Hey Rennlist,

So I have a 1980 US 928 auto that I've been wanting to get into to upgrade for quite some time and have finally found the time to do it. While I've enjoyed the car so far, I'm just not satisfied with its current level of performance.

Let me say what I'd like: I'd like to be able to get around 300 hp (the more the merrier) from the car.

So now my questions...

I've scoured the forum for engine swaps and frankly, I'm swamped with all the information. (This is my second post and one that I presume is on a hot subject so if I take a public beating for this, I'll take it...) So my first question then is with a 4.5L US, what sort of modifications to the engine itself or to other components apart from it (exhaust) can be done to produce around 300 hp? And if the 4.5L is too much trouble, what options are there for engine swaps? What sort of problems arise from putting in a 4.7L or 5.0L? Can 4.5L heads be used on a 4.7L or 5.0L block? For whatever option, I think I'll be able to devote about $8k.

Schfive

 

If you are looking for a 300hp 4.5 there are plenty of supercharging kits for around $5,000 that will get 300hp without too much trouble, if you want more hp you can add a smaller pulley or put on a bigger supercharger. Engine swaps are hard and take a lot of time and it is hard to find a Euro S or S2 engine lying around. But in the long run stick with the 4.5 it will be much easier to service then a swapped in S3 or S4 engine because of not having to constantly worry about breaking a timing belt and ruining an engine because the 4.5 is non interference and the S and S2 engines have bent valves before and the S3 and S4 engines are definite interference engines and will destroy a head and then you will end up right back at square one having to swap in another engine. Not to mention the items required for a good reliable swap will be over $7,000.

 

^^^ what he said. Boost that baby. Freshen her up and slap a turbo or SC on there and you are good to go

 

How much can I get from better exhaust?

 

The single best way to improve the performance of a USA 16v is to free up the exhaust......you can gain 40+whp by changing the exhaust.... most 4.5L L jet cars will dyno around 170-180whp....with a full exhaust..headers, Y pipe, single 3.5" exhaust should get you above 210whp.....my 84 did 215whp....good news is exhaust is cheap

2nd best mod is a set of Euro S cams.......with those added to the exhaust you can have around 250whp..... The engine in my racer is a 4.5L jet engine (1981) with full race exhaust, Euro S intake and cams (187-188) and "ported" heads.....it makes 265whp-289 torque but it is a 5 speed...auto will be slightly lower...however it is VERY loud with only 1 small muffler....I'd say far too loud for a street car

 

Familiar story, my first 928 was an 81 AT, and while it was actually pretty fast, just not rapid from zero, it was kind of boring and I traded it on a 944T. I now have a US 83 5 spd and 85 Euro S 5 spd and neither are boring. To me the AT vs 5 spd is the biggest difference.

Much as some think its great, I would not boost a 4.5L AT, too incremental of an increase and kind of dead ended. The fuel injection brains on the early cars have no real tuning ability, just tricks with a fuel pressure regulator, no knock detection, like I said, limited and dead ended.

First suggestion, get your car running 100% in stock condition, good motor mounts, no vacuum leaks, with maybe a cheap exhaust upgrade like 85/86 manifolds and a magnaflow muffler instead of the factory pumpkin. Maybe look at some weight reduction.

If you are still not happy maybe you should be looking for a 32v 928 as a starting point.

 

Yes I am biased!

If the bottom end is healthy (good compression test, no excess oil consumption), why not put a supercharger on it?

 

What about the cams from 928 Motorsports if Euro S cams can't be run across? (I saw some on 928 Int'l but they total to about $100 less than what 928 Moto sells them for.) Is a valve job required with such cams? Is the benefit to the 4.5L worth the hassle?

Also, in regards to danglerb, what about a new engine management system? (The 928 Moto TEC GT? Or is that also, for the 4.5L, not worth the money for the benefits?) And what sort of weight reduction are we talking about here?

Looking at a whole new car is just beyond me for now. One car, one car.

 

Mine came from the P.O. with a straight through Y pipe. I have to pass CA smog so I bought a cat. Been wondering if it will stay on the car and now I know it will only be on briefly every two years.

Now would be a good time for me to do cams... Lots of seals to replace on the engine, decided to pull it. What would be a good source? Money is an object but don't want to be penny wise but pound foolish.

 

I don't see running a stinker, no cat, as a material gain in HP, maybe 10 crank hp over stock cat and 2hp over a modern high flow cat. Exhaust system upgrade is a no brainer no matter what other choice.

The two options at the top of my list are Euro hybrid motors, Euro S heads and intake on a US 85/86 block, with the second option being to bore the block to 104mm and use 968 pistons. Many many other options considered, these look the best to me with the caveat of using a hotter cam than the Euro S, but bumps cost due to need for better valve springs. Any new cam I've been advised should have new lifters as well.

With an AT going to the 32v means a big bump in torque, and day to day I think that will mean more than anything done to a 16v.

Sourcing parts is about time and knowledge vs money. Our fine vendors know the 928 and can deliver parts right away, but if you educate yourself and are willing to take some time you may find bargains on some items.

 

the single biggest variable is where you live (smog laws) and your budget.....

if you are lucky and don't have to smog, then the options are much wider....but not necessarily cheaper

IN terms of being cost effective....exhaust is by far #1......... cams are a 2nd no doubt.....I have proven over 310 crank HP is possible (335 torque) with a 4.5L L jet.....sure my stand alone system helps, but not that much....

A 5.0L euro hybrid is a great option....it can and will pass smog and will throw down 300+whp....not too pricey either depending on how much work you do yourself

 

funny, that's what we said about catalytic converters when they first came out.

 

Schrive,

What these guys are saying is true.... the early 4.5 motors are rather ideal for supercharging with their stock low compression ratio of 9.0:1 and their very mild camshafts with low overlap - they respond very well to a little boost and raising them to 300-320 CHP is fairly easy. The throttle response with those early cams is fantastic.

That said - there is a bit of a glass ceiling in place on both K-Jet and L-Jet cars that once we get to about 320 CHP, its hard to get more fuel to go higher (if that's your goal).

I did end up getting my K-Jet 4.5L to 560 CHP, but it was so set up for that end that it was hard to start and hard to idle. I had sacrificed street drive-ability for racing HP. Many will not want to do that.

But consider that 300 to 320 CHP in a 3400 pound car isn't bad at all - in fact its a lot of fun. You may find (as many have) that you are very happy right there and need not go higher in a street driven 928.

If I can be of any assistance, let me know.

 

The single easiest way to get a 300+ HP 928 is to buy one. Sell your old car and find a good '85-86 and add Ken's chipset and a couple other bits like fuel pressure regulator and injectors, and you have around 300 ponies in the early body style. Or step up to an '87+ car that came with those ponies right out of the box, in the later S4/GT body style. Ultimately way less total investment, less work, more reliable than boosting the older engine. Plus with the '87+, you get brakes, gearbox, and suspension designed for the higher power level.

I've been down the road of buying a lesser/earlier car and updating it to later performance. Money and time both wasted. Would have been much cheaper/faster/better to just buy the performance I wanted already in a car that came with it from the showroom floor. Doing the piecemeal "upgrades" also meant that I ended up with a relatively bastard orphan car that was really hard to sell later.

 

cheapest way to get some big hp with little cost and effort, is a block swap to a 5 liter. just a stock block. re -ring it and put new rod bearings on it and have the pistons cut for the valve reliefs. DONE, put it back in. better if you put on a set of euro heads with euro cams. (that should be another 2-4 K)
then you have a 350hp 928 sleeper and no other changes.

have someone do the labor for you and it will drive the cost way up.

5 liter conversion costs.
$1k for block
$500 for piston cuts
$400 for bearings and rings
$2k for heads and cams used.
$40 for timing belt
DONE! $5k in parts and even if you have someone do it, there is $3k to put in to labor.
no exhaust changes and you will be at 260 to 270 rwhp.

put on headers and the euro intake and you get up to 290rwhp.

much easier than making a supercharger set up, IMHO