# 8v dyno results



## Keif (Dec 28, 2012)

Hey everyone, I got my 1990 mk2 scirocco gt2 dyno'd the other month and I'm not sure if the power outputs are a bit small?

110whp and 146lb/ft at the wheels. (will come back with what revs this was at when i get a hold of the sheet again)
1.8 8v (golf mk1 engine originally)

The speclist is:
288 cam
40thou oversize bore
uprated pistons (not forged)
skimmed head
balanced lightened and shotpeaned crankshaft
uprated bigger valves
polished/ported head
4-2-1 manifold
twin 40 weber DCOE
polished and ported intake manifold
blueprinted
gas flowed head

I would like to add here that I do not know the compression ratio of this engine unfortunately, the guy who built it didn't have the figures on his when i asked him, but he said it's easy enough to calculate on my own apparently.


Another thing I wanted to add was:
on the road sitting at 50+ mph cruising the car pulls smooth and clean through gears.

However after sitting at idle in traffic when the engine gets a bit warmer it can be a bit of a nuisance to get up to speed, 
for example the problem i'm having would go like this.
>sitting in traffic waiting for lights, engine hotter
>lights go green, rev to 1500-2000 rpm and pull off
>gradually gain speed in first gear with minimal throttle
>if given any more than 1/3 throttle at this point, the car severely bogs down and has no power until put back to low throttle

the only way to fix this it seems is to slowly build throttle pressure over time and accelerate very slowly 

Why does this problem occur? what is happening? Is it because my car has bigger jets/race cams etc? 
Is the bowls in the carbs empty/full?


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## nemo1ner (May 5, 2004)

Wow. 110whp is a bit low for all of that work. I managed 100whp on just a g grind cam, header, straight pipe, larger TB and some advanced timing. This was on a JH with stock internals on CIS. I don't know much about carbs, but with that setup, you should be hitting higher.


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## Hummdog (Nov 23, 2009)

I bet the carb forum could help you out. Probably have to tune the carb differently is my guess. If the timing is off you can have problems too. 

Here are a few generic links, they may help for finding your compression ratio.

http://www.wikihow.com/Calculate-Compression-Ratio

http://www.csgnetwork.com/compcalc.html

Awesome to see you got a dyno on it, thanks for posting it up. Gives me ideas for what will work with my 8v


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## Keif (Dec 28, 2012)

Found the sheet printout, here it is.

I still think this engine should be spitting out figures more in the 150whp region.. The engine was rebuilt 4000 or so miles ago, I wasn't told what the compression ratio is and I'm not too sure how to find that out accurately. I'm also seeing that the car never went over 6000 rpm, which leads me to think something could be pretty wrong in there since a lot of 8v's rev to 8k ish
Is there anything else that you guys can see that's noticable on the sheet? thanks


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## ps2375 (Aug 13, 2003)

I'd find another place to dyno. How well do their numbers translate to the real world? You have way more TQ for that rated HP than I would expect. Unless that is also FW TQ. Find a place that doesn't worry about putting FW power on the sheet, cause that is just an estimate based upon what they think driveline losses are. IMO, if they are willing to guess about that, they are willing to guess about what you are putting to the ground.


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## Keif (Dec 28, 2012)

Well that was the only pleace within 100 miles of me that knew how to set up carbs.. 
He told me the carbs were already well balanced (the engine was built and set up aleady in the 90s in south africa before the last rebuild)


The main problem I have driving it daily is 80% of the time it won't keep running at idle unless I'm putting my foot on the accelerator a bit. And after pulling away from standstill at traffic lights or something, the car doesn't accelerate properly if you put more than 1/3rd of the throttle in, it just grunts and sounds like its sucking nothing in..

The man that dynoed it also took the vacuum advance pipe off, not sure if this is a normal thing to do? 
I live in scotland and as of right now, it's cold and the car was dynoed in summer, when its around 10 degrees celcius (right now its around 0-5) Not sure if the temp changes are resulting in the car running too lean now?


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## ps2375 (Aug 13, 2003)

Dunno about carbs, I've never owned a vehicle with one(or two). I may in the near future, but that could be headed for MS in the long term.


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## Tom A (Oct 20, 2004)

What I don't see on that printout is AFR. Carbs being balanced is important, but doesn't help much if the jetting is out to lunch.

What size chokes are you running? Looking at the weber chart, seems like 40 DCOEs may be a little small for a high revving 1.8l engine.










Carb tuning is equal parts art and science, suggest joining this, and looking at some of the tuning info and whitepapers in the docment library:

https://groups.yahoo.com/neo/groups/sidedraft_central/info


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## Keif (Dec 28, 2012)

The chokes are on the graph as: '55F21 Idle'

not sure if this is what you were wondering? My father said when the engine was built the builder recommended 40's over 45's to him so I'm not too sure.


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## Tom A (Oct 20, 2004)

Keif said:


> The chokes are on the graph as: '55F21 Idle'
> 
> not sure if this is what you were wondering? My father said when the engine was built the builder recommended 40's over 45's to him so I'm not too sure.



55F21 is not a choke size, I think it is a idle jet size, but not 100% sure. The chokes, also known as the main venturies, are going to be a number in millimeters, with a 40DCOE the most common options are 28mm, 30mm, 32mm, 34mm, and largest available is 36mm. Odd numbered sizes do exist, but are less common.

You may need to pull one out to check, they are numbered. Was this engine built to a race series rule set? I know the US SCCA production category specifies what size venturies are allowed, and are generally smaller than ideal.

If it has 34mm (or smaller) chokes, it could explain it running out of breath around 6000 RPMs.

Did the dyno place have a wideband 02 sensor measuring the air to fuel ratio across the RPM range?


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## Keif (Dec 28, 2012)

I have no idea about the venturies, can't remember anything about their size.

when this same engine was in my fathers car (1984 vw passat) with a 5 cylinder rev counter he said he remembers it going up to around 7-7.5k rpm on there, which is around about 8000 rpm ish.

This was just built for my dad as a fun street car, no racing regs.

The car has no ecu, it's a mechanical dizzy and carbs, no ecu type cables going into a computer anywhere that i can see. it's just a black little box that sits behind the firewall, so i don't think there's an o2 sensor on the car


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## Tom A (Oct 20, 2004)

Keif said:


> The car has no ecu, it's a mechanical dizzy and carbs, no ecu type cables going into a computer anywhere that i can see. it's just a black little box that sits behind the firewall, so i don't think there's an o2 sensor on the car


I am not asking about the car, I am asking about the dyno shop.

Normally they put a probe in the tailpipe and monitor the air:fuel ratio during the runs, and it is normally displayed on the graph, like on the bottom of this one:


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## Keif (Dec 28, 2012)

There was definitely something in the exhaust that he stuck in, but that wouldn't explain how there's no 2nd graph with that.


It wasn't very modern. the reading from the dyno itself was on a dial type thing; which ive never seen, as opposted to digital.


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## impulse byer (Mar 8, 2003)

It sounds lean to me. things to check would be fuel pressure no more then 3.5 psi but more important is the volume of fuel. can you get the rest of the jet sizes it would help. 

maybe some of this will help
http://cnx.org/content/m37431/latest/


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## Keif (Dec 28, 2012)

My idea of what was happening was the fuel pump is a low pressure electric one, i previously set up a pressure regulator and the pressure guage showed nothing at all when tested. I think what's happening is the bowls aren't getting enough fuel supply to fill the bowls inside and the car is running lean consequently, does this sound like it could be accurate?


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## impulse byer (Mar 8, 2003)

Does the fuel system return or dead end at carbs? It does sound like your on the right path.


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## Keif (Dec 28, 2012)

I don't think there is a return pipe, will check next time im at the car


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## Keif (Dec 28, 2012)

The fuel return has been blocked off


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## kens_74_911s (Mar 5, 2014)

*tuning*

What type of exhaust are you running ? Make sure you don't have to much backpressure. It seems you are set up to flow pretty well. What goes in needs to come out efficently. 

Where are your idle mixture screws set? They should be about 1-1/2 turns out, that may give you an indication if your idle jets are to rich as they transition you from idle to just short of mid throttle where the emulsion tubes pick up Mid RPM / leading to main circuit. May also want to check accelerator pump diaphrams to make sure your acc pump circuit is helping your low rpm acceleration.


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## wveuro31 (Jul 25, 2009)

With the way your graph looks id say the carbs need tuned better... the power curve is erratic, it needs to be smooth 

Sent from my SAMSUNG-SGH-I537 using Tapatalk


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## G60 Carat (May 14, 2004)

288cam and hp is falling off at 5500rpm? And they pulled the trigger at 6000rpm? Something doesn't set right with that, should be reving to at least 6500rpm (redline for a stock 1.8 8v engine/cam), or somewhere between that and 7000rpm with that cam, and it should be building HP the whole way to 6500rpm.

There is definitely a setup issue here.


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## Keif (Dec 28, 2012)

(Sorry to bump an old thread!)

Hi all, after keeping the Scirocco off the road for a year I've decided to finally get it sorted in the next few months, I'll do my best to keep you guys posted with upcoming jobs to be done 

G60 Carat: I know, I thought that myself when I had a good look over the graph. A couple weeks after the tune I was having a little check over on the carbs and I found that the car had left the workshop only opening 3/4 throttle.. Says it all really doesn't it.


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