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I just completed a swap to a 408 NA engine in my 68 Camaro and had it dyno tuned. I am a little underwhelmed with the result. I was hoping for 500+ RWHP and ended up with 483 RWHP at 6120 RPM and 474 FTLB at 4530 RPM. Don't get me wrong, this thing is a beast in mid range and won't hook unless I have a serious tire under it, but I wanted more. See below and tell me if I was being over optimistic.408 Build sheet
LQ4 Iron Block
Manley 4” stroker assembly with 4.030” -10 cc pistons (Part #592730C-8)
ARP Main studs
Air Flow Research 230cc Cathedral Port Heads 62cc combustion chamber, 2.08”/1.600” Intake/exhaust valves
Comp cams rocker trunnion upgrade
0.045” Head gasket
Comp cams 235/243 degrees at .050 0.621” /0.624” lift 113 degree lobe separation
11.4:1 Static compression / 8.59 dynamic compression
25% underdrive pulley
FAST LSXR 102 mm intake with FAST 102 mm throttle body
4” Intake tubing with LS3 style blade MAF
Art Morrison 1 ¾” long tube headers with Pypes 2 ½” exhaust with X-pipe and Borla Pro XS mufflers.
Doesnt have to be 2” headers, but 1 7/8 will usually show a bump.
A Dual 3” with straight thru mufflers would be the most beneficial here.
also to note, don’t compare dyno to dyno and think they are the same. Yes, every tuner swears their dyno reads low, bit this one might. More accurate measure of power is dragstrip times… but a manual shift car that doesnt want to hook will be hard to get accurate times anyway.
were you present for the dyno? Possible tires were slipping on the drum?
So I am still making 14-15" vacuum at idle of 950 RPM so the power brakes are still fully functional. My AC also turns on with out dragging the idle down , so I guess i made good compromises.
Trap speed at the end of the 1/4 along with the weight of the car will tell the real story. As has already been said, way too many variables with a chassis dyno, and none of them matter as much as how the car drives. If the MPH ends up low, then worry about why.
From: Coast of San Mateo County Between Pacifica & HMB
My .02 your dyno curve looks great! I would expect that to drive very well on the street.
For 408" 230 CCs is a "little" on the small side, especially with a schmedium cam &
definitely SMALL Headers & Exhaust.
The Fast and Small header/exhaust combo are definitely holding it back above 6000 rpm.
If I was chasing 500 (I Know the feeling of spending to chase a # LOL).
1. I would purchase a Tony Mamo Ported MSD Intake from Mamo Motorsports.
This would extend your HP peak out at least 300-500 rpm and provide more Air
at least 20-25 HP on your combo and the easiest cheapest labor!
Viola! 500+ Stop there
Could also sell the Fast to recover some cost.
This would soften up the low end just a hair and be alittle
easier to hook up.
OR
2. 1 7/8" headers, X Pipe, & 3" Exhaust.
More expensive parts & labor plus louder exhaust & possible drone.
Would add ~ 15-20 by itself, and or work really well with the MSD.
Combo + 40-50 with next to no loss in low end especially with 4.11s.
3. slightly larger Cam something like ~239/245 114*+2*
(still mild for a 408" with 230 CC Heads.
4. MMS 243 Cathedral Heads, (JK!)
(Absolutely needs MSD & Larger headers & exhaust)
Where does it end? LOL
Again just my .02
I suggest enjoy for the next 6 months and re evaluate.
Last edited by NAVYBLUE210; Apr 11, 2025 at 09:49 PM.
I've got a MAMO FAST 102 and port Matched Nick Williams throttle body I'll sell you. Never been out of the boxes. Purchased them before I blew up my SBE. Now I need an intake that's more suited to 8000+rpm for my combo. I'll gladly ship them too. Message me if interested.
That thing is way down on power.....it should make more than my 5.7.
Like others has said the fast is likely holding it back.....amoung other things like the 4" tube. I'd be inclined to run more compression. Pistons and ring pack??? Getting good power starts by not screwing up the combo gm gave ya.
Hey OP, I had some exhaust/intake woes (technically testing) with my 418 LS3.
Original Combo:
11.8:1 compression with cathedral port 247cc heads from PRC.
251/258 duration cam on a 110 LSA.
FAST 102 (initially unported).
1 7/8" Speed Engineering headers.
TSP 3" Y-Pipe (necked down from dual 3" to a single 3" dumped at the axle). 560rwhp.
Second Combo:
-Mamo ported FAST 102.
-Added a Magnaflow 3" to dual 2.5" exhaust on the Y pipe because the drone was making me go insane. 522 rwhp.
-Tuner was wondering what was going on, we pulled the catback and it made 582 rwhp.
Final setup:
-ARH 2" primary headers to ARH 3.5" Y pipe to a Hawks Sinister 4" single cat back.
-Vacuum pump 600 rwhp.
I think that puppy just needs to breathe with all of those added cubes. Though track times will tell all. Hook up a vacuum gauge to the intake and see if that is restricting it, should have little to no vacuum at WOT. My Mamo FAST 102 still has a bit of vacuum at WOT, but I feel like an intake change would ruin my car's drivability even further.
Or alternatively dump the exhaust a bit after the headers for a pull or 2.
I bet the intake is holding you back. The Fast 102 has a square port that mates to the cathedral head and the head creates a "wall" at the top of the intake. I'm pretty sure Mamo fills the intake and port matches to the head. I don't have numbers yet on my home ported 102 but the 90/90 made 560 RW on a 441 CI and TFS 235 heads with 1 3/4 1 7/8 stepped headers
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408 NA Build Underachieving? 
