Multi-Discipline Racing Engine

[j_green]

I'm building my '74 right now to run in both ARA rally and hill climb events and I'm trying to put together an engine plan to work towards over the next year or two. Would love some advice from those of you who have more experience in this department.

Currently I have a 3.0 from an '83 SC that's been converted to EFI and a fuel system that should be able to support up to around 450ish WHP.

Ideally I'd like to just have one engine with potentially multiple setups (e.g. an N/A setup and a turbo setup, or small turbo and big turbo, N/A and supercharged, etc)

For ARA looking at the current rule book displacement is a bit tricky with the displacement caps and weight minimums... which makes me think staying N/A is the better route.



For hillclimb it's much less restrictive:

C. Rally Two Wheel Drive (2WD)

a. All two wheel drive with engine displacement limits of 3.5L if forced induction, or 6.3L naturally
aspirated.
b. Not required to run turbo inlet restrictors or restrictor plates.
c. No minimum weight

Eventually the plan is to run this car in the Pikes Peak Hillclimb, and even with that aside altitude is real consideration for where this car will generally be competing so that's why I want to figure out a turbo setup.

So at this stage really just looking for good ideas, what would you buy/build if you were in my shoes?

[Jeff Higgins]

With any combination that makes good power when normally aspirated the compression ratio will be too high to run it with any form of forced induction. With any combination that makes good power on forced induction the compression ratio will be too low to make any power at all when normally aspirated. I think the two are mutually exclusive.

[DonNewton]

In addition to what Mr Higgins has told you, you do understand that to run Pike, you'd be doing yourself no favors without a forced induction system.

[j_green]

I definitely do understand that, it’s kind of the crux of the matter here I think actually.

Here’s where I’m at:
If I keep the 3.0 and run it N/A I’ll be fine for rally, but leaving a lot on the table for hill climb and have no real shot at Pikes.

If I keep the 3.0 and go turbo I’ll need to significantly ballast the car to meet min weight for rally, but be in great shape for all the hill climb stuff.

The 2.6L cap in rally for the lower weight class is the sticking point, what would be excellent is if there’s a proven way to de-stroke a 2.7 to 2.6/2.5 or something. Then I could run that with a turbo and be set for anything. That’s just an example, but hoping for something that kind of solves for everything in that same way.

Appreciate your input guys

[stownsen914]

Agree that it would be difficult to build a race-spec engine that would be suitable for NA and forced induction. Compression ratio and camshaft selection are two key things that are very different for the two configurations. It could be done if you insist, you'd just be leaving a lot on the table in NA.

As for reducing the displacement of a 2.7, there are a couple options. Keep in mind that putting a turbo on a mag case engine might be tempting fate, as they are not the strongest. An earlier 2.0L aluminum case could be up to it, but they are $$$.
- Use a 66 mm stroke crankshaft from a 2L. This will naturally lower the compression ratio, so piston selection will become important.
- You could use smaller diameter P&Cs. I don't recall if 2.7L heads have a bevel at the outer edges of the combustion chamber. You'd need to check the diameter there and make sure the cylinder diameter doesn't go smaller than that. Worst case you could use 2.2/2.4L heads.

[faverymi]

Get 2 custom gear transmissions
one for each event
play with tire diameters too.

[j_green]

Originally Posted by stownsen914

Agree that it would be difficult to build a race-spec engine that would be suitable for NA and forced induction. Compression ratio and camshaft selection are two key things that are very different for the two configurations. It could be done if you insist, you'd just be leaving a lot on the table in NA.

As for reducing the displacement of a 2.7, there are a couple options. Keep in mind that putting a turbo on a mag case engine might be tempting fate, as they are not the strongest. An earlier 2.0L aluminum case could be up to it, but they are $$$.
- Use a 66 mm stroke crankshaft from a 2L. This will naturally lower the compression ratio, so piston selection will become important.
- You could use smaller diameter P&Cs. I don't recall if 2.7L heads have a bevel at the outer edges of the combustion chamber. You'd need to check the diameter there and make sure the cylinder diameter doesn't go smaller than that. Worst case you could use 2.2/2.4L heads.

This is super helpful, thank you!
Hadn't considered that the 2.7 were mag case, I'd rather not grenade this thing so that option might be out.

Starting to think that maybe my best bet here is to just stick with the 3.0 as-is for now and start building a turbo 3.2 over the next year or two specifically for pikes. It'll take me a while to try to qualify either way, so no time lost doing so.

[j_green]

Originally Posted by faverymi

Get 2 custom gear transmissions
one for each event
play with tire diameters too.

This kind of got me thinking, with the plan above (building the 3.2). I need to re-gear and get an lsd for my 915 either way, so doing that first and pairing it with the N/A 3.0 then in the meantime I might go for broke and get a sequential to pair with the 3.2.

With that as the end goal, I wouldn't be too worried about having to ballast the car with 2/300 lbs for rally

[jmz]

Changing and engine is quick.

A 2.6 turbo sounds bad ass though.


Search up about a user that just did a turbo 2.7 with strong results. ~415hp