"ANOTHER" Virgin engine rebuilder needs some direction

[loosecats]

I read the post from vwbobd and I really liked the replies to Bob regarding his 71T engine rebuild.

I too, am a Virgin 911 engine rebuilder, and new forum user - Unlike Bob, my car/engine is a 73T (MFI)

The car is undergoing a complete (basically) Stock Restoration and therefore I want to keep what I assume to be the original engine in the car.
( "Schnee" and her History can will be seen in "My Garage" )

Notwithstanding the forementioned about keeping the car basically stock, I live in the Beautiful Rocky Mountains, and the 140HP just will not do

I have a long before gotten the advise to go with an "E" Spec rebuild vs. an "S" spec., since it will be an driver not a racer.

I have purchased Wayne's and Bruces books - and they are a wealth of knowlege, however they seem to be geared more towards race engines - not drivers.

Everyone that replied to vwbob's thread sounded like they have alot of knowlewdge so I thought I'd ask for some direction with my rebuild.

I am going to mod my engine, but not sure what combo to go with. I LIKE torque, ( My two favorite rides are my Audi RS6, and my Ducati 1098)

I was thinking of the 2.2 piston suggestion in Waynes book, but his favorite 2.4 mod is with "S" Cams and I'm leaning towards "E" cams ( Actually purchased some from Tom1394racing (registered forum user)

Now I'm curious about the Mod-E cams. And, now I'm thinking I should (might want to) go with bigger bore JE pistons with Biral's, but not sure how big???

Did I mention that I like torque? ( I think I forgot to Mention the HP thing I like that also )

Other stuff - I want to keep the MFI, and I know it will need to be retuned - so which is the best place to send it? I've heard of a place in the San Francisco Area, and I think there is one in the LA area? I know I can't have it tuned until I get my
engine specs figured out.

Also from reading this post and the books - I get the idea I need to keep my compression ratio down because of the street gas...

So any one with some optimum 2.4 engine builds??? The perfect equation?

Any advise would be appreciated

Thanks Much !

JC

[Flat6pac]

With the 2.4 T there are several combinations available. The biggest thing is in compression ratio. The T uses 7.5 cr, E is 8.0 and the S uses 8.5, all use regular gas.
Ports on the T and E are the same. Lots of the limits are set by the fuel injection. The pump can be metered differently but cost efficiency limits your throttles because there isnt enough plastic in the stacks to open and flow more.
Any of the engines of this size are not going to give you massive amounts of torque because of the volume/ size limit. Freely revving with higher compression and more butt horsepower gains are available to be enjoyed.

Bruce

[loosecats]

Bruce,

Thanks for your reply.

I am a realist on what I can achieve in low end torque from the little flat six.

Maybe I should just build an " E " spec engine but I have to think I can get more out of it than the 165hp -151lb/ft of the 2.4E.

Confused about your comment regarding the MFI Stacks - Seems I've seen lots of built engines running MFI. Is it that they are fully able to breath with an "S" type high end torque engine but not on the low end? Was there a larger MFI stack available? Any Aftermarket Stacks?

[tom1394racing]

JC

Be careful when you consider using 2.2 pistons with your 2.4 crank. The increased stroke boosts the 2.2 piston's CR up by about 0.5 over the 2.2 value.

2.2E pistons will give around 9.5 CR and 2.2S pistons will be around 10.3. Both are sporty for pump gas on single plug.

[Flat6pac]

I think youre confusing MFI with EFI. Your injection is MFI and was made through the early 70s EFI is the newer digital fuel injection made to run the big cubes.
The T throttle bodies have a lesser amount of plastic walls than the E and S so theyre not able to be opened for more flow.
Bruce

[Flieger]

Magnesium stacks can be bored out for the 3.0RSR race engines. You can make the MFI work for whatever horsepower, it just depends on how much you want to spend.

[loosecats]

Thanks for the input.

Bruce,

No, I wasn't confusing MFI w/ CIS - however you did tell me something I was not aware of - that the "T" stacks don't have the wall thickness of the "E" and "S".

Looks like I'm in the market for some new stacks...

Tom,
I agree, the 9.5 on pump gas would be a bit sporty.
Maybe what I should aim for is a 911/42 - 75S 2.7 spec. engine; 8.5:1 - 175HP - 175 lb/ft @ 4K.

That would mean new Crank and boring the spigot bores.

I think I'm gonna here that that the 2.4 case wont handle it...

[loosecats]

CORRECTION

Bruce -

I meant I wasn't confusing MFI with EFI (not CIS... I guess I had CIS on my brain)

But anyway, maybe I am?

What did the 2.7 RS run? MFI ?

[Wayne 962]

Drive an 'S' and then drive an 'E' car, and then decide. Nine out of ten people go with the 'S' spec each time...

-Wayne

[Eddyvdw]

Send your pump to Mike in Seal Rock, Or.
He has a MFI test and calibration set up.
Next to that he has tons of advice.
His Pelican name is 356RS.

I have an E engine (1973) in a T body (1972).
The original T pump is set to E specs.
Works beautifully.

Ed

[Flieger]

Originally Posted by loosecats

CORRECTION

Bruce -

I meant I wasn't confusing MFI with EFI (not CIS... I guess I had CIS on my brain)

But anyway, maybe I am?

What did the 2.7 RS run? MFI ?

The 2.7 RS used MFI and had 8.5:1 static compression ratio, S cam profiles, single ignition, and could run regular fuel. 8.5:1 compression is quite low, especially with high-overlap cams. I think 9.5:1 with 90mm bore is about the sweet spot for street fuel. It should run alright with single ignition and twin spark would be added insurance and allow more favorable ignition timing for a touch more power/efficiency. The high-overlap cams allow a little more static compression due to the dynamic compression effects with valve timing and engine speed. Many people up the compression to 9.5 when doing "RS spec" builds.

9.5:1 compression, 90mm bore, single ignition, MFI would provide an RS+ spec engine with a little more bite than the 210 hpower and 188 lb-ft of torque. Makes for a nice, zippy driver.

[tom1394racing]

If you want to build the 2.7 RS spec, with 9.5 CR, start with a 2.7 7R case.

These are readily available and show up on the classifieds. I have several on the shelf should you decide to go that route.

[DannyP]

I am also a virgin 911 builder.

Post #7 above states "new crank" needed, not so. 70.4mm stroke for 2.4 or 2.7. Cylinders go from 84 to 90mm though.

Mine is a 2.7 also, 7R and all the goodies. JE 10.5:1, NOS nickies, s cams and dual plug heads on mine.

[911st]

Most the time with stock gears a 2.4E is faster than a 2.4S. However, the S feels more entertaining. I think the 1973 R&T reported the E was faster to 60.

I would guess the limit of the 32mm 2.4T stacks is around 200hp no mater the build.

Building a 2.4E requires a new space cam and MFI pump redo. So dose a 2.7RS motor. This can add greatly to the expense.

As to how far you can stretch the stock T pump. A 2.5 should not require many clicks richer to make it work well.

On the lower cost side having the cylinders bored out to a 2.5 and get a set of J&E pistons for around 9.5/1 CR could make for a nice running car keeping the T cams. I would put an E rotor in the dist in it to expand the red line to 7100rpm. Then add a nice single or double pipe sport muffler and dial things in on a dyno.

One might be able to build a 2.7T motor and adjust around the pump but you would not know until you try it. It would not scare me to try this but I have played w MFI pumps a bit.

On the upper end, I believe the plastic 2.4 T stacks can be bored to about 36mm to support a 2.7RS motor but that is it. I would not be afraid to hone out the stacks and mill the bottom of the throtle bodies to 35 or 36mm myself if the shafts seem tight. Or they can be sen out to a known builder. I knew one 2.8 SCCA racer that ran 35mm ports on a 280hp+ motor very successfully so they do not have to be much of a limit.

As Porsche used 36mm stack on there 3.0RS motor building a stock appearing 2.9RS MFI motor using Nickies' cylinders or 2.8 using bored and plated 2.7 cylinders could be a possibility. I ran a modified S cam on a 2.8 I had w a 2.7RS pump and it ran well. The mod S cam I think fills in the HP curve a bit. This should move your TQ from 148 to over 200# and your HP to around 240 or so. My 10.5 CR 2.8 twin plug was around 260fwhp using factory 2.4S stacks.

As noted, cost is the only limit.

[YTNUKLR]

What's the budget?

[Flieger]

Originally Posted by 911st

... As to how far you can stretch the stock T pump. A 2.5 should not require many clicks richer to make it work well. ...

Displacement is not the most important factor in pump tuning. The horsepower determines how much fuel and air is needed to be combusted. 2.5 short stroke motors are often found in racecars making more horsepower than a 2.7RS spec. They are stressed more and use high compression, of course.

[al lkosmal]

Originally Posted by eddyvdw

send your pump to mike in seal rock, or.
He has a mfi test and calibration set up.
Next to that he has tons of advice.
His pelican name is 356rs.



Ed

+1

[911st]

Originally Posted by Flieger

Displacement is not the most important factor in pump tuning. The horsepower determines how much fuel and air is needed to be combusted. 2.5 short stroke motors are often found in racecars making more horsepower than a 2.7RS spec. They are stressed more and use high compression, of course.

I do not think the pump's delivery is correlated to HP directly or very much.

It is correlated directly to air flow per stroke and thus is more correlated to displacement and thus bassicaly to Torque.

Mess with air flow per stroke and you mess with the the pumps ability to fit a motor.

Thus, it should be easyer to adapt a T pump to an E cam that makes almost the same TQ but dose so higher in the RPM range than is would be to adapt it to a 2.7. Stretching it to a 2.5 where the peak TQ stays close to the same point in the RPM range would probably be the easyest of the possable builds in referance to the using the existing pump.

A "T" pump can maintain balanced AFR's at idle and up to a peak TQ of up to about 150# of TQ.

The difference between the high and low spots on he space cam determine the range of TQ it supports. A 2.7RS space cam is cut into deeper than a T cam as it needs to deliver enought fuel to support fueling at idle and up to 200# of gross TQ. Thus, the RS cam supplys about 33% more fuel at peak TQ and the space cam is cut about 33% deeper to achive this.

If you try to readjust a T pump it to support a 2.7 that makes 170# of TQ compared to 148# for a stock 2.4T the bottom is probably going to end up very fat. Adjusting the rack dose not increase fueling as a percentage. It gets increased in the gross amount along the hole range.

That is, if you need to increase fuel delivery to support 20 more # of TQ at at WOT it is gong to deliver enough fuel for another 20# at idle. This could end up being a 50% increase in fuel at idle. Some of this can be adjusted around to a small degree using the link to the pump and with the air bypass screws but probably not that much.

The centrifugal weights determine at what RPM the max fuel is delivered.

The shape of the space cam then sort of fine tunes the deliver to fit the shape of the TQ curve.

It is probably easer to support building a motor that makes more TQ at a different rpm (more HP) than more gross TQ if it is signifficant. Thus if one wanted to use a T pump on an E or S build it might ge doable by tightening up the springs on the weights in the pump to delay peak fueling to the later peak TQ point. However, the shape of an S space cam is a lot different than a T's so there will probably be points along the curve where things are off some.

The pump dose not care about increases in TQ from better timing and higher compression. Thus, 2.4T motor set at 10/1 with twin plugs would probably be able to use a fresh T pump quite with out compensation even thought the motor is making 10% more TQ.

At least this is what I belive so far.