2.7 ITB with stock pistons & cams / bigger cams & HC forged pistons??

[chrismorse]

My Dad's original 2.7 needs upgrading. I'm doing the suspension, quicker ratio rack, slightly bigger t bars, new busings, bilsteins, ft brake cooling, pedal cluster maintenance, light flywheel and all aluminum pressure plate, Carrera bars w/ adjustable drop links. Mostly "fast" street driving/ a few track days. I'll have installed cooler lines, factory thermostat and an 85 fan assisted Carrera cooler and will be recovering a pair of 84-944 sport seats. (I love this car).
The tranny will get refreshed with new 7/31 or 8/35 R&P, Guard LSD, bearings, supports and side plates, synchros and other bits.

So, I am pondering going to PMO ITB's with COP, or possibly, (finances permiting), doing the forged 10.0 or 10.5 forged slugs, slightly bigger ports and cams, maybe dual plug.

So, with a bone sock, (perhaps healthy) 2.7 what hp/throttle response can I expect, just putting 10 K into the FI versus the perhaps unknown cost of upping the compression and going to bigger cams????

I have read a lot of threads and have the impression that a roughly healthy stock engine with ITB's added will gain a few horsepower and a significant increase in throttle response with some improvement in mileage, (over CIS).

The car has been "under repairs/out of service" for several years and I am anticipating the possibility of gunked up CIS/fuel tank. hould I cut to the chase and go EFI or flush the CIS??? Before the car got retired for repairs, it had been running well, previously line bored, repaired heads, new stud inserts, valve job and Dad did a lot of maintenance on it, or rather, he paid a lot to have it done before he passed.

Started working again to fund my car "problem". Hope to get the old Rotary twin post installed this summer and getting Dad's car screaming again.

He had a lot of interior work done, a glass out re-spray, and refinished the Fuchs.

I know this a VERRRRY slippery slope.

Opinions welcome,
seriously troubled car guy,
chris

[Trackrash]

If you never have to sell the car, then no smog worries. You lucky dogs in Humbolt.

Basically you need to look at the entire function of the motor and what you want to achieve within your budget.

In other words, your cam choice, needs to match your intended use and it needs to be compatible with your intake, exhaust, carbs/ FI. If you choose a cam that will work with carbs/EFI, you will need to change out the pistons, since CIS pistons don't have the clearance needed by say an S cam.

Anything much over 9.5 to 1 CR will require twin plugs. $$$$

A dream motor IMO would be 92 to 93mm P&Cs, S cams, twin plugs and around 10.5-1 CR with Webers or MFI.

Good luck.

[chrismorse]

Hi Gordon,

Thanks for the input.
I am taking the work in three major steps, front suspension/brakes/steering, second, trans work, rear suspension/brakes and third, engine work.

The engine work may get divided into two steps, since the top end was done about 10K miles ago, so I may just do the ITB/engine management on the stock engine, save my pennys :-) then as money permits cams, pistons, head work, maybe even twin plug.

I know it would be less costly to do it all once, but I haven't won the lottery yet. I will have to do the tuning/optimization twice, such is life.

I am looking for a general idea of what to expect in HP gain, throttle response and mileage improvement by going with an ITB/engine management, (& COP) on a healthy/stock 74 2.7.
I am considering this because the car has been sitting for 3-4 years, so I may need to spend some ($$$???) cleaning and refreshing the CIS.
I just don't have an idea how much this might take and would rather put the $$ into upgrading the fuel/ignition system..

Any experience with this scenario??

Thanks,
chris

[Trackrash]

Originally Posted by chrismorse

Hi Gordon,

Thanks for the input.
I am taking the work in three major steps, front suspension/brakes/steering, second, trans work, rear suspension/brakes and third, engine work.

The engine work may get divided into two steps, since the top end was done about 10K miles ago, so I may just do the ITB/engine management on the stock engine, save my pennys :-) then as money permits cams, pistons, head work, maybe even twin plug.

I know it would be less costly to do it all once, but I haven't won the lottery yet. I will have to do the tuning/optimization twice, such is life.

I am looking for a general idea of what to expect in HP gain, throttle response and mileage improvement by going with an ITB/engine management, (& COP) on a healthy/stock 74 2.7.
I am considering this because the car has been sitting for 3-4 years, so I may need to spend some ($$$???) cleaning and refreshing the CIS.
I just don't have an idea how much this might take and would rather put the $$ into upgrading the fuel/ignition system..

Any experience with this scenario??

Thanks,
chris

On my current motor, a '78 SC, I changed the pistons to JE 9.5-1s, added custom cams by John Dougherty, and am using Webers.

I'm guessing I gained 50+ hp over the stock CIS.

The problem you face is if you go with ITBs on your current setup they will be matched or tuned for your stock motor. It takes a bit of expertise and work to setup an ITB system to run correctly.

Later on if you make changes to your motor, you will have to start over with your ITB setup. Maybe even change out the entire system.

Have you considered carbs? Maybe not as sexy as ITBs, but you gain more flexibility and the cost is much less. And you can use your current ignition.

[burtm5]

1974 heads have smaller intake and exhaust ports 32/32 than 75 and above 35/35. but 74 stock exhaust is better. to make 200 hp or above you need the bigger heads, cams, compression and 74 or better exhaust. As stated needs to be a matched set. cis and cis pistons will not make much hp unless turbo, 40 webers 35 mm intake manifold, early S or 36 mm from pmo will work very well. best Henry

[Neil Harvey]

There’s that term again, “slippery slope”.

It doesn’t have to be.

Ignorance and poor planning creates a slippery slope. If you understand what you are doing and have all the costs known before starting, there is no “slippery slope”.

My advice is to fully understand the proposed use of the car. If you want it to be a fun car and not be too concerned about its resale value, do what you are suggesting. In stages is a good idea. Once you have the handling dialed in, you can then add engine performance.

I can guarantee you will spend all 10K on the EFI system but cannot guarantee any added performance. If the tuning is bad, you could end up with less than what you have now. If done correctly and with all safety limits, you can expect better mileage and throttle response. Wide open performance can only be compared to how good the current system is working.

When customers ask me what to do, I always ask then two questions. What are your performance expectations and what is your budget? The two are always far apart.

Here starts the “slippery slope”. I tell them it will cost “this” much, which is always a lot higher than what others have estimated. The low cost is always taken, and poor-quality parts and labor typically follows. Now you are on that “slippery slope”. What’s that saying, never enough money to do it right the first time, always enough to do it a second time. Do your diligence and ask lots of questions.

On a performance note, keep it simple. I would suggest the following on the engine as this is my area of questionable expertise.

Make the system sequential, so no adverse noise is generated on the engine over run. Use the distributor for spark distribution as this keeps the ignition sequential, install a hall sensor in the distributor for sequencing the system and use a CDI not COP in the ignition system. The one guarantee I can give you is that CDI will do more for throttle response than EFI can. It also keeps the wiring simpler too.

If you decide to increase the engine displacement, do a full rebuild. This way you start off with all fresh parts and know exactly what you have. You do not want to put brand-new Pistons and Cylinders at risk if there is trash trapped in the system. The heads can be checked for sealing and have the guides checked for wear, as you have no idea how good the previous work was done. Keep it usable for the street, more than for the track. You will do more driving on the street than at the track. Twin plug systems add in lots of costs. Head work, wiring and twice the Ignition parts. This does make a huge difference in extended performance, so when the heads are off, do the machine work. Even if you stay single plug until you can afford all of the other parts.

We have a full EFI kit coming that we are doing for “aussie Jeff” (home built Jeff). Its a full plug and play EFI kit. Jeff is planning another visit where he will do more of the engine work along with building the harnessing. He makes good YouTube videos’ which should be helpful to the DIY community. We are also thinking of having an engine “build” school while he is here, that will encompass a lot of the machining required along with our assembly ways and procedures.

[Mark Henry]

EFI doesn't add any HP, but programmable EFI does allow you to run things stock FI won't.
Just like twinplug doesn't add any HP, put it on a stock engine and you'll be disappointed. What it does do is with the correct pistons allows you to run a full point higher CR.

ITB's, headwork, cams, displacement, CR (pistons), headers, etc. does, but it has to be a well thought out combo.
The gain is the sum of all the parts.

[chrismorse]

Thanks Guys for your thoughtful input and advice,

I'll finish the suspension/brake work, get the trans upgraded, (iti is noisy), then do the engine.
Doing the engine in stages is sounding problematic, not just theduplication of the tuning work, but the 32mm port restriction seems a deal killer - no point having a ITB sized for a larger port hit that lip.
To avoid the slope, the plan is to pull the engine, take it down to the last nut and bolt to see what it needs, after building a comprehensive list of machine work/parts likely needed. I could do it on a spread sheet and call it a "guesstimate"������

My slippery slope on the suspension/brakes started with a simple sticking front caliper repair.....only to find torn rack boot, add rack overhaul, worn out torsion bar, bigger t bars, bearings discs,blast and powdercoat suspension,bilsteins, worn bushings, aww hell, master cylinder, pedal cluster, adjustable spring plates, brake cooling for front discs,adj drop links for late model Carreras rear bar...that wasn't a slope that was a cliff.

I'm pretty sure I can do better with the engine ��

Chris

[Trackrash]

Neil nails it as usual. A couple of things to add.

According to the info in Bruce Anderson's book the ports are 35mm, not sure where the 32mm came from. At any rate 911 ports can be easily enlarged if need be.

Once the motor is torn down, the two big expenses will be case work and cylinders.

If you have Mahle cylinders AND they are in spec, you are in good shape.

As far as a spread sheet goes, list all the costs for any and all options you are contemplating, such as cams, pistons, cylinders, ignition and induction.

Do some research on the cost of all the required parts to do a rebuild, like gaskets and bearings.

You don't say if you are going to do any of the work yourself, figure about $4k for labor, I think. If you search carefully there have been some rebuild receipts posted to get an idea of the total costs.

[chrismorse]

Thanks Gordon,
This build is a couple of years out, still working & saving the folding money, while doing a lot of reading. I've done a few engines and am looking forward to both the learning experience and the work.
Thanks,
Chris