input please? a high-comp 2.4 or a low-comp 2.7

haycait911 · haycait911's Garage

I have all the bits to rebuild my 2.4 T engine into something as little funner. it will be MFI.
I have 2.2E pistons, giving me a 9.8:1 2.4. I also have a set of 2.7 RS pistons and cylinders, giving me a 8.5:1 2.7.

which way to go? any thoughts? thanks, Don.

Steve@Rennsport · 08-19-2010, 10:37 AM

Don,

What cams wil you use???????

haycait911 · haycait911's Garage

I have 'in-stock' a set of MFI 'E' cams, and a set of solex cams with an attached MFI drive . my thought was to use the E cams probably.

Steve@Rennsport · 08-19-2010, 02:26 PM

Do a 2.7,......you cannot beat torque.

Eagledriver · 08-19-2010, 07:09 PM

2.7 with the Solex cams. You won't be disappointed!

-Andy

Walt Fricke · 08-19-2010, 09:11 PM

Per Anderson:

The 2.7 Carrera RS was an 8.5/1 CR 2.7 with MFI. Of course the MFI was set for this, and it had the S cam. 210 factory HP at 6,300 rpm. 188 lbs/ft at 5,100.

The '72/3 S, with 8.5/1, made 190 at 6,500, and torque of 158 at 4,000.

Looks like the 9.8 CR might boost the HP of a 2.4 enough (a lot of guys put 2.2S pistons in their 2.4s back when) to equal the 2.7 you might build, but it would have to be at a higher RPM. But an equivalent boost in torque wouldn't equal the 2.7's torque.

Which I suppose is behind what Steve is saying. Plus I bet he built some high squeeze 2.4s when that was popular.

haycait911 · haycait911's Garage

well, my leaning is toward the 2.7. probably an easier/cheaper build as I have a freshly built more-or-less RS spec 2.7 that I need to tear down to fix a case half leak. I'd just need to machine the heads for the MFI and install my MFI cams, and it's good to go. I built my 3.0 for torque and I really enjoy the low end grunt more than a higher HP number at 7K rpm.

also, this would let me put the numbers matching mag 2.4 case on the shelf for posterity, and run the 2.7 case.

Flieger · Flieger's Garage

I thought I heard that Mahle makes a set of RS pistons and cylinders in 9.5:1 compression ratio? (Of course, Mahle measures their compression ratio with zero deck height, so 9.5 may be not much more than 8.5)

RoninLB · 08-20-2010, 04:50 AM

gas is crap and getting worse

my engine will run nicely on tweety bird piss from farm country although 2.7 9.8:1/9.5:1, MFI, and early solex cams is a party waiting to happen imo

Henry Schmidt · Henry Schmidt's Garage

I was faced with a similar question and chose to build a new engine spec for my own project.
I took the matching numbers 2.0 case from my 69 T and built a 2.45 liter.
Of course I could have built anything I chose but to keep it matching numbers so I really wanted to try something new. I hate boring early case out to fit
2.7 (90 mm ) cylinder.
The 86 mm cylinders slip into the case with no modifications.
The pistons are 9.5:1 JE and the cams are DC Mod "S".
I added a long stroke crank from a 2.4.
Because fuel will continue to get worse I chose to twin plug this project. "Over kill" but twin plug is cool if you have the budget.

Cupcar · Cupcar's Garage

The "10.4:1 high compression" Mahle 90 mm pistons came out at 9.9:1 for me in a 2.7 liter. This kit can be hard to find though.

BTW, IMHO, If you build an 8.5:1, 2.7 with forged RS pistons instead of a high compression 2.4 with E cast pistons, you won't regret it.

whackit · 08-22-2010, 07:00 AM

I run a carbureted 2.7 8.5:1 with e cams. It's super fun as a street car since it has significantly more low end torque than some of the "sportier" cams. I am really happy with the combination.

haycait911 · haycait911's Garage

thank's for all the input. here's the plan......

keep the numbers-matching 2.4 case on the shelf.

rebuild the 2.7 with solex cams. I'll drill and tap the heads for MFI as I have a complete 2.4E set-up. run the engine on carbs to get things dialed in. someday switch over to MFI.

Henry Schmidt · Henry Schmidt's Garage

Quote:

Originally Posted by haycait911

thank's for all the input. here's the plan......

keep the numbers-matching 2.4 case on the shelf.

rebuild the 2.7 with solex cams. I'll drill and tap the heads for MFI as I have a complete 2.4E set-up. run the engine on carbs to get things dialed in. someday switch over to MFI.

We built that exact engine for a customer about 6 years ago and it was a truly nice driving engine. There was considerable tuning required to get the MFI system to match the Solex cams but it was well worth the effort. The customer loves it.
enjoy