Advice on Inlet Port sizes

[CroS13]

I  have a spare L28 that i plan on sending off to get rebuilt one day not anytime soon, I would like the motor to be stroked and i hope to have head work done.

 

I have the standard L26 in the car, and im in the process of fitting Gareth's old blackbird carb set up to it. I am making a custom 1 piece manifold for it.

 

I know it might be hard to give a exact figure, and i know i should really choose and engine builder and ask what their specs are, but when having a head ported, what is the typical size they open up the inlet ports to? standard they are 35mm.

 

I need to know, as i plan on match porting this manifold to the new motor, but also using it on my stock L26.

 

Here is what my flange looks like on the spare L28 now:

 

 

as you can see, i already need to smooth out the edges in a few places.

 

Currently the inlet port on the flange is drilled to match the factory head at 35mm.

 

My plan is:

 

If typically the ports are enlarged to 37mm (for example) , i will open up the holes to 37mm on the flange, bolt it to the L28, and scribe the new port sizes into the head.

 

Then i will bolt the flange to the stock L26 engine in the car, and i will match port the head of the stock motor, only to make a smooth transition from the 37mm inlet manifold to the 35mm inlet port. so i don't have big right angles to cause turbulence in the head. This way i can at least have my carbs working on the standard engine until i get my spare motor built.

 

I am trying to work this out now, as when i weld the runners to the flange, i wont have any way to do it.

 

Rudolf.

[luvemfast]

I'm sure someone like Peter Mac can go into detail further.

But..........

I think what you're proposing isn't going to work.

Build it for how it is now and mod it in the future.

[C.A.R.]

I  have a spare L28 that i plan on sending off to get rebuilt one day not anytime soon, I would like the motor to be stroked and i hope to have head work done.

 

I have the standard L26 in the car, and im in the process of fitting Gareth's old blackbird carb set up to it. I am making a custom 1 piece manifold for it.

 

I know it might be hard to give a exact figure, and i know i should really choose and engine builder and ask what their specs are, but when having a head ported, what is the typical size they open up the inlet ports to? standard they are 35mm.

 

I need to know, as i plan on match porting this manifold to the new motor, but also using it on my stock L26.

 

Here is what my flange looks like on the spare L28 now:

 

 

as you can see, i already need to smooth out the edges in a few places.

 

Currently the inlet port on the flange is drilled to match the factory head at 35mm.

 

My plan is:

 

If typically the ports are enlarged to 37mm (for example) , i will open up the holes to 37mm on the flange, bolt it to the L28, and scribe the new port sizes into the head.

 

Then i will bolt the flange to the stock L26 engine in the car, and i will match port the head of the stock motor, only to make a smooth transition from the 37mm inlet manifold to the 35mm inlet port. so i don't have big right angles to cause turbulence in the head. This way i can at least have my carbs working on the standard engine until i get my spare motor built.

 

I am trying to work this out now, as when i weld the runners to the flange, i wont have any way to do it.

 

Rudolf.

 

[dat2kman]

It is an art of blackness and skullduggery.

There is smoke and mirrors involved.

Much cursing, some whistling.

 

Use the Gasket, Luke, the Gasket, and may the force be with you.

 

 

Those that have done it for years, have a "feel" they can slide fingers in, down, around, know where to, and where not to, remove.

 

Do ensure you dowell the intake and exhaust flanges to the head, do not rely on the loose sloppy fit of the studs or bolts.

Oh, and helicoils are your friend.

[d3c0y]

Most of the gains are on the exhaust side and if you are going 37mm watch out for those water jackets!

[CroS13]

Most of the gains are on the exhaust side and if you are going 37mm watch out for those water jackets!

 

I'm not necessarily going 37mm, it was only an example to explain what im trying to do.

 

I am not planning to port the head myself, especially the spare L28. I wont touch that motor.

 

All i plan to do is match the L26's stock ports to my inlet manifold, which will be made to suit the spare engine.

 

Dat2kman- Good idea, the gasket will work, machine the gasket to match the L28 when it is built, and bolt it up to the inlet manifold and use it as a template.

 

Rudolf.

[1600dave]

Those that have done it for years, have a "feel" they can slide fingers in, down, around, know where to, and where not to, remove.

 

I think I saw that in a porno once ??

 

From my very limited / amateur porting attempts, what you're proposing isn't very practical. The person doing the porting probably won't remove exactly, say,  2mm from the port and probably won't remove material in a "concentric" manner (ie they may remove 3mm on one side, and 1mm on the other side) depends on how they want the finished port to look, where the water jacket is in relation to the port, etc, etc.

 

What's your flange made of ? Alloy ?

[CroS13]

I think I saw that in a porno once ??

 

From my very limited / amateur porting attempts, what you're proposing isn't very practical. The person doing the porting probably won't remove exactly, say,  2mm from the port and probably won't remove material in a "concentric" manner (ie they may remove 3mm on one side, and 1mm on the other side) depends on how they want the finished port to look, where the water jacket is in relation to the port, etc, etc.

 

What's your flange made of ? Alloy ?

 

I guess the best bet will be choose a engine builder and talk to them first.

 

yes its alloy, currently its 16mm thick and is a rectangle block so hopefully it wont warp much when  the runners are welded on. After that is done, ill cut out the template for where the exhaust will sit, and get it milled flat down to 12mm to suit the headers flange, so i don't need stepped washers for the studs that share ports.

 

Rudolf

 

 

 

 

 

 

[luvemfast]

yes its alloy, currently its 16mm thick and is a rectangle block so hopefully it wont warp much when  the runners are welded on. After that is done, ill cut out the template for where the exhaust will sit, and get it milled flat down to 12mm to suit the headers flange, so i don't need stepped washers for the studs that share ports.

Not conviced thats going to work 100%. Think there will still be some warpage.

You may be better off milling down face, checking thickness and spotfacing where the washers will sit, making it 12mm thick.

[Riceburner]

When I did my alum manifold for the FCR carbs I bolted the flange to a spare head to try to stop any warpage. Worked very well, the flange didn't need any surfacing after, probably depends on how it's welded too. My flange was 16mm thick to match the stainless headers.

 

Simons idea sounds really good.

 

 

[peter mc]

There are big port gaskets out there we have them in stock , there 40mm , all our race ports are 40mm on the big engines , but as its a road car 38mm is about it , ,make your inlet 38 and you will be fine