2.4S engine upgrade options

[thback]

From Wayne's book, I read there are four options there are with a 2.4S engine upgrade (need to rebuild the engine, so now's the time to make a choice):

1) remain bone-stock 2.4S
2) 2.4S base w. 2.2S pistons High Compression
3) 2.4S base w. 2.7RS p/c
4) 2.4S base w. 2.7RS High Compression p/c

Unfortunately, Wayne mentions a "huge difference" in performance, using the 2.2S piston upgrade, but mentions nothing on the HC 2.7RS performance increase.
In the book, he also mentions it's possible to use all the standard 2.4S stuff on the 2.7RS HC; is that so?

Any experiences / opinions on these engines?

thanks!

[Trackrash]

Motors built after '71 had lower compression ratios. Thus the 2,2 piston upgrade.

If you want to go with a 2,7 (90mm RS P&C) that motor only had 8.5-1 CR.

I guess you will want to get 90mm cylinders and use something like a JE piston to get the CR.

If you use 90mm cylinders you will have to bore out the case spigots and heads for the larger bore.

If it was me, I would either go with a high reving, high compression 2,4 or if you are OK with machining the cases for larger cylinders, go to a 92 or 93mm bore, and a 9.5 CR. The next step would be dual plugs and even higher CR.

I know a guy who has a 2,9 built on a 7R case with dual plugs. It is a real screamer.

The biggest decision, aside from the budget, is weather or not to bore the S case. Might be a better idea to just start with a 2,7 and save the S case.

[thback]

thanks Gordon, will use another pair of 7R cases, so not cutting the original, matching ones. But want to stick to a factory original set-up, possible within the 2.4S base (as Wayne Dempsey described).

Trying to get more info on the 2.7RS HC option; If high compression is offering so much more HP on the 2.4 with 2.2S pistons, why isn't the high compression doing the same on the standard 2.7RS? Or is it? Wayne mentions the upgrade, but gives no in-depth info (or HP/torque gain).

T.

[Trackrash]

The 2,7 RS was rated at 210 HP. There are guys running much more power than that out of 2,7s or 2,8s.

[Nux]

I would contact LN engineering who offers slip-in Nickies. No need to bore the case. Maybe they have 90mm (or similar) slip-in for your project?

[MST0118]

If it were me, I would not bore case if it is a true 2.4S case. I like the higher compression option. Not sure if you can go 2.5 slip in. If so, maybe 2.5 bore with 9.5 compression?

[thback]

I have '74 7R cases, so not cutting the original ones. And the '74 are already 2.7 sized.
Looking at a Mahle 2.7 high compression set, don't want to go 2.8 L. But want to know what's required (other than 2.4S components) and what the HP/TQ gain is.

[jpnovak]

Target a 2.7 with 9.5-ish CR with a DC40 cam and you will be quite happy.

The induction system and exhaust will play a big part in the overall results. Are you moving over the original MFI? Are you considering EFI or maybe carbs?

Just remember, The engine and transmission have to work as a complete package. Its not just displacement and compression ratio that define the car driving characteristics. Make sure you plan all of it according to your driving style, road types, and expectations.

[Walt Fricke]

My 2.7, with Mahle 10.5 (nominal - using the Whistler to check CR showed less than that, maybe 10 max - I didn't write it down at the time but was disappointed) pistons, an Elgin 315 cam, Weber 46s, ported some, and a so so set of headers with stingers, dynoed at about 220 RWHP. Twin plugged, so ran on pump premium. Showed I was OK at assembly, not so good at design.

If I resurrect this sand cast engine, I'd run EFI, and maybe bump it up to 92s/2.8. I think the mag cases would be worrisome, though you save some weigh and cost.

[thback]

plan is to transplant all from the 2.4S into 2.7RS HC. So, yes, including MFI , induction, stacks, cams, etc. Want to keep it as "stock" as possible (no experimenting). Not looking for absolute maximum output, but max. within 2.7RS. Exhaust is another question I have (recommendations, etc.) but will keep that for different topic. First want to get more info on the 2.7RS HC, which doesn't seem to be much around?

[Trackrash]

If you have Bruce Anderson's Porsche 911 Performance Handbook there is some discussion about 2,7s. The reality is the 2,7 RS motor was nothing very special. It was an MFI S motor bored to 90mm.

Good advice above. If it were me I would plan on 9.5 or so CR. I've seen that a 92 or 93mm bore will give a big boost in performance over the 90mm 2,7 size.

You will most likely need to have some 2,7 cylinders redone and you will need custom pistons anyway so 92 or 93mm bore is really a no brainer, IMO.

Any heads from 2,2 - 2,7 will work, you will just need to match the port size to your MFI. Although the 2,2 and 2,4s will need to be bored.

Any of the cams listed above would work well for your motor.

The stock 2,2 - 2,4 exhaust is a match for your motor. I would add a sport muffler and use K&N air filters. That can give you around 10hp over stock.

Of course, if you want to take it to the next level dual ignition and 10.5-1 CR would add some more HP.

The biggest issue is getting a good mag case then doing the machine work it may need to get it in spec.

You can search around this Forum. There has been much discussion here.