Tech:Engine/K Series/Boosted K motors

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Due to popular demand I am going to endevour to write up a new section here for boosted K motors.

This is going to be a work in progress and may take me a little while to complete it so please bare with me while I get it done. Once its completed this message will be deleted.

Cheers, Si (Taz_RX)

Firstly, obviously there are two way to build a "Boosted K motor" by using a turbo or a supercharger. For deffinitions or how each work (if you don't know and are intersted) please do a wiki/google search.


What to use: The most common superchargers used on K motor are Toyota SC12 (4AGZE) and SC14 (1GGZE) units. These are readily available from import motors, wreckers etc and are quite reasonable priced. Others have used other SC's like the AMR300 or AMR500 however both of these units are quite smaller compared to the SC chargers. This isn't to say they won't work though, its just by the time you get up in the revs a bit the small capacity of the charger may restrict top end flow. At the other end of the scale you could use a bigger charger like and Eaton M series (M90 from S pac supercharged commodore for example) which geared correctly could give great top end flow, however some boost lag would be expected in the bottom end of the rev range. Choosing the size of the charger, and the gearing used is just like picking a cam shaft or turbo A/R ratio. It really depends on what you want to use the car for and where you want your power range.

How to mount it: The easiest way to hang a SC off a K motor is to source yourself an air-conditioning bracket off any K motor. With a few minor mods to the bracket and/or the charger itself you can mount the charger in the position normally occupied by the A/C pump. As the mechanical fuel pump attaches to the block inside the A/C bracket, removing the pump and blocking its mounting point with a plate would be required. You should be upgrading your fuel system anyway so this won't be an issue. As the geometry on how the charger is mounted (compared to stock) some custom pipe work to the inlet and outlet would be required to suit your application.

Connecting a belt: K series motors use a "V belt" and most SC's (including Toyota SC12/14) use a "Ribbed belt", obviously this poses an issue of getting drive to the SC. You either need to convert the pulley on the SC to V-belt, or convert the existing K belt arangement to ribbed-belt. Another thing to bare in mind when choosing this setup is the fact that the Toyota SC12/14 have a electronically activated clutch pulley. If you want to retain this clutch (to be able to de-activate the SC) you'll have to get a bit crafty with the belt setup. As my personal experience is with turbos not chargers I'm going to PM some members here and ask how they went about the belt setups. Hopefully I'll have a run down of how to use both V-belts or ribbed-belts once I've heard back from these members.

Response from Kickn5k: (V belt to S/C) I haven't changed from v/belt yet. I made a custom blower pulley in v-belt and ground out the three rivets on the STD clutch hub and then tapped pulley. To do it that way I have to bolt the pulley on first with the lock nut 4 bearing, then bolt the clutch hub onto it. This way you don't need to cut a spline in the pulley and it's also quite stable load wise which means you can run the belt a bit tighter and not damage the blower driveshaft.

Response from 1jzke55: (Ribbed belt to S/C and V belts for alt & water pump) We turned up the custom alloy bottom (crank) pulley so it bolts up to the front of the harmonic balancer. This way you can still use the standard V belt to run the water pump and alternator. Once that was made, bolted it up and made the blower bracket and made a little tensioner out of a couple bits i had laying around.

If any member has some info on how to convert the whole pulley setup to a ribbed belt, please send me a PM with the info.

Gearing the Supercharger: I've copied and pasted to below info from a post by 1JZke55:

When fitting a supercharger, you should match the swept volume of the supercharger to the size of the engine. If the choice is made carefully, problems from overboosting and the required paraphenalia to solve these problems will be minimised. The supercharger will also be kept in its safe operating speed with correct selection.

To choose a setup you need to know :- 1. Engine capacity 2. Maximum engine speed you will be using. 3. Boost level desired

I am setting out the calcs needed for a 1200cc engine in the steps below.

FIRST CALCULATION (Engine Litres/min @ 0 Psi ) Multiply engine capacity (in litres) times maximum engine Rpm. E.g. 1.2 litres x 6000 rpm = 7200 litres/minute. Divide this figure by two as engine only fills every second stroke. (7200/2 = 3600 litres/min. This is the engines air requirements in litres/minute at 0 Psi boost.

SECOND CALCULATION (boost ratio) Add the boost pressure desired (7 Psi) for the engine to 14.7 Psi (atmospheric pressure). (7 psi boost desired +14.7 =21.7 psi) Divide this answer by 14.7 and this gives the boost pressure ratio. (21.7/14.7=1.476) This is the boost pressure ratio above atmospheric pressure.

THIRD CALCULATION (Actual air requirements @ desired boost)

Multiply the boost ratio by the litres/minute obtained for 0 Psi and you get the actual air requirements in Litres/min for the engine at that boost. In our example this is 3600 litres/min X 1.476 = 5313.6 litres/min for 7Psi boost.

To decide on the correct size of supercharger you need to know :- 1. The swept volume per revolution of the supercharger. (Eaton M62 1 litre/rev, SC14 from a 1G-GZE 1.5 litres/rev, SC12- 1.2 L/rev) 2. The maximum continuous safe operating speed for the supercharger. (Eaton M62 14000 rpm continuous, Toyota SC14 12000 rpm??) 3. The maximum pressure that can be safely produced by the supercharger continuously. (Eaton M62 12 psi, SC14 10-12Psi??? teflon on rotors melts??)

CALCULATION (Supercharger rotor speed) Divide the desired air flow (5313.6 L/min) by the swept volume of the supercharger (SC14 from the 1G-GZE is 1.5 litres per revolution). This will tell you the maximum speed the supercharger rotors must be run at to produce the volume required. 5313.6/1.5 litres = 3542.4 rpm for the SC14. 5313.6/1 litre = 5313.6 rpm Eaton M62

CALCULATION (Pulley size ratio) Divide the rotor Rpm by maximum desired engine rpm to get the drive ratio of the pulleys. For an SC14 on a 1200 @ 7psi boost the desired supercharger pulley ratio is 3542.4 /6000 rpm = 0.5904.

EXAMPLE OF CHANGE OF DRIVE RATIO If the 1200 cc engines supercharger pulley ratio is increased to 0.75 using the 1.5 ltr/rev SC14 charger, the volume of air produced when running to 6000 would be 6000 x 0.75 x 1.5 litres =6750 litres/min

Boost produced would be 6750 litres/3600 litres (at 0 boost) =1.875 boost ratio For Psi boost ((1.875 x 14.7) - 14.7)=12.86 Psi.

if you want to get even more technical the sc14 is actually 1.42

As 1JZke55 illuded to above apparently the Toyota SC12 and SC14 have teflon coated rotors and don't like being spun to about 14psi. I'm not sure if this is a shaft speed or general pressure problem but apparently the teflon can chip/flake off the rotors and cause a loss of compression. Hopefully somebody will read this and give us a definative answer!!!??? PM me (Taz_RX) if you do.

I have been PM'ed a response on this now and have been told: The rotors in the SC12/14 chargers are actually hollow. When spun above 12,000rpm the hollow rotors can expand causing the outsides to touch, this can then flake of the teflon coating. Info came from Toymods.

Plumbing the supercharger: Once you've got your supercharger mounted and you've worked out your drive ratio and pulley arangement, the next step is to look at plumbing it up. Just like a turbo you can run the SC in either "Blow-through" or "Draw/suck-through". Draw-through seems to be the most popular way on K series. This may be due to the fact that you don't need to ensure the SC has carbon seals like you do with a turbo to run fuel through it. Any carby that will provide adequate fuel/air flow (beit downdraft or sidedraft) for the application can be used in draw-through. You just need to make some sort of custom inlet to the charger so you can have a carby mounted off it. If this is the method used then the outlet of the SC simply needs to be plumbed into the intake manifold. For blow-through the inlet out the charger just needs some sort of air filtraion, and then the outlet is plumbed into the carby. Please see below for more info on blow-through carby setups.


Choosing a turbo: One of the single most important decisions you will have to make is choosing a suitable sized turbo. Yes it’s great if a mate donates a turbo for free or very cheap, but if it’s simple too big or too small for your engine it can ultimately cost you more by the time manifolds, water and oil lines, cooler pipes etc have been changed. It’s a good idea to pick a turbo that flows around the same volume of gas as your engine. For example if you have a 4k – 1290cc one of the twins from a GTR might work well. RB26 – 2600cc/2 (2 turbos) = 1300cc. Be aware though that most stock fitment turbos are quite small for the engine they’re on. This means you can have a bit of lea-way in the bigger side of options. For example I have used a T25, T28 and a TD04-L which are all off 2000cc motors, on a 1500cc 5k. You wouldn’t want to go too much bigger than these though. Yes a T3 off an RB20/25 would work on a 5k, but you wouldn’t get any boost until well into the rev range. At the other end of the scale you wouldn’t want to use the turbo off say a turbo charade at 1000cc. Yes it’ll spool mighty quick and probably give some great torque, but will really restrict flow in the top end – A mildly worked 4k with a cam would probably make more top end power. That leads into another factor to bare in mind – The size of the turbo will determine where you get the majority of your power. A smaller turbo like a starlet CT9 or ET/EXA T2 will give great response and midrange but will restrict top end flow. In comparison a WRX TD04 or S13/14/15 T25 or T28 may be a little laggier in the mid-range but will pull harder and harder the further you rev. By modifying the A/R ratio of a turbo you can change the response of the turbo, but I’m not going to go in A/R here. Do a wiki/google search if you’re interested in A/R’s. One last thing to keep in mind – Are you always going to be happy with the turbo you first pick? Or is the turbo you got cheap off ebay actually any good? You might find that at some stage you need to change turbos, so your initial flange choice can be important. Personally I chose to use a turbo with a “T2” flange. This gives me the option of using any T25, T25G or T28 from a CA18 or SR20. I then also have the option of using any internally waste-gated, bolt on upgrade turbo designed for a CA/SR like a GT25/60R, GT28R etc. As mentioned above EXA’s and ET also have T2 exhaust housing inlet flanges, as do the T25’s on 300ZX’s and T28’s on GTR’s however they all have slightly different dump pipe flanges. So the availability of replacement turbos and future upgrades is something you should be thinking about when you pick your flange type.

Connecting the turbo to your engine: There’s two main options when it comes to connecting a turbo to your exhaust system - Manifold or J-pipe.

When it comes to performance a properly built manifold is always the better option, unfortunately is also the most expensive. Any decent mechanic/exhaust shop should be to build you a manifold, however makes sure they’re aware of all of the constraints of your engine bay. Taking them the whole car or getting them to come to you might be a better option.

J-pipes are effectively an “adapter pipe” that allows you to retain the stock exhaust manifold, and as it is only one simple pipe they are a lot cheaper than a proper manifold. KE70 manifolds are the easiest to use for j-pipes as they have a single outlet. You could use a twin outlet KE55 style manifold but the j-pipe would be a bit more complicated and expensive. When using a j-pipe you also have a bit more choice on where you mount the turbo, especially if working in a tight engine bay. Don’t forget when mounting your turbo that you need to get a dump pipe and exhaust back out of the engine bay also!

Both a manifold and a J-pipe should be made of ‘steam pipe’. This is a more resilient metal which is designed for the high heat of the job. Mild or stainless steel just isn’t really suitable, as it can droop or crack over time. I also had a noticeable drop in response after a few weeks of using a mild steel J-pipe.

Another thing worth mentioning is the fact that K series manifold gaskets aren’t really designed for the increase in exhaust temperature. The main problem area is between exhaust ports 2 & 3 as it’s obviously the hottest. For this reason I strongly recommend AGAINST using a 2x piece gasket (ACL etc) as the two gaskets but up to each other in this problem area. If you have regular 4/5k inlet ports (un-ported) then the best gasket to use is a genuine Toyota 7kc one (not a 7ke gasket as the ports are different again). They’re a one piece, 3 layer metal gasket which is also re-usable. The next best thing is a Permaseal EM30. This is also a one piece gasket, that does only last around 6 months but is around a ¼ of the price of the 7kc item. The good thing about the EM30 is it actually has 3k big port sized inlet ports, so if using a 3kbp or ported 4/5k head they can be quite handy. I know one NZ member of RC used to make his own copper manifold gaskets, so this is always another option, no matter how big your ports are. The flange gasket where your j-pipe bolts on can also burn out after 6 months or so. I did want to try using a tempered copper ring to replace this gasket but sold my j-pipe setup before trying it. Another thing that might be worth trying is getting your j-pipe professionally welded onto the cast manifold to eliminate the need for a gasket here. Bracing your manifold or j-pipe back onto the block is also highly recommended. The 6x bolts that hold both the inlet and exhaust manifolds onto the head are only just adequate for the stock setup let alone the extra weight of a turbo.