BisimotoSales

I also agree with Iceman. Determining your budget will be the first step for your project and will end up dictating your power goals as well. Smog can also be an issue, but if you live in an exempt area or do not mind going around the smog it will open up many options for your project.

If you are in need of assistance with aftermarket upgrades such as camshafts, valvetrain upgrades, or forged internals, we would also be more than happy to help with your project. Bisimoto Engineering is also a official dealer of Web Camshafts and offer both shelf specifications and custom specifications that can be tailored specific to your project.

- Julio A.

Tony320

Will boring over to 104mm work in a 4.5L? I read through some earlier threads and it seemed like some were saying that boring over that much would compromise the integrity of the block.

I'm looking for more power and happen to have an extra complete 4.5L L-jet to play around with.

mark kibort

boring??? ive done that. first of all, you cant do it on a 4.5. bores are too small. did it with a 4.7, and it works, but its a lot of work.
why do all the work, and its a LOT of work to bore when you can have an entire NEW engine for half the cost? used 5liter. complete with pistons, better crank, and rods!!! otherwise you are messing around with the old crank, rods and having to buy all new pistons AND bore the engine out, AND have to get the block stripped down for a boring job too! way way too much work even if you could do it.

Trust me, its very easy and simple to just get a 5 liter block and assemble it. you can do it in your garage in a few nights and be done with it!

if a blower costs $5k, this is much easier and will put down some good power to meet the budget mentioned on the first few posts.

smog will not be an issue. the 5 liter runs just like the 4.5 liter, with the same smog stuff.

Hilton

Dr Bob has hit the nail on the head; this cannot be emphasized enough.

A US '85 with Porken's chips and an x-pipe will have about the same power as boosting your 4.5L, and have better brakes too. If you can find an 86.5 then the brakes will be better again (the 4-pot brembo's which the S4's came with started around in January 86).

Or if you want, find a 16V "Euro" 928S - the 80-83 ones are K-jet and have 300hp from factory, and the 84-86 16V "Euro" is 310hp from factory.

Plus you get the bonus of hunting for a 928 armed with experience

For the $5k a supercharger kit costs, plus what you can get for your 4.5L car, you should be into the realm of good condition early-32V cars with manual transmission.

danglerb

4.5L doesn't have the thickness, I would bore a 85/86 100mm block to use the 104mm pistons, its not especially cheap due to the need for custom rods, but the increase in cubic inches pushes the rwhp into the 335 to 350 range, and that is a sweet spot IMHO.

Schfive

Thank you all for your responses.

From everyone's opinions, I suppose there's a big decision to make: 1) upgrade what I have or 2) sell the car for one more modern to use as a platform. Of course, I'll have to come decide for myself but your opinions have been valuable.

If I think of selling it, what recommendations do you have? First let me tell you about the car some. So I haven't driven the car in two years. It's been in my garage because two years ago, the fan belt failed on the road and I decided that that was a good time to start fixing the car up. Unfortunately, uni has prevented me from having the time to really getting into it. I've been planning to replace, repair, or upgrade a lot of the components (especially the rubbers and plastics - they seem to need replacement everywhere) but it may be cheaper to sell the car and take a small loss now and buy a better condition one that doesn't require as much love and care (and money which is depleted far faster). Are people still looking for early model 928's? (I realize I'll have to become a member if I decide to sell.)

If I stuck with the car, no, 300 something hp would be nothing I could complain about. If I could get something close to 300 without a supercharger, I think that idea is more appealing though I suppose there is something special about forced induction. And thanks Bisimoto for offering help.

Carl Fausett

Mark,

you aren't really suggesting taking the cast 4v per cylinder piston and cutting in two more valve reliefs to fit 16v heads and putting those pistons in use, are you?

That's what it reads like....

mark kibort

its nice to think about the newer cars already having the larger engine (5 liter) and the bigger brakes, IF you get the newer 85 or 86. and the transmissions are much better too. BUT, if you are on a budget and you like your existing car AND you have the ability to do the work yourself, the block swap is an easy bolt on.

that's a great mod, in addition to going to a 5 liter block. But, as long as you are buying all the new stuff (pistons and rods), may as well get a stroker crank too! this is why the 85 block with cut pistons is the easiest and cheapest way to get over 300hp . its just a block swap and some light assembly work.

THATS EXACTLY WHAT I AM SUGGESTING! (and have done, recommended, assembled, and raced!)

your not suggesting that there is any kid of problem in doing so?

Schfive

I know mathematically additional relief cuts must (minutely) change the compression ratio but does it practically do so too? Is it just two cuts and that's it or does it require any other tweaking?

Tony320

Ok, I get it now, I was just being a little daft earlier.

Hilton

Yes, its a fairly easy mechanical job.. but it still needs head gaskets, piston modifications in the new short block, plus getting a good quality scratch-free 85/86 block, plus to make use of the extra engine capacity you'd need a new exhaust (headers or early 32V manifolds). Oh, and the cost of Euro heads/cams to let the engine breathe on the intake side.

Then there's the issue of "tuning" L-jet for street driveability (not just for track high-rpm duty) including cold starts, idle, high-rpm etc. So factor in at least an AFPR to compensate for the fuelling at the high-rpms, or better, megasquirt EFI setup to be able to adjust the car properly (just ask Ducman how many hours he's into his conversion for).

To make better power, starting from a better base than an asphyxiated L-jet car makes a lot more sense.. e.g. a 16V Euro 4.7l, or any of the 32V motors. That way you get an immediate 60-80hp for "free" before you even start to mod the car.

OP - if your car runs and drives and you've got clean title, it should be worth $3+k on craigslist, especially if you're handy with a digital camera, buffer and vacuum cleaner to make a better quality ad than the usual dross. You should be able to find a better car for not much more (did Smudaaar's euro ever sell?)

mark kibort

they are small two cuts that dont do much as far as effecting the compression (2cc). in fact, it keeps the compression in the streetable range. (i.e. 10:1)

[QUOTE=Hilton;10531533]

Yes, its a fairly easy mechanical job.. but it still needs head gaskets, piston modifications in the new short block, plus getting a good quality scratch-free 85/86 block, plus to make use of the extra engine capacity you'd need a new exhaust (headers or early 32V manifolds). Oh, and the cost of Euro heads/cams to let the engine breathe on the intake side.

Then there's the issue of "tuning" L-jet for street driveability (not just for track high-rpm duty) including cold starts, idle, high-rpm etc. So factor in at least an AFPR to compensate for the fuelling at the high-rpms, or better, megasquirt EFI setup to be able to adjust the car properly (just ask Ducman how many hours he's into his conversion for).

To make better power, starting from a better base than an asphyxiated L-jet car makes a lot more sense.. e.g. a 16V Euro 4.7l, or any of the 32V motors. That way you get an immediate 60-80hp for "free" before you even start to mod the car.
[QUOTE]
there is no tuning needed. the stock system is perfect to adapt to the larger engine. so, yes, put a $90 RRFR on it and you are done. pressure at 50psi and you are done. the Ljet is a litte "asphyxiated", but its only a slight reduction in HP. ive done a few of them. 290rwhp every time. (but thats with headers and euro intake and cam. if you bolt on the stock stuff, im sure its around 300hp, with only a set of cams.
drivability is stock. cold start is an easy mod and it runs like stock. no issues at all. So, there is no tuning time. i was on the dyno one time. 3 tweeks of the RRFR and i was at exactly 12.6:1. no tuning and it was around 13:5:1
The ONLY think i left out was the head gaskets and the exhaust manifolds, but they are not that bad in costs.
It ran and drove like a dream. no issues.

we are trying to get to 300hp easily and cheap. the 5 liter bottom end is an easy way. sure a used 86 is easier , but you need to cut a check.


thee

Carl Fausett

To suggest modifying a cast piston with two more valve reliefs, adding stress risers to the crown, adding who-knows-what turbulence to the frame front, removing material and not re-balancing the crank fly-weight.... as an engine builder, these ideas just raise the hair up on my neck.

The stock valve reliefs are cast into the pistons. Yours will be cut in and likely add stress risers to the crown. The alloy on a forged piston can take it. The alloy in a cast piston I am less sure about.

Are you saying that you have done this and it has worked well for many miles? Or is this just a hypothesis of yours?

Have a look at these 2 pictures sent to me by customer in Europe. All he did is take his stock engine racing - so he thought he'd start shifting at 7000 rpm. The stock cast piston separated at the oil ring land.

My point is: the stock pistons work well (very well) in the stock application. But they don't have the strength or the alloys to play with. No sense of humor, either.

When I build a 5.0L motor for a 16v customer, they get new forged pistons built to suit. I think that's the right thing to do. So I think its better if the 928 owner considering "sliding a 5.0L block under his 16v heads" knows in advance that he should budget for a set of pistons.

James Bailey

Actually Carl many 5 liter hybrids using Euro 16 valve top ends have been built and raced over the years using notched stock 100 mm pistons. The pistons were never a problem, crank oiling yes....

mark kibort

ive done this a few times Carl. my first one is still running today, 10 years later. and the second has also raced for many years as well.



don't confuse abuse with a safe modification.

the mods we make are very minor. two very shallow .175 cuts to copy the stock two valve pistons. Its very easy to do and MUCH safer than trying to design a piston from scratch and have the proper coating on it as well. this is proven and has worked on MANY 5liter hybrids.

this is the entire reason why a 5 liter hybrid works so well, financially, and performance-wise. it uses the entire 5 liter 85 engine, and doesn't require any additional parts. the pistons are strong and it is safe to do this modification, which again, is very slight. if you had to make custom pistons, you may as well just spend the extra 4k and get new rods and a stroker crank.

anyway, I don't understand how you have missed all the 5 liter hybrid build posts. there is a bunch of them out there. I know I had one of the first and raced it for more than a full season and scots is still running strong built exactly the same way.