Head milling...

[sick620]

Ok I searched with no luck....

Want to mill a u67 thats running on an l20b bottom end.... A. How much should be milled for a nice compression for street use on premium . Compression is stock otherwise.... B. Whats the max it can be milled? .... C. what does the average mill cost? thanks!

[nathan_454]

C. what does the average mill cost? thanks!

 

I just payed 36 dollars last week to have the head for my L20b milled.

 

 

The other two questions i cant help ya with, sorry

[datsunaholic]

Milling the head solely to increase compression isn't really the best idea. Remember there's a timing chain that now becomes that much more slack. Solvable by shimming the cam towers, but that then changes the wipe pattern on the rockers, which may necessitate new lash pads. All that just so you can pay more for gas? You want real power, you need to have the head ported and polished. Might as well start out with a closed-chamber A87 or W53 if you're gonna do that.

 

Also, if you max mill it now, you won't be able to mill it again. Rule is take off ONLY what's needed to make it straight.

[banzai510(hainz)]

Rule is take off ONLY what's needed to make it straight.

 

 

 

EXACTLY!!!!!!!!!!!!!!

can you afford to buy Premuim?

buy a 38/38 weber thats going to be the best bang for the buck on a L20

[JustinB]

Agreed. Don't over-mill your head.

 

You might be able to get different pistons to up your compression, I've never looked into it.

[sick620]

well im building an l20b. Im just keeping the bottom end stock and rebuilding it.... Main bearings, rod bearings, rings, gaskets, hot tank, and new timing set. Then Im putting the work in the head.... l28 intake valves, port n polish, valve job, milling the head, bigger cam.... (not much bigger), bigger lash pads, shiming the towers, etc... Im running a u67 head for sure..... NOT A PEANUT.

A u67 head is the same as a sss head, u67 just has more flow. Only thing a peanut head has going for it is compression.

After motor im going bolt ons, Lightened fly wheel, offy intake, headers or l16 exhaust ( i have one of each), Weber 32/36.... only carb i ever run :rolleyes: . I already only run premium in the datsun, but thats not what i asked :rolleyes: . Can anyone answer the ?'s I needed answered?

[sick620]

C. what does the average mill cost? thanks!

 

I just payed 36 dollars last week to have the head for my L20b milled.

 

 

The other two questions i cant help ya with, sorry

how much was milled?

[Jesse C.]

I would just hunt down a peanut chamber head and start from there. No hassle with cam tower shims and you can surface it later if needed without worrying too much.

 

If you want more compression and want to keep the head you have, then I would suggest L28 Pistons. As for the Offy manifold, is it the dual plane one?

[datsunaholic]

The peanut head isn't just for compression. It changes the quench area which avoids pinging. That's the big problem with the open-chamber heads, when the compression is raised they have a tendency to ping even running premium fuel.

 

The U67 is nothing like a SSS head. The SSS head had more flow stock than a U67. The U67 had bigger ports than a A87, but an A87 isn't a SSS head no matter what anyone says. A true SSS head is a 219 or V912.

[nathan_454]

how much was milled?

 

I Don't know....JUST enough... which seams to be the correct answer lol

[datzenmike]

Ok I searched with no luck....

Want to mill a u67 thats running on an l20b bottom end.... A. How much should be milled for a nice compression for street use on premium . Compression is stock otherwise.... B. Whats the max it can be milled? .... C. what does the average mill cost? thanks!

 

 

A u67 head is the same as a sss head, u67 just has more flow.

 

A U-67 head is NOT the same as an SSS head. A true 219 (or later re-issued V912) SSS head first, has a closed combustion chamber while all U-67s are open. Second, while the valve sizes are the same, the intake ports are not. In fact the true SSS head has intake ports that have over 19% larger cross sectional area. That's almost 1/5 larger! So no the U-67 does not have more flow than an SSS head.

 

Only thing a peanut head has going for it is compression.

 

While it is true that the peanut, or closed chamber head has more compression than an a U-67, (or any open chamber head) this is not the only thing going for it. If the peanut chamber head was designed to be the same size as the U-67 head it would still be superior in performance. Here's why.

 

As the compression ratio goes up so does the temperature of the compressed air. Sometimes enough to set the fuel air mixture off before needed resulting in pre-ignition or 'pinging'. When gas and air enter the cylinder they are not a thoroughly homogenized mixture. There are rich and lean areas possibly very fine droplets suspended in the in-rushing air as well. Some amount of trapped cylinder heat is used to vaporize these droplets thus cooling the cylinder head, spark plug, valves and piston top reducing the cause of an ignition point or hot spot. Lean areas tend to run hot while rich areas run cooler and can build up carbon deposits which themselves can trap heat and become glowing hot. Add the heat from compression and there is an increased chance of pre-ignition. This is typical of all open chamber heads where the combustion chamber extends out over the full width of the piston top and acts like a domed roof.

 

The closed chamber or peanut L head is much different. Here the open or domed roof does not extend fully to the cylinder edge and there are places where the piston comes up to TDC and almost touches the head surface being separated only by the thickness of the head gasket, about 1.2mm. This thin gap is known as the quench or pinch area and on the L head extends around the whole combustion chamber. When the piston reaches TDC, the air caught between the rising piston and the head surface is violently 'pinched' out into the remaining combustion chamber and generates turbulence or swirl. Turbulence is good for two good reasons. First it homogenizes the air/fuel mixture like stirring milk into coffee. A homogenized mixture burns more readily and efficiently with less waste. Power and mileage increases. Second the turbulence helps to remove heat from problem hot spots and evens out the average combustion chamber temperatures, lessening the chance of pre-ignition. With less chance of pre-ignition more timing can be added and/or compression ratios increased for a further increase in efficiency.

 

 

... but thats not what i asked :rolleyes: . Can anyone answer the ?'s I needed answered?

 

By my calculations... L20B with open chamber head and stock compression of 8.4.

 

Remove

0.5mm (0.020") = 8.7

1.0mm (0.040") = 9.08

1.5mm (0.060") = 9.48

2.0mm (0.080") = 9.9

 

 

I see it took me an hour and a half or more to write this out. :lol: Thanks Doug. It's raining and I got the morning off so nothing else to do.

[sick620]

how come in "how to modify your nissan datsun overhead cam engine" it says that the u67 is the same as sss?

[sick620]

 

 

 

By my calculations... L20B with open chamber head and stock compression of 8.4.

 

Remove

0.5mm (0.020") = 8.7

1.0mm (0.040") = 9.08

1.5mm (0.060") = 9.48

2.0mm (0.080") = 9.9

 

 

I see it took me an hour and a half or more to write this out. :lol: Thanks Doug. It's raining and I got the morning off so nothing else to do.

Thanks mike!

[datsunaholic]

how come in "how to modify your nissan datsun overhead cam engine" it says that the u67 is the same as sss?

 

Because the writer of the book was more concerned about 6-cyl L-series engines and did very little proper research on the 4-cyl engines. That's not the only inaccuracy. It's a decent book but it's not the definitive work that some make it out to be.

[datzenmike]

how come in "how to modify your nissan datsun overhead cam engine" it says that the u67 is the same as sss?

 

Either you're wrong (or mistaken), or they are wrong or mistaken or printing error. Haven't seen it.

[deadmonkey]

As for cost, I had Mulder here in Boise do all my work, he charged $50 for the milling and $115 for the valve job.

[john510]

Listen to what these guys are saying ,dont mill a head if it doesnt need it.If you want more compression use L-18 pistons they are the same as the L-20b except for the dish size,L-20 is 11 cc dish and L-18 is 4 cc dish.I dont know what compression would end up being but that will be better than milling a head.

[sick620]

but more expensive..... poor mans build :(

[nismo dr]

my .02 if your doing all that head work your going to be under carbed with a 32/36.

 

i had a ported and polished U67 with a big cam and it was very mediocre until i swapped out the 32/36 for dual su's. then when i swapped out that head and went to a stock closed chamber w53 its way moar better. night and day, I cant even put into words how much better it runs through the whole power band.

[datto510]

my .02 if your doing all that head work your going to be under carbed with a 32/36.

 

i had a ported and polished U67 with a big cam and it was very mediocre until i swapped out the 32/36 for dual su's. then when i swapped out that head and went to a stock closed chamber w53 its way moar better. night and day, I cant even put into words how much better it runs through the whole power band.

 

You still got that u67? Hmmmmmm?

[nismo dr]

I do, the cam broke, found that the head shop didn't put one of the tower dowels in, so they got to go through it again and buy a new cam, just got it back from the head shop - still in the bag

[datto510]

I do, the cam broke, found that the head shop didn't put one of the tower dowels in, so they got to go through it again and buy a new cam, just got it back from the head shop - still in the bag

 

 

Have you eve thought about parting with it? ;)

[nismo dr]

took the thread jack to pm :P

[john510]

but more expensive..... poor mans build :(

All the stuff you want to do is going to get expensive.Im building an l-20b right now and ive spent over 1500 bucks and im not done spending yet,whats a few more dollars for pistons.