Engine Tuning

[winstonb]

Ive just read the piece in the new Golf+ mag on how to tune up your mk1 8v engine.  Very interesting, especially that they reckon a exhaust manifold+exhaust+air filter *and* a port polish will only get you in to the high 120s BHP, a figure most people reckon they get from just adding a back box  

Anyhoo, im not exactly clueless when it come to how engines work and how this affects that, but ive come away with more questions than answers.  Main question is this:  If going 2L on the original mk1 block will yield 140+ BHP, then how come the stock 2L mk3 8v unit only gives 115?  Or more significantly, whats restricting the mk3 unit?  Has i been deliberatly de-tuned?  It doesnt seem to make alot of sence.  What bearing does this then have on the 16v units potential?

[AdamB]

I read the same article and am now saving my pocket money for a Silverstone engine. Running it on my 14" wheels should show the traffic light racers a clean set of heels.

[golfvr6]

the mk8 8v unit is detuned, and has all the emissions equipment.
the mk1 has not.

[winstonb]

hmmm, so if one was to take a Mk3 8v lump, bin the injection system and attach a K-jet system, it would produce... alot more BHP?  can this be done, ie is there any significant changes to the head?

[davidhawkins_78]

I wouldn't put the K-Jet system on there - alot of work I'd say to retro fit it ...

Probably better getting a Weber carb replacement .... full throttle performance from a carb is identical to that of an injection system, just won't be as fuel efficient elsewhere. That's the main reason for VW binning the K-Jet system over digifant - fuel performance.

[golfvr6]

use an audi 2.0l short block in the mk1, as a straight swap for the 1.8.

[winstonb]

VR6 i must have read your mind as i was just thinking of Audi blocks (there was a 2.2 on the Audi 80 too, wasnt there).  Shirley the Audi 2L block has been done, so whats the BHP like?

It also occured to me that fitting the Kjet would be a bit silly - if youve got a donor, just out the whole head onto the mk3 short engine.

Webers are expensive, and the thought exercise here is that one could produce 16v level bhp on a 8v without spending a fortune.  Obviously im missing something, else everyone would already be doing it.  

[golfvr6]

The mk3 8v block is tall, so there may be clearance problems putting it in a mk1.
The 2.2 audi engine is 5 cylinder so no good.
Audi did a 2.0L 4 cylinder, 3A i think.
This would be a straight swap for the 1.8 block, keep the 1.8 head and k-jet.
No messing about, straight swap, just need to set it up for optimal running.

[golfvr6]

A 2.0L 8v with cam/exhaust/filter and a bit of head work will easily be good for 150bhp.

[davidhawkins_78]

VR6 is spot on as usual, and when I said weber carb I didn't mean twin DCOE or DCNF type carbs - just a straight twin choke single unit as supplied with some of the TSR engines.

You can pick them up quite cheap, and new they're only ?200 odd. The main benefit is when converting / moving a foreign engine there's often wiring / loom issues. Dealing with carbs it's all mechanical, so often can be alot simpler.