LUV94RX7

iTrader: (3)

LaBreck has been doing lots of analysis to find the optimum rear end ratio for his V8 FD project. Looks like that might be 2.91. His car with street tires should run high 10s and high 130s in the ¼ mile.

I’ve been using one of the tools Jim is using for well over a year now. I’m currently studying the plus and minus of running at different boost levels. As we probably all know our cars need boost to get good power. Until the turbo(s) spool up we really don’t have much power before 3k rpms. This analysis is not for the really hard-core drag racers that will do anything to gain a 1/10 of a second at the risk of blowing up their engines. For the person like me that just wants good street (highway) performance do I really want to risk blowing up my engine to gain a few tenths of a second. I’m currently thinking I’m not. I loaded real-world dyno graphs into my Cartest2000 program at 12psi(350rhwp peak), 16psi(400rwhp peak) and 20psi(450rwhp peak).

This analysis was running street tire (275/40-17 Nitto drag radials). Please remember this is just for comparison numbers between the different performance options.

These are all optimum launches and the numbers are a little surprising to me.

12psi 12.57 118 mph
16psi 12.28 122 mph
20psi 11.90 128 mph

So for me I’m willing to run 12-16psi, but am I willing to run 20psi and really risk my engine for a .38 and 6 mph gain in the ¼ mile over 16psi. I am beginning to think not.

From a dead stop and racing these three options here’s what I found. Obviously during the ¼ mile the 20psi model will be ahead. Now for the fun of it just how much behind are the other models during the ¼ mile run?
16psi 12psi
At the 330’ mark –17’ and –25’
At the 660’ mark –38’ and –59’
At the 1000’ mark -52’ and –75’
At the 1320’ mark –70’ and –118’

So, I’m thinking that at the 1000’ mark I’m only behind by 3 car lengths at 16psi. Big deal. I don’t think the risk is worth it.

What do you think?

Ken

relvinnian

For a properly setup RX-7 on slicks -

118 trap should yield 11.70-11.90 QM
122 trap should yield 11.10-11.30 QM
128 trap should yield 10.70-11.00 QM

ET Streets aren't far off.

The difference in acceleration between each of these trap speeds is very large.

I think if you want to run less boost, then you need to make up for it in other areas. Larger porting, larger exhaust housing, higher peak tq.

RICE RACING

Ken ther is no risk so long as you stick to well proven parameters, there seems to be a lot of misconceptions about the reliabilty of rotaries, especially from people who have given up on them. This is quite perplexing to people like me who have had reliable engines running pump gas and making 500 to 600bhp, sure we have ALL had failures due to system cinditions or just plain mistakes in the tunning or engine building (tolerances, specifications)...but it is proven "least in this part of the world" that you can have a 100% reliable daily driven pump fuelled 13B making 500bhp and closer to 600bhp with a few detail mods and precise tunning.

Some of the parameters that work for me are the following.

B10egv plugs minimum.
water temp below 92degC
Charge temp below 45degC
Ignition advance @WOT 12deg
AF ratio around 11.0:1 no leaner than 11.3:1
Water Injection 250 to 300ml/min (if running 600bhp level with street port) ie this means boost in range of 20 psi or 1.4 bar

As you well know power is a function of boost, rpm or increase in VE ..... boost levels in the region of 20 psi on 9.0:1 compression are not a problem when staying with in limits.

I have a couple of cars including my own street car that run 20 psi boost all the time on our 98ron pump gas, day in day out.

As you increase the boost the tunning is critical, if you have this under control, reliabilty or lack of it will never be an issue.

regards

PS I have run up to 22psi on 98ron pump gas with water injection, no detonation.

LUV94RX7

iTrader: (3)

Well one of the reasons why I got water injection(up to 320ml/min) was to run higher boost safely and to help cool the air intake charge. KDR will be doing the tuning, but 2s 3d water injection mapping is new for him and he'll be tuning a Power FC with datlogit. I assume if he does both correctly you're saying 22psi is not out of the question on 100 octance(usa) gas. I feel more comfortable if you were doing the tuning. You have experience with water and high boost tuning.

Here's my mod list, I think you have seen it before.

Thanx

Ken

'94 white, pep, red leather,
mods: Street port & polished stage II, 3mm Hurley racing seals, upgraded coolant seals, Power FC ecu, XS T04e single turbo kit, SMIC (400+cu.in.), Aquamist 2s water injection kit, Pettit ss resonated MP, Pettit ss cat-back, RP Racing fuel pump, 1600cc injectors, Profec B (12&22psi), under pulley kit(no air pump), Evans Coolant

LUV94RX7

iTrader: (3)

Yes, I can get numbers close to what you are saying if I had slicks, did a burnout and dumped the clutch at 6k rpms on drag strip surfaces. I will not be doing that.
I'll be street tires, on public highways, with no burnouts and dumping the clutch at 3k rpms. Big difference.

Ken

j9fd3s

iTrader: (3)

if the risk of running high boost is blowing the motor, and maybe ruining the turbo, does that bother you?
if you had to put another motor in the car sooner rather thatn later would that be a big deal? to me its not, i hate putting motors in so i keep the boost down. maybe for you its not a big deal though, and if everything is set-up right the motor might last

mike
20b fc

peejay

98RON is anywhere between 95 and 98 by our rating scale... good luck finding anything better than 91 or maybe 92 in most areas. Also it's normally mixed with ethanol (maximum 10%) as an anti-pollutant, so wouldn't that make a 11:1 A/F ratio dangerously lean?

LUV94RX7

iTrader: (3)

If I ran high boost I'b be mixing in the proper amount of 110 octane unleaded at $4.00 a gallon with the normal pump stuff.

Ken

LUV94RX7

iTrader: (3)

Here is my problem, I go to a weekend place where tons of hot cars come to hang out. I mean Vipers, turbo and supercharged you name it, Mustangs, GTOs, Camaros etc. 60's muscle cars, street rods. Many of them like to boost about there power etc. I'd like to be able to safely once in awhile run high boost when I know I can kick their butts.

Here's a neat story, my nephew has a true 9.3 150+mph Busa. Time slips to prove it. He was there this weekend and a bunch V8 bikes came rolling in. 600bhp V8s on these bikes. They dyno them and then calculate the power to weight ratio and it tells them 1/4 mile times.

One guy said his will do 7.75 in the 1/4 mile. They were kinda making fun of his 9.3 second Busa. He said you want to go out and try me now. The guy said he would not want to waste his time. Then he said how about for $500. He guy backed down real quick. He did go out once against one of them weeks ago, the V8 bike was all over the road at 120mph, while my nephew was way ahead of him. Don't believe all the B.S. people claim.

Ken

relvinnian

The thing that would bother me the most is my own lack of tuning, or improper setup. Pulling and rebuilding the engine is incredibly simple in a highly modified rx-7. Standalone ems and removal of all un-needed parts makes pulling it a quick job, and the engine is held together by 18 bolts. I have also never personally seen a turbine damaged from a blown motor, which includes my own. I don't doubt it can happen, I just have not seen it yet.

In my opinion the risk is worth it, and will be running 26-28 psi on race gas with my new engine.

AJC13B

Boost + fuel = power

Power is your friend.
Fuel is your friend.
Boost is your friend.

LUV94RX7

iTrader: (3)

Maybe take Rice Racing's advice and add water injection for a safety measure at those boost levels.

Ken

relvinnian

Actually Peter will hopefully be building manifolds for my roomate and I. He's given me lots of good advice, and I am very grateful. I will be running water injection among other things.

j9fd3s

iTrader: (3)

i am assuming that you are running the proper setup to run high boost, but the premise is still true, are you willing to risk your motor to make more power? like i said i have no desire to pull my engine out, but maybe its not a big deal for you? but this seem to be the only downside, you know you built the car for stuff like that...

mike
20b fc

RICE RACING

Power is your friend.
Fuel is your friend.
Boost is your friend.

Tires/driveline/cops/neighbours/rta/WRX's are your enemy.

RICE RACING

Bro, its a big deal for all of us, I enjoy building motors, but ONLY when required...... building them due to mechanical failures sucks **** to put in mildly, I much prefer to be driving the car instead of be working on it, not to mention the financial side of the equation.

I think that the biggest problem is that we all just want a little bit more (hands up all of you!) and we just do not know when to stop untill we have either fucked ourselves to death like a little chipmunk during mating season or run out of money fixing and upgrading **** constantly...you can have too much of a good thing

I recon with road cars and the current level of knowledge pertaing to us the limits we have mentioned will stand you well, but remember its a performance thing and as such needs to be in top tune in every respect, hey if it was easy Mazda would have delivered the RX7 factory with 500+bhp 13B's

LUV94RX7

iTrader: (3)

Rice Racing, are you saying that if my setup was tuned properly I could get 500rwhp at 25psi????

Thanx

Ken

jimlab

Yeah. With a tank full of C14...

Ken, you chose to go with a smaller turbo for improved streetability. Stick with that goal and you'll have more usable power than someone with a sick turbo and tons of power that they can't put to the ground without slicks or achieve without a tank full of high octane.

Kick their asses by building your car to hook up the power that you can make safely on the pump gas available to you. If you get beat, then it's time to decide whether or not it's worth pushing your engine harder and keeping a drum full of race gas in the garage.

When we're done tuning, I'll have two sets of maps for my car. One for 91 octane pump gas and one for C11 (104), just in case.

RICE RACING

Ken, not with the to4e, with the "s" yes this is possible for sure.

Me and Jimlab do not agree on some things, but he is dead right you need to be able to use the power you make, and I will tell you from personal experience, with non warmed street and semi slick tires it is hard to get the power down in first, second, or third gear once you are making 500bhp let alone 600bhp (500rwhp near enough) .... My rx7 is basically "use less" in terms of acceleration, for tire smoke it is great This is the facts with non warmed tires with suspension settings for road/circuit work, soft springs and shocks its a different story.

Stick with the 500bhp limit as your upper target, as I think you will find that unless you tune the chassis for straight line work, including warming up the tires with a decent burnout you simply will not have the grip you need to use all the power, especially in the first two gears.

LUV94RX7

iTrader: (3)

So 500bhp is about 425rwhp. I should stick with about 20psi and I should get that? With the T04e I'll have a nice low end power curve. Sounds good to me. Run 12psi on the street with 91 octane and 20 psi on special occasions with high octane like JIMLAB recommended. Do you have experience with a Power FC?

Thanx again,

Ken

RICE RACING

Limited experience with PFC, tunned one on a "SP" rx7 my friend owns....they are a good ECU from what I have seen of it.

Greg

If everyone was dickless and didnt want to experiment to make power then we would not dominate almost every class of racing.

mmaragos

Classic. "*****" and "dickless" together.

j9fd3s

iTrader: (3)

two things:
1) only keep race gas if you get along with your neighbors, it's not really that legal to have sitting in your garage.

2) i'd like to see the car that makes you haul out the 104

mike