bigftruck

So i spun #1 rod bearing on the dyno with my stock bottom end ls1. Perfect opportunity to go bigger/better so this week i take delivery of my new 408! New build will be
lq9
wiseco -10cc dish pistons rings gapped for a 200 shot( will be 11.1-1 comp)
compstar rods and crank
Stage 2.5 prc 5.3 heads unmilled
ms3 on 113lsa
42#lucas injectors
walbro in tank upgrade
fast ported 92/95 combo
1-7/8 Lt's with true duals dumped
ls7 lifters / chromoly 7.4 pushrods

My question is how bad will my heads choke down flow on the bigger cubes? I am just swapping all the brand new parts from my 347 to the new 408. Any thoughts or experience with a similar setup is greatly appreciated. Any ideas what power this combo is capable of?

SICKSS/Z28

wrong heads and cam but should be alot stronger than your 347 but not what most people expect out of a 408

BlackTA96

iTrader: (3)

So these heads would be a no go for a 408 huh??

StreetSilverado

iTrader: (17)

I call a big NO on the 5.3 Heads

muayyadf1

If you have 4" bore you will have much much better choices like L92 heads!!

PREDATOR-Z

What I would do is get the heads independently flown. If they put out 300cfm then you could change the intake seats and stick bigger valves in (2.055), massage the chamber and open it up to 4.0 bore (I did that on mine and you'll get around 315>320 cfm intake).
That cam will make good midrange and alltogether with proper intake you'll be looking at around 460rwhp/430+tq
Imo that is a good start and you can always chnge heads and cam at a later date.

SIC LSX

iTrader: (10)

you will make more power with those heads then some ls6 head or 6.0 heads! I seen it

willyfastz

As mentioned those are the wrong heads and cam for a 408ci stroker. You would be better to sell them and get something better suited for your new cubes.

BIG_MIKE2005

iTrader: (116)

I wouldn't say they are the wrong heads. Cause thats a incorrect statement. They may be the wrong head for "some" people but exactly what others are looking for. I have seen plenty of cars with these heads get close to 500rwhp in a 408. Some of the higher end better flowing heads are just overkill for some people as well as outside their budget.

If you want a nasty street car down low & midrange, these heads are perfect. You won't lay down a monster dyno number, but thats not whats important anyway. I'd say they are actually one of the best street car heads to choose from. I mean unless you just have tons of extra money to spend or your building a solid track car with huge cam spinning to 7k. Then those high dollar heads that flow so much more will definetly shine over the 5.3's anyday.

In the end it all depends on your build purpose. Not everyone builds their car to be ***** out with the best & most expensive of everything. So if your on a budget or already have a set of these & your not worried about making monster numbers but just a solid stout combo without dumping a ton of money, these heads are perfect.

willyfastz

What makes the 5.3 heads so great? And who said anything about needing to buy exspensive high flowing heads? Dart 225's only cost around $1600 and would be better suited for the 408. And a smaller cam than the MS3 would actually be better for street use and power.

BIG_MIKE2005

iTrader: (116)

What makes you not like the 5.3 head?

Everyone is gonna have their opinion but in the end it's the owner who will make the choice.

I personally like the 5.3 heads b/c they have great potiential. you get a automatic bump in comp. ratio & they can flow great. So why wouldn't I like them as a option, not to mention they have been proven to make power on many different combos.

My point was not to try & say they are better than other heads but that they aren't the "wrong" choice just b/c someone else wouldn't pick them. They do perform & they do work, so they aren't a wrong head for the build. But at the same time they are also not gonna be a optimal performing head either.

Thats the beauty of this hobby. Everyone doesn't have to use the same parts to be happy with their car. Who cares if someone else doesn't like your parts choice as long as the owner is happy at the end of the day. And if these heads are what they have to work with & don't have the money to change heads, these heads are perfectly fine & will make power.

SIC LSX

iTrader: (10)

4.8, 5,3, 5.7, 6.0's all are the same ported! Eveyone always has to mil the 5.7 and 6.0 heads to get the compression some 5.3's give it. My friend with 233/239 cam and prc 5.3 heads put down 490whp with his 408ci only made 470 with ported ls6 heads

john563

iTrader: (17)

I have those same heads and just plan on re using them when I go to a 402-408, but with a bigger cam than my 232/238

BrianC98Z28

iTrader: (11)

The heads are fine for a 402/408, just get them opened up for the bigger bore. Some people on here make claims off info they have only seen on the internet and not in person real world results. 403 I helped tune with PRC 2.5 5.3s and 248/254 615 622 112 made 491/472tq. That was with an unported 92/92 and no EWP to get some of the all might dyno #s that some on here are after. Car screams everywhere and is fun as hell on the street. Use the heads and have fun! Keep us posted on updates and Im interested in what your setup makes.

DVS99TRANS

iTrader: (7)

I am reusing the PRC 5.3s on my 408. I do plan on getting a set of ET heads and re-camming later but need something that will work for now. I do agree that the heads won't make the superb #'s that everyone sees with TFS and AFRs, but they will still make more power than the stock 853 and 241 heads I have sitting in the garage. I am using about the same setup as bigftruck except my LSA is a 114. It will make close to 475-500whp in my honest opinion and an insane amount of torque. Hell a MS3 in a 408 is technically a mild cam.

RyanSws6

iTrader: (72)

You should be fine just double check your comp #s.

I sold my 5.3s when I was doing my 408, but I had ported 243s new. I just didn't want comp issues...I want to go l92s later.

SICKSS/Z28

for the price of the L92 set up its hard to beat heads around 500-700 assembled buy springs 250$ and a 400$ intake (new) 200-300$ 90mm cable tb

cellulis44

iTrader: (11)

I had that setup..

2.5 5.3's on a iron 408..

made a lot of torque.. but really NO top end.. a pair of stock L92's would perform way better.

like everyone else said, you need a head setup for a 4" bore.. your quench isnt going to be right. AFR 225's would be about the only thing I would put on my 408...

but now I'm running a turbo, so my 317's are JUSSST fine

BIG_MIKE2005

iTrader: (116)

L92's are great except the limited intake options. Thats the only thing I don't like about them.

cellulis44

iTrader: (11)

that will be addressed in due time I'm sure

what impresses me most is the mid lift numbers on stock l92 heads..