496 BB

Ok so spun rod bearing and block is heading to machine shop someday soon. Just trying to get a grasp on what I want to do. I know what my head wants to do but from a reality standpoint I cant see all that happening. So thoughts are as follows:

- Forged pistons
- Stock heads for now
- Better cam
- Modify intake and remove baffle
- External PCV already done

Rest is same as before rod bearing and mostly stock. Already have long tubes and all that with EFI Live.

My question is what brand pistons should I buy? Should I add deeper valve reliefs for more cam? Should I raise CR one point? Head gasket size? What rings? Also what cam if I go bigger on reliefs? Ive seen Raylars post on Comp springs so does this still stand? What about roller arms?

Im wanting as close to 450-500 HP as I can without heads for now. I will add those later. Maybe it wont happen IDK. Just want a solid foundation now.

This truck is a fun truck for my son and I. Its in good shape and lifted (4" as of now). It plows snow in winter but thats not often and I dont want the build to just follow around that aspect. I dont tow with it. Have a dmax for that. Ive had an 8.1L for years in my other HD so its not new to me. Just modding it internally is new to me.

Thoughts and ideas?

Chris

Raylar Engineering

The most power you'll make with long tubes, cam and stock heads is about 435hp at the crank. You'll be basically building a 496HO (425hp/455ft-lbs) with a couple more degrees duration in the camshaft (provided you go all-out). Here are the answers to your other questions, and a few you didn't ask!


Cylinder Heads
The stock iron heads flow very poorly, limit aftermarket camshaft lift to .530 and weigh 80lbs each! The castings are too thin to port and the compression can't be stepped up because of detonation concerns. You can get decent power out of the stock heads, but they are the primary restriction on the 8.1L engine. Stock heads kill all power over 4500RPM, despite whatever breathing mods you threw at the engine.

Camshaft
There are lots of places to pick up cams for the 8.1L, Comp, Crane, Raylar, etc. The engine responds very well to the additional air and lift, though with any aftermarket camshaft make sure to replace your springs for the additional lift. Roller rockers are a great way to reduce valve train friction and you'll pick up 18hp doing it. Roller rockers for traditional BBC engines will not fit (won't clear valve covers). You can modify old school big block valve covers or slice and weld your own to solve this issue. If you want to run with ours, Raylar's roller rocker kit clears the stock valve covers.

If you want to run a traditional BBC cam with a distributor, you can. However, the engine has a different firing order than traditional big blocks, so if you do try to run a ZZ502 cam, make sure to swap the connectors around to match the firing order. You'll also need to pick up the Dart carb intake manifold which has a provision for a distributor.

Rotating Assembly
The pistons in the 496 / 8.1L engine are weak and like to shatter / chip / grenade at about 550 crank hp. The connecting rods fail around 575hp and the crank snaps (usually at the snout) around 700hp. Additionally, the pistons have very shallow valve reliefs, limiting your max camshaft lift to .530. If you're going to throw boost at this motor or you're considering a performance build, its best to replace the pistons.

The 8.1L can be stroked with a 4.5 inch crank or a 4.75 inch crank to produce 511cid or 540cid. The marine side has run the 4.5 crank for years and its very reliable. The 4.75 crank has been in our shop truck for the last 2 years now (as well as several other vehicles out there) and we've abused it daily - it runs like a top. One thing to mention - the 511 kit is a drop in replacement and the 540 kit requires clearance work for the connecting rods.

Headers
Any BBC header will bolt up, but if you're looking for silverado / sierra specific headers, JBA and Gibson make shorties, Stainless works makes a nice set of long tubes. The shorties will pass smog (15-20hp), the long tubes (25-35hp) will not.

Superchargers / Turbochargers
Kenne Bell, Whipple and Paxton all made systems for the 8.1L but all have been discontinued. If you're lucky enough to find a blower kit, it will typically be a 2.3L screw or roots blower (whipple / kenne bell) and it will be running about 4lbs of boost so it has a minimal chance of breaking the stock pistons. The Paxton system uses a small centrifugal supercharger which is also set at around 4lbs of boost.
The only turbo kit made for the 8.1L is a downstream style single blower made by STS.

Raylar just released a 2.9L whipple kit which makes 8lbs of boost on the low boost setting and 12lbs on the high boost setting. 800-1000hp is possible if you have supporting mods (heads, cam, etc). You MUST replace the bottom end with forged parts if you're going to run our blower kit on this engine and probably should consider forged parts for general use as just about everyone has heard a story of a stock 8.1L popping its stock rotating assembly.

496 BB

Great info Larry (I assume??). While Id love to do all in and build it to the gills I have to look at it from a business investment as well as essentially that is what its for although I want some main things done first.

- That being said what brand pistons do you like? Im for sure going forged. I doubt Im going over bore as my walls look great from what Ive seen. Have not measured them though so time will tell.

- Im planning on stock crank for my application. Say Im at the 435hp mark would I be able to throw a 200 shot on it without concern or no? I know tierod has but not sure if that was with forged crank or not. Didnt think it was.

- My main reason for doing this engine was the FI setup so plan on keeping that. Will the stock injectors be maxed out on 435 hp? What do the marine injectors flow an hour?

- I wouldnt mind the ZZ502 cam. Id have to look thru my tunes to see if it could be changed in there (firing order) or I could just swap coil input plugs to old BBC firing order. Whats rpm range would that cam come on at with stock heads? Is lift too much?

Really do appreciate the help. I know its been awhile since Ive been around but nice to see you guys shed light on these motors again. I love these things.... especially when you buy em for $350 cause the guy doesnt know what it is...lol.

Raylar Engineering

You're very welcome, we just want to get the info out there as theres so much misinformation about these engines floating around. I should also mention that now that I think about it, if you added the modded intake to the pile, you might be able to hit 450hp crank, but thats assuming you're running 2+ inch headers and 4 inch dual exhaust like a marine application would.

For pistons: if you're only doing replacements, I would look around online for forged drop-ins. I believe Diamond makes them, but I have no experience with anything but our own kits. This still doesn't get you away from the connecting rods being the next weak link, but you'll be safeish to about 550hp. If you're adding 200hp of nitrous to the setup, you'll want to at least have forged connecting rods, if not the crank as well. Tierod had our 206 camshaft, heads and forged connecting rods / pistons on a stock crank I believe. His truck is the one featured in our 496cid truck stage 3 video.

The stock injectors (which I believe are 27-28lbs) are pretty maxed out on our 202 camshaft and you'll need marine 42lb injectors to run the 203 camshaft on most late model trucks. The ZZ502 camshaft is a little bit smaller but pretty similar overall to our 203 camshaft, except the ZZ502 is setup for the shorter intake runners in old school big blocks, so you'll drop a bunch of low-end torque in exchange for the mid-range and it will take a bit more tuning to get it to idle.

496 BB

Yea Im running 1.75" long tubes I believe. Running 2.25" exhaust dumped at mufflers but plan on changing to 3" when I put engine back in if I can get it to fit. Should be able to with the new np205 tcase going in as its smaller than my current np203.

For pistons I like yours. Who is making those btw? If you guys do please accept my apologies as last time I heard they were by Mahle. Probably going that route anyways since you guys are so familiar with what works plus I really like the deep pocket in it. That being said on stock crank what is max I can go on cam lift with your pistons and still be safe? What head gasket size is your max lift based off of?

After looking more at zz502 cam Im not feeling it. Seems kinda small for BBC. Really to be honest I just want a chop idle. Seems cliche I know but lets face it this isnt a race engine. BUT I want the most out of what I buy as anyone does. I dont plan on spinning this anything over my limiter which I think is at 5100 now so thats it. Dont really want to loose low end tq either with a cam so if it stays same as stock and gains mid for the idle I want Im good with that. Whats the difference between your 205 and 206? Didnt really see any sound clips of either on youtube. Have any?

For connecting rods I would possibly entertain the idea of going forged. What is the stock length of these? I cant seem to find it and my pistons are still on mine so cant measure them right now. Do yours come with bearings or no?

Speaking of bearings (rod and crank) which do you guys prefer?

Thx again for all the help. Maybe this thread will help others doing a budget small build on 8.1L's or maybe its been beat to death before IDK. Havent been here for awhile.

Raylar Engineering

You're asking for two different things.

The BP-203 cam is as big as you can go on stock heads / stock pistons - both of which limit lift to .530. The BP-203 cam has a bit of a hot rod idle, but not the chop of the 206 camshaft.


If you want more lift / duration / lope, you have to swap the pistons, connecting rods, and cylinder heads. You will lose some bottom end torque (probably 20-30 ft-lbs compared to the BP-203) with the BP-206 camshaft (.600+ lift) on the stock 496 displacement. The stage 3 496 kit (TieRod's video) is an example of what our 206 camshaft sounds like.


Our piston kits are made specially for us through RaceTec and Mahle depending on the application. They do not include bearings, your machine shop should have recommendations as to which way to go on those. The crankshaft and head gasket have no bearing on the lift of the camshaft. Valve reliefs are notched in the pistons, they are what provides the clearance you need for maximum lift.

Lots more here: http://www.raylarengineering.com/vor...nce-parts.html

496 BB

Maybe I was confusing. What I was trying to say is I am for sure going to swap out to your pistons. For time being I want to KEEP stock heads but wanted to know if I could go with one of your bigger cams (bigger than 203). Wouldnt all I have to do is grind valve guides? I plan on running your rocker arms as well. Maybe Im way off but thats what I thought I gathered from other threads. Or is there no way I can run a 205 or 206 on stock ported heads? Or is it going to hurt power.

You say you loose some bottom end tq with 206 compared to 203. Just to be clear is that loss from stock tq or from what the tq the 203 adds after its installed?

What lift is the 205 at ish? How much does it loose on bottom end? Thinking this maybe is a better cam? Your thoughts?

Yea ok I reread my post and see what your saying abour crank not affecting lift. Brain wasnt working like it should have. What I was trying to ask is what would be max lift on a cam with YOUR pistons? Such as with the deeper valve relief what is the safe lift. Asked about head gasket because if I went lower (dont even know if you can on these) that obviously would affect piston to valve clearance therefore lift would have to be reduced or have other changes made. Just wanted to know since I may mill the heads a bit to clean em up and deck block a bit to do the same. How much room do I have to play with with your pistons and say a 205 cam? I dont really care about this now as Ive decided on your stuff anyways. I know you know your **** and everything works together and thats what I need. Plus your waaaaay nicer than a previous someone and I wont be mad about spending money with you.

Sorry for the earlier confusion. Working long days and 2 kids wearing on me and my brain.

Raylar Engineering

Yes, you can run our notched pistons and one of our high lift series of cams if you grind the valve guides on the stock heads way down, but this is a custom install that can lead to valve train failures if done incorrectly so we don't typically encourage people to go this route. Additionally, the combustion chambers are garbage and the heads don't flow enough air through the ports to really justify all that effort.

I've personally ported a set of stock heads to prove that 12 hours of port work is good for about 10-15hp, provided you don't go through the castings which are very thin. We threw those heads in the trash, put a set of old 1st generation Raylar aluminum heads we had lying around on and made 63hp at the rear wheels. The current heads (4th generation) would probably make closer to 75hp..

All of our high lift cams are between .600 - .660 lift. The 205 and 203 are the same duration / lobe sep specs, but the 203 is the low lift (.530) and the 205 is the high lift (.600+). The 205 or 206 won't hurt power on modified stock heads / pistons, the added duration just advances where the power comes on in the power band. Even with heavy modification, the stock heads really cant keep up with the 203/205 cams, so running a 206 would push the power band past whats really useable (3000-5700) on the iron heads.

I honestly don't know what the max lift is on our pistons its been so long since we measured. They clear .660, so we'll say roughly .700 but we only run our parts combos because why mess with what works? As for milling the heads down, again, not really worth the effort but if you do - don't push em too far - poor combustion chamber design is a recipe for detonation.

496 BB

Ok thanks. What Im trying to do is get my short block built the way I want and all I will do next year is your heads. Dont really want to be buying 2 different cams in a years time. So with that being said I would prolly go with the 205 now. Do you by chance know how much to be milled on valve guides or are they all different? Also what springs works best with that cam and your roller rockers?

I should be hearing back from my machine shop soon and be ordering these parts within the next two weeks.

Raylar Engineering

No idea how much you'll have to mill the guides, but it will be a pretty substantial amount. The 203 cam is cutting it very close - its basically an improvement on the HP3 camshaft. So.. I would expect somewhere in the neighborhood of 0.150 - 0.200, but let your machine shop decide whats best.

We don't offer spring packages or make spring recommendations for the stock cylinder heads. You'll want to talk to Comp cams for the best solution for your vehicle: 8.1L Springs - Comp Cams