Custom intake manafolds

Josh · backyard mechanic Joined: 04 Oct 2001 Posts: 602

I am hopeing to build myself a new engine after i get my 3 points back on my lincence at about the end of the year... I want to build a straight LPG turbo 1.6L... Anyway would i be better off constructing the intake manafold out of 316 stainless steel or aluminum? i work in a fabrication shop with a mandral bender so making the runners shouldnt be a problem. Also what should i do with the water jackets/ports that come out of the head? I dont use the heater so would it be ok to blank the rear port off or does it have to connect to the pipe that goes to the front of the head.... I'v tryed to trace the way the water flows around the head and stock intake manafold but i get lost so yer any help is appreciated..

Josh (WA)

Getafix · tinkerer Joined: 16 Jan 2002 Posts: 146

A couple of things to consider between the two materials:

1) Aluminium will have a different thermal expansion coefficient than steel, could be a problem

2) Depending on the grade of Al (very important), Al "ages" at low temperatures (~60 C) so over time, it will have completely different mechanical properties as it did when you first put it in. Again, depending on the grade, it may start to embrittle

3) Al tends not to be able to plastically extend as far as steel (strech), so depending on the shape, the Al may crack.

4) Stainless steel is heavier, dunno if it would be a huge difference in weight considering the size though

5) 316 Stainless is pretty good for corrosion resistance (a step up from bog stock 304)

-Id go for steel for all mechanical and important parts, especially if youve got a nice bit of 316 lying around. sorry for the long post.

TimD · tinkerer Joined: 04 Mar 2002 Posts: 456

also, SS is more brittle than mild steel and will crack before mild as well something to think about

NUT161 · tinkerer Joined: 30 Dec 2001 Posts: 225

the forces that a manifold has on it when in use are no where near the forces it takes to damage/break the steel, as long as the welds are good u should have no problems with the Al or SS.

Ben Wight · backyard mechanic Joined: 04 Oct 2001 Posts: 946

Myself and friends have always used aluminium. 10-12mm thick plate for the header plate, (the bit that bolts to the head) CNC routed. and about 8-10mm for the throttle body plate. Joined by 1.6 wall thickness tube.

From memory, the water flows from the pump where it pressurises the head. The water port at the back of the head has to stay there, as it circulates water through the head and back to the pump. The pump pulls water from the bottom of the radiator, and pushes it through the head, through the thermostat, and back into the top of the radiator.

One thing I have done is block the port on the back of the head, and drill out the existing hole at the extreme rear of the head. This has the benefit of not needing to incorporate that middle rear port into the manifold design, and better water circulation through the head. I simply threaded a 3/4" barbed fitting with 1/2" NPT thread into the hole with a sealer to stop any weepage.

Ben Wight

Josh · backyard mechanic Joined: 04 Oct 2001 Posts: 602

Thanks ben... i'll probley go aluminium for the intake and theres heaps of 8mm,10mm,12mm and even 16mm laying around at work. Should I attempt the turbo exhaust manafold in stainless steel? What size turbo should i be looking for??? They arnt as expensive as I thought. And would a 500cfm Gasresearch carby be big enough?

Josh (WA)

GasGem · backyard mechanic Joined: 05 Nov 2001 Posts: 755

Hey Josh,
have a look at my car below, it is simular to what you are decidiing to do,

http://www.hotgemini.com/cgi-bin/gallery2.cgi?action=sv&vid=235

my car is using a GRA 350 CFM, and runs fine,

Also the stainless pipe work was done by Grant from Per4mance in welshpool/kewdale WA, really good job he also supplied the Turbo while I was there, have a chat to him, he has a mate who is really good with LPG and GRA,

for a turbo a GT25 or GT28 would be plenty big enough, and my exhaust manifold is made from steam pipe,

Cheers
Eggy

Ben Wight · backyard mechanic Joined: 04 Oct 2001 Posts: 946

Josh,

If planning on running a GRA throttle body, as Eggy said, he is making great power with a 350cfm unit, so a 500 will be more than enough.

Another thought, something which Eggy might be doing, I cant remember, is using a 2.6 4ZE1 inlet manifold and bolting the GRA throttle body onto that, it would save making one, but for you, probably wouldn't be any cheaper.

Stainless would be fine for the exhaust manifold, but even mild steel exhaust mandrels will do, providing it is designed well, or braced for support.

As far as turbo size goes, I have a little philosophy, that is a bigger turbo makes more power. Unless you have heaps of cash to spend on a late model turbo such as a GT unit, like a GT25 or GT30, then get at least a T3 spec unit, there are many available. Dont restrict the engine to using a small T2 or T25, even though they may be cheap. VL comodore, RX7, nissan FJ20 and VG30 all have similar spec units and will work great.

TXcoupe · petrol head Joined: 05 Oct 2001 Posts: 1675

hey u ever done the Stromberg WW carby swap or even thort about it for the gemini?

GasGem · backyard mechanic Joined: 05 Nov 2001 Posts: 755

it's not a 202!

Ben Wight · backyard mechanic Joined: 04 Oct 2001 Posts: 946

I've thought about it, but never bothered as I have had single downdraught webers that flow more. It is exactly the same procedure though, as far as I know, an adaptor plate is not available off the shelf.

One could easily be made though, but the carb might hit the thermostat housing, much like a 350 holley would.

Ben Wight