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Can you get a lot of gain by running pistons that are 1mm larger?? It seems to me that the CB originally made it this amount because it wasn't enough to make a big difference but it was enough to repair an engine if needed. Has anyone seen/heard of any real gains from going the 40 over?
Stephen
You would need a Dyno, but everything else remaining the same, there should be a small power increase.
That's why you hear the expression: "There's no substitute for cubic inches" (even though it might only be a couple cubic inches in this case)
Don't forget that just by going to oversize pistons you'll also increase compression ratio.
I let you ponder that...
http://Forums.ImprovedTouring.com/it/smile.gif
MC
#14 gp VW Scirocco
Quote:
Originally posted by racer14itc:
Don't forget that just by going to oversize pistons you'll also increase compression ratio.
I let you ponder that...
http://Forums.ImprovedTouring.com/it/smile.gif
MC
#14 gp VW Scirocco
I was under the impression that the compression would stay the same. It may raise a tiny bit since your recess depth doesn't get deeper in comparison to the larger dia. piston. However if you change nothing but diameter I wouldn't think it would raise it by that much. What is the equation to measure the compression? That would be the easiest way to figure it out.
Does anyone have any Dyno results??
Stephen
Mark's correct. It will raise the ratio.
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Bill Sulouff - Bildon Motorsport
Volkswagen Racing Equipment
It will raise the comp ratio, but the amount is negligable. My .040 motor still needed a healthy cut to the head and block (stock heights to start with) to make my allowable ratio.
Steve
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87 ITB Scirocco
www.geocities.com/highspeedconnectionracing
What is a "Healthy Cut"?Quote:
Originally posted by Scirocco#28:
It will raise the comp ratio, but the amount is negligable. My .040 motor still needed a healthy cut to the head and block (stock heights to start with) to make my allowable ratio.
Steve
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
Yep, slight increase. Since the volume at TDC doesn't change (assuming piston is flush w/ the deck), but the total cylinder volume increase (because of the larger diameter piston), the ratio of total volume to volume at TDC (the CR) goes up slightly
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MARRS #25 ITB Rabbit GTI
SCCA 279608
The 'healthy cut' on my engine was in the .010 to .030 range total http://Forums.ImprovedTouring.com/it/smile.gif Not sure what it would be for you. Cutting from the head will raise comp ratio faster than taking it from the block. So we took the bare minimum for straightness off the head and then took the rest off the deck height. Ended up with a CR of 8.9:1 which is good enough and close enough for me. This is the 1st motor I've built to the limit of the rules, and I must say that it works like a champ. No hp #'s yet but I will in a few weeks hopefully. Probably in the 103-105 range. It feels a lot stronger than my now illegal HT engine from last season. Good thing I drive a VW on the street, at least the motor isn't collecting dust. http://Forums.ImprovedTouring.com/it/smile.gif
Steve
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87 ITB Scirocco
www.geocities.com/highspeedconnectionracing
[This message has been edited by Scirocco#28 (edited September 02, 2002).]
From what I know about Sciroccos ,Steve,[which is not a lot!]good JH motors"legally"
put out mid 90's for hp on the dyno.
Dino
JH is a good 15hp shorter than a HT, both with legal cams. and compression. If ya got a Jh and 10-1 and a G cam than that is about the same as a stock /legal HT.
So; if the JH- GTI is running with a HT Golf , the GTI has too much scoot...
40 over is 3-5 hp. If the clearances are right and ring gap is proper. "Total Seal" makes the power for a long time. Read the instructions!!!, No oil on the rings for installing rings!!!. deck the block a tad to flatten the block and bump compression. .020 is fine.
.03MM
You're so modest saying you don't know a lot about Rocco's http://Forums.ImprovedTouring.com/it/smile.gif Willy was telling me he put down 100hp prior to the July races. And he pulls me most everywhere.Quote:
Originally posted by Vantage #51:
From what I know about Sciroccos ,Steve,[which is not a lot!]good JH motors"legally"
put out mid 90's for hp on the dyno.
Dino
I might have to get the butt dyno recalibrated. Maybe this motor just feels stronger and has better torque over the whole rpm range. I'm going to have some actual dyno time in the next week or so, that should give me a good idea as to what I'm running for power. The HT last season put out @ 103hp, with a stock bore. But it didn't last more than the last weekend at that setup. More likely was in the 98-100 range for the most part of the season. I won't be shy when I find out what my #'s are. And if they are higher than what everyone would expect, then I'll have to give my engine builder a pat on the back http://Forums.ImprovedTouring.com/it/biggrin.gif
Steve
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87 ITB Scirocco
www.geocities.com/highspeedconnectionracing
You guys are both too modest. Had a heck of a time cutting the old cage out of the car Derek. I cant wait to hack out the perfectly good sunroof to get the hoop to fit....
ah you're lovin it Burch! Let me know when yu're working in it next, I'd wouldn't mind having a look at it.
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87 ITB Scirocco
www.geocities.com/highspeedconnectionracing
Corey and I will be putting it in next week.
We were given'er so hard Corey had the case of the grinder melting and hissing at him : )
As well I was bleeding like crazy after I wacked my head on the corner of the camera mount. Its sore today. I have to get some metal tubing for the attachmentsand then some 2" x 1/8" Metal flatbar for corner braces.
I really dont want to hack the sunroof and weld her tight. Its a super clean little car. But hey I got it for 600$ CDN : )
Andrew
Yup, you'll have to come down after work some night. ill get the beers
Hey Steve, you'll notice I said "legal"
JH Scirocco motor, I dont know of too many around these parts
Dino
Well, usually these are top secret confidential files, but I'll open the vault just this once haha http://Forums.ImprovedTouring.com/it/smile.gif
http://lowmotion.getmyip.com/uploade..._28/piston.jpg
http://lowmotion.getmyip.com/uploade...o_28/block.jpg
http://lowmotion.getmyip.com/uploade.../headclose.jpg
She's even got the JH stamp still visible on the front, a rare find in these parts. Rust is not our friend.
Steve
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87 ITB Scirocco
www.geocities.com/highspeedconnectionracing
Steve,
That's a sweet engine build. Where on earth did you find brand new manifold bolts?! Seriously, where can I get some of those good-looking .040 over pistons?
The stock JH made 90 HP with the solid head and 92 HP with the '88-'89 JH hydraulic head. They took away our compression ratio but NOT our head (since Bentley and VW both confirm later JH engines came w/ the hydro head). The orig. stock exhaust manifold was terrible, so I can't imagine any well-built LEGAL JH with a good header or Techtonics downpipe making less than about 99 BHP, IMHO. Sure, the 10:1 C.R. was worth a few more (my guess is 3-5) HP, but NOT 15!!!
As some know, my pro-built 0.020 over JH only lasted one race plus half of another warm-up this year. Frankly, it did feel slow compared to last year's HT, but it was also a nightmare inside, as attested to by the sloppy aux shaft bearing which had the timing chattering, and which may have led to a lack of oil pressure to #1 rod. It also had some of the most mismatched ports I've seen in years. I still can't believe I paid money for that piece of junk.
If I ever get around to building a new LEGAL JH, I think it can still be competitive. In the meantime, I'm going to try the old 0.040 over 1.7 that's been gathering dust for a few years... At 160lbs lighter (must be the smaller valves), it just might be OK http://Forums.ImprovedTouring.com/it/smile.gif
Eric
BTW, the 90-92 Cabriolet with the 10:1 2H engine (basically the HT but w/ Digifant injection) still made only 94 BHP with the same or similarly restrictive exhaust manifold (and a bigger throttle body). Since the Digifant engines in the Golf made 105 BHP vs. only 102 BHP for the CIS, Digifant was not the cause of any BHP reduction. Therefore, the 10:1 C.R. vs. 8.5:1 C.R. seems to be worth only 2 BHP, FWIW...
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.
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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
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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. http://Forums.ImprovedTouring.com/it/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 http://Forums.ImprovedTouring.com/it/smile.gif
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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!
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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').
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MARRS #25 ITB Rabbit GTI
SCCA 279608
Hey Stephen wanna buy my Audi????Quote:
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
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Phil
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]Quote:
Originally posted by philstireservice:
Hey Stephen wanna buy my Audi????
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" http://Forums.ImprovedTouring.com/it/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 PhilQuote:
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]
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Phil