An example of how to move forward

[Neil Harvey]

We are currently involved with a 2.9L build for 1975 car. The original brief was to increase the displacement, work on the friction, dual plug the heads, lower the component weights and just do a good efficient build. Most of these parts I have shown in my air-cooled development posts.

The original manifold was to be retained along with the cylinder head port configs. Valve sizes all stayed the same, just new guides and new seat inserts with better flowing seat profiles. We designed a brand new camshaft after flowing the rebuilt heads with the complete 1975 intake manifold attached including the filter and plenum.

This was no little task. The new camshaft required 4 designs, 4 masters made, 2 per lobe as the lobes are A symmetrical. New shafts, grind, mico polish then DLC. Not a cheap undertaking.

Then the customer decided to go full EFI. We looked at modifying his Mech. injected intake for EFI sensors etc. If we were to go full EFI, then use a newer intake system designed for EFI. FYI, we are in the middle of making up a kit so the original mech Injected manifold can be used with EFI injection.

We looked at what was available already without redesigning something ending up the same, at additional cost. We have a relationship with AT Power in the UK with some other current custom projects, so looking at one of their existing systems ticked most of the boxes. We gave some design changes we needed including runner shape and sizes.

We then ported the Intake side of the heads to match this new runner size. Today we reflowed the heads with this new Intake system attached including the filters that will be used. The flow numbers jumped over 50 CFM across the board.
This now changes what we need for the exhaust lobe profile to keep the intake flow ratio to the exhaust where it wants to be. We are starting to redesign the Exhaust lobe but have also decided to run the cam as we have and see what the end performance is. We do understand that we could have a wider power curve with a redesigned cam, but we also feel our new existing cam should make this engine perform very well.

So, this sort of thing can happen to us, too. My point is, as I tell a lot of people, design and engineer the engine on paper completely before starting any work or buying any parts. Changing mid stream only adds further unwanted compromise. Often it gives sleepless nights wondering, "should I have gone ahead and changed the cam".

The main consideration if you ever get caught like we are, is, understand the compromise as its easier to accept when you know what the cause and solution is.

[Neil Harvey]

[lvporschepilot]

Interesting stuff. I like they way it's all looking, but have to ask why go this far and not change port sizes?

[Neil Harvey]

We did. Maybe you missed it in my original post.

[jpnovak]

Drivelines should always be considered a full system. All decisions have additional impact down the line from air in to fuel in to exhaust out. I also include gear ratios and tire size as part of this puzzle as well.

When it is all matched it is bliss.

[Black 993]

Really interesting stuff Neil. Thanks for posting.

[Neil Harvey]

I have enough trouble trying to figure out things I think I know about.

I start poking around in gearboxes, springs and chassis stuff, I'll really screw something up.

Those black and round things at each corner of car are tires, right?

Back in my race days I used say to my team mates, stop putting those tires on the car, it gives the driver reason to go wear out the engine.

[Discseven]

Nice looking hardware Neil.