Supercharging my GJ on the cheap

[starfire]

Here is my 81 "yellowstone", or roadkill sigma. Its a minter, no rust, straight as a dye, and believe it or not is about to click over to 300000ks. 5 speed manual, 2 litre engine. I have always found it to be a little underpowered, Im not a racer, I just like cruising, but a bit more would be good. Last year I fitted the old style mag wheels, and lowered the front/rear a few inches. The front has Honda springs.... I forget which model, so no cutting or bodging required there. The rear I did cut the coils,.... the cut ends nicely hidden up inside the spring towers.... modified the bump stops, and fitted Holden shocks... these are very much shorter than the originals and keep the springs under tension when jacked up. One way to arrive quicker without getting a speeding ticket is to improve the cornering ability.

So, enter the SC14 toyota supercharger. The project had to be cheap, quick, and reversable, and have no bad effect on the engine. I decided on a simple blow through.... this allows just a simple bolt on without major changes. The first problem was room. I thought it may sit under the carby, but no such luck. I eventually settled on mounting it above the alternator. By using a longer vee belt, the alternator can be lowered a little to get it out of the way. The three unused tapped holes on the cylinder head front made for a strong mounting point, and gives the required belt tensioning pivot adjustment for the SC. The top SC inlet manifold was made from 2mm steel plate, the strength needed as it also holds the SC in position. The original SC outlet manifold was cut, and a U bend of 2 inch alloy tube welded to the stub, a small "crink" needed to clear the standard exhaust manifold.. Finally, the carby "hat" was made... this is a 10 inch length of 2X4 steel box section. A 2 3/4 hole was cut to fit the carby inlet, the original air cleaner bolt used to clamp it down to the throat with a plastic gasket ring. The ends were capped, the far end having a section of 2 inch steel tube to pick up the SC outlet. I also added a small bracket down to an unused stud on the rocker cover to support the end. Alloy box section would be nicer, but couldnt find any. This way, with the one fabrication, we get an inlet, a plenum, and a plenty of room to fit a BOV or other addons. It also gives enough clearance to close the lid! The front pulley was turned up from a alloy front hub from an old BSA motorcycle wheel.... I am not prepared to pay ridiculously high prices for simple pulleys. This fits inside the sigma original, and is held by the center bolt, 4 depressions in the hub fit over the bolts that hold the Sigma pulley to take the torque. This was the most difficult bit to make, took 2 hours. Im glad I did, the 7PK1220 belt cost $45NZ!!

Now, just a little bit about blow through supercharging.
SCs are a constant pressure device, the faster the engine goes, the more air it sucks, the faster the SC goes, the more air it blows. By and large the pressure, whatever it is will remain fairly constant as the engine and SC spin together. This all comes unstuck when the throttle is snapped shut. This will deadhead the SC, the air has nowhere to go, and will load up the SC, and the engine, and blow the butterflies out of the carby. Unlike a turbo, the SC can only slow at engine speed. We need a good relief valve. A normal type is not much use.... superchargers blow a huge amount of air.... always, and we need big orifices to dump it quickly. If we want say, 6 pounds of boost, all we need to do is set the BOV at 6 pounds. How simple is that? Mine is nothing more than a round disk of stainless, an old valve spring, a few washers and the adjusting nut . When the SC overruns, the BOV will open and spill air. As the pressure again reduces below 6 pounds, it will close again. There is no big deal with wasting the air.... its no good to us, and the SC power requirements are dramatically reduced when spilling... even at part throttle. Another more annoying problem with blow through..... the carb is subjected to internal pressure it wasnt really designed for. Fortunately with the emission reductions, carburettors since the late 70s had all the internal venting referenced to the atmospheric side of the butterflies. This means that poking 6 pounds into it, the pressure is the same to all internal cavities, therefore it wont spurt petrol everywhere, the Sigma carb included. This does mean that the float bowl is also 6 pounds above atmospheric.... the normal 4.5 pound fuel pump wont have enough push to overcome this, I have used a 9 pound electric.... this causes no problems as the needle valve assembly still only sees around 3 pounds across it..... 9 - 6 = 3. The electric SC clutch is a bonus, and there are several ways to work this. I will just switch it on and off manually. You could have a microswitch on the throttle arm, activating the SC automatically above say, 3/4 throttle, or put up with the added whine and hiss by having it on all the time.
Pulley sizes. The SC14 displaces 1.4 litres of air per revolution. The 2l sigma ingests 1 liter of air each revolution. Rough theory means that a 1 to 1 ratio should give a 5 to 6 pound increase over atmospheric. By overspinning the SC, and I believe they will run to around 10000rpms, higher boosts can be obtained. I have mine at around 1.5 over, not to get more boost, but to have more boost at lower revs, and spill the rest over 2000 revs. Blow throughs do have pressure limits, but I dont know what they are. ... depends on the carburettor I guess.


Theoretically at least, this method should not greatly affect jetting and mixture from standard. At the very least it will have a similar effect to opening the ports, bigger valves, and other breathing improvements without all the drama and expense. The pumping efficiency too should increase, as the engine no longer has to suck so hard. This is a current project, so will update this as I go. I got the new fuel pump today and will fit it some time over the weekend and try it all out. I also need a pressure gauge of some sort just to see Im not over doing anything.....
Ill get some new pics up later.

[smithdavidjames]

Interesting thread you have opened up here was thinking of doing the exact same thing to my GE sigma, all be it with the added complication of Gas Research LPG System. You've already mentioned a couple of things that hadn't though about so really keen to see where this goes, keep the experiences/pit-falls coming (plus photos would be great). This a couple of other threads here on with SC14s which blew the head gaskets at only 4psi so caution may be need at 6psi.

Dave

[starfire]

Today.... pissing down, dark too, almost like a nuclear winter! Took it for a shakedown cruise after fitting the new fuel pump. It pumps to 9 pounds and appears to work fine. Do these need a return line???? Instructs dont say.
Anyway.... Im pleased to report the car went NO better than before!!! I removed the inlet , and drilled and fitted a tyre valve fitting. Im too cheap to by a boost gauge, figured a tyre pressure gauge will work just as well. And, yes it did. ONE pound of boost!! I have completely overestimated the pressure I was getting, so will put a tighter spring in the BOV tomorrow when I get time and try again. Im spilling too much air. This also means my outlet hose needs to be far more substantial than what I have used..... it grows considerably in a very frightening way when revved, like an angry snake, ready to strike the unwary.


The BOV is seen here on top of the inlet box. The surface area of the disk is around 9 square inches, wanted boost is around 5 pounds/sq inch, therefore the spring needs to be around 40 pounds... NOT the 6 pound one I had! Maybe that will make a difference.... bloody hope so. The carby is behaving itself, no fuel leaks, and the new electric pump seems to be doing the raspberries. 5 pounds boost should see another 30/40 more horses. Yes, part of the above embarrasment was due to my concerns over engine damage, head gaskets, detonation, overheating........ I was being a tad cautious me thinks.
Here is a very interesting page on supercharging for those interested.... I should of read this first.
http://www.hiperformancestore.com/Magnu ... argers.htm

[starfire]

Another quick update. Redesigned the BOV with a modified valve spring.... we now have pressure, and LOTS of it. So much in fact it blew the fuel out past the accelerator pump plunger of the carby! I measured 8 pounds at around 2500 rpms. This leak is cured, I made up a simple sealing grommet from a small silicon rubber blanking plug. This is inserted , big end underneath, and cannot leak. pressure pushing it against the carburettor body. With the carby apart, I noticed the float... I was worried with this being crushed with pressure.... is made from a very hard plastic, so I cant see any problems there. A brass one would be a different story me thinks. So, one good test rev in the garage blew the reinforced plastic SC outlet hose to smithereens... a cost effective bend of 2 inch radiator hose should work fine.
..... looks like any further progress waits till next week..

[starfire]

Next week came very quick. Tidying my workshop unearthed a 2 inch bend of suitable rubber radiator hose. Now have full boost. Havent had time for a road test, but a problem has surfaced. The engine hunts when idling under boost, almost like a governor thing, and the blower outlet air gets HOT.... much quicker than I had anticipated. I think for the short periods I need to use it, this wont be a major. From cold, its warm after 30 seconds at 2500 rpms, and really hot after 1 1/2 minutes... probably too hot for good performance. I did have two cunning plans..... to plumb in the door sills as an intercooler, the few holes are easily sealed, but unsure if these are able to be pressurised because of the door pillars. If so, this will save a heap of time... I also have a rather nice radiator that I think can be pressed into service to cool the air and it fits quite well in front of the existing one. It has a 7 pound cap, so should have no trouble with 5 pounds or so of air..........to be investigated, it may constrict the flow. Funny what a tidy up will find. The BOV is far too noisy, this will need more work.... on overrun, the hissing is incredible.. boeing 747 stuff! I may need to vent it back into the SC inlet to quiet it down.

[A112H]

I am really enjoying reading this thread, you are much further down the track than I remember anyone on this site getting before, well done.

[starfire]

Thanks Jason. This forum stuff is all new to me, so Im just copying what others have done. I thought I was the only Sigma nut in the whole universe, but it seems not. To get the SC hooked up and running is only a days work really.... but to get it running right may be a whole different story!!

[A112H]

I think if it was something I was going to consider this I think I would go with EFI and pretty much pinch everything from the MR2 that I could including the cooler. Well done though, you will have to hit us with a video once it is running and sorted.

[starfire]

Today I finally had time to get this thing out on the road. The performance gains are very very pleasing, insert happy face here. I estimate another 50 horses easily. The acceleration is much improved, the rear breaking away on wet roads in second gear. and SC noise is actually lower than I thought, although it is obvious that something unusual is happening under the lid. The BOV noise is annoying, but the SC can be switched off during overrun, or even better, have the electric clutch wired to the throttle linkage I will do this, as well as a manual off/on. One reoccurring problem is fuel leanout, caused by low fuel pressure. After a 10 second thrill, the float bowl level is very low causing surging... I dont know yet what to do about this. The new electric fuel pump is at 9 pound pressure, the next one up is 70 pounds.... far too much for a needle valve and float to cope with. As for boost pressure, I estimate 4 to 6 pounds sq inch at full throttle, and the carburettor handles this fine with no leaks. SC outlet air temp remains low with short periods of boost, so in practice I dont think any additional cooling is needed. With the standard compression engine, no pinking/detonation has been heard, or any other unusual noises. I call this a success!!!


For the total price: ( New Zealand dollars)
1 x SC14 Toyota supercharger $250
inlet manifold $ 20
outlet manifold $ 20
plenum and BOV $10
ribbed belt $45
Crank Pulley $5
Hose $15
electric`pump $118
Clamps/bolts etc $10
total $493

Thats around $10 per horsepower not counting time ..... I think this was worth the 12 hours spent, and quicker/cheaper than multiple carbs, porting and other head work for a greater net gain. The complete installation can be removed in around 15 minutes and the car returned to original if need be.

[Superscan811]

After a 10 second thrill, the float bowl level is very low causing surging... I dont know yet what to do about this. The new electric fuel pump is at 9 pound pressure, the next one up is 70 pounds.... far too much for a needle valve and float to cope with.

It may be the flow, not the pressure that is causing the low level in the fuel bowl. it may be possible to open up the seat a little to increase the flow rather than having to go with a higher pressure fuel pump (as long as you are under 6lbs of boost).

Another thing to do would be to use 2 low pressure pumps in series. The first pump will boost pressure to 9lbs, the next would take the 9lbs on the inlet and boost it up to around 15lbs.
Grab a cheap $20 carb fuel pressure regulator and place it inside the plenum, it's now boost referenced.

Food for thought.

Cheers.

[starfire]

Thank you! Yes, I will try opening the seat and see if there is any improvement, thats a good idea. Im not an expert with modern pumps. Unlike the old SU pumps of years gone by, this one never stops ticking..... is this normal, or could it be faulty? Im unsure if it should have a bypass maybe, but this would further reduce its volume/pressure I would think. Its bloody annoying that its its just not quite there yet. The instructions dont mention anything at all.

[geezer101]

The 'ticking' must make it one of those solid state pumps. If you want to improve the fuel starvation situation, take the inlet barb off the carby and find a larger diameter one. Have a look at the fuel gallery behind the inlet barb and check the diameter in there too. If it looks like it's on the small size drill it it out to increase fuel flow from the inlet barb (yeah, it means taking the top off the carby to do this, but better than getting a bigger carby etc). I don't think it will require upsizing the fuel line as well. It should be able to handle the extra demand for fuel after these easy (and cheap!) mods. What carby is that you're using by the way? A hitachi or something?

[starfire]

The carby is the standard one, not sure what make/model it is, but has the wax pellet and water jacket on the side for the auto choke... removed some time ago. Thanks for those suggestions.... looked at it today, but no sign of any restrictions there at all. I did try running some air pressure from the plenum into the fuel tank via the now unused fuel return line to semi pressurise the tank... this helped... the thrill now lasts 20 seconds!! This I think confirms the pump is not beefy enough. Looking at the Airtex website.... the graph for my model pump also tends to confirm this. (EP8012) It will hit 9 pounds at no flow, and pressure rapidly declines as flow increases. Very misleading.... these things should have a poundage at a certain flow rate... no one uses a pump into a deadheaded pipe!! I will need to search for a suitably cheap alternative, or perhaps modify the old mechanical pump by increasing the return spring pressure.... not easy in a sealed unit!! These small nuisances are a pain in the arse. I will also try the other suggestion....feeding the electric pump from the mechanical pump in series.... this may increase the pressure a little depending on whats inside the Airtex.... if it relies on spring pressure then probably no improvement, but if the outlet is referenced to the inlet, it will add another 3 to 4 pounds.. The danger here is me ending up spending more on a pump and a regulator than the rest of the project cost!! I did learn many years ago with cars.... that satisfaction increases in an inverse proportion to money spent.

[Billsy]

if you can, try and get hold of a electric pump from a 80-91 subaru Carby, MY and L series cars.
theyre a pressure set positive flow diaphram pump that will flow more than the crappy click click pumps (although it also goes click click, its not the same)

[starfire]

A final update. Sorted the fuel problem, thanks to all the help on here! I fed the electric pump from the original mechanical pump, this has increased the fuel pressure sufficiently and works fine. Also bit the bullet and purchased a CHEAP boost gauge. After another trial run, discovered fuel seeping from the accelerator pump yet again.So, I rebuilt a Hyundai carburettor from my stockpile, and removed the accelerator pump entirely, filling the plunger exit hole with a silicon rubber washer and a small nut and bolt. Another test run, absolutely perfect, but the boost gauge was reading 7 pounds. A bit of thought, figured the second carby barrel was not opening. This uses a vacuum dashpot arrangement, Vacuum pulls the secondary open.... boost forces it closed!! A very easy mod ditched the vacuum servo, and I coupled the primary linkage directly to the secondaries... the secondaries opening at around 3/4 throttle and above. Performance now even better! Boost back down to 5 1/2 pounds with plenty of kick. The final job was to make a small bracket on the carby to activate a small microswitch... this turns the SC on at 3/4 throttle and above using the electric clutch. Jetting remains the same, fuel consumption at less then 3/4 throttle is as standard, above that, yet to find out. Outwardly, there is no visible sign the car is modified in this way, I have even not bothered to fit the boost gauge as it serves no useful purpose. The car pulls very nicely from 2000 rpms to redline, and except for the howl of the SC when engaged, it remains the nice quiet car its always been. The BOV is now quiet.... it doesnt do anything, when the throttle is shut, the SC freewheels and pressure drops immediately. All in all, a very satisfying and cheap performance gain without too much drama. The car can be driven very sedately, and when called upon, it lowers it arse into the road and with a screaming howl, accelerates forward without any hesitation. LOVE it!!

[Superscan811]

Now all we need is a vid (with audio of course) of the beast in action.

Great result BTW..

Cheers.

[A112H]

+1 for vids

[webby]

+2 for vids.
Sounds like it was well worth it man, nice work

[starfire]

Thanks for the encouragement everyone. Unfortunately, I only have dialup here, so a video is out of the question. What I will do though, is post some performance figures later on when I have clocked up a few miles. This way you can judge for yourselves , and maybe have a crack at fitting one yourself.... or even improve on it would be good! Thanks too for a very good website, LOTS of ideas here for us Sigma owners. Theres still a few left here in NZ. and some are in very very good nick too ... a really nice one will still fetch around 2-3000 NZ$$$

[ddt]

Sorted the fuel problem, thanks to all the help on here! I fed the electric pump from the original mechanical pump, this has increased the fuel pressure sufficiently and works fine.

Does the extra pressure from running the two pumps in series cause any issues when you have the supercharger switched off?

BTW, I really like what you've done here- I really like how essentially the engine stays stock

[starfire]

What I have done is connect both the SC electric clutch, and the added fuel pump to come on together. With normal driving, the mechanical pump only feeds the carby. So far, there has been no problems with this arrangement.

[starfire]

Here is the my process to modify the carburettor for blow through operation from a supercharger. This is an old carby I used to demonstrate how simple it is to do.

All these 70s/80s era carbys are similar in construction, the only two needed changes are the accelerator pump and vacuum servo that opens the secondary butterflies. First, lets ditch the accelerator pump.... this will leak, and is really not required, a slightly rich idle mixture will pretty much compensate for the omission..


Remove the split pin or circlip, and remove the rod linkage from the primary throttle lever to the pump lever. Remove the pivot bolt and remove the pump lever. Withdraw the pump plunger and spring after removing the top carby housing. Take a small bolt, nut and fibre washers, and blank off the hole through the top housing.

This will seal the plunger hole. Reinstall the top plate. Make sure the float is not bent or the adjustment is altered when doing this.

The vacuum servo must also be removed. Under boost, it will work backwards and try to close the seconadaries.


Remove the circlip from the servo actuator rod, undo the two screws and remove the vacuum servo. Now study the primary and secondary throttle linkage, you will see the secondary shaft is spring loaded via the linkage that was connected to the servo rod. The servo rod pivot point must be held in a certain position to allow the primarys to open the secondary without it going over center. A small aluminium bracket is made, like this. Measure this carefully , as the secondaries must not go over center else this will jam the throttles open.


It mounts where the original servo was held to the carburettor body by the two screws.

Once reassembled, double check for correct operation without jamming. A dab of grease will help smooth operation. The main spring that ensures throttle closure will need to be repositioned, as it was originally mounted to the vacuum servo bracket.

Thats it! The carby will now work under pressure without leaks, and the second barrel will open as designed, boost or no boost. All the carbys I have modified have worked fine, and have hard plastic floats that have not caused any problem with crushing under boost. The main throttle linkage can have an additional arm attached to actuate a switch for the magnetic clutch on the supercharger to engage it automatically as the secondaries open, this seems to be the best and easiest way of switching it to boost... there is no point having it boosting under 3/4 throttle in a blow through situation. Modified in this way, the SC will develop around 5 1/2 to 6 pounds of boost at full throttle, irrespective of revs. The BOV is required to spill excess air as the SC overuns when the throttle is suddenly closed.... it takes 1/2 a second or so to wind down when the clutch disengages. As the carby works as normal 99 percent of the time, jetting/ economy and performance remains unaltered. Under boost, the carby compensates by the extra velocity of air through the secondary venturi, the mixture here can be selectively altered simply by changing the secondary jet size only, I havent found this necessary. I have read on several websites that the magnetic clutch will be destroyed if engaged at higher revs. I suspect the biggest experts on many sites are the people who havent actually done anything, or have yet to get around to doing it. The clutch issue is total misinformation and can be safely ignored.

[Benharjon]

Great job mate, fantastic budget bonus hp!! And a super neat install... Love it!!

[Superscan811]

I have read on several websites that the magnetic clutch will be destroyed if engaged at higher revs. I suspect the biggest experts on many sites are the people who havent actually done anything, or have yet to get around to doing it. The clutch issue is total misinformation and can be safely ignored.

Too true.
The electric clutch is exactly the same as used on the air conditioner pump and they engage/dis-engage successfully at all rpms. It may well wear a bit quicker because of more use but they should still last more than a year or so with spirited use..

Cheers.

[starfire]

Well, nothing is as ever easy as you would like. After a few hundred miles, have figured my excessive fuel consumption is not totally caused by my right foot. Seems the car is running way too rich, and this is caused by having the carby sucking through the stationary supercharger during normal driving. There is enough drag to limit the air getting to the engine. So, another add on, finished today. I have built what is in effect a throttle body, a 2 inch diameter pipe with butterfly, this is mounted on the plenum. The idea is that this closes under boost, and opens during normal driving, bypassing the supercharger restriction. I have mounted the butterfly off center, in such a way that the boost pressure forces it to close automatically, and spring tension keeps it open at all other times. The car should now give me the 35 miles per gallon I was getting before I buggered with it. The new throttle body is big enough as it only needs to supply air for the primary barrel, both the primary and secondary supplied by the SC. So, add another $20 to the setup costs. Pics later.

[starfire]

Here are the pics of the bypass.
The small spring seen here keeps the butterfly open, and the alloy bracket keeps it on a very slight angle to allow the air to see it.





The butterfly is a bit obscured, but it is offset by around 3/8 inch, the larger side has more pressure under boost than the smaller side, so it closes automagically when the SC comes on. When the SC pressure drops, it again springs open.

[ddt]

so it closes automagically

Automagically! i love it.
What does the butterfly seal against?

[starfire]

The butterfly is an oval shape, slightly too big to fully rotate inside the tube, so when it closes, it seals against the walls of the tube. I didnt think this would work, thinking that if it was closed, the pressure would equalise over the whole butterfly causing it to open again. Sometimes its good to be completely wrong. I am often wrong and its often not good.

[bruggz351]

You are one cluey man...
excellent work...

cheers

[damian]

agreed