2.4S to modify or not to modify?

[beginner]

Originally posted by curtisaa
After all...didn't the factory do that when it created the 73RS ??

Back in '72, factory had to drop compression ratio significantly due to strict US emission laws and also because US gas was crap 30 years ago, which is why they had to make 2.7RS to overcome the power loss. Today's fuel are better so CR can be raised.

[rst73]

The 2.7 RS built was MFI and was NOT intended for the U.S. market. The CIS 2.7 for 74 had the compression lowered so it would run decent with the CIS. Compression was being lowered in 72 because of the new unleaded fuel that was on the way and to keep the Cylinder head temps down.
"A 911 2.7 was planned in addition to the 2.4-liter version. It's output was to be 210hp, but except for its wider tires and rear fenders the car was to be identical to the 911 S 2.4." (Carrera RS
by Dr. Thomas Gruber & Dr. Georg Konradsheim, page 56)
My suggestion is to drive a RS spec engine and decide, it doesn't need to be in the high RPM range to get power like the 2.4S. Mine pulls real good from 2,000 all the the way to 7,200 in any gear. I can even start in 2nd gear from a stop without a wimper.
Another thing to consider is it still looks period correct and could be special ordered on the 73S. To me it's a win win.

All the best!

Roger Grago
R Gruppe #27
73 RS-T
70 2.4MFI VW Bus

BTW, Curtis I'm really going to have to push to try to keep up with that new 3.8 RSR motor going in your car.

[RSupdate]

[i]......If I had the $$ to buy an S, I would certainly would not be deterred if the "owiginal" case was made to 2.5, 2.7,2.8, or even like Daves' RS...2.9...

After all...didn't the factory do that when it created the 73RS ?? [/B]

Good point Curtiss.....Take Cain's 911S purchase as an example....
according to him, it has a factory RS motor riding in the back....

[ttweed]

Originally posted by rst73
The 2.7 RS built was MFI and was NOT intended for the U.S. market. The CIS 2.7 for 74 had the compression lowered so it would run decent with the CIS.

Roger-
Are you sure about this? The RS 2.7 and the USA (50-state) 911S and Carrera 2.7 with CIS for '74 both show 8.5:1 compression in BA's book. I think the power loss between the two was due to the milder cams necessary for the CIS induction, not from lessening compression.

TT

[rst73]

Tom,

You're correct, about the CIS motors for 74. Also the 73 1/2 911T
is included in this bunch. The power was down on the CIS motors due to the cam grind, port size, ignition timing, etc. But lowering the compression on the MFI cars had very little effect on the horse power although the stroke was increased for better low end grunt. And to help off set the lowering of compression for the unleaded gas.

All the best!

Roger Grago
R Gruppe #27
73 RS-T
70 2.4MFI VW Bus

[Bobboloo]

I'll throw in my .02 or should I say PWDs .02

Get yourself a nice core motor from a 74' 2.7 (pre thermal reactors) and use your induction to build an RS motor. Save your motor incase down the road you want sell and the potential buyer is persnickety on originality. This way you don't have to cut the case and you have a better starting point for an RS motor. If you can spring for it. Get the Mahle 2.9 P+C's 9.3:1(93mm) conversion. They are bolt on for the 2.7 case. If you go twin plug then get the 2.9 P+C 10.3:1 conversion kit. If your on a budget then get the Mahle 2.7RS P+C's. You can pick them up for about $1500.

Paul suggested the alternate case idea to me and it makes sense in my opinion.

This is what I would do if I wanted to modify. Otherwise I would just go stock since there's really nothing wrong with a 2.4S that's healthy.

[a911s]

If you consider that Chuck's '73S has RS flares and a factory ducktail already, then converting his 2.4 case to 2.7RS spec MFI seems alot more reasonable in my mind. Of course, Chuck driving my '72S with prior owner mods as per Roger's engine (as it stands now), probably has something to do with his current decision making process. I'm sure chasing Roger around for the last ten years hasn't helped either!

Anyway, my 2.7RS spec conversion on the original '72S case is holding up fine after 50K miles of thrashing.

Chuck, I say go with your heart buddy...

Randy Wells

[heirplane]

If you consider substituting a later engine/block, consider that the Calif. legislature is contemplating a return to smog checks for our cars. A check station will not be able to discern a difference between a 2.4 S and a 2.7 RS. Serial number will reveal a different year block too.

When I converted my 73 S case from 2.4 to 2.7, there was only a nominal difference in market value for T, E or S cases. FWIW

[pwd72s]

Originally posted by Bobboloo
I'll throw in my .02 or should I say PWDs .02

Get yourself a nice core motor from a 74' 2.7 (pre thermal reactors) and use your induction to build an RS motor. Save your motor incase down the road you want sell and the potential buyer is persnickety on originality. This way you don't have to cut the case and you have a better starting point for an RS motor. If you can spring for it. Get the Mahle 2.9 P+C's 9.3:1(93mm) conversion. They are bolt on for the 2.7 case. If you go twin plug then get the 2.9 P+C 10.3:1 conversion kit. If your on a budget then get the Mahle 2.7RS P+C's. You can pick them up for about $1500.

Paul suggested the alternate case idea to me and it makes sense in my opinion.

This is what I would do if I wanted to modify. Otherwise I would just go stock since there's really nothing wrong with a 2.4S that's healthy.

Thanks Bobby...What can I say? Other than I do know there are guys out there who wish they handn't cut their original #'s 2.4S case, in order to go to 2.7. Cases are (relatively) cheap...most of a rebuild cost goes beyond case cost. Just offering food for thought here...

[Bobboloo]

New un-numbered 7R 2.7 mag case, here in the UK cost £2800 GBP. How much is it at your side of pond...?

I wouldn't know. I wouldn't even know where you could buy one. However, used cases are not hard to find. I recently picked up a used 74' 7R case that has a good straight line bore for $225.