Larger pistons??

Have to agree with Eric,

I have dyno sheets of two well prpared engines one HT, and one JH, Same dyno, same day, there was 5 or less Hp difference between the two. The HT is may produce more power in some ways and at some points on the dyno and sometimes it does not..... and when you get a hold of .040 over pistons, its pretty damn close. I ve said my peace.
 
One of the reasons the CIS-E and Digi motors in the A2 cars make more power (besides an extra 1.5 pts of compression) is the intake configureation. The A2 intake has much better runners than the A1 intake. Couple that w/ better exhaust and that's why they make more power. Of the 12 hp difference (JH vs. RD), probably 3 of that is due to the higher compression, the rest is because it flows better.

------------------
MARRS #25 ITB Rabbit GTI
SCCA 279608
 
So the general consensus is that there should be a 3-5 hp difference betweeen a well built 8.5:1 motor and a similarly built 10:1?

I was a little surprised when I pulled the valve cover on the stocker from my 87 rocco. Hydro head, 8.5:1 bottom and the engine code on the tag in the trunk said JH.

I've always liked the solid lifters though, like the adjustability. Where does the hydro head make the extra 2 hp at?

I think the thing that will help my numbers the most is the exhaust. It is custom built to my specs, and is most likely the biggest reason why I have better top end this season.

She's on the rollers friday for some tuning. I'll post up some graphs after I'm done.

Eric, those pistons came from good old Tectonics Tuning. Not a bad price either.
And the intake bolts are from the local VW dealer. I was feeling very vain the day the motor went together and didn't want some rusty bolt holding it together haha

Steve

------------------
87 ITB Scirocco
www.geocities.com/highspeedconnectionracing
 
HT, bigger cam, more comp,bigger throttler body. I've had and built both. HT much faster if they are legal. IMHO. I have a Jetta and a Rocco, guess which one gets the good stuff?
The A2 can draft up to and pass the A1 but not the other way around. The Rocco does handle better, stop better, for a while.
Also I have never seen a real hydro JH in any Rocco up to and including the late 87.
The cheap books show em but they have never turned up in my shop. Believe me I have looked for them. The real VW parts books say that they dont exist. MAYBE in a Cabrio later than 90. The factory made a pile of Cabs from old stock.
SO: if you got a Hydro head on your Rocco ,you better have a factory shop manual saying it came that way. You wont find one, I think. MM
 
Don't want to rehash old stuff, but the hydro head JH is covered in BOTH of the official VW publications, including the Factory Authorized 1985-up Scirocco Bentley Manual (e.g., '88 Scirocco "JH" does NOT get valve adjustments), and the genuine factory microfiche for the 1984-up Scirocco(only). I just scanned in some of the microfiche, and would be happy to email the 3MB tif file to anyone who wants it. It clearly shows the JH engine code and the 026G hydraulic camshaft for the '88 Scirocco (and 049J solid cam for '84). BTW, a friend's original 1988 CIS Cabriolet has a genuine JH with hydraulic head, as confirmed by the trunk label, so the engine was definitely produced in that configuration.

Yes, all else being equal (which it is), the 8.5:1 JH should only be down 3-5 hp from a 10:1 HT. Keep in mind that either engine will be down compared to a Golf due to the untuned A1 intake manifold runners. I think the 026G hydro JH makes the extra 2 hp at the the same 5500 or slightly higher rpm compared to the 049J solid JH, but I'll try to double-check that.


[This message has been edited by Eric Parham (edited September 12, 2002).]
 
Ok just a little update, and then I'll put my flame suit on and get ready for the barrage.
smile.gif


Dyno results are in, but I have to figure out a way to make them a web friendly file. Might get to it early next week.

But the results......JH, .040", Solid lifter head, very custom exhaust, made 105hp and 104ft/lbs

Talk amongst yourselves
smile.gif


------------------
87 ITB Scirocco
www.geocities.com/highspeedconnectionracing
 
Well Steve, those are some stout numbers for a 8.5:1 engine! (I know...9:1 with the allowed increase) Well done, it just seems hard to get my head around how my 0.020 engine with 10:1 will only make 107hp. I would have thought that there was more then 3 hp in a extra point of compression, and the better intake manifold, and hydro head... No need for the nomex, it's good motor no doubt and that's all it is...a good motor.

I guess I'll have to really get my ducks in a row to stay ahead this weeekend! It's mallards first then sea ducks right??

Double weekend...double fun! Just leave JP's advice at home OK?

See you Saturday!




------------------
Colin Harmer
ITB 2-Red Golf
Halifax, NS

http://www.motorsportsolutions.ca
[email protected]
 
I have actually heard of higher numbers then that for a legal prepped JH motor from a very respectable engine builder. But, from the same builder, he said that the hydro motor should still put out at least 5 hp more than that. We all need to realize that there are different variables. What gear was being used, different dynos, Different final drives, etc. All of that makes a difference. Unless of course you were speaking of a chassis dyno? But then the other stuff still affects it on the track.
 
I've spoken to most of the well known VW folks in the US (at least from an IT perspective). Seems that the general concensus is that the A1 is the better handling chassis, but the additional power you get from the A2 cars more than makes up for the 100# weight 'penalty' and they 'shortcomings' of the chassis. One place only builds A1's for ITC, they build A2's for ITB. But I imagine that would change if they drop the Rabbit GTI weight to where it should be (based on 'the formula').

------------------
MARRS #25 ITB Rabbit GTI
SCCA 279608
 
Originally posted by RSTPerformance:
What is a "Healthy Cut"?

Also does anyone have the equation for compresion? How does SCCA measure it? I want to probably shave the head over the winter but I want to know how to calculate it!

Stephen
Click to expand...
Hey Stephen wanna buy my Audi????


------------------
Phil
 
Originally posted by RSTPerformance:
What!!! Explain!!! Are you still going to the runoffs? Are you burnt out, got a new car or just ready for something new? E-mail me at [email protected]
Click to expand...
Sorry it took so long to get back to you Stephen. I have two reasons for wanting to sell my Audi. Yes, I have a line on another car and two is a business reason. They kind of go hand and hand.....can you say "sponsorship"
smile.gif
....as you can tell by now I didn't make the runoffs. Sorry it would have been fun, I'm sure. Tell me what happen. I haven't heard anything about it yet. Sooooo if you are interested let me know. I'm willing to negotiate.....see ya Phil


------------------
Phil
 
You must log in or register to reply here.
Back
Top