John V

I have an '81 928 which was one of the more anemic 928's built. I've gone through the vehicle to the point that I wouldn't trade it for a 90's 928 with average upkeep. The one let down about the car is its modest power by todays performance standards.

I have evaluated many performance upgrades from forced induction, to NOS, to newer 928 engine or even small block chevy upgrade. I'm disappointed that any performance increase comes at a very stiff cost. One option that I've found appears to offer very high bang for the buck improvement with significant power increases. I'd like to explore that option and would love any input the community might have.

This option involves improving engine breathing. Studying numerous dyno graphs on the net, I have found that like displacement engines benefit greatly from improving breathing efficiency, many times even making more power than larger less efficient engines. This can be seen in the euro 928 4.7 litre engine that made 310HP back in the early eighties, while newer even larger 4 valve engines made around 288 many years later. What made that small engine perform that way? Not withstanding slightly higher compression, the intake tract was larger and incorporated a less restrictive air flow sensor (wire type) instead of my flapped air flow meter.

Sorry for the long post... to the point. Has anyone gone this path and with what results? I know runners have been extrude-honed, but how about port & polishing
heads (very DIY), swapping out the air flow meter for an MAF sensor, exhaust system? I would like to stop short of cams because of cost but from my research, (exhaust system aside) a good do-it-yourselfer should be able be able to port and polish the entire intake tract and heads for around $500 which would include a new gasket set and valve job. You could go further and incorporate a MAF sensor swap out if someone could correlate the signals and levels? My car was factory rated at 220HP, I like to get in the range of 300 with out spending thousands. Any thoughts? Don't be shy, If I'm all wet, post your thoughts. I'm thick skinned.

j

Randy V

You're on the right track, although an easier approach might be to upgrade the exhaust to a dual pipe from that constricting stock single cat bottleneck, and go with a higher stall speed torgue converter.

Finally, swap out the rear end for a shorter ratio differential.

928 Maniac

Randy's right on the button. The most HP for the least amount of money comes from better breathing and unloading the crank.

My 2c plus change...

1. Replace the viscous fan with an electrical unit.

2. Lose the phony air pump.

Now you've taken a lot of weight off your crank, so lets see what else we can do to make it turn quicker...

3. Have the heads polished and ported by someone who knows 928 heads.

4. Headers, dual exhaust and RMB.

Now it can breathe better and the crank is not weighted anymore...

5. Higher stall speed torgue converter. (Thanx to Randy.)

John, I suggest you go about things in that order and do before and after dyno runs on the same dyno so you can see how many hp's you gain with each mod. HTH.

Jim Nowak

John,

I'll let you know my results when my engine is finished. I have a 2-valve engine 5.4L 104mm J&E pistons, extrued honed euro s induction, Electromotive engine management(MAP sensor), Devek cams, Jet-Hot coated headers, etc, etc.....
I had 270 RWHP and 315 RWTQ on a Dyno Jet dyno, same hp and more tq than the C5 Corvette dynos, with an extrued honed US induction and CIS injection. The engine builder says the Euro s induction alone will make a huge difference in the engine performance and the electronic engine management will have a great effect as well. He said, "It's kind of like breathing through a straw, with the US induction, and really kills the performance." The builder said I should see a 30%-40% gain in RWHP after the modifications and should be around 350-370 RWHP or 420-440 crank hp. I will dyno the car on a Dyno Jet when it's finished.

Jim Nowak

John V

Jim,

your setup sounds killer and should really stomp. No doubt your doing it right but I can't imagine that approach being "cheap". I'm trying to come up with some low buck, (Okay if high labor) but DIY mods that might yield big gains.

BTW. my car is a 5 speed so the tranny mods wouldn't benefit me. I have already done some work.. Borla s/st exhaust, no air pump, "refined" some of the emmissions plumbing etc. I Haven't done headers or dual exhaust because I don't think my intake side is free enough to benifit proportionally with the added cost. Also, the O2 sensor on a dual system might be an issue and I'm in a smog sensitive state.

Jim, your comments regarding the euro induction are very interesting. Have you (or anyone) gotten any input regarding what makes it so superior? I know it flows more but how much of that is size versus the MAF? Any thoughts on whether the USA systems can be worked to similar results? I haven't seen any posts regarding head work either. Are there any substantial gains to be had there or are the stock castings already pretty efficient?

I think the engine management system is killer too but the cost would put it out of scope for me. My thoughts are to replace the air flow meter with a replacement MAF from a 5.0L + Chevy or ford poduct (low bucks). The trick, I think, is to get one that has sililar outputs to the ECU. Even if the voltage levels were close, I could probably work out a transition circuit to make it work. BMW has gone to (2) seperate air flow meters for better flow and that system has been largely credited for the 400+ HP that their 5.0 litre v8 makes.

I'm not looking for 400 hp.. correction, I'm not willing to pay the price for 400 HP. My goal is a real & reliable 40% power increase on pump gas at the expense of lots of labor but no more than $2K. I think it can be done. Keep the dialog coming.

J

928 Brothers

I have the euro intake and the euro dual exhaust on an 83' american model. Their is some modest power gains but not much. The cams is what gives the euro S power. I would not spend any more money on that car. If you want power, go for an S4. They are getting very cheap. But remember that you will have to upgrade the engine in the S4 also. S4s were fast a long time ago. Today, a Nissan Maxima is faster. Also if you are going to race, go for the 5-speed only.

Jim Nowak

John,

The euro s induction is soooo much better because the runners and throttle body is much bigger. I think the euro s throttle body is 80mm vs. the US's 65mm in diameter. 928 brothers are partially correct, the cams do make the biggest difference but if they can't breathe they won't be very effective. Larger cams on the US intake, even extrued honing them, won't gain the hp you what. The euro s runners, dog-house, and throttle body are the keys to the euro s' ability to make 300+ hp. Not-to-mention, the euro s has 10.0:1-10.4:1 compression vs. the US 2-valve's 8.5:1-9.3:1 compression ratio. The euro s would suffer a 30hp-40hp loss without the extra breathing capacity and compression.

Headers: I noticed a big difference, in seat of the pants, in hp and tq with the installation of the headers on the 2-valve US engine. I have heard some Rennlist members say they picked up 40+ RWHP on a Dyno Jet after the installation of the Jet Hot coated headers.

Jim Nowak

Thom1

Hi John,

You already have received good advice. Here are some minor tweeks: K&N Air Filter, and Synthetic Fluids. See below:

Synthetic Fluids Plus:

Mobil 1 synthetics are good for: Automatic Transmission (Use the same “ATF” for power steering.), Rear End (Use the same “75w-90” weight gear oil for Timing Belt Tensioner.). Mobil 1 has a good rep, and is less expensive than most - $7/qt for gear oil $5-6/qt for ATF and motor oil. Castrol Synthetic Blend motor oil is good. The blend is about half the price of the 100% synthetic - $2.6/qt. I have heard that you can change oil less frequently with synthetics. Distilled water and aluminum safe antifreeze - like Prestone (non synthetic) work for Radiators, but NOT the new Prestone in older cars. (Check the archives for other antifreeze recommendations, if you want something more exotic.) Use Valvoline synthetic Wheel Bearing grease. Use ATE Super Blue Racing brake fluid, alternate flushes with Gold. It is German with a high boiling point.

Replace caliper and master cylinder bleeder valves with check valve type for easier bleeding. Crush washers for the differential fill and drain plugs were 17mm id.


HTH,
Good luck,

John V

Thanks for all the input. I understand the tendancy to want a newer base model for the immediate power gains but, If some of you are like me regarding upkeep, it doesn't make sense. My car has had every major system overhauled. It's in close to new condition despite being 20 years old. Plus, I know what I have, weaknesses and strengths. Buying a later model with even good upkeep, would cost way more to bring up to my standards than any engine mods I would contemplate. Just my opinion.

I guess it all depends who you talk to relative to mod dependant gains. I've heard from the some of the "Big 3" that there is very little if any real HP gains from a K&N or Headers alone. On the K&N, My experiences would agree... I've tried them on a couple applications and couldn't "feel" any difference (I would expect to be able to feel 5%). I've also been told that if you do headers alone, the benefits won't be noticeable without freeing up the exhaust after the headers also (IF thats the bottleneck, you just moved it downstream). Even then, I've been told that freeing up the whole exhaust, without adding fuel to the mixture (and ideally pumping more air in as well) will not add the 10-15% that is often touted.

On the euro system, I thought the real secret was in the less restrictive wire type air sensor??? I didn't know it had a larger throttle body (BTW,I don't think it can be 50 mm larger, that would make it nearly 5" in diameter as mine is already close to 3" (75mm ??). I just had my intake system apart to polish the outside. In my pea brain, the smallest relative restriction was the air flow meter. Granted, each intake port at the head is smaller but thats ingesting the contents of 1 cylinder. The air flow meter is substantially smaller than the throttle body depsite feeding all 8 cylinders.

I do agree the cams play a large role but from what I've seen, new or even good used ones are not cheap. Also, in keping with the low cost approach, there are some interesting sites on head work. Most, from guys who are tuning small block chevy's but real informative. Many of these guys are showing (with dyno graphs) that porting and polishing intake the tract alone can produce better flow characteristics than swapping out the cams. (Obvoisly, doing both is best) Maybe this is because the chevy castings have that much room for improvement... and prehaps the porsche units do not. I think the higher compression factor plays a role also but the good thing about this approach is that the heads would need to come off for the job. Its pretty cheap to have them decked during the valve job and that would increase the compresion ratio modestly. Most engine builders focus a disproportionate amount on time on the top end. I'm surpised that there aren't a ton of guys in this community that haven't gone this route. Or maybe they have and are either keeping their extreme success or failure, secret.

J

John Struthers

John V.,

Every builder learns that money equals horsepower. Generally,the more you spend the more HP you make . Obviously there is a ledger of caveats : from getting burned with a lousy builder, to outrageous claims to a
missing or faulty game plan at the out set.
I will give you the short, read that incomplete HP shopping list.
I say short because I am not sure of the following or couldn't locate so did not list them:
1.If the Euro S Brain is mapped differntly.
2.Dampner weights(for auto)
3.Intakes - no listing - has to be a difference
4.Dual exhaust several - you find and choose.
MAF - Different on Euro's? -.
List:
1.Left and right 80'- 83'cams, used; $650.00 each.
2. O2 Sensor 80'- 82' $75.00
83'- 84' $195.00 (ouch!)
3. Tube exhaust manifold 78'- 84'
left and right, new $995.00 each
left and right used, $250.00 each.
4. Cylinder heads, left and right, used
$500.00 each. And what with the apparently tragic loss of so many left cams over the years the left cam may be somewhat higher.
So just with the incomplete list we/you are spending $3000 - $4500. This could go much higher, will go much higher if a 928 'WRENCH' is involved. And if you are heading in the general direction of 300+ HP you might want to drill the crank, throw in new mains... before installing the heads you would want to go thru them... the new cam drive belts seals gaskets, rollers/bearings T belt water pump ad naseum...
My opinion - here it comes wanted or not -
with the low initial cost of buying a 86 1/2' model year on you have 'adequate' HP, upgraded brakes, and suspension.
So rather than turn your project into a Panama Canal project, start saving, now! I got a 7.25% loan on the net for a used car the lender and I hadn't even found yet... no money down. Took all of 20 minutes.
I'd have an S-4 right now but for all the lying scumbag 928 abusers out there.
Spent over 1/2 a year and $$thousands$$ on transportation/lodging /expenses flying and driving from coast to coast and much in between...My wife said bring one home this time or forget it. I'm happy with my sHARk,
but I, like you, could be happier.
Summary: Save your money till you can buy what you want/need. BTW my sHARk payments are $149. 00 a month. Can't beat it with a stick. Try picking up a used Hyundai or KIA for that.
HTH, LOL
John S. 82'Weissach, Auto., 'Pattycakes'

John V

John,

points well taken and I've done the math several times with similar results. (I'll probably get flamed for saying this but) for me, if I were interested in bringing my car up to todays top standards,(which I would consider in the rage of 375-425 crank HP), I wouldn't do it with a Porsche engine. It's way too expensive to extract that kind of performance. I'de be better of transplanting an lt-1 or even ls-1 set up. Thats a real 325-375 hp (and even higher torque) power plant thats lighter and can be had with low miles complete with brain for under $2K. Hell you can now buy brand new crate ls-1's with 350hp direct from GM for about 3k with waranty! Thats not an easy DIY project and surely upsets the purists. But, its some serious bang for the buck with very high potential for even more relaible power.
I think it would be great if a "recipe" could be devised to take the abudance of low cost 928's and give them enough grunt to not be outdone by maximas or now even altimas, (without having to spend more than the cars worth on the engine alone).

I have been in many nice cars and, power not withstanding, I like my 928 better in most ways (feel, comfort, rigidity, exclusivity, looks). I think the new 405 hp vette is nice but every vette I've ever driven "feels" like a fiberglass kit car. Granted they have gotten better but my freinds 4 year old vette doesn't come close to my 928's level of refinement,stiffness and quality (even if he can smoke me at will). And my cars 20 years old!

j

928 Brothers

I say that you need to start of with an S4 if you want to go fast. If you don't, you are just wasting your time and money. If you spend about $4,000 (the price of the actual car) on the engine, you will still be slow by today's standerds. It's a fight that can't be won. That said, faster is NOT funner. Automatic S4s are very boring compared to early 5-speed cars. They also feel slower under normal driving conditions, unless you are giving it full power.
If your car has everything already done to it, keep it simple. Try taking of some weight (it's cheaper). Take of the fan and pump, bypass the cat and most important - advance the timming. If your car feels tired, this will wake it up.

2V4V

John,

FWIW, Jim has done about the same thing that I am doing (Jim, dyin' to see those dyno sheets!) and I think that he will see 360+ at the rear wheels with no forced air induction.

As they say, HP is all (90% anyway) in your head(s) and intake system. Everyone that I have spoken to that has built 928 motors will go LH (hotwire) sensor over CIS, but has not see major gains from it, mostly 4 or so HP. Does it matter?, of course. Do you get more out of euro intake and runners? Yup.
Most everyone who builds, runs aftermarket engine management, and that's good for a few more ponies here and there.

I would try to find a euro intake system-I think without delving into the heads, this would be my next step. And it is not hugely expensive for the parts.

HTH,

Greg

MikeK

John,

have you considered forced induction. I have seen a couple of supercharger kits available for the 928. With modest boost pressure, you can easily deliver the hp figures you're looking for while maintining the Porsche'ness of your car! This was an option that I myself was considering. I think the cost was around $3k - $4k if my memory serves me correctly.

Sure increasing the abdiatic efficiency of your engine gives you more hp, but it's relatively small gains for lots of dollars. IMHO, leave the euro cams and 15hp headers for the boy racer crowd. My 928 is used as what it was built for, a GT. I don't want a high HP, high revving race engine. Get a formula ford if thats what you want. I want a street car with usable of torque. My $.02!

Jim Nowak

Here is a list of what you can expect to spend for a race ready 400+ hp 928.

Euro intake & throttle body $1,000

Euro heads $600-$1,000(I use modified '851/2 944 heads)

Bore engine for greater displacement $600 or sleeve motor $1,000 and save on piston coating(recommended) or stroke motor $3,500 - $5,000

Pistons that will work with a 5.0L or larger 2-valve $1,000(included in the stroker price)

Piston coating so they will work in Alusil bore $800-$1,500

Euro Cams used $700-$1,000 or Devek new @ $2,000

Extrued hone intake $600

Jet Hot coated Headers $600+

Porsche fuel injection $1,000 or aftermarket programmable for $2,500 to $10,000

Custom exhaust $600+

Redrilled crank to fix oiling problem $650

Labor est. $3,000

Soooo, around $10,000 + for normally aspirated done on the cheap side


Chevy transplant is not exactly cheap:

400+hp streetable motor $4,000 - $5,000

Conversion kit $1,750

Labor for conversion(Renegade Hybrids quote $7,000+ for parts and labor to make kit work )

Chevy motor transplant with 400+ hp will cost between $12,000 - $15,000


Supercharge your stock S4 or US S3 to get 400+ hp will cost around $5,000 - $7,000 depending on parts and labor with the FAST kit. However, supercharging this engine with the base motor and tracking the car for an extended race isn't recommended.

Jim Nowak