John Veninger

Feel free to PM me.

Yes, you can get almost 360HP out of a 5.0L hybrid with good cams, and a very free flowing exhaust. That is about the limit so far using mainly stock stuff. That a good amount of power for a street only car IMO.

I would plan what you want to do carefully to avoid re-work and wasted dollars.

I would start the build of a motor that will be either a NA or boosted motor from the start. A typical hybrid build can handle some boost, but not to much due to the compression and your use of CIS.

I liked my old CIS since it worked for my application and was simple, but once you boost past 400+crank HP you need to make modifications that I have no experience with.

FlyingDog

As usual Mark, you can't get off your high horse and realize that A) you're taking your (questionably accurate) anecdotal evidence as the rule and B) you aren't reading (or understanding) what anybody else says. A 5L hybrid would need valve cuts over 9cc to get to 9:1. Normal 2cc (your number) 84-86 Euro S valve cuts would be 9.8:1. As John V said, it should be either built for boost or NA. The hybrid idea is not worth it for boost unless you start throwing custom parts (pistons and/or rods) in it.

Since you've repeatedly proven that you don't understand hp and torque numbers I won't bother responding to your blabbering about piston 'width' and GTS engines.

FlyingDog

Deck height differences make CR somewhere around 7:1, maybe less.

RicerSchnitzzle

Thanks for the great info so far and the cut out diagrams!!

Let me understand one thing though, Scott's car went from a stock 4.5l US @ 220, to 250 by just changing the bottom end to 4.7L and then to 290RWHP with just the addition of the 5.0L bottom end? Sounds like any US OB can hit shy of 300 by just swapping the bottom end? Sounds like getting a 5.0L block and 78 cams with headers would be cheaper for most than swapping out a complete Euro "S" engine..

On to my project, I am not 100% sure what boost I will use. Might go turbo as parts are cheap for a DIY project or 928MS for the SC. Either way I'll be keeping boost under 10psi. Then again I might be happy enough with the hybrid power with better cams and headers. In that case I would just jet up the nitrous another 50hp or so and be done much cheaper.

gruffalo

You might wanna consider using an S4 bottom end, that will give you a CR slightly above 8:1 with no modifications. And I would check carefully if one could get away with not cutting the pistons at all... you might.

SwayBar

Wow, that's low!

I know 951 pistons with an S4 block and heads will yield a static cr around 7.5:1, which is still pretty much too low for a street car.

RicerSchnitzzle

I already have a good '85 bottom end. Don't think I could swing getting an S4 bottom.

FlyingDog

S4 head volume is 42cc and 16V heads are all around 53cc. If it's 7.5:1 with S4 heads it's 6.8:1 with 16V heads.

With S4 pistons in a hybrid, it would be below 8:1 after valve cuts.

John Veninger

Why aren't you just boosting your current motor if boosting is your end game is?
8:1 and lower CR will make a street car a real dog when there is no boost.

Good luck with boosting and NOS a 10+:1 cr motor using CIS to produce 500hp. Let us know how that works out.

hacker-pschorr

First step is to figure out how to fuel that much boost with CIS and without knock sensors.

Yes Carl had a good race engine setup making good power with CIS, I'm not sure that setup would translate into a good street motor. I'm willing to bet he's running some level of race gas on top of that.

Have you looked into cam profile's for boost? The best cams for a N/A motor are not always the best for high boost numbers. Something to do a few searches on before dropping all of that money on custom cams.

As for how strong the lower end is, I've seen 24psi on a 928 engine already with no issues with the lower end.

My #1 concern with your motor is CIS. Before boosting my 79 the first change will be to dump CIS.

I wouldn't worry so much about a low CR if you are able to manage the engine properly. Jean-Louis is running 6psi on a EuroS race car with 10.4:1 CR. Yes the boost is low, but his engine sees WOT under the most extreme load for 20+ minutes straight. He also dumped CIS after going boosted, the CIS system with the blower just never worked out quite right. Dialing in the LH setup took a few minutes on the dyno.
What he said.

Not to mention, why not use your stock motor now to "test" boost with your CIS setup. That way if you have issues and grenade the engine, you already have the spare stuff for round two.
You are going to have enough issues trying to get the boost to work with CIS on the stock motor.


Quick question: What is the most powerful 928 you have driven?

tommytomaso

^^^^^^^^^^^^^^^^^^^^^^
THATS sound ADVISE!!!
WORK out the bugs on a motor that you arnt worrying about.
Its more work (unless you get it perfect the first time) but think of all the anxieties that you will avoid .
A test mule...lol and if you blow the motor and have to redo ull see the weak points and hopefully be able to correct.
With my luck it would be the TT and trany that would blow..

John Veninger

Can I answer that

hacker-pschorr

Did Murphy let you drive his car?

mark kibort

Thanks for the insults about not knowing about "hp numbers" as usual, i think the high horse you are on is a little higher than mine .

fact: euro heads are near 48ccs. US heads are in the 54cc range.

fact: I've built two of these engines over the last 7 years and they are both in service today and have dyno proof of the performance due to the euro changes.

fact: scot's was the most telling of the HP gains do to the 97mm to 100 changes. With NO other changes and multiple pulls, 250rwhp went to 290rwhp for JUST the 5 liter bottom end change. the other engine that i built, went from 240rwhp, to 293 rwhp with euro heads being the only change vs scots engine.

Now, I dont know the real differences of a piston width vs stroke, it was a thought, based on nothing more than my own intuitivness. feel free to comment on those differences. I also will openly admit, i know nothing about boost on our engines. However, i do have a lot of experience with running many bottles through a 928 engine, both 4.7 US and 5 liter euro.(50-75hp shot)

One great idea, was to use S4 pistsons as that would bring the CR to 8:5:1 or so, and I also do agree that you should build the platform for one way or another. (boost or NA) However, the boost way, ONLY alows for boost, where a 9.5 by slightly deeper cuts, if you can make it, would and could be dual purpose (but with lower boost potential)

Mk

PS As far as "questionable results", let me ask you. How many 5 liter hybrids have you built??? none? thats what i thought. also, how many are out there? How many do we know make near 285 to 300rwhp, all of them??? So, all you need to do is look at the vast number of euros and US part euros and their dyno runs to see what the improvement is.

mark kibort

wise thinking. to see how fast scot was this weekend in our race at thunderhill, posting times very close to equal drivers in cars with 100 to 200more hp, was pretty telling that the 5 liter gets you to a pretty high level of performance. with a NOS shot, you can have a button for 375rwhp without much effort or cost. (make sure you do a dead pedal foot button for activation)

also keep in mind, scots still runs (and so did mine) Ljetronic. thats a pretty restrictive component of the intake. i would imagine a well tuned CIS system to make more, as we have seen with JV and Dean K. (more near 300rwhp)

MK