dvls-7

Let me be the first to volunteer if you are ever wanting to drive that thing with the boost cranked up to 20-25psi.......

RX-Heven

iTrader: (1)

Go widebody with 335's out back.

ZoomZoom

iTrader: (2)

doesnt matter how wide the tires. Just make sure the compound is soft enough.

Terrh

iTrader: (7)

wow.

NICE car.

who cares about the powerband if you never can get on it, anyways?

I'd rather have a 350HP car than a 650HP car for that exact reason...

dvls-7

I agree. Go with the BFGs dr, those are some very good tires. I know of a couple high hp (700+) supras that don't spin. As a matter of fact a buddy of mine broke his drive shaft trying to do a burnout with them on.
I like the idea of the widebody with the 335s, that would give it a real mean looking stance.

sillbeer

Red, What size exhaust is on your car? Do you have a backpressure gauge or any way to check to see what your backpressure is? On my car i'm running an 80mm dp and it Y's off to 2 80 outlets. I'm not real fond of the twin setup and would like a medium sized single exhaust. Maybe a good 3 1/2". Something not real restrictive but not obnoxiously loud.

-Destin

Howard Coleman

iTrader: (6)

hi Red,

i am finding the thread very interesting from a number of aspects. having logged around 700 miles in dick lamberts FD/20b i have a partial understanding of what it is like to have almost uncontrollable hp...

and yet..

when i look at your dyno sheet, which you showed me at the April Rotary Revolution, i see something far from optimized. your dyno sheet is essentially flat from 4800 to 6100!

there is this need to get the line moving upward even though it would be hard to figure out how to hook it up. ( of course alot more rubber in the back is the answer).

the deal is that the compressor map is just not suited to running 14 pounds. look where you are: flowing around 63 lbs/min at 1.95 bar. way off the efficiency scale. the compressor would work at much higher boost. note at higher ( 2.7 bar) boost it flows around 73 at much better (75) efficiency. it should move rwhp to 730.

that's why your hp is flat. the compressor is generating too much heat from 4800 up at your current boost setting.

i do like efficiency and you are in the postion w your very well engineered car to go either way. either go for a different compressor that works well around 1 bar boost and 70 lbs or buy a huge set of tires, some plastic rear fenders raise your life insurance and turn up the boost on your current turbo.

and hang on it won't be pretty.

good luck,

howard coleman

SPOautos

Your maxing your turbo out. Its basically giving its all to you man, thats why your wearing it out. Even though it can flow 82lbs a min doesnt mean its going to live a long healthy life doing it. I think you need to upgrade to a T76 but keep the power about where its at so you dont kill the turbo all the time.

I have a conversion for "approx" hp on a rotary at the wheels given a specific air flow and at 82lbs/hr you should be able to make "approx" 625rwhp....sound familiar? It was so close its scary lol. Anyway, in my eyes your running the turbo to its max and just going to keep killing them unless you upgrade to something that can flow 82lbs/hr without being maxed out

Stephen

Wargasm

Do you still have the stock transmission? If so, forget about it tolerating any more abuse. One 20B I saw that was making a lot less power than yours blew the trans out on a dyno pull! I'm guessing you have a Guru or something neat in there?

paximus

iTrader: (1)

i've also enjoyed following this thread.
i'm in the middle of a 20b project as well and i'm trying to figure out which turbo would be best for my application, which is similar to Red-rx7's (see below).
it seems we both have the same goals, but i dont have as much porting done as he does, no uim/lim porting, (actually its still stock ports, (but rew housings), i'm tearing it down and getting it ported before i heat cycle the rebuild). i typed the above almost word for word when talking to sean at aspec. kinda funny.
i would love to have as much response as he does, but with the turbo higher in the efficiency range of course. i was thinking the 1.32 a/r GT42R. but maybe i'll need to go bigger also? it'll be interesting to see what happens with red. i'm cool with ~600hp though, any bigger is even MORE crazy.

Red-Rx7

Wow, lots of replies. Let me start at the top and go down.

I looked into this originally, for I thought it would also be neat to have that meaty stance back there. But, I was turned away by most designs for I factor in a few things: 1) Stability & Structure, 2) Looks. With regards to #1, most I have seen peel or crack away from the car (for they are fiberglass) under load & stress. This would result in me having to have something molded via metal on to the body, sanded down and repainted. This gets expensive, and decided to spend the money on other areas of the car.

This was my thought for the next plan of action. Yet, the turbo died with less than 1800 miles on it. The drive home from NJ with the car to Kansas was 1200 miles, and the other 600 or so were to Indy for the Revolution. The turbo gave out while I was in Indy.

Ultimately, I will try some DR's and see how they hold up.

Thanks for the compliment. The thing about it, I haven't really had the chance to drive the car the way I want to. Each car, in its relative performance category, the driver will have to learn its abilities and adapt. I started too, then never had the chance to get all the experience I was looking for in it. I will, just will be dependant on time. The 650 rwhp isn't something to take lightly, but it is nice to know it is on tap; and the driver really learns foot peddle control.

As I mentioned above, thats a route I want to look into. I will most likely do this after these tires are gone. I attempted to build the driveline up to hold it all, but the driveshaft is one piece that isn't extra special on the car. So, if anywhere, I would expect that to be the place for failure.

Destin, I run a 4" exhaust all the way back. You can see it in this picture here:

(I have linked it, for it is very large!)

http://home.comcast.net/~mhaun5/rx7/snake.jpg

I do not have any gauges to check the backpressure, but was hoping 4" dp and mp would mostly kill any. With regards to being loud, my car isn't that bad. Ask anyone who heard it run at the RR, it has its moments. When rapping above 3500RPM, it does sound like an F1 car; but very dosile in comparison to other 13b's with their full dp/mp/catback setup.

Howard, you wrote a lot so I won't quote you. But I will try to hit on a few items which you mentioned. First, the HP does flatline at a very early RPM range and holds it throughout the powerband. It does show the turbo is out of breath. Now, if that is due to the compressor efficiency mapping or the AR of the exhaust side; that has been talked about a bunch in here from what I seen.

With regards to the power band, what is a flat hp curve ultimately best suited for? (anyone?)

SPOautos, you make an interesting arguement that I haven't looked at; with regards to the longevity of the turbo do to its inefficency. Can a turbo burn itself up in 1800 miles from this?

Also, I have no scientific way to indicate my CFM at the moment, so it all seems like guess work. I have seen many people quote anywhere from the low 60's to your indication of 82lbs a min. If I did know this number exactly, then it would make it easy to select a turbo. One of the routes of this conversation, can we further discuss which airflow result most accurately relates to my car? What formula are using?

I do currently have the stock unit in the car, and that has been a worry. I do own a GURU box; but it sits in Australia at the moment (due to financial funds). As soon as I can get some more money, I will have it shipped over.


I look forward to everyones replies.

Thanks,
Mike

Trav

Red, where are you in KS? I'd love to swing by and see that beast sometime...

Red-Rx7

Olathe, Johnson County area.

You?

SPOautos

I got a formula from Chris Anderson, he posted it years ago on the board (back when he used to actually get on here and discuss tech) and I wrote it down and kept it in my desk at work. I've compared the rwhp people were making with a spacific turbo against the compressor map, and using the formula Chris gave its always been very close. The formula is simple as pie....you take the lbs/min on a compressor map, divide it by .069 to get cfm, then divide by 1.9 to get rwhp. So far all the compressor maps and dyno readings I've checked it seems to be a pretty good formula. Running the numbers for you car to come out that the lbs min you should be flowing happened to be exactly what the max was showing on the compressor map.

You can take that for what its worth, I didnt come up with the formula, I just tested it and found it to always be pretty close.

STEPHEN

Red-Rx7

Interesting. Very interesting.

Using the forumla, I came up with 82.34 lbs/min of airflow. Looking at the compressor chart, I am at / near 1.93 - 1.94; which can be graphed at 1.95 of the pressure area.

That is WAY outside the box. Looking at this chart, it seems to make more sense. We tuned the car to handle 25 PSI of boost; but it yeilded small gains in the RWHP department. We were thinking it would give a lot more HP, but even at 25 psi (which translate to a 2.7 on the pressure axis); it is still outside the island.

Is there some way I can have the car tested for CFM or Lbs/Min? In reviewing all of ITS's turbo maps, the closest one which puts me in any efficency range is the GT80; which puts me at the 65% efficency mark; if indeed my airflow was 82.34lbs/min.

The GT76 even puts me below 60% efficency, but way closer to the line; again assuming that I am at 82.34lbs/min.

How much does the efficency come into play for additional horsepower? Also, how does it compare to spool up time? Would it be correct to assume that the further to the right of the compressor map in airflow, the faster the spool up?

So going from something that is in the 30% - 35% efficency rating to a 65% efficncy rating, sounds like it would produce a large hp increase. Thoughts?

Red-Rx7

...

What factors influence airflow for lbs/min? Is this something that is like the VE of an engine; whereas the increasement of PSI / density doesn't effect the actual lbs/min? Or can it be changed with other items?

Red-Rx7

I was reading on this site: http://www.gnttype.org/techarea/turbo/turboflow.html

Depending on the intercooler (basic intake tempatures into the manifold), VE of the engine, and the absolute pressure; all determines the lbs/min.

Therefore, these figures should moslty be static when evaluating a turbo; with exception to the abs temp pressure. But ultimately to figure out via a measurement tool, I would need a turbo that is already working on the car to measure it; for these are influencial in the final result.

Which further makes me wonder... I was seeing good intake tempatures on the car. Anything from 90o to 130o while driving outside at 85o. If the turbo was way out of its efficency area, wouldn't it be very hot air coming out? Or am I seeing the intercooler doing its job efficently?

Howard Coleman

iTrader: (6)

did you log/observe intake temps when you dynoed? the compressor inefficiency should only surface when your foot is on the floor above 5000 rpm.

something very major is going on. from 4800 to 6200 no increase in hp and yet a 29% increase in rpm. all that additional hp potential is being offset by either backpressure or superheated oxygen-starved air into the motor.

IMO, it is most likely the cause of your turbo failure.

if you look at alot of (2 rotor) dyno sheets it is not uncommon to make 50% more rwhp at 6000 v 4000. all that energy is going somewhere as backpressure or heat.

looking again at your compressor map... i think it is a good setup if you want to run 1.7 bar and make 730 rwhp. if you want to make 630 i would look for a different setup.

most people on this forum have not driven a street FD making 630 rwhp and may possibly wonder why the 630/730 question is even worthy of consideration.... of course 730 is better than 630.

the 20b/fd that i have driven extensively has a t66 on it and consequently is capable of 515 rwhp if properly tuned. it is a click below full tune and it is a major handful to keep on the road. i can only imagine what 630 is like.

please let us know as to whether the flat hp curve problem/turbo failure is from the hot or cold side.

good luck,

howard coleman

Red-Rx7

Howard-

I don't have the exact numbers during the dyno, but have some from the road driving experience (which was anywhere from 90o to 130 on average, occasionally going up higher when near a slow speed.). When driving at 60 mph, the intake charge was pretty good.

I will have to go and see if I have any datalogs available to review, but this was from my memory.

With regards to backpressure; wouldn't a 4" exhaust eliminate quite a bit of backpressure?

I also applied the 1.92 X rwhp and came out something simular to what SPOautos did on airflow. I am quite surprised that this engine is flowing that much air in reality. What I am having a very difficult time right now with, is finding any compressor map for the boost range to be near any good efficiency.

The idea was to run no more than 1 bar of boost (max). That puts me in the 1.95 - 2.00 range on the compressor maps. Being that the car flows 83-86 lbs/min; most efficiency ranges are below 60%; with the best I have seen being a GT80 turbo @ 65%.

Can you offer any insight to the efficency island differents; with regards to relative horsepower and spool up time?

Also, when you say run 1.7 bar; are you talking about 25 PSI of boost? And at 25 psi of boost, I would have figured it would have been more than 730 rwhp.

Red-Rx7

Also, look at this one:



Notice I would be in the 78% efficiency range with this turbo. Interesting. Still would like to see some relative information for different efficiency islands.

twokrx7

iTrader: (1)

My suggestion to estimate the CFM would be to take some performance data during a dyno pull. While making a run, measure turbo in/out pressure and in/out temperature. You can easily calculate the pressure ratio and efficiency if you know the atmospheric conditions (barometric pressure and humidity). Don't assume manifold boost is the turbo discharge pressure, may be a few psi lost thru piping and IC and TB at that monster flowrate for 600+rwhp. My thermodynamics are rusty so I would look for some canned program floating around the internet to do the calcs, otherwise, look for a local ME to dust off his/her thermo text.

I would lean toward the GT76 on the compressor side. It requires less rpm for 1bar boost than the GT72 and has a broader efficiency island. I'm sure that 3 rotor can spool it but you never know for sure until you try it. On the exhaust, it should be easy to tap into the hot side and measure exhaust backpressure with your curent setup. Do this during a dyno pull at 600+rwhp, if the bp is greater than mani boost you may need to consider a larger A/R and/or wheel.

Wargasm

Here's the way I see it... and no, I don't have a simple answer

1 - Most people agree that every 10 rwhp on the dyno is around 1 lb/min of air. so you're -currently- flowing around 61 lbs/min of air at 6100 rpm. Your engine probably would like MORE AIR as you can see because the hp is flatlining. (we're assuming ignition advance and so on are within a reasonable range and are not a problem).

2 - Causes for a flatlining dyno at high rpm are almost always either that the compressor is too small or that the backpressure in the exhaust side of things is too much. Another possibility is that the intake system including everything from the turbo to the engine itself is too small. I've never -heard- of this before, but hey, there aren't too many 600+ rwhp 3 rotors running around either.

So... let's take it case by case.

If your compressor is too small, you should see air intake temps rising up pretty badly at high rpm but they are OK in the mid range. Cruising around at 60 mph is not a valid test, you've got to be boosting. The way to test this is with a thermocouple that reacts quickly so you can see the problem. I am not sure if the stock one reacts quite quickly enough to "see" anything. Also, on a Dynojet with no ability to hold the engine at one RPM, it might zip through the RPM range too quickly to see jack anyhow. You've also got to understand that any time you compress air, it heats up, so you WILL see it go up no matter what. The thing you're trying to figure out is if it is going up much WORSE at higher RPM. In reality I think you'll have a hard time figuring this out. The solution? Get another compressor.

If your exhaust has too much backpressure I don't think your 4 inch system is to blame. Tee hee. If anything, I'd say the A/R should be bumped from 1.32 to 1.52 which would free it up some. To test this, measure the pressure in the exhaust manifold before it passes through the turbine (you might have to drill some holes and install some fittings). If your intake is 13.5 PSI, but your exhaust is 20 PSI, you've found your problem. Keeping them closer to a 1:1 ratio is better. The fix? Larger A/R or larger wheel.

----

Now that that stuff is out of the way... compressor-wise... I am still not sure why your Innovative map looks almost identical to a Turbonetics T72, but shifted by 10 lbs/min, but if the maps are right, going to a Turbonetics T72 wheel would shift the sweet spot about +70 hp. (sweet spot = staying within the middle two islands). Also, your "max hp" before you were off the map would bump from 65 lbs/min to 75 lbs/min. This is all at pressure ratio = 2.0. Of course, maybe somebody has a misprint on their compressor map and they are the same damn thing and then you'll really be mad Also, 75-100 more hp will still probably barely be enough hahah.

Moving up to a T76 wheel/cover will be another bump up. You might suffer a little more lag, but from what you have said already, it sounds like you already have virtually instant response.

Then again, a WHOLE different turbo setup... something huge... I don't know what might be great... but now this is getting expensive!

On the turbine side, you're already at Q trim, so if you move to the 1.52 housing, that's relatively cheap to try and pretty easy too. If I had to take a random shot in the dark, I'd say to go to 1.52.

If it was my car, I'd install a fitting either the exhaust manifold before the turbo or in the turbine housing itself and measure the backpressure in the exhaust. Then get on the dyno (or street if you're feeling lucky) and measure the backpressure there and compare it to the intake manifold pressure.

You never know... anybody know if a T04 footprint turbine can even flow enough for a 6-800 rwhp car? At some point, those little rectangular holes just become too small.

Brian (Man of many ideas, but few answers )

sillbeer

The turbine on my car is a t88-34d with 22cm exhaust. What is that in Turbonetics sizing? When you compared the 2 dyno charts, like you said mine has a little bit more lag but didn't give any indication of peaking out.

-Destin

Howard Coleman

iTrader: (6)

the thread continues to be quite interesting..

i have used stephen's hp/airflow calculation for 2.5 years and have found it to be very helpful and accurate. i use it for compressor sizing.

applying it and looking at 630 rwhp you are indeed flowing 83 lbs/minute or 1200 cfm. wargasm's formula differs and calculates out around 63 lbs/min or 911 cfm.

using either formula your current turbo, if the correct compression map is posted on page 1 of the thread, is really out in cavitation territory at 630 hp and 13 psi. whether your hot side is properly sized or not your cold side is superheating the intake charge. i run a Power FC and it logs intake temperatures.... do you have any logs (E11?) that might have your temperatures at wide open throttle?

the compressor map you post on page 3 looks alot better. at 2 bar ( about 14 psi boost) it is spinning at a leisurly 60,000 rpm and not breaking a sweat and certainly not overheating the charge air. the sweet spot is in the boost area that you want to run and there is really nice flow in the 80 lb/minute range.

as to your hot side... even though it sounds like you have a killer exhaust ( congrats on going the extra mile/inch ) it could be that exhaust restriction might be part of your problem. the restriction of course would be (might be) in the sizing of your exhaust housing and the sizing of your turbine wheel.

other than trial and error ( and i really suggest you talk to Kevin Draper as my PM suggests) the process, as suggested previously is to plumb your manifold preturbo.
you want to see no more exhaust pressure than boost.

i will be interested in what you come up w turbowise. i haven't spent too much time on the bigger turbo compressor maps as my r&d was spent looking in the 35 lbs/min range. i run two turbos that make about 70 lbs/minute on my 2 rotor.

howard coleman

Trav

Wichita.



...great stuff folks... I feel like a sponge at the moment -- trying to soak up all of this.