Joe-Racer

Tonight we (finally) dyno'd the RX7 race car. From the very first pull it appears to be down about 15hp from where it should be at peak compared to the other RX7s out there. At least thats what I have been told. We used a dynojet




We adjusted the fuel pressure and timing. Notice the peak numbers didnt change much on the graph. But look at the difference after 6K rpm. I gained 32whp and 15wtq. The curve is much flatter. Should have more punch now.

Timing is 26 and 16 (locked dizzy). Fuel pressure is 2.2lbs

A/F was 11.5 accross the board.

I need some suggestions on what to do next. The car runs in a spec class and no internal modifications can be made. This includes the intake manifold.

The car has a Nikki carb (Yaw).


I'm ordering some jets in var sizes to get the A/F up to a more reasonable level. What should I go for - high 13s or more/less? And should I reset the timing after finding the right secondary jet size?

I haven't checked the float levels or needle settings. The car runs and idles fine (read: smooth). Should I work on the floats?

Also, the coils are: stock leading, and Blaster coil trailing. The wires are all pretty nasty and frayed around the clips (and will be replaced). Would the 2gen coil mod be an option?

Any other ideas/suggestions are welcome.


Thanks in advance for the help.


FYI - here is a video of the last weekend's race at Barber Motorsports. I ran a 1:52.1 in the dry. And a 2:11 in the wet. Started 7th - ended up 3rd

http://media.putfile.com/Barber-Moto...ARRC-July-2007

Joe-Racer

Pictures of the race car.

dbragg

iTrader: (7)

bump for a great looking car

vipernicus42

iTrader: (4)

First thing I would do if you've got a Yaw carb is contact him. He keeps saying in all his articles that he wants people with his carbs to be as fast as possible, so maybe he'll be able to help more with jetting.

Don't touch your damn floats! If the car is running fine, there's no reason to adjust float levels.

If your wires "look pretty frayed" that could definitely contribute to problems. While 2nd gen coils are an option, I'd start with new stock wires, new plugs, new distributor cap and rotor, and switch the blaster coil to your leading. Your trailings are only really there for emissions purposes and I bet that if the next time you dyno you run one with them and one without them, you won't even notice a 1hp difference. So you might as well have the better coil on the leading.

Can you share more details on the engine? Stock or rebuilt? Stock ports or ported? Any upgrades?

Which clutch and pressure plate are you running?

You'll gain a bunch of hp by jetting the carb I'm sure. IIRC Yaw's carbs are like Sterlings, so they use 10/32 Holley Air Bleeds as jets and as air bleeds (the emulsion tubes are drilled and tapped to accept them).

If you haven't already, read all the stuff on Yaw's site. Here are three of them:

http://www.yawpower.com/secret.html
http://www.yawpower.com/fueldel.html

and he's got one somewhere where they show dyno tuning with changing air bleeds... but I can't find it right now.

Jon

Jeezus

iTrader: (4)

^^No porting, cant touch the internals

VintageMazda

11.5 is way too rich. Shoot for 13.4

It sure breaks up above 6500rpms

Joe-Racer

Jon,

I appreciate the advice on the coils. Switching the Blaster to leading was on my list as well as updating the coil wires. Someone suggested to me switching to the MSD6AL set up. Not sure if that's worth the cost.

Here is a rundown of the motor
1. Carbon seals, rebuild 12A. Used housings, probably 8 of 10 in condition.
2. RB header w/ custom exhaust. Seperate chambers till 15" post header, then single.
3. Race pulleys, inc ALT pulley
4. Shimmed Oil press - 100psi.
5. Taylor plug wires - 8.5mm. Ignitors(appear original) , dist cap (1 season)
6. 81 flywheel with 4 puck unsprung hub and PP


I've read the Yaw suggestions and sent him a couple emails. No reponses. All the vac ports are capped off. ANother person suggested removing the return line and cap that off. Not sure if thats a good idea or not. Supposidely the FP is more consistent without a return line.

Joe-Racer

Also - how are my curves..

Does the motor appear down on power

dj55b

iTrader: (2)

I think you should really quite a bit more in the top end HP and torque curve if you get your Ignition upgraded and your engine leaned out a bit more toward 13's as mentioned.

If you browse through this forum, there's the DLF ... can't even remember what its really called but it basically takes second gen ignition and adapts it to first gen. Really cheap and should be able to do it all for under 100$. Second gen ignition when just testing spark again a ground source, the sparl appears to be twice as thick. So definatly more juice. when I tried it out on my engine one the dyno, We dfinatly saw an upward shift on the on the HP and torque curve.

j9fd3s

iTrader: (3)

i'm echoing everyone else...

i'd be looking at ignition, at least new wires and either the msd6 and or an fc leading coil.

next step would be to lean it out

then play with timing again

imo you should be 120-125 at the wheels....

Joe-Racer

I was thinking I was down about 15hp or so. Dynojets are usually more liberal in their ratings. So if anything, my numbers should have been higher.

Since ignition is wide open for me - and with a budget of about $200-300, what is the absolute best option?

Also, I ordered a selection of jets from holley from #62s to #99s, in pairs. I suppose only focusing on the secondaries is important since the revs never drop below 5k. And its either full load or no load.

j9fd3s

iTrader: (3)

msd6 + FC leading coil, run you $150 tops... new wires and plugs

Joe-Racer

A new cap and rotor are in order. The wires are fresh 8.5mm

FC coil ='s FC leading plugs?

dj55b

iTrader: (2)

FC coils pack. If you pop the hool open on an FC you will notice that coil and igniters are all in one pack. I bought them from the Junk yard for 50 bucks for both leading and trailling.

dj55b

iTrader: (2)

You really thing that high for a stockport?

vipernicus42

iTrader: (4)

With a yaw carb, hellz ya.

Check this out:

http://www.yawpower.com/niktest.html

Right in the second paragraph he says

Which is followed up at the end by

and when they fully opened up the exhaust they ended up with this:


Which is exactly why I'm hoping to take my Sterling on the dyno at some point in the near future and see what we can do

They never did say if this was with the engine directly on the dyno or in the car though.... I know there are pictures on his site of engines bolted directly to the dyno.

Jon

Joe-Racer

Some have said it helps to run the FC plugs on the leading side. Its performance has yet to be proven - AFAIK

dj55b

iTrader: (2)

Jon,

That's making my Setup look like a joke right now. I knew my Holley carb was sluggish but no that bad. I made 147HP with the holley and the Sp engine. I can't wait to get my ITB's right now and really get that thing tuned in properly with a better ignition. I would really like to see somewhere around 170whp maybe even 180 but might be a little too optimistic.

Never saw that article on Yaw website. Really good people.

Joe-Racer

I've never seen (or heard) of a 150whp, non ported 12A. Not that I doubt Paul's claims. I just question them

Formerly known as jgrewe

I think you might be worrying about comparing wheel HP to crank HP with that 156 reading. The numbers I've seen for a good ITA engine are about 125-130 to the wheels. There is a lot of money testing to get the last 5-7 HP once you get above 120.

j9fd3s

iTrader: (3)

ive seen 116rwhp on a stock port stock manifold pro7 car, header should add 10hp?

RussTypeS

iTrader: (3)

Who's dyno did you run on? I usually shoot for low 13s for afr, just to be on the safe side and help keep things cooler.

I have a yaw carb on my car too, stock the thing was pig rich. Yaw couldn't figure it out and eventually stopped calling me back. After much experimenting I found a setup that works. My afr is far from perfect, but it's way better than the out of the box carb.

don't mess too much with the primarys, going much smaller with fuel jets there will give you poor throttle response and bad drivability.

You can try some smaller secondary fuel jets, but they didn't do much for me until i drilled out the secondary air bleeds. try playing with that a little and see where it gets you...

vipernicus42

iTrader: (4)

Well, I just edited my post to mention that it could definitely be just the engine on a dyno. There are pictures on his website of just engines bolted to dynos.

In that case, you make up for the drivetrain loss and come back into expected territory of 130ish hp

Jon

Joe-Racer

I couldnt gleen from the reading if it was a bench dyno (heck..is that even the right term) or chassis dyno. He talks about the exhaust being changed out - but again, that can be done on either dyno.

My 105whp equates to 120ish with a 18% loss factored in. Maybe thats conservative with the panasports and 81 flywheel.

dj55b

iTrader: (2)

K ya .. if thats just bench dyno, that more believeable ... but about 150ish at the wheels I find that really hard to believe. Because really that would equate into about 170 to 175 at the wheels.