L20b build questions

[Five10er]

I'm in the middle of a mild l20 build. I'm using stock pistons, a u67 head, l20 block, a reground cam with .305 lift at the lobe, twin sus off a z car, a long tube header and 2 or 2.25 inch exhaust piping. I have some questions.......

 

1) Whats the easiest way to check piston-valve clearance through the combustion cycle? I'm going to shave the head for a 9.5-10.0 CR, and dont want to overdo it.

 

2) Will the 46mm l24 carbs be too much for my engine? I need it streetable

 

3) HP estimates???

 

Thanks

[banzai510(hainz)]

2inch exhaust is enough

whats the cam duration??????? if its not a too long a duaration I wouldnt worry about it.

the lift is .305 x 1.48=.451 which isnt all that big of lift. Personally I would have went bigger.

A new cam/regrind news new retainers and lash pads for sure. You might be able to get away with new lash pads only, but your on your own.

 

How much you going to shave?????If alot you need cam tower shims otherwise the cam will retard abit cause it thinks the chain is longer.

 

bst way to raise compression is to get a W53/A87 or a SSS closed chamber head to get a 9-1 compression motor out of a L20 as a stock L20 is about 8.4-1

 

You could buy L18 pistons also to raise the compression up as the stock L20 is 11.46 dished and the L18 which is the same bore size but only 4 cc dished.

 

However a U67 head is prone to detonation(but does have the bigger 1.375 intake ports) if higher compression aand cheap gas. a closed chamber is less prone to detonation.

 

a closed chamber head and L18 pistons will give you enought compression with out milling the head.

 

But to keep things on the cheaper DAILY DRIVER side I would get the cam set up and carb and just call it good.

 

My estimates are about 115-120 at the crank as a stock L18 SSS is about 112hp from factory spec book I think.

a stock L20 I think I seen on a engine spec in a car was 105hp

Edited December 22, 2008 by banzai510(hainz)

[Five10er]

Sweet, Id never heard of cam tower spacers before. As for the head shaving, I think its worth a try since I can do it for free, and I can always water inject if detonation is a problem. Looks like about 90 thousands would come off to get a good compression ratio. Dont know the cam duration yet, but has anyone had piston valve clearance problems with this mild of a setup?

Thanks again

[banzai510(hainz)]

.090 is alot to shave esp if you dont have too. Cause if the cam timming is wrong .090 isnt going to make this motor any faster or better thAn A STOCK HEAD

also the valves are now .090 closer to the block. So I havent done this

But I can tell your dead set on doing this YOUR way

 

I hope you know what your doing.

 

this might help

http://www.guba.com/general/search?query=hainz&set=5

[datzenmike]

Stock L20B with open chamber head and 11.34cc piston dish with:

 

Head shaved:

2mm or 0.078" cut = 9.94 compression

2.1mm or 0.082" cut = 10.03

2.25mm or 0.088" cut = 10.17

2.5mm or 0.985" cut = 10.54

 

 

These three options require no head shaving and have no valve clearance or tower shim issues.

 

Stock L20B with L18 4.36cc dish pistons = 9.2

 

Stock L20B with closed chamber head = 8.9

 

Stock L20B with L18 4.36cc pistons and closed chamber head = 9.91

Edited December 23, 2008 by datzenmike
edited for clarity

[banzai510(hainz)]

Mike means UNCUT head youll get those compression ratios

[Five10er]

So you both think I shouldnt go this route? Dont get me wrong hainz Im open to suggestion, but Im inclined to use what I have. Argh I just assembled the bottom end with standard pistons!

[banzai510(hainz)]

Shaving V8 heads in large amounts is no big deal I guess as it has nothing to do with the timming on those motors.

Since you have a Overhead cam motor that uses the long chain .090 is alot of material to remove.

 

Now if you have option/access of these parts listed above that I and Mike mentioned?????

 

I myself would just do a clean up cut on the head. meaning just enough to get a nice straight surface.

I would do the Cam and twin carb route and just be happy with what comes out.

 

remember to do a cam correctly is still going to costt money. You never really said anything about retainers and lash pads or anything besides you have a cam.

You can get away with stock springs if under 475 lift if thats what you want to save money.But its best to tell us specfics on what you have and we cant tell you what you can get by with if parts are still avail.

Notice photo#4 if head is milled.090 .the upper cam sprocket will be .090 closer to the lower crank sprocket so where will all the extra slop in the chain go.(head shaver shims come in .015 thickness,so would you stack up 6 .015 shims? kinda tacky dont you think?)

Edited December 23, 2008 by banzai510(hainz)

[banzai510(hainz)]

this was emailed to me

Hainz, go to silverseal.com it is like page 56 in their> catalog. Part# 0591000. I called them and they said they had> a lot of the head saver shim kits, $8.10 per/kit. Silver> Seal- phone 800 521 2936 part# 059-1000

 

redeye,maybe you could post this or Mklotz put it as a sticky somewhere

[Five10er]

This is great info, thanks a lot. I'm not sure on the lash pads and retainers that I have, since I bought the head off a guy with the reground cam already installed. I could get parts like these from Isky, no? Also, would it be worth it to get aftermarket valve springs, or would something else be holding me up rpm wise before those?

[Five10er]

I see what your saying about the cam timing being thrown off by the distance between the two timing sprockets; the chain tensioner would take up the slack on one side, causing the cam to rotate in respect to the crank. I wonder if I could modify the stationary chain guide on the right to take up more slack? This might cancel out the timing shift. Just thinking out loud

[datzenmike]

The tension side should remain straight, that's why it's called tension side. There's a lot of force pulling it down. The guide on that side would be ground away if it was holding the chain over. The tensioner is just to prevent a loop of slack from jumping over a cam sprocket tooth.

[Five10er]

Good point. Bad idea.

[Jason]

I would think that going with the A87/W53 head with the smaller combustion chambers would be a more conventional way of raising compression. Coupled with the smaller dish pistons and you're close to your 10:1. If you use a closed chambered head, you get more detonation resistance which would be helpful with that ratio...

 

The Z car SU's ought to work fine. After all the roadster SU's on a U20 where 42mm already. They aren't so good for the top end though ...

[RacnJsn95]

If I remember right, the "head saver shims" are .045" (ea kit)... You can stack kits, but it is not advised to stack more than 2 (.090")... If I personally did not have, or have easy access to a peanut head, I would shave Large chamber head...

[Five10er]

SUs arent good for top end? How come?

[Jason]

Without some real custom needle work they won't flow enough fuel for the really high lift cams. Great for low and mid range torque though.

[Dudeman]

Aren't most SU's 40s or 42s? It seems like even dual 40's would flow more cfm than a comparatively small weber

[datzenmike]

I think Jason is saying they don't flow enough fuel for the air. Run lean at top end. If this is the case the tapered needle needs to be sanded down even thinner to allow more fuel past it at WOT. This is where an O2 sensor would come in handy.

[Jason]

Most 510 SU's are 38mm, U20 Roadster ones are 42mm and harder to come by. The 240Z ones are 46mm and pretty plentiful. Mike's got it right, I'm confused :(!

[datzenmike]

You don't sound confused at all. I read a thing on SUs. (the British kind) It was before O2 sensors and wide band. It involved the fine art of reading spark plugs and filing the needles down and sanding them. Some times the set up would be lean in the middle range and the needle would be slightly hour glass shaped.

 

I have a pair or SUs from a Volvo and they are so simple to work on. No choke plate or any fast idle circuit, choke un-loader linkage or setting and no accelerator pump or linkages. Damn that's great.

 

 

Here's a tiny SU from an Austin Cambridge:

 

http://i138.photobucket.com/albums/q251/datzenmike/nondatsun/AustinCambridgeLarge.jpg[/img]"]

Edited December 27, 2008 by datzenmike

[Five10er]

I actually stole these carbs from my dad's U20 build (he wont be needing them for a while). At first I thought they were 240z carbs, but from what I understand they have too big of piston return springs to be 240z carbs. I know the U20 came with more than one type of carb option, but I think 46 mm SUs came stock on some 2000 roadsters.