So I finally got my LT-4 build buttoned up, installed and then dyno tuned. I got CLOSE to the numbers I hoped for and I think I know why. Id like everyones guesses before I share the dyno results, which should help me decide on a few changes before going back to the dyno with the Nitrous setup installed.

Stock block bored 030 (355 ci)
Stock heads and valves with Lunati Voodoo spring kit
Comp Cams Ultra Pro Magnum rollers (1.6)
Stock crank 10/20
Manley 6" H-beams
JE 2618 forged 11:1, file fit AP/Ductile iron rings
MLS head gasket .040 quench (zero deck block)
Stock intake port matched to 7777 Gasket
Stock Throttle body and MAF, SLP triple tube intake
Hooker slick long tubes, no cats, X-pipe, no mufflers
Lloyd Elliot Custom cam 565/579, 227/235 110 lsa
Spec Stage 2 with aluminum flywheel and ATI aluminum balancer
Mezierre elctric pump, mechanical pump and hardware deleted (running standard SBC single roller)

Vegas altitude is around 2000 ft, I think density altitude was around 3200.

If I remember correctly, I added up 27 pounds of reduced rotating mass combined.

Lets hear everyones hp/tq guesses! =)

 

Well if it was a stock longblock lt1 with that cam I'd say 350rwhp with a m6. Being refreshed and little more compression I'd say 360-370rwhp

 

380 rwhp

 

you have the .006 (advertised) duration numbers and ICL on that cam?
or valve events off the cam card?

 

 

If my dyno sim is worth a crap...435 flywheel at 6k
370 at the wheels sounds close to me.

 

I’m going to be a little optimistic and say about 390.

 

Crap.... idk now I just looked at that DA again. That’s some suckass air!

 

lmfao

 

Because I know how potent a LT4 really is (stock heads flow over 250 cfm compared to ~215 cfm of a LT1) especially with a Lloyd Elliot spec'd cam and lots of other bolt ons. The 6" rods will only help in reducing friction as well.

410 RWHP @ 6,600
380 RWTQ @ 5,200

Most dyno's apply a standardized correction factor. Meaning the final calculated HP number is adjusted for air density, temperature, etc.

I bet that setup would still trap 120-122 mph in that weather in a full weight C4.

 

I also just noticed the OP did not specify a part number for the JE piston. Typical piston manufacturer compression ratio is based on a 64cc chamber. Assuming the piston in question is a JE flat top with 2 valve reliefs (+5cc) with the LT4s 54.4cc chambers the compression ratio is slightly over 11.7:1. I cannot imagine anyone building a LT engine and running less than 11.5:1. You could get the compression down to 11:1 but one would be running a more expensive dished piston which kills your quench effect.

 

Compression was achieved by milling the heads and decking the block, then CC'ing the heads. I specified zero deck, 30 to 40 quench and 11:1 as we only have 91 octane in Vegas...

https://www.jepistons.com/Products/367094.aspx

 

Not sure what your heads CC'd but unless the chambers have been opened up or the valves recessed into the valve seats the milling should have decreased the chamber volume. The chamber volume is 54.4cc nominal on a LT4 head. A 0.020" mill will drop the cc by roughly 1.5cc. So your heads may be as small as 53cc. The JE piston you provided the spec for shows 11.1:1 with a 58cc chamber. With the specs you provided and a stock spec LT4 chamber. See how the numbers just don't add up to 11:1.



​​​​​​
​​

 

FWIW with a 20 thousandths shave and ~53cc chamber volume the calculated compression ratio is 11.96:1 with the specs you provided.

With the LT4s reverse cooling system, properly tuned this should not be a problem even on 91 octane.

 

I'll check the build sheet for the CC's when I get a chance. The heads were only milled to achieve the proper smoothness for the MLS gaskets, not to flatten or decrease volume. The seats were cut when they did the valve job so the valves were ground as well. That's why the chambers were CC'd after to verify...

Did you account for the head gasket volume?

 

The head gasket volume is roughly accounted for by the calculator. Assumes the gasket is the bore diameter and specified compressed thickness. Pretty close. It does not account for the volume above the upper ring land but with a flat top piston and modern ring package that should be minimal. The calculator is reasonably accurate. Atleast to within +/- 0.2. Variance would be actual head gasket diameter and other volume above the rings not accounted for by the pistons dish size.

 

My guess is 370rwhp, anxious to see your results. I figure ~300 wheel for a stock LT4 and then a bump of 70 wheel from the headers, cam, compression bump, lighter flywheel, etc. My estimate might be a little on the low side now that I think about it but I'll run with it for now. Numbers are just numbers though, more importantly what are your impressions thus far?

 

Yeah that JE piston has the compression height we wanted due to the Nitrous so there is definite extra volume there. When I get home today Ill dig up the build sheet from the machine shop and post up the exact specs.

 

This thing is a MONSTER! The effect of that 28 pounds I removed from the rotating assembly alone has this thing revving so fast it surprised the hell out of me the first time I ran the car! Just a quick kick of the clutch pedal to rev on someone had the tach BURIED almost 7k!

The stock C7 tires were USELESS! The car would go sideways on the freeway at 75 mph! Thats why I stuffed those Nitto NT05's in there. The car will still destroy them if you want but they are much easier to recover and FAR more predictable. In fact the car PUSHES in corners now like a Porsche! (Nitto 555 G2's up front are no match).

 

If you haven't already, get yourself a shift light. Set it to a few hundred RPM above HP peak once you get it dynoed.
I'm with Fast355 on this in thinking it should be a little north of 400rwhp and about 380 for torque SAE corrected. It's possible the shop you use will not use SAE. It'd be interesting to get sheets for both their correction and an actual.