I came across a set of low mileage 823 heads today. I was wondering if anyone could tell me if they would be a good fit for a 408 stroker? Obviously my next build will be a 408. I already have the rectangular port NNBS intake from another tear down that I did, but just stumbled on these heads today. Does anyone know how much lift the factory springs on these 823 heads can take? Anything else I need to know before bolting them on my 408? Are there better head options out there? This will be a naturally aspirated, high compression, limited use daily driver... By that I mean it won't be driven every day, but when it is driven it will be driven on the street ONLY. Never run at the track, and never on a road course, or anything like that. This engine will be replacing my current .030" 6.0 that is in my personal truck now. Why am I pulling a good engine? Because I want MORE! Like all of you! Hahaha!!!

Also if anyone can recommend a good Rec port cam for this engine. I can post compression static/dynamic #'s, and anything else that is needed. Again.. Daily driver.. Low RPM grunt more important than HIGH revs.

 

823's heads make good power on a 408 but the cathedral heads and truck intake will give you more torque down low.

 

Almost the same as LS3 heads (#821), but with 2cc more chamber. Same ports and valve sizes.

 

^^^ like mentioned, if this is a street driver, go with the cathedral port heads, get that power down low where you you can use it.

 

My perception is LS3 821/823 heads are a bit trickier to cam correctly for a given desired outcome than the more forgiving cathedral 706's/243's/799's etc heads.

I wanted basically the same as thing out of my 416 w/LS3 heads that you do out of your 408 w/823's. Darin Morgan custom spec'd a 237/245 on a 114 w/~.625 lift that cranks out Pontiac 455 style torque at low rpm, makes 400 wtq at ~2,800 rpm.

I'd contact Darin Morgan (at Mast Motorsports, now BES)or similar master cam guru to custom spec a cam for your 408 set up if you want to use the 823's. I'd also plan a new spring kit, decking heads and maybe fresh valve job.

 

Thanks everyone for the suggestions so far. As per 99 Black Bird T/A's suggestion, I'll have someone KNOWN spec me a cam for it. Bottom end torque sounds awesome.

 

Summit stage 5 cam and PRC 260s will make 560+ rwhp onna 408 and drive like stock

 

You'll want to think about the complete picture. Quite important will be what weight, and what transmission+rear gears.

Next you also want to think about what compression ratio you want. (The previous question factors in here). Do these heads get you where you want in terms of CR and quench? I believe 823s are 68cc.

Where do you want to make power? This is will play a big part of the decision. Low end, yes, but what do you consider low end/how will you drive it.

Example: I have a 1971 GMC with a 6.0 LQ4 and a 223/231 cam. I've had people ask about low end.. but I have 4.56 gears and a 3200 stall converter from a quality vendor. There is no need for 'low end' in my application, even though I'm driving around at 4500lbs on 33" tires. Whenever I get into the power, the converter will get me up to the start of my powerband. But if I had less gear or a stick shift, then I would need to think about it more.

In general rec port heads lose out below 4000 rpm compared to cath ports... stock for stock. Seriously, they will lose to the larger chamber 317s below this. But, they pull away significantly above this, especially at the top. So a car with a 3600 converter doesn't really care, but a heavy truck with a small converter or stick does care.

IMO, either setup will work OK. Its not so life and death. I would think some well ported 243s would be more enjoyable to street drive in a truck. Make sure you spec the pistons as needed. I have AI ported 243s on my 403 with flat tops, I'm at ~11.8:1. Its in a light corvette, so I can bleed off a little dynamic compression with cam duration. You'll probably want less cam in a heavy truck, so you are probably going to be more in the upper 10s in your CR, maybe 11.0. TBSS intake with a 92 or FAST/102 for the intake.

Good quality converter and proper gears (or just the gears if its a stick). Lot of times the difference between OK and Great is the rest of the package. A stock converter, poor axle gears, and torque management can really hobble the performance. These engines are fine running some RPMS on the highway.

Springs: Stock are usually limited to .550 lift, IIRC, chuck them and get new better ones.

Without knowing everything about the truck, I'd guess something around 235 intake duration. Give or take a few degrees.

 

Darin is at BES now

 

A++
Thank you! For the information!

That really helps planning my LS2 stroker build
since BES is here in Indiana.