LizardFC

iTrader: (1)

After weeks of reading through threads, googling, and writing handy little .txt lists on my desktop, I've started collecting parts for a 12a blowthrough build. I'm using an S4 turbo and a Nikki carb that I'll be boost prepping myself. The car is an '85 GSL stock port with 128k. Here's the parts I have or have ordered so far:

S4 turbo, ported scroll
S4 turbo manifold
S5 FMOC
FMIC, 25" x 12" x 3", 2.5" in/out
2.5" intercooler pipe kit
Autometer 20 psi boost gauge
AEM EUGO Wideband 02
SuperNikki

And my list of things I still need:

Walbro 255 inline pump
Mallory 4309 FPR
Carb hat
Exhaust manifold of some sort
Custom exhaust
New plugs (NGK 9's???)
Oil lines
Battery and coolant overflow relocation
Locked dizzy

Anything I'm missing? I've got some events coming up so I want to keep my car in running condition for as long as I can before I start pulling stuff apart. I have an oil change to do soon so my plan is to install the FC oil cooler and tap oil pan and front cover for the oil lines while I've got it drained. I can plug those up until it's time to boost and enjoy lower oil temps in the meantime. This brings me to my first question for the 12a turbo experts:

Where should I run my oil feed and drain lines? If anyone has pics of their setup it would be most appreciated.

Second question for anyone whose run an FC turbo, what do I do with the coolant passages? Can they be blocked off or left open?

Third question has to do with boost prepping the Nikki. I've got the general idea and I've done my fair share of Nikki mods, but I'm not clear on what I need to do to reference the bowls to boost. Is there a certain place I should drill holes?

I'm not shooting for big power here, at least not initially. Maybe 150rwhp or so. I'm going to keep boost down to around 5 psi while I get it tuned and ultimately shoot for 10-12 psi. Any help from those who have traveled this path before would be greatly appreciated.

coldy13

For the oil feed line you can use the oil pressure sensor fitting, put in a T fitting and use one outlet for the feed line and the other for the sensor. The better way is to get an adapter block that goes underneath the oil filter, I believe racing beat and re-speed sell these. For the oil drain you can weld a fitting onto the oil pan, or drill and tap the front cover just below the OMP, I'll try to get a pic of this on mine.

If you're not using the coolant passages on the turbo, you can just leave them open, no need to block them off.

Nothing needs drilled on the nikki carb but there is one solenoid you need to leave connected.

LizardFC

iTrader: (1)

Thanks! I'll go with the oil pedestal approach. I saw that on someone else's setup and it looked pretty clean. My omp is disabled and needs to be blocked off so that sounds like a good spot for a drain. So that's a couple more things to add to my list.

I'm guessing the solenoid I need would be the vent solenoid? That one and the richer solenoid are the only two left on my carb.

85Gen1

I just finished my 12a blowthrough set up the link is in my sig i you want to take a look, i have some pictures on it that might be helpful, BTW 12a turbo kits are a pain in the *** but they are very rewarding when they re complete so dont give up! mine took about 4 months. you can pm me with any questions and i can try to help you out.

i feel my walboro 255 is a little too strong for the application because mine is pretty close to yours. i had a hard time getting my FPR correct. Good luck!

coldy13

Are you still using the stock fuel return line? That pump should be fine, but you're probably overflowing the return line at anything other than full boost. I had the same problem until I ran a new larger line for the return. You could also use the stock feed line as the return line and run a new line for the feed, or just upgrade 'em both while you're at it.

85Gen1

i am running a much larger return fuel line and the problem was fixed. i wasnt sure if yours was larger or not.

LizardFC

iTrader: (1)

I've been following your build thread. Good info there. What's your base fuel pressure at now? I'll probably have some more questions as I start digging into things, so thanks.

85Gen1

base fuel pressure at in the range of 3 to 5 psi depending on how it idles. if im correct your mallory 4309 is a 1:1 refrence. so if u run 5 psi at ful boost you should be 9 to 10psi. what jets are you using? i found out you can leave the primarys they handle it just fine but the secondaries have to be allmost doubble.

LizardFC

iTrader: (1)

That makes sense, I guess it really wouldn't need much more than the stock amount of fuel at idle. Right now, the way I have my carb set up is 105's on the primaries and stock 160's on the secondaries. I'm running redrilled stock jets, although I might order some Mazdatrix secondary jets.

I'm going to keep my primaries the way they are and still run larger secondaries, although probably not as large as yours. My hope is that running the larger primaries will help aid the accel pump in keeping the mixture rich as the secondary plates open. Even with a properly tuned accel pump, there is still a minüte delay in the fuel delivery as the unsaturated air in the venturis is pulled through the plates as they open. Since I'm running a manifold with a large open-ported plenum underneath the carb, having some extra fuel from the primaries in the plenum should reduce this effect and provide a smoother, safer transition. At least that's my hope, we'll see how it works in practice. There's still a lot of stuff I haven't figured out about the Nikki when it comes to higher than atmospheric pressures.

85Gen1

ya ill be honist there kidna confusing, they way i have heard people fixing the accelerator pump issue is enlongating the accelerator pump plunger.. though havent tried it but there is a thread on here somewhere about a guy doing that and i guess it worked.

LizardFC

iTrader: (1)

Lengthening the arm does mostly solve the problem, as long as you increase the size of the chamber along with it. But it's my understanding that the accel pump only operates with a significant "romp" on the throttle (someone correct me if I'm wrong). So it still leaves a gap when you're at part-throttle only using the primaries, and then ease into full throttle, which is a situation I encounter a lot in the mountains and during autocross.

I'm probably getting ahead of myself here anyway. I won't know how this thing is going to act until it's built. It may just explode when I turn the key

An update - I'm still in the "spend large amounts of money, wait for boxes to show up on the porch" stage of my build. Most of the easy stuff has arrived. Still waiting on my carb hat from Rotaryshack and I have to find a shop that can weld up an exhaust manifold for me. Another thing I ordered that can be added to my list is a RESpeed oil pedestal.

theNeanderthol

iTrader: (1)

The accelerator pump is active whenever you are opening the throttle, not only when you romp on it. You can slowly open the throttle and watch the accelerator pump "gently" squirt fuel down the throats. No matter how slow, the accel pump always works it's magic.

cshaw07

iTrader: (14)

my advice (as im currently building mine):
1. Expect to spend way more money than anticipated
2. Expect to do way more things to the car than origionally anticipated
3. Expect it to take way longer than anticipated
4. When your all done, forget about 1-3.

justinfox

iTrader: (3)

Prepare for an engine rebuild.

cshaw07

iTrader: (14)

^ nah

85Gen1

ya all of those are true but the end procust is so awesome. but plan on going over atleast 2000 haha thats how mine went

LizardFC

iTrader: (1)

Well this is good news then. I've already enlarged the jet by quite a bit and adjusted the arm for a longer shot, so I should be good.


I'm already in it about $800. I'm saving quite a bit of money by using the stock carb and doing the work to it myself. Final cost will depend a lot on how much I can have an exhaust manifold and system built. I might be able to use some of my existing setup since it's 2.5".

If it blows, it blows. But it's hard to blow up a 12a if you keep the mixture right. Mine is still quite strong at 128k miles. If it does go, then that's just an excuse to do some porting and reliability mods to go along with the boost.

85Gen1

haha thats the same mindset i have with mine. if it blows big port!

Oneiros

Re the accelerator pump, the only way you are going to get more fuel into the barrels is by increasing the AP displacement. Adjusting the arm and jet will change the RATE that fuel is pumped in but you are still using the same total displacement. So with the same displacement, a longer shot will give you a lower RATE of fuel pumped, meaning a leaner acceleration mixture.

The only way to increase the AP displacement is to max out the movement of the diaphragm. This can be done like Sterling suggests by adding extra gaskets, or you can also remove the metal stops that prevent the diaphragm from being pushed to its limits. IMO this is the only mod that needs to be done to the AP, as it maintains the same rate of fuel injected (same acceleration mixture) and increases the length of the shot.

Check this thread for a pic of ground down stops on the AP - https://www.rx7club.com/1st-generation-specific-1979-1985-18/nikki-carb-modding-964025/

Note you can also grind back the AP cover to increase movement in that direction also.

LizardFC

iTrader: (1)

I added a really thick gasket to increase the volume when I built the carb. If that's not enough, I'll pull it off and do some grinding as well. Thanks for the link.