nine-44

What is the overboost protection set at factory on a 87 951 and how high of boost can you get from the K-26 before it just pumps hot air. Still looking for a compressor map on the K-26.

Dan87951

I think the overboost protection is set at 12psi before it cuts fuel. My K26 will pump 18psi of boost but will fade away closer to redline to 12psi. I set of aftermarket chips will take away the overboost protection.

Danno

The overboost-protection is actually in a table on the chips that's RPM-based. In stock trim, it's something like 7psi@1000rpm, 9psi@2000rpm, 10psi@3000rpm, 12psi@4000rpm+ or some such.

The K26 turbo (as with all turbos) will always be pumping hot air. It's just a matter of how much over the theoretical 100% efficiency. Here's a K26 map:

Nocturnal_Breed

Hey Danno,

Where did you find the compressor map for the k26? I've been looking and came across something that said that KKK does not publish these maps for the general public to get. If you have them can you post the maps for the k27/#6 & #8 and k29 or email them to me at nocturnal_breed@yahoo.com
I am aware these maps will not reflect the hybrib type steups we have available just would like to check them out.

Thanks

nine-44

Thanks, not everyone likes to share their homework. About some other maps, I found a few at an Audi site if I can find the maps I printed I'll post the site. Still wondering what is the max useable boost from a K-26? Anyone heard of using a cam from an N/A in a 951? I worked with a guy at Porsche that was talking about the N/Acam is a descent low cost upgrade, but he had no experience with that setup.

TonyG

That map, Danno, looks like the K26 Audi 5 cylinder Turbo map.

<a href="http://www.geocities.com/motorcity/street/1859/924turboinfo.html" target="_blank">http://www.geocities.com/motorcity/street/1859/924turboinfo.html</a>

This<a href="http://www.geocities.com/motorcity/street/1859/924turboinfo.html" target="_blank">K26 Compressor Maps</a>

Further... this website shows 3 different K26 compressor maps for the K26 for different vehicles, all of which are different maps.

How do you know for a fact which is the map that the 951 K26 cars use?

Danno

"Still wondering what is the max useable boost from a K-26? Anyone heard of using a cam from an N/A in a 951?"

Max usable boost is based upon how well-matched your fuel-delivery is to the flow. The higher the boost, the hotter the air gets. With the hotter air, you have to inject more fuel than normal (counter-intuitive, but that's what is needed to combat detonation, forget about proper air-fuel ratios). Also the intercooler gets heat-soaked after about 5 full-throttle runs. Above 16psi on the stock turbo, you're not going to get much more, so forget it.

And the Turbo and early-NA uses the exact same cam. The later NA cars have only 8-degrees more exhaust duration, not enough to make any difference. What you really want is a later lobe-center and intake closing, and on both cams, the intake-timing is identical. So forget about cam upgrades since it's the least effective mod for the money. After you've upgraded your exhaust, intakes, headers, pistons, head/valves w/p&p, turbo, engine-management, fuel-injectors and intercooler, then it's time to consider an aftermarket cam. And even then, you want a custom one ground to match the particular flow-patterns of your particular configuration. That means a Milledge or Gomes cam, nothing off-the-shelf will work.

'How do you know for a fact which is the map that the 951 K26 cars use? "

They're all pretty similar charts. I picked the chart that had the closest part# to the one that's printed on the turbo. Even then, I doubt that looking at a compressor map for the stock turbo yields much useful info; you already know you have to replace it anyway if you want more than 300rwhp.