I need your comments on port sizes for hot rod 2.7
 

Hi,

I'm in the final stage of gathering parts for my engine build. I will have the heads at the machine shop next week. I read almost everything ; here, S registry, books,... and talk with builders ; but I'm taking a last chance to get your comments !

What will be the best heads port sizes for the following engine ?

2.7l (90x70.4) 7R case, PMO 40mm, Rennwerks Twin plug dist, JE pistons 10.5:1 CR, 46/40 valves (2.4T heads) MSD, DC60 cams, SSI, 2 out sport muffler, stock rods : red line at 7300 or so.

It will be a High Performance street engine in a stock body 70S, (but with all the upgrade : polybronze, monoballs, 21-26 tbars, 19/19 Torsion, Koni, Zimmermann, ...)

I was thinking 36/36 ; will it be too small ?? but I would like to maintain good torque curve at low rpms... YOUR RECOMMENDATIONS ??

Thanks for you time and advice !!
Regards
JD

"I would like to maintain good torque curve at low rpms... but I am going to use DC-60 cams."


define "good torque curve at low rpm"...

I know that DC60 go with high end performance, I also have a set of Mod S cams on the shelf... I sometime think that I should stay safe with them instead, but I also think I will regret the feeling of the wilder cams...

''good low end'' : I still want to be able to drive the car with my wife on the sunday afternoon ; cruising in back country road and some traffic lights to go to restaurant...

I may look completely lost, I know, there is no combination for everything... Just want to hear some feedback about ride you have or had with such an engine !

Regards
JD

well any 2.7 in a '72 will be more displ. than it had stock

what you really need is Vario-cam...

You want to use those Mod S cams, if thats the case. :)

JD,

Steve is right on the mark (naturally).
The DC60 is a cam that likes to really breathe in the 7500+ rpm range.
It does this at the expense of ‘civil’ driving in the 2500 – 4500 rpm range.

Use your ‘ModS’ cams.
You will enjoy the ‘coming on the cam’ feeling.
Match the 911T ports to your PMO manifolds and 40 mm carbs.
Remember to match the phenolic insulators also.

This should be a fun engine.
Enjoy.

Best,
Grady

just my take among the pros


the "medium" valve overlap of the mod-S cam connects me with the early Solex cam in function. If so then the Solex cam in a 2.7 was considered a great street cam with the right head work. What that means is beyond my pay grade except that the "correct" head work is important. Years ago Stoddard was prepping 2.7s engines for this cam, as was Competition Engineering in Calif. I'm not up on what's happening today except that CE is still around building superior high torque specific street/track engines and that Rennsport is one of the best engine/tranny builders in the US.

i'll readily accept that i'm wrong on the cams but i'll always buy in to the correct 2.7 head work, when pushing the envelope, by highly respected 911 engine builders

don't throw out the DC-60s right away -- drive the car for a while and if it is not exciting enuff....

or: put the DC-60s in and see if you can live with it re wife, Sunday drives...

when you get old, put the milder cams in and buy tires with higher sidewalls...

Thanks Guys,

That being said around the cams ; should I go with larger the 36/35, in/out ports ?

JD

I have a 2.7 with a GE40 cam, and Ollies opened my heads up to 36/35.
Sounds like your cam is a lot hotter though. I have 72e heads, and while
I don't know the original specs, from 70 to 120 mph my car runs like a
raped goat with the 36/35 heads.

From a low speed rolling start, with the original heads, I could hold off my
friends 88 911 turbo to about 80mph. After the heads were opened up, I
could easily hold him off to 110mph. When my buddy left me, he left me like
I was standing still. I thought it was a feet to hold him off for so long. The
head work, really turned my 3rd gear into a beast..