JP95ZM6

I visited the machine shop today, to set up block work for a 350 refresh for my LE2 project. I more-or-less got talked into doing a forged 383 now, instead of waiting for the stock bottom end to fail. My LE2 heads haven't been delivered yet so I still don't know the chamber volumes, but they were set up assuming a 350 if that makes any difference. I do not know how to adequately specify the pistons and deck height, and I don't want to just take what the shop recommends without knowing better myself.

I will update this post with the chamber cc's when I get the heads but anybody who has done this already knows. Please enlighten me.

With an LE2 head/LE3 cam 383, is 11.1 SCR right so the cam develops the target DCR?

What gasket, deck height and piston combination works best in this application? I prefer to use MLS 0.029 head gaskets and compensate if necessary with the decking.

Thanks!

SS RRR

you've got to figure out what your combustion chambers are going to be before going any further. More than likely you will need a dished piston to achieve 11:1 especially now that you're going with more displacement. But first things first... find out the size of the combustion chamber...

seawolf06

You really should talk to Lloyd a lot more about this. You should choose your pistons first and then he can make the heads whatever chamber size you need. Also, I'm pretty sure his cam selection will be much different for a 383 vs. 350. I think you should research pistons, rods and crank if you really are going to go 383 and then talk to Lloyd about the heads to make it all work. If you have the heads already, or they are on their way, then that will limit your options on what else you can choose.

It seems that most people going NA will say to zero deck the block and use a flat top piston. Then you can get your quench where you want it. With the .029 gasket you'll want about .005 in the hole, but you can decide what quench you want to run. The dish of the piston will then determine SCR and DCR will be determined by the cam. Lloyd will tell you what SCR the cam is made for as well.

Since you said you were "talked into a 383" you should also research the pros/cons of 383 vs. 355 if they're both forged.

JP95ZM6

I appreciate the initial advice guys; I will follow it. My heads just showed up, so I'll have the chamber volumes in a few hours.

I spoke to Lloyd, and you were right about the cam requirement changing. I have an LE2.2 cam now and would need to swap it for an LE3. I have researched pistons/rods/crank quite a bit, too. I'm planning 6" rods. Once I get to a desired dish volume then I will need to balance quench vs. dish volume to match an available piston. I expect there will be a few options and that's where I'm not sure what to prioritize. Sounds like I'll try to use 'hemispherical-dished' pistons if an appropriate one is available, based on what I know so far.

Well, talked myself into it is more accurate, I guess. I always wanted to do a forged 383 eventually, but I was going to wait until something broke. When I learned yesterday it will 'only' cost me another $1200 vs. doing just rings/bearings/hone & ARP rod&main studs, I started seriously thinking about doing it now instead. That's with Eagle forged crank and H beams, JE or SRP forged pistons, 2-bolt ARP studded mains, and 'qualifying/detailing' the crank. Shop says the Eagle cranks are often less-than-perfect as made, so will check surface finish and dimensions.

As I understand the 383 will peak at about 500 less RPM and make about the same peak HP as a 355, with a fatter curve for better streetability. It might not be any faster at the track, and will not rev as high, but will like my 3.42 gears better than a 355. Did I miss anything?

Machinist says 6800 RPM is no problem with good balance, forged crank and a studded 2-bolt. Cam/heads would want to be shifted around 6500 tops if I understood Lloyd correctly, so I think the 2-bolt is ok? Bret has said the forged crank is overkill with a 2 bolt and I trust him more than the shop, so I am debating using cast steel vs. converting to 4-bolt. But I will probably do the forged crank in case I want to take the engine further some day. Should I be worried about studded 2-bolt mains?

JP95ZM6

Update: Chambers all measure 54 to 55cc's. I expected more like 57 based on searches, so I guess all LE2 heads are not the same. Lloyd must vary the chambers for different applications.

seawolf06

This has been a very useful calculator for SCR and DCR:

http://www.empirenet.com/pkelley2/DynamicCR.html

You have to download the program, but it's pretty close. With those small chambers, you will need some deeper dishes than most. I'm not sure what's available. Also, you should be able to get the MLS head gasket in any thickness you want. If you're trying to get quench to .035, then you'll need to measure your pistons to .006 in the hole with those gaskets, and I'm not sure how much harder that is for the shop than simply zero decking it.

At my initial calculation, you're looking for around a 15cc dish piston to get to 11:1, but check with Lloyd on what SCR you should shoot for with his cam. I'm going to run around 11.5:1 with a DCR at 8.7

JP95ZM6

Neat tool, thanks Seawolf! I have a call in to Bret, since I need the LE3 cam specs and target DCR before I can spec the motor. Hopefully he will share enough info for me to spec the motor before I get my cam. I won't fully commit to the 383 until I know if I can achieve the target DCR.

JRE makes 16cc dish pistons (p/n 139628) and that gives me 11.1 SCR at -006 piston height. That seems perfect, IF the DCR calculates the same for the le3/383 as it did for the le2.2/350. That's a big IF. I'll run the DCR numbers after Bret calls me back.

seawolf06

I doubt Bret will give you the specs. More than likely he'll just tell you what SCR to have the motor set up for. I'd think he would tell you to run more compression, especially with that large of a cam. I'd go to at least 11.5 or 12:1.

1racerdude

Your IVC will determine your static compression ratio needs to be to stay between 8.5-9.0 DCR.

JP95ZM6

Thanks, Larry. I hope I can at least get the IVC spec, then.
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I reread all the related posts I could find, including the big '355 vs 383' thread, and it made me re-evaluate the 383 a bit, considering I already have LE2 heads. From what I can find, I still think I want the 383. If I go 383 and it is no faster than a 355, but has similar reliability and better torque, I will be very happy with it. For me, going faster with less noise/rpms/gear on the street is a plus, since I will attract a little less attention that way. That is what I expect from 383 based on what I have managed to learn so far. Plus, it leaves more room for improvement later in the intake/heads. With those considerations I can't find any real drawbacks.

Am I missing something? I can still do 355 instead, if someone shows me that I am failing to consider anything important.

Plus, I want a torquer. I already have a car I can spin to 12 grand when I feel like revvin'. Gotta keep the portfolio balanced.

SStrokerAce

On all the LE packages that are NA a flat top piston with .035-.042" quench is optimal.

If your chambers are 54cc then a 355 with the larger cam (LE3) will work awesome, that added compression will work well to make up for the larger duration down low.

Bret

reamo04

when ive talked to lloyd, we pretty much decided for me to go with le3 heads with a le4 cam, and -5CC heads to help it run on pump gas and still keep my compression up there

JP95ZM6

Wow! I get 12.9:1 SCR with 355 and those numbers. Gotta go read more DCR posts I guess.

SStrokerAce

54cc, Felpro Gaskets, Zero deck, -5cc Flat tops = 11.72:1

JP95ZM6

Ooooh, I missed the -5cc on the flat tops . And the Felpros are 0.010 thicker than the MLS .029's I was calculating for. Now the math works. Thanks again!!!