Bryan

Having temporarily abandoned the idea of swapping a 3.0 S2 engine into my '88 944 (higher compression 160hp motor), I'm looking into other ideas since I'm going to have the original engine out and apart this spring. The thought of increasing the displacement of the 2.5 to 3.0 liters has occured. So questions abound:

- Is this even possible, and if so is the displacement achieved through bore or stroke or both?

- If bore is increased, where do I get the appropriate 8-valve pistons?

- How close do I get to maxing out the stock injection, and how restrictive does the stock intake tract become with more displacement?

- I would need about 190hp and 190lb-ft with plenty delivered at lower rpms to make this worthwhile. Is this a realistic target?

Has anyone done this or have a link to someone who has?

Bryan

John Anderson

We have bored and stroked the 2.5 liter engine to 3.1 liters. On a stock 8 valve head it delivers 200+ at the wheels.

YOu can get 190/190 on our 2.8 liter high compression all bore motor, with some headwork.

Take Care

Jfrahm

The 2.5l is 100mm bore and 78.9mm stroke.

The 3.0l is 104mm bore 87.8mm stroke.

To stroke a 2.5 to 2.8l most people get an S2 or 968 crank and rods:

3.14*(100mm/2)^2* 87.8 = 689230mm^3. That times 4 cyls is 2756920 or 2.76 liters.

Your compression ratio for the 1988 motor is 10.2:1, so I suppose the combustion chamber is
60.75 CC's or thereabouts. (619.75cc per cyl / 10.2= 60.75). So with a 2.7l you have roughly
11.4: 1 compression. Manageable, I suppose.

(689.25cc/60.75 / 60.75 = 11.44:1 compression.)

To bore the 2.5 for the 104mm pistons you would need to sleeve the block, and with these same 60.75cc heads your compression goes up to 12.4:1
(750cc/60.75= 12.35:1)

It'd be hard to live with a 12.4:1 motor on the street, you might be better off with an earlier head to reduce that compression at that point, or dish the pistons like the 951 or Calloway.

-Joel.

D. Autry

Ever thought of using the 968 3.0 Vari cam?? Mate that with a 944 limited slip rear with a 9.35 ringset.

The engine will bolt right up and all you need is the engine management and variocam brain. (you'll have to redo your DME if you mod your original engine anyway).

You can probably do this for app. $5k. That's the engine, brains AND transmission, if you get them used.

What you get is app. 235hp from the 3.0 N/A car. That adds app. 70 - 80 more hp. No mods, so you can expect an engine, WITH the power, that'll still give you long life.

Have you thought about your brakes???

M758

What are going to do with those stock pistons? Need them any more?

Bryan

Good information folks, thanks!

I just picked 3.0 liters out of the air because the S2 and 968 had 3.0 liter engines. But it sounds like building my 2.5 into a 2.8 gets me into my target output area. I have no problem feeding the car 93 octane, so high compression isn't a huge deal.

So the question becomes bore versus stroke. If my goal is a torquey, flexible street engine, then isn't stroke the better thing to increase? The engine is already undersquare with a 100mm bore and 78.9mm stroke. Stroking it would make it more "square" and enhance torque especially at lower rpms. In theory...

Also, when do I hit the limits of what the fuel injection can handle? At some point, the air flow meter will be pegged open and can't register and more incoming air. Am I anywhere near this limit with 2.8 liters?

I've thought about using a later engine (S2 or 968) and it's just too much money and work. There's torque tube issues, electronics, cooling system, etc. The list goes on and it has become too much to try and take on. Plus I just put a brand new water pump, lifters, and assorted other stuff on my 2.5 that would be a shame to ditch.

Bryan

Bryan

If I do this, and I decide to bore the engine, no I will not need the stock pistons. If I stroke it, then...I guess I would re-use them? Not sure. They've got about 135K on them. But we're really puttin' the cart in front of the horse.

Bryan

Sami951

A very interesting discussion so far!

Few questions I'd like to throw in:
- if you stroke a 2.5 using the S2/968 crank & rods, what happens to piston speeds? Of course, those factory 3.0 engines seem to work fine, but could there be any issues here..? Esp. if you'd like the engine to rev to 7k (+?) rpm..?
- what would happen to the compression if one did this to an already-quite-high 10.9:1 engine?

<img border="0" alt="[cheers]" title="" src="graemlins/beerchug.gif" />

Jfrahm

I think you would need a cam to get to 190 HP with a 2.8l, and I think a stock NA transaxle would have a reduced lifespan behind that motor.
If your transaxle hasn't been rebuilt I wouldn't expect it to last too long. You would also need an exhaust system. I don't know if the DME, AFM, etc. will support this HP level either.

Consider that the cost of rebuilding your engine + the value of your car as-is + the cost of an S2 crank and rods would get you pretty close to just buying a Turbo or S2, especially if your time is worth anything, and then you get the upgraded chassis and better resale value (or insurance valuation if need be.)

You would spend maybe $1k on a crank and rods, then you need pistons, rings, and a head job. You could easily spend $2500 building the stroker motor plus many hours of work. Add in the cost for a cam and exhaust system too. If your car was worth $3000 now it wouldn't be hard to afford a turn-key S2 with that kind of money. You wouldn't get a fresh engine but you would have the nice chassis.

-Joel.

Huntley Racing

There is more to a 2.8 or 3.1 than the motor work. To be happy with the drivability and performance you need to upgrade the fuel injection to handle the added power. So when you budget for this type of work make sure you are getting the whole picture. You can see these big bore motors we pioneered on our website as well as several fuel injection upgrades which can be used to properly manage the motor you choose. If you need more help feel free to give me a call at the office to go over the ins and outs of all the options. Good luck.

MHT

if you are going to bore it out why not go to 4", small block chevy size, all sorts of pistons available cheap and can be made to order in any config. you like.

Jfrahm

Chevy 396 or 402 big block pistons might be a better choice, the 396 is 4.094" (around 104mm) and the 402 is just a .030 over 396. That's about 104.75mm. You can get overbore sizes up from there too. If you could fit .060 over 402 pistons you could get 3.1 liters, or 4.25" chevy 427 pistons for 3.2 liters. God knows how the pin diameters, rod length, etc. work out though.

To use these pistons you would need iron sleeves or maybe nikasil plating? Has that been tried in a 944 motor?

-Joel.

John Anderson

"Also, when do I hit the limits of what the fuel injection can handle? At some point, the air flow meter will be pegged open and can't register and more incoming air. Am I anywhere near this limit with 2.8 liters?"

No, infact we ran our bored and stroked 3.1 liter using the stock motronics, and a simple fuel pressure regulator on the tracks. We had plenty of fuel and the air fuel graph showed an almost perfect 12.5:1 accross the rpm band.

We have upgraded lately to our MAF kit, which added quite abit more power. But for the street and track, to keep it simple and on budget, you do not need to add expensive electronics. Our car is living proof of this.

"Few questions I'd like to throw in:
- if you stroke a 2.5 using the S2/968 crank & rods, what happens to piston speeds? Of course, those factory 3.0 engines seem to work fine, but could there be any issues here..? Esp. if you'd like the engine to rev to 7k (+?) rpm..?"

Again, we are using a 3.0 liter crank, and a bored block of 106MM, its flawless, just keeps getting stronger each time out on the track. When racing the car lives between 3500 and 7000 rpms. We check and inspect the engine before during and after each race, and its been perfect each time.

"- what would happen to the compression if one did this to an already-quite-high 10.9:1 engine?"

We are running our motor at 14:1 compression, and yes...we do use race gas, but 11.5:1 or even 12:1 would be fine on the pump. When we build your motor, we ask you what you want the compression to be, and we build it for that. We do not use a off the shelf scheme in any motor we build. So, you decide what the car will be used for, and go from there.If you want to run the motor at 10.9:1, then we build it to do just that, even bored/stroked or both.

As far as the tranny giving up, well...we have not reached that point. We are running the NA tranny, and have yet to have any problems.

"Consider that the cost of rebuilding your engine + the value of your car as-is + the cost of an S2 crank and rods would get you pretty close to just buying a Turbo or S2, especially if your time is worth anything, and then you get the upgraded chassis and better resale value (or insurance valuation if need be.)"

Actually, the cost of a 2.8 liter bore engine complete would not approach the cost of selling/searching/buying an S2 or 951, not even close. Especialy if you take into thought that many NA owners have invested serious cash in keeping thier car in mint condition. Most NA owners and P car enthusiasts that visit our shop have the best of the 944 examples and I doubt they could recover even close to HALF the amount they have invested in the car if they wanted to sell it.

I won't go as far to say we "pioneered" the big bore motor. But we do build a great motor :-)

As a shopper, I would definately be sure and do a thorough check on any vendor I would consider for this job. Ask for references, get on the list and ask about the company, do your homework. Its not an investment, rather a hobby...so be sure you get the best for your buck and deal with a good company. And remember, never get caught up in the bigger is better hype, keep it simple, and drive it hard.

Take Care!

Danno

So far, I think AMW is the only one offering a standardized big-bore engine. Using proven Rolls Royce chromoly sleeves with matching JE pistons. This combination is a tried & true configuration that works.

So you have two choices. You could ship John your engine and get a 2.8L high-compression engine in return for not much more than a stock rebuild. Or you could by a set of his JE pistons & Rolls Royce sleeves for much less than overbore pistons alone from the other guys. With the savings, you can throw in a set of Pauter rods for a 300-400gm savings each!

*Michael.*

John,

Very good information. What is the ballpark price for a 3.1l??