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Just some L81 ideas.

Peer81

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Hello everybody,

This week I begon rereading things about static and dynamic compression, quench, cam details, exhaust mods, head calculations etc etc. Every nice to have a desktop dyno so I can see (to some degree) what some changes will do to an engine.

So here it comes. At this moment my seats are at redone with leather and the interior will be next after that (read $$$). But this gives me some time to think about these things and maybe look on ebay oid to score some nice deals.
I have some things I don't know for sure so I hope you people could help me with this.

First off all the L81 will be looking like an original L81 from the outside with all the emission stuff in place! So the CC q-jet will stay, stock dual snorkel aircleaner, the alu inlet will also stay. Next things, I already have a new crank with speed pro (hyper) pistons with 5cc dishes so they don't go either (so no 383).

At this moment I have a comp cam. XE256H (256/262, 212/218, 0.447/0.462, 110)but I am willing to change to a XE262H (262/270, 218/224, 0.462/0.469, 110)(maybe higher?). I don't have the budget for roller cam etc)
I still have the original 462624 heads and I wonder what I could buy to changes them. Another this is standard 1.5 rockers or 1.6 (for what I want?). And last thing. The exhaust system will be a 2.5" true dual with x-pipe and dynomax ultraflows. I want to keep the block hugger style short headers but the 81 headers have a 2" collector and the 82 has a 2.5" collector will the 2" collector be a big restriction with a 2.5" system. Of course I'll be willing to grind out the exhaust to match the heads but maybe it's better to buy a set of 82" and grind them out? (82 for AIR tubes)

Now what I had in mind. I don't want something like 400hp, I'm looking to optimize my engine and I'll be happy with something like 300. More important is I'm not into high revs so about 5000 to 5500 is the limit for me. Better to give me some low end torque the high end hp. It would be nice to have the static compression around 9.5:1 and the dynamic around 8:1 (just a thought and it still has to run on normal 89 or 91 pump fuel). Behind all this is a 700R4 with stock diff (2.87:1) and could be changed to a 3.07:1 (I have ready) Also important is that I want some nice MPG numbers.

In all of this the head choice will be the most important. At this moment I don't want to change to alu, iron is good enough for me. Looking at the Dart side the say when you're looking for 300 to 350hp you'll need a 140 to 160cc inlets. 140 to 160 is very small because most aftermarket begins with 180. At this moment I'm looking at some Iron Eagles or World Products heads.

Well that's about it. Let me know what you think. The more replies the better. Ow and one thing, this is all in theory and maybe maybe future music :)

Groeten Peter
 

Sensei

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393
Location
Jacksonville, Fl
Corvette
'81 dark blue
Peter, I think I have built the engine you describe. This is what I have:

Dart 180 cc Iron Eagle heads, 72 cc chambers
Flat top hypertuetic pistons
Comp XE262H cam
2.5" true dual exhaust
TH700r4 tranny w/ stock rear gears

I am very happy with the results, I get 350-400 hp, 17 miles per gallon in town, 23 mpg on the highway. But here is what I would have done differently if I could do it over:

Go ahead and bite the roller cam bullet! With all the problems of flat tappet cams and new formula motor oils, you end up paying the difference anyway for oil additives to keep your cam alive, not to mention the performance benefits of the roller cam. Either way, don't get the comp XE256H, it is not enough cam for the car. The 262 is good, but I think the XR264HR would really be the ticket for you (I'm thinking of going back in and using an XR270HR). Get the roller, pay now instead of regretting forever.

As far as the heads, I really like the Darts, but I wish I had fully ported and polished them. I was in a hurry and just polished the chambers. Again, do it right now, don't regret later.

The 700r4 is good with the stock gearing. If you want more performance, I'd re-gear to 3.31:1.

God bless, Cris
 
B

bandit

Guest
sensi,
when you put the 2.5" exhaust on how did it fit? i'm looking at a 2.5" for an 82 true dual. my q is will it bolt up to my 81? or will i have to change the manifolds? thanx
 

Peer81

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'81 Black
@bandit,

An 81 has stock manifold with 2" collectors and 82 stock manifold have 2.5" collectors. So if you want to use the stock manifolds, no it doesn't fit directly.

Thanks for your reply Cris,

Of course I also searched some forums on this subject and at least 3 times I saw the same reply (from you) about changing to a roller :D But as you say they really look similar. But why did you take the 180cc over the 165cc? Smaller faster flow(?) but bigger more flow.. I don't really see a clear explination about this anywhere.

I already have the XE256, I also want to drive this engine but if something comes my way who knows. :) I also have a nice book here about porting and polishing heads so that my come in handy to.

And your stock diff still holds up pretty good, gives me hope :cool

Greetings Peter
 

Sensei

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393
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'81 dark blue
Peter, keep in mind that the cam/ head descriptions from the manufacturers are very general because a small block Chevy engine is as likely to go into a truck or SUV as a car. For a heavy vehicle, you need more torque, especially if you might be towing something with it. As V8 powered vehicles go, Corvettes are on the light side. You want your power band a little higher. A little more cam and a little more runner volume will give you the efficiency you want.

God bless, Sensei
 

Peer81

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Thanks, good thing you pointed out the usage for truck and normal car, I didn't think of that. Here in Holland you only see V8's in sportscars and the exceptional US pickup.

Groeten Peter
 

KANE

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Dark Blue 1982 Trans Am(s): Polo Green 1995 MN6
.... Let me know what you think. The more replies the better. Ow and one thing, this is all in theory and maybe maybe future music :)

Groeten Peter

I have the GMPP 290HP crate motor. It comes with an L82 cam and comes in under 2k from Jeg's. Adding a custom tuned TPI chip and intake parts fortified with SLP goodies it makes for a rock solid motor. I added 16 roller rockers to give it approximately .480 and .490 worth of lift. Yeah, that is a lot of lift for a low squeeze motor, but it provides room to grow when I upgrade to fastburn or Vortec heads.

I am really happy with the mill I have.
 
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Peter,

I concur with Chris on the cam tappet Vs. Roller. Besides, it is just a little clearancing required to fit the roller cam, but it should be done by a machinist with the bare block, and this is how I ended with the same flat-tappet. It did not even crossed my mind while the block was at the machine shop, but then again, I was really done taking my Vette to the track. ;shrug

Keep in mind that there is a maximum cam overlap that the L81 computer will take without triggering fault codes, should you plan to continue using the computer with the Electronic Q-Jet. The particular cam manufacturer should be able to tell you which version of their cams will work with the computer.

On the head question, the runners size is important, but what really will give you a good idea is the ratio between the intake and exhaust runners. The ChevyHiPerformance.com website has a head database that they have been building for a few years now. It is accessible, and it is worth reviewing to help you make up your mind about the heads. They have flow-checked and dyno'ed every single head in their database from a basic configuration set-up (i.e. header size, intake size, carburetor size, and so on).

STATUS of DATABASE
(well, on the issue of the database, apparently they have not listed the database, for the way is configured does not work well with the new website's code, apparently...Where did it go??? – Chevyhiperformance.com Chevy High Performance Magazine Forum ) But they do have an article on small block heads...Flow Database | Research Flow Database and find Photos, Articles, Videos, Blogs and Forums at Chevy High Performance Magazine
 

Sensei

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'81 dark blue
Keep in mind that there is a maximum cam overlap that the L81 computer will take without triggering fault codes, should you plan to continue using the computer with the Electronic Q-Jet.

Actually, I have recently found a way to trick the computer into working with any cam. It is a simple mod that costs about $20. I am playing with it right now and was planning to post it some time in the near future. A more radical cam may be in order soon!

God bless, Sensei
 
Joined
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Messages
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1981 HD Suspension; ZN1 Option
Actually, I have recently found a way to trick the computer into working with any cam. It is a simple mod that costs about $20. I am playing with it right now and was planning to post it some time in the near future. A more radical cam may be in order soon!

God bless, Sensei

Cool Chris! I can't hardly wait!
 

Peer81

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Thanks for the info. Keeping the E4ME is top priority! Most people say it doesn't work so it's up to us to prove otherwise. :)

On www.corvettefaq.com there is a link with all (i think) the heads with flow data. Easy to put them in the desktop dyno. I'm not planning to take out the entire engine. And a roller is not that more expensive but what needs to be changed to the block?
I'm not into radical cams, the more cam the higher the top hp will to and the less low torque.

But for my engine 180cc will be good i think and 200cc to much?

Groeten Peter
 

Sensei

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180 will be good, and you can buy roller cam retro-fit kits from Comp that do not require any block modification that I am aware of.

God bless, Sensei
 

Barry08

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Portage La Prairie,Manitoba Ca
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Actually, I have recently found a way to trick the computer into working with any cam. It is a simple mod that costs about $20. I am playing with it right now and was planning to post it some time in the near future. A more radical cam may be in order soon!

God bless, Sensei


Sensei,
Since I am getting an itch for my power on my stock 81 I look forward to this simple mod.Also don't be suprised if I start asking a lot of questions about the mods you already have done!

Thanks.... Barry :beer
 
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...and you can buy roller cam retro-fit kits from Comp that do not require any block modification that I am aware of.

God bless, Sensei

Chris,

Perhaps I have not been keeping up with the latest after-market products, but I recall that Pre-1986 blocks had to be modified slightly...the high ridges between the lifter bores had to be shaved-down to allow for the lifter bridge that keeps the roller lifters from rotating ion the bores. The post-1986 engines use a roller lifter retainer called a "spider" plate, and those same engines have a higher lifter bore than pre-1986 blocks, and there was something else, but I can't remember what it was...;shrug

It is hard to find the information now, for so many people are using post-1986 chevy v-8 blocks and the older ones are becoming scarce.

its been a little while, but this was still true in 2006 when I assembled my Vette's engine....I don't know...;help
 

Sensei

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'81 dark blue
I could be wrong. I know I got instructions from a guy on how to modify an older block for the stock roller lifters and spider, but I thought the Comp retro-fit kit just dropped in. I guess a call to Comp is in order.

God bless, Sensei
 
Joined
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I could be wrong. I know I got instructions from a guy on how to modify an older block for the stock roller lifters and spider, but I thought the Comp retro-fit kit just dropped in. I guess a call to Comp is in order.

God bless, Sensei

That would be good to find out. :thumb I hear one gets better vacuum signal with roller cams, so I would put one in my Vette if there would not be any modifications needed:ugh;shrug.

I believe that one also has to use a cam button together with some sort of spacing adapter behind the cam as well.
 

Peer81

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I looked at the roller stuff. Well, a roller cam isn't that expensive but the roller lifters (and the rockers).... ;help
I'll look into this, but with the limited miles I drive with the vette I'm in doubt if it's really necessery. :)

Groeten Peter
 

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