Lars944

F18Rep, just have to say one thing to you....

Wise words!!

Porsche-Lars

deni durrell

i'll second all of you guys.... not that i have been even close to doing this sort of thing, i have been enamoured with the idea of putting a whole car together with my own tool set. sounds like fun, and something that can't be realized in a dollar amount, but very high worth in pride, learning/education, and fun..! one day.. glad to see that no one is saying "you are all wasting your money!"

nonetheless i haven't had the gusto to ask any of the yards (you know the long list) "how much for the whole thing, (provided nothing major has been removed like the trans., etc.)"? also i didn't know about <a href="http://www.autobahnparts.com/New_Arrivals/" target="_blank">Autobahnparts</a> until recently, but there seems to be a huge supply of salvage places that have all the goods out there in our country.... woohoo! it's like legos for adults..

btw: anyone know of anyone who knows anyone who's done a conversion of an early 924 engine to 944/951? i've heard a lot of mixed stuff..

nine-44

I can't keep from working on something either, that's why I'm doing the swap. Keeps me buisy while I'm saving money for more stuff to work on. I too have as much fun working on it as I do driving it.

Olli Snellman

Do as Danno wrote.
It is quite dangerous just but turbo goodies without good brakes & other undercarriage components. I found out that my 951's brakes are not good enough after some performance mods (Guru chips etc).I am now converting to S4 brakes. If factory installed bigger brakes for 220hp version and even bigger for 250hp how can some of you think that N/A brakes are good enough for turbos !
I have owned a N/A and now have a 951.I can tell, there is a huge difference in braking power.

F18Rep

I guess there are a few of you guys that are WAAAAY ahead of me on this. You must give us details on how your conversion has progressed. Are you puying pieces one at a time or do you have a turbo parts car? Details, I want details.
Here's a photo I stumbled onto while doing some early dreaming. Maybe someone could please explain why a lower compression engine would be desired as a basis for the 951? I don't get that.

For now I'm just hoping one of you 951 guys will give me a chance to buy your wrecked car before it goes to the salvage yard...Bruce <img border="0" alt="[burnout]" title="" src="graemlins/burnout.gif" /> <img src="http://arnnworx.com/TuboVsNA.jpg" alt=" - " />

pete944

Turbo engines generally run a lower compression than naturally aspirated engines. With a lower compression ratio you can run more boost pressure before detonation occurs. Boost effectively raises the compression in the combustion chamber by packing in more fuel and air in a given space giving you more power.

Geo

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by 944pete:
<strong>Boost effectively raises the compression in the combustion chamber by packing in more fuel and air in a given space giving you more power.</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">While I understand what you are trying to say, I'd like to take this opportunity to dispell an Internet myth: "Dynamic Compression Ratio." There is no such thing. Compression ratio is a static measure. The rest is actually volumetric efficiency.

That said, what you are trying to say and effectively saying is that boost increases the pressure in the combustion chamber and this is indeed why turbo (and supercharged) engines are generally designed to run with a lower compression ratio.

F18Rep

OK, I get the raising compression thing (duh), but lets just suppose we have enough boost to raise our compression to 12:1. Why is it better to begin with an engine of 8:1 than to begin with an engine of 10:1? The only thing I can image that this might gain would be (maybe) use of regular gas or less average stress on the bottom end....Bruce

pete944

You're right. I meant to say "boost effectively raises the 'pressure' in the combustion chamber". The compression ratio cannot change. It's the ratio of X# of cc's with the piston at bdc and X# of cc's with the piston at tdc. The ratio will not change no matter how much you pack into the cylinder.
I gotta start proofreading these things before i hit the button.

hrk

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> Why is it better to begin with an engine of 8:1 than to begin with an engine of 10:1? </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">In short: Lower 8:1 compression ratio allows us use more boost which allows more mixture to be burned in each cycle and higher boost also helps to overcome restrictions in intake system.

hrk

tifosiman

I agree with Olli. Ugrade the brakes if you add the HP. Heck, upgrade the brakes even if you don't add the HP.

Tifo

GOBOGIE

I went through this idea over the last several years. I finally decided to part with my beautiful '86 n/a and bought a even nicer turbo. Granted it did cost me but I'm very happy with my choice.

Geo

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by 944pete:
<strong>I gotta start proofreading these things before i hit the button. </strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">No problem. I've got your back.

BT
DT

Geo

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by F18Rep:
<strong>OK, I get the raising compression thing (duh), but lets just suppose we have enough boost to raise our compression to 12:1. Why is it better to begin with an engine of 8:1 than to begin with an engine of 10:1? The only thing I can image that this might gain would be (maybe) use of regular gas or less average stress on the bottom end....Bruce</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">OK, first of all, boost doesn't raise your CR. It improves your VE (volumetric efficiency) to over 100. Your CR remains the same, however, the pressures in the combustion chamber does increase.

As for why we start with a lower CR, I'll take a monkey stab at it.

For a given combustion chamber pressure, you'll get more fuel and air when you start with a lower CR than a higher one. More fuel and air equals more boom, equals more zoom.

DangerIsland

Danno posted once about the difference between running low CR high boost, or high CR low boost. Wish I could find that post. In essence: There's a nice medium between the two, which is where around 8-9:1 or so seems to fall. More CR up front will give you more torque when off boost, but will end up hindering your top power that you can make safely because you can't cram extra air/fuel in there when on boost without risking detonation and other problems. In the end, for turbocharging a 944 engine the CR of the NA motor is more than ideal, and that's what's important.