CanadianVRss

iTrader: (1)

Hey guys. I have a 408 stroker and its not performing. in fact its just as fast as my old 6.0. i can't get it to 60' for ****. i built it for boost and torque while out of boost down low, but it should be performing better than it is NA.

408 stroker:
-10.9:1 static CR
-224/228 .581 .588 114LSA
-L92 heads, milled 0.005" just to clean them up and make sure they're flat
-1 3/4 long tubes 2.5" primaries. 2.5' duels to X pipe, then duel inlet outlet muffler, then a glass pack for each bank and 45* then out the side before the rear tire. whole system is straight through but added the glass packs because it was too loud.
-ring gap is 0.026" top 0.028" second, obviously for boost, but this should't effect NA a whole lot.
-Holley Hi Ram
-90mm LS3 TB
-plugs are autolite 103s (6 heat range) running 0.040 gap
-stock TB converter flashing to 2600

truck has high parasitic loss (AWD)
track is at 2100 feet but DA is usually AT BEST 2700, we have a freak day every once and awhile around 1800, but very rarely.

things being equal (DA wise) the 408 trapped 13.8 at 99mph with a horrible 2.1 60'. old 6.0 trapped 13.8 at 98ish mph with a 2.05 60'

the differences in the build are as follows:

-the 408 now has a 2.84 ratio first gear vs the 6.0s original 3.06 (i know, thats not helping, but it'll help not cook the tires when its boosted)

-the 408 has a lower stall 2600 TB converter vs the 6.0s 3000.

-408 shift is 6200 1-2 2-3 vs 6.0 6600 1-2 6500 2-3

- 408 CR of 10.9 vs 6.0 CR of 10.2

-tune is pretty well dialled in on the 408 maybe a tenth left. 6.0 was bang on.

now i would think the 408, even with the taller first gear and lower stall would out perform the 6.0 everywhere especially with the extra compression. i can say that the 408 bests the 6.0 in daily driving for sure, torque all over. can accelerate from 60km/h uphill in 4th at 800rpm no issues. Under load (turning left or right) and going wot from a stand still will break all 4 loose. thats something the old 6.0 could never dream of. truck is 5050lbs without me in it. why such a shitty time? the 6.0 went a BEST of 13.6 @99 with a 1.9 60' when the DA was 1800. which is respectable for a truck of 5050lbs with high parasitic loss and a horrible DA at my track. for reference. here are times for stock "performance" vehicles at this track
second gen lightning: fastest i seen was a 14.2 with some sticky rubber
SRT8 jeep: fastest i seen was a 14.0
stock silverado SS: 16.1

all this seems a little crazy to me, the 408 should be snapping low 13s with low 1.9-high 1.8 60's. and high 12s if the DA gets around 1500 (hoping). any thoughts? ill be doing a compression test tomorrow (i know a leak down test would be better, but i dont have a leak down tester) to see if there is a big variance between cylinders. was just wondering if others had any issues like this? thanks for reading.

03sierraslt

iTrader: (22)

What kind of piston and rings? That's a lot of gap, how much boost do you plan to run? Also your exhaust is going to be way too small. That's too small for a na 408 let alone one with boost, what kind of fuel? 10.9 is a decent amount of compression for pump gas and boost if over 10psi. Now if you plan to run e85 then it's different. The cam and head combination is less then optimal for the setup, for boost the cam is even further out depending on turbo or supercharger.

TXsilverado

iTrader: (19)

cam is too small/wrong events for a n/a 408 with l92 heads, exhaust is way too small from primary size, collector size all the way to the tail pipe. high ram intake is known to suck for N/A application but good for FI...your cam events are wrong for this intake style too (on a N/A combination atleast)

I assume you plan to go turbo based on your intake selection? if so, confirm your cam is right for a boosted l92 heads and high rise and put the turbo on.

a 2600 stall with a large intake and l92 heads will make for a soggy bottom end.

CanadianVRss

iTrader: (1)

Mahle powerpak pistons and rings

Plan on running as much as possible with 93 pump gas and hosing the meth (50/50 or 40/60 depending on what's on the shelf) to it.

I understand the exhaust is pretty small and choking the set up. But it's only on for a short amount of time before boost.

Compression will be dropped to 10.5 before boosting.


I understand that the hi ram sucks for NA but the extra cubes should be helping tame it a bit compared to the 6/0. It's definitely for boost on this particular set up. I'm considering just throwing a 3600 stall in it for the last month of the season before its parked for winter to negate that "soggy" bottom end. Even so, you would think the truck would leave with that 4" arm.

TXsilverado

iTrader: (19)

High ram sucks na, then you compound the issue with the wrong cam. L92 heads like an exhaust biased duration due to a weak exhaust port compared to the intake side. Cams for a single plane style intakes are usually on a 106 or less icl vs the 110 youre running.

Dont worry about the na times and force some air down its throat.

CanadianVRss

iTrader: (1)

you're right, i should just pour the boost on it and see how it does, considering thats what its set up for. i just figured id ask and see if you guys found it odd it pulled the same times with the stroker.

Atomic

iTrader: (42)

My 402 was a lazy pig NA, but it was built to handle 25psi from a turbo. 6psi felt ok, 16psi felt great, and 22psi was hope you are holding on!

AkSSS

Like Atomic said. My motor is 9.6cr and my rings are not near as opened up as yours. But my motor really comes to life with the boost, especially up above about 13 psi. I have a cathedral setup and Atomic has a l92 like yours. So hard to compare.

Just seems like a lot of compression for 93 octane and mixed meth. How far are you trying to go with the boost? Goal?

CanadianVRss

iTrader: (1)

Low 11s high 10s. I'm not too worried about the CR. Like previously stated I'll bring it down to 10.5. I'll take the boost as high as it needs to go to reach my goals. I shouldn't need to run as much PSI with the higher CR to make power that's all. LS2s are 10.9 and ls3s are 10.7 from the factory, people throw some mad boost at them on pump gas and meth so I'm not really sweating it.