Same with ports on a rotary.

One thing Id wonder is how rotaries which are known for going at lower boost ratios and porting could get a higher intake than exhaust pressure.

I understood your original post, I was mainly making a statement about how the 3 engines internal combustion pressures and temperatures would be nearly the same regardless for turbo size and boost pressures. Even though my post was slightly of topic, I just wanted to make that point.

Yes, you are right, I didn't understand what you were saying but you are correct...if there is better filling it will stress the engine more. I like you to consider a couple of things though:
1. Highest combustion chamber pressure happens at peak torque. Just by moving it up in the rpm band just gives you more HP not more pressure to bust your engine. Granted the VE of a ppprt is higher but I just wanted to make this point that it is not proportiante.
2. Also you should consider, less boost means less heat and with less boost you won't chase your tail as much...
3. Also, with a larger intake port, mainly closing later you will effectively reduce the compression ratio which is advantages for higher boost applications. This is probably also one reason why your filling, i.e. VE is so much larger in a pport.

CW

Hey BDC....be easy on yourself !! how were you ignorant ???
475.7 rwh and 382 rwt @ 23psi with a crappy idle and crazy fuel consuption is NOT an accomplishment over a street ported 13B.
You don't think you could build and tune a street port motor to make ~500rwh @ 23psi ??? I personally think you could....
I know you mention the same car made 499rwh @ 23psi but I did not find a dyno sheet to compare.
Look at your dyno sheet compared to 2 other street ported dyno sheets...
Street-port have better low end, at 5krpm both have ~50 rwh/50rwt more over the bridge motor.

JD

Sorry, but none of your dynosheets reflect that...but that's also affected with turbo sizing and manifold design.
I could show you street-port dynos that carry the hp past 7.5krpm and maintain a very flat torque curve all across the upper rpm range.

Just wondering how came up with these flow numbers for each port?

JD

Hey John,

An original dyno comparison did actually reflect it, truth be told. Unfortunately, it no longer exists. That first vehicle was the only one I'd ever done (or am familiar with, atleast) that had literally nothing else changed except those two, small bridgeport cuts. All three of us that worked on the car noticed the same, surprising effects. That's why we stuck with it.

B

Thanks for the compliment John but I still feel I was ignorant to it. One problem I do know that Tony's car had was a problem with the lower intake manifold to engine sealing. We never had a good gasket setup throughout most of the year, I don't think. At the same time we were dynoing with the big turbo and BP, I was experimenting w/ using a series 5 NA triple-metal gasket (the black one) but came to find out later that it was not sealing on one chamber, letting a good deal of air bypass its way right around.

Another point of note on this turbo is that it was using a 0.83 A/R back housing. While I suspect it, I am unsure as to whether or not this was leading to a drop in power up high. This engine was still using the same, 1/8" wide x 1.25" poorly cut bridgeport cuts with stock Mazda 2mm 3-piece apex seals.

A similar car, with a fairly larger port and beveled rotor housings' edges, made 447rwhp with a T66 at 1bar of boost. It, too, also had manifold leaks. I didn't have a good year in 2003 battling manifold leaks. :) I'll post one more graph of another car from last year in June on the next reply.

I am currently in the process of getting my own car re-done and hope to show the capabilities of this setup even further. I don't know what kind of experience you've had with yours, and I'd really love to know what it is, but so far I've honestly found this to be beneficial. Another thing I've noticed is that any change in the allowance of more overlap via porting seems to have a great deal of an effect of idle, fuel consumption, and power output.

B

Like I said it is backed out of dyno numbers.

There are a few assumptions I had to make:

IC eff .8
CP eff .7
air temp 70
elev 0, 14.7 psi
cfm na stock ports at7k 324, VE .85

Like I said these numbers are best guess but helpful when you try to mate up a turbo.

I saw the chart! It was very surprising.

If finding the right turbo was the only issue, then most racers would be running turbo-PP motors by now.....

You're kidding, right ?
If many on this board would explore other porting(PP or BP) as you suggested, then their cars would spend even less time on the road.
I well street-ported/tuned motor will run/idle like a stock motor and make over 400rwh @ 15psi.....more then enough for most board members.

JD

For both BP and PP what dyno charts did you use to come up with those numbers?

I noticed you posted the following on the Ausrotary.com forum...

--------------------------------------------------------------------------------
Any results ?

I used anything I could find on the forums. For the pp I tried to incorporate the VEs published in the SAE papers. I don't have a list of info I used.

As for my own motor, it isn't build yet. I am building a custom intake and haven't changed the Xmanifold yet to accomodate the different flange for the pp. I hope I will be running late spring.

CW

1-Yes, highest combustion pressure does happen a peak torque....
if peak torque is moved up in the rpm band this pressure you mentioned follows, therefore your likely to bust your engine with either scenario.
VE on a PP is higher when in NA form...now turbocharged it and now you know why we're having this debate.
3-Since the engine cannot begin making chamber pressure til intake port closes there's a loss of thermal efficiency and compression, overall lowering power output.

JD

VE on a PP is higher when in NA form...now turbocharged it and now you know why we're having this debate.

JD[/QUOTE]

What are you saying that the VE drops when turbo charged or that since VE is higher in NA form that the PP will make more power turboed?


3-Since the engine cannot begin making chamber pressure til intake port closes there's a loss of thermal efficiency and compression, overall lowering power output.

JD[/QUOTE]

The bigger difference is when the intake port opens! The IC isn't what differentiates a pport from a side port. Delaying the IC just moves the peak tq to higher rpms.

Dyno charts on turbo PP or even BP are pretty much non-existent and both of these ports behave quite differently when introduced to forced induction, mainly with turbos.

Keep us updated on your engine setup...