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Tue Jun 10, 2008 4:17 pm

Hello,
I`m working on an 1835 69mm crank 92mm pistons full flow Heads are new with heavy duty springs.I have the deck at .000 should I get more shims?Looks like head are stepped where the pison might go it it loosens up.I have a .090 and a .010 under the cylinder already.Any suggestions I don`t know what compression ratio I want.Whats recommended?Thank you in advance.

Here it is.

1835cc Longblock
Refurb Case open 94mm for TW Cylinders (Thick Wall)
69mm C/W Crank
Straight Cut Cam Gear
Cam Bolts
12lbs Flywheel
Cam W110
I-Beam Connecting Rods
92mm Pistons Standard Thick Wall
DP Heads Stock Hi-Rev Spring Moly Retain
Solid Shaft Rockers 1.1:1
Main Bearings
Cam Bearings DBL Thrust
Rod Bearings
Steel Pushrods
Hi-Po Lifters
Swivel Feet Adjusters
Push Rod Tubes
Engine Seal Kit
Rear Main Seal
Gland Nut / Washer
Dist. Pinion & Brass Gear
Engine Nut/Bolt Kit
Lash Caps
Oil Pump
Head Stud Kit
Deep Sump 1.5

Tue Jun 10, 2008 4:23 pm

92x74 is a 1968cc engine.

Tue Jun 10, 2008 6:47 pm

A safe clearence from piston to head is around .050. I've seen as little as .040, but I would stick to the .050. You are going about the build correctly in the sense that you want as little deck height as possible. If you can get your deck around the .050 mark with your desired compression ratio, the gas will get burned the most efficiently. Some people set their engines up with zero deck then use a copper head gasket to make up the minimum deck clearence. Some people are chicken, like myself, and like to leave a little clearence from the piston to the copper gasket of around .005, so that the piston has minimal chance to hit the gasket. I would use a .090, and a .020 cylinder shim to get a .010 piston to cylinder deck, and then use a copper head gasket of .040 to get your .050 total minimum piston to head clearence. By using this method you will either need your heads hemi-cut to increase the size of the combustion chamber, or flycut to decrease the size to obtain your desired compression ratio. As for compression ratio, it depends on what you are going to do with the engine. Higher c/r will give you a little more HP, but you will need to run the higher octane pump gas that is more expensive. Lower c/r will allow you to run the least expensive pump gas, and the engine will probably run a little cooler. I have a similar configured 1776 with the exception that it has ported 40x35.5 valved heads. I have a dual set of 40 IDF's, and have my c/r at 9.5:1. I would use a c/r anywhere from 8.0:1 to the 9.5:1 depending on what you are doing with the engine. Maybe some others will chime in about recomended c/r.

Tue Jun 10, 2008 7:11 pm

You also have to remember that the recommended squish is .060 or less. The Squish is the distance from the top of the piston to the deck of the head.

The height of the step will enter in to your squish setting.

Tue Jun 10, 2008 7:18 pm

I measured the step that was cut from the head if the piston loosens up and it`s about .030 I always run 93 octane in my car.Daily driver just like messing with those neons with body kits.

Tue Jun 10, 2008 7:55 pm

Like timsvw mentioned, if you still have the step in the head, it will need to figured in your calculations. The minimum clearence is the distance between the piston, and the deck of the head. Usually the step left in the head is smaller in diameter than the piston, so that the piston will not clear it, so you usually need to consider the face of the step the deck of the head. I have seen more than one engine that was built using the step height of .050 as the deck height minimum clearence. Since the step inner diameter was still around the 85.5mm of a stock piston, the larger than 85.5 piston that was used hit the head at the face of the step. You will probably need to set your minimum .050 total deck height to the surface of the step. If the step is .030, this will add to your combustion chamber cc's. If you are going for performance, and are running 93 pump gas, I would go in the 9's for compression. If you had a total .050 deck, you would need a combustion chamber in the high 40's cc range to get in the 9's for c/r. Less than 50cc's is fairly small for a combustion chamber. I would guess you would need to have your heads flycut to make the combustion chamber smaller. This usually removes the step entirely, and then you don't have to worry about it affecting your calculations. The cylinder seating surface would then be level with the deck of the head, and you would use this surface for your head to piston clearence. An 1835 with a .050 deck, and 46cc combustion chambers would give you around 9.4:1 c/r. Take and cc one of your heads to get an idea of what size it is, then you can figure if you need to make the combustion chamber smaller.

Tue Jun 10, 2008 8:11 pm

If he has a .050 piston to step clearance and a .030 step, that will give him a .080 squish. Anything over .060 is too much. The lower the squish setting the better. Do a search on quench and/or squish.

If he is going to keep the step, it's better to machine it to allow the piston to clear it and set his piston to step clearance to .030 or less.

Wed Jun 11, 2008 6:11 am

Yes, the lower the squish setting the better. This is why I am suggesting to him to run a total deck height of .050, or .050 "squish" that you are referring to. I also suggested he should run 9.4:1 static compression. To achieve 9.4:1 c/r with an 1835 with .050 deck/squish, you would need a head combustion chamber of 46 cc's. Most of the stock heads I have seen have combustion chambers in the mid to low 50's for cc volume. To flycut a head that has, say 53cc's, to 46 cc's, you would have to remove quite a bit of material. The amount of material removed would most likely completely remove any step, plus a little more of the head deck. This would remove the variable of the step from the calculations all together. If he were to keep the .030 step, then yes, you could machine the step to allow piston clearence. Then all he would need to do would be to use a .090, and .030 cylinder shim to achieve a .020 piston to cylinder deck, then the remaining .030 of the head step would give him his total .050 deck/squish. Let's see what he comes up with for his head cc's to see if they would need to be flycut enough to take the step out of the mix.

Wed Jun 11, 2008 8:14 am

Beatles_1969
The ideal static compression ratio for your combo is right about 8.8:1 give or take a little.
To properly answer your question we must first know the CC's of your combustion chambers, I don't like stepped heads unless the the step has exactly the same bore diameter as the cylinder. The edge of a protruding step into the cylinder bore is a hot spot and a reduction of the quench pad, You may or may not need some machine work done to correct that.

Wed Jun 11, 2008 7:49 pm

Hey SRP1, I'm not disagreeing with you, but just out of curiosity, how did you arrive at 8.8:1 as an ideal c/r?

Wed Jun 11, 2008 8:00 pm

Im not a big fan of high compression either and I think you are both too high :D

But Id like to hear the explaination too.

On most cylinder heads, isnt the ridge completly covered by the cylinder?

Wed Jun 11, 2008 8:34 pm

While trying not to give Beatles_1969 information overload, my reasoning for such a high static c/r is based on dynamic c/r. While reading some posts by jamestwo, he was talking about dynamic compression to set your static c/r. Dynamic compression is the actual compression that is calculated while both intake, and exhaust valves are actually closed. The opening/closing of the valves, and piston speed due to different length rods changes what the dynamic c/r ends up being. Jamestwo has had the best experience from his many engine builds with running a dynamic c/r of 7.5:1 for a pump gas street car. I'm assuming the I-beam rods being used are the stock 5.4 VW length. With the 5.4 rods, .050 deck, 46cc chamber, and 69x92 displacement, this comes out to have a static c/r of 9.4 with a dynamic c/r of 7.3. I'm always looking to gather more info on engine building. Why do you like lower c/r's Jimmy111? As for the cylinder head ridge/step, the cylinder does cover this ridge, but there is usually additional material that extends past the cylinder opening that the piston can come in contact with.

Wed Jun 11, 2008 9:31 pm

[email protected] wrote: Hey SRP1, I'm not disagreeing with you, but just out of curiosity, how did you arrive at 8.8:1 as an ideal c/r?

Experience, trial, and error, dyno time.
Your explanation of setting deck height is good, .040-.060" is the "optimum" window for the correct amount of squish.
I find that when it comes to compression ratio's, if you ask 10 different builders you will get 10 different answers to the question, based on the list of parts and [email protected] providing the correct deck set up procedure, I know 8.8:1 will run really good in this combo. Had Beatles_69 opted for the Mahle cylinders instead of the AA's I would have recommended 8.0:1 give or take a little based on the thinner cylinder wall of the Mahle, and its poor ability to maintain shape and transfer heat efficiently.
Also based on his cam and a 50cc combustion chamber the static compression ratio with a .050" deck is 8.848:1. The dynamic compression ratio based the cam specs of a 110 work out to 7.824:1, pretty good for a strong running reliable street engine IMO.
As I said to correctly answer this question we need to know what the combustion chamber CC is.
Jimmy I have seen in some instances where ID of the step runs into the cylinder, not good IMO as it forces you to run your piston deck down from that step. The step ID needs to match the bore of the cylinder.

Thu Jun 12, 2008 6:44 pm

SRP1, thanks for the info! Like you said there are many different answers to this question depending on who you ask. I, by no means consider myself an expert on engine building, and I'm always wanting to learn more. I've been talking with friends that have had engines they built that just seem to run really good compaired to others. They were built not knowing anything about dynamic compression. Once we figured the dynamic c/r, we found that the good ones were all pretty close to this "magic" 7.5:1. Jamestwo, who got me started looking into dynamic c/r's, uses a calculator at a site; http://www.kb-silvolite.com/calc.php?action=comp. This calculator gives me a dynamic c/r of only 6.8 when I enter the info for the 8.8:1 you recomended. I don't have a E110 cam card in front of me, but I estimated the intake closing point to be 52 degrees ABDC. For some reason this calculator adds 15 degrees to this number to do it's calculations. Do you use some type of online calculator to figure dynamic compression? How did you come up with the 7.824:1?

Thu Jun 12, 2008 8:27 pm

Same calculator.
W-110 closes at 48* ABDC.

Sat Jun 14, 2008 10:43 pm

The head is about 55cc`s

Sun Jun 15, 2008 4:41 pm

I just found out that its not a 69mm it a 74mm crank so its a 1968cc engine.If it matters.

Sun Jun 15, 2008 7:58 pm

Yes, having a 74mm stroke crank instead of a 69mm one will make a difference in the calculations. If you went with a total deck/squish of .050, you would end up with around the 8.8:1 compression SRP1 is suggesting. Why don't you go with that. If you are going to leave the step in the head, have a machine shop open the inside diameter to the same size of the cylinder like timsvw mentioned. This way the piston will have no chance of hitting it. If the step measures .030, then all you would need would be a .020 piston to cylinder deck height to get your .050 total. You never listed anything about carb's. I would run at least a set of dual 40mm IDF/HPMX carbs. Some people like to match the venturi size of the carb to within 4-6mm of the intake valve of the head. If you are running the 35mm intake valves of a stock VW Head, a 28mm venturi of a 40mm carb would work good. You could get a bigger 30mm set to open up the 40's also. 44's come with 36mm venturi's that you could choke down to a 32mm set if you wanted to use them.

Mon Jun 16, 2008 4:17 am

Heads have stock fly on them.I have a Weber progressive 32/36 to go on it.Ran out of money so thats a carb I got.Unless someone wants to trade parts for a set of Dual carbs.

Sat Jun 21, 2008 5:49 am

I`d like to thank everyone for the help you gave me.