Hi all, its my first time building an LT1 but I've tried to pay attention while putting this together. I am working on finishing up my build and I wanted to get some feedback before I get everything buttoned up and installed in the car. I was originally planning on doing a LE2 HCI on my stock 140k mile '94 LT1. So I spent some time picking out my valve train and getting the heads, cam, and intake. After taking the cam out of the engine and seeing the worn cam bearings I decided to do a forged 383. Yep... that escalated quickly! I'm trying not to cut corners, however I am on a "budget" and already over-budget (lol). I started getting items for the original LE2 350 HCI build like two years ago, so as the build evolved I have accumulated some questions:

1. Is my stock throttle body going to be a restriction?
2. Are my pacesetter long tube headers a big restriction or probably fine?
3. Will I have problems keeping the engine cool?
4. Do I have to upgrade my stock steel driveshaft before breaking in the engine?
5. Are my non self-aligning 3/8" rockers fine given I am using ARP studs?
6. Is it really a big problem to break in the engine with conventional Valvoline 5W-30?
7. If there is so little time to seat the rings, why do some break in procedures have you hold the car at 2000 rpm for 15-20 minutes while you check for leaks, etc rather than just get do a quick 5-min check and roll out? I understand the higher rpm helps the oiling, but not the time part of the procedure.

 

Here is a mostly complete list of the mods and the build....

Intake:

• SLP cold air intake
• Stock MAF
• 1LE rubber elbow
• Stock 48mm throttle body
• Lloyd Elliot ported LT1 intake manifold

Exhaust:

• Pacesetter long tube headers, 1 Ύ primaries, 3” collectors
• ACDelco O2 sensors w/ O2 extensions
• 3” x-pipe
• Moroso spiral flow throughs
• Dumps before rear axle
• EGR delete
• No cats

Fueling:

• Walbro 255 pump
• EVAP delete
• Braided -6AN SS fuel lines
• Bosch EV1 408cc/min injectors, 280155811 (“36lb/hr white GTP injectors”)
• 93 pump-gas, almost always 10% ethanol blend

Accessories:

• Stock AC and heating
• Stock 140A alternator
• Stock power steering pump

Top-End of Engine:

• Lloyd Elliot ported heads, stage 2, 52cc combustion chamber, 2.00” intake 1.56” exhaust Manley Valves
• Lloyd Elliot spec’d COMP CAMS 227/235 duration (@0.050) 0.587/0.600 lift 110 + 4 LSA
• Lunati Hydraulic Roller Lifters
• Lunati valve springs, 73925K5, 379 lb/in rate, installed at 1.780” w/ 163lb seat, 385-390lb open
• Lunati NSA 1.6 ratio roller rockers, 3/8 ARP rocker studs
• COMP CAMS adjustable guide plates
• Mr. Gasket 0.026” head gasket

Bottom-End of Engine:

• 2-bolt main 1994 LT1 bored to 4.030”, 9.015” deck height, 11.237:1 CR, 0.041” quench
• Mahle PowerPak 4032 pistons, inverted dome 16cc, 1.125" compression height, 4.030” bore
• Eagle Forged 4340 no-twist crank, 3.750” stroke, 1 pc. rear main seal
• Eagle Forged 4340 6.000” H-Beam Rods, ARP 8740 cap screws
• King bearings
• Cloyes stock style timing chain
• ATI super damper, 7.48”
• Stock mains, ARP main studs
• Moroso 7 qt oil pan and Moroso pickup for 8.25” pan
• Mellings standard pressure standard volume shark-tooth oil pump
• Stock LT1 knock sensor

Cooling:

• Stock fans, programmed to come one earlier
• Stock radiator
• 160 degree thermostat
• Meziere HD electric water pump
• Throttle body bypass

Brakes:

• LS1 front and rear brakes, Hawks HPS pads
• ABS delete
• Wilwood proportioning valve, SJM line lock kit

Driveline:

• Strange 12 bolt, 4.11’s, posi, 35 spline axles, 1350 U-joint
• McCleod dual friction clutch, stock-style flywheel and pressure plate (both neutral balanced)
• Rebuilt and upgraded T56 (thegearbox.org stage 2) (the one with a 0.5 6th gear over drive)
• Staggered ZR1 replicas with 315/35R17 in the rear and 275/40R17 in the front; 25.7” outer diameter

Suspension:

• Wolfe drag bar (only connected when at the drag strip)
• Founders lower control arms
• UMI adjustable panhard bar
• Stock torque arm w/ energy suspension bushing
• New (stock) upper and lower A-arms
• Bilstein HD stocks and SLP springs in the front
• Competition engineering drag shocks in the rear
• New ACDelco springs in the rear with heater-hose-mod
• MWC K-member, 1 poly engine mount and 1 new rubber one

Pending:

• Still need to measure pushrod length
• Still need to decide what a good rev limit is… thoughts? Cam should make peak power at 6000 rpm and will probably shift at 6500 rpm.
• Still need to upgrade stock steel driveshaft to 3” chromoly or 3.5” aluminum

Use case:

Reliable performance is very important to me. I daily this car from mid spring to late fall. I take several long highway trips (4-500 miles in one day) every year. I go drag racing, autocross, and I hit the backroads hard. Currently the car weighs 3700 with a driver. Best pass at the drag drip (back when it had an automatic transmission and stock stall) was 13.5 sec at 103 mph. Hoping for 12.0 or better on street tires.

Future upgrades:

MGW shifter, adjustable torque arm w/ driveshaft loop, UMI adjustable lower control arms, aftermarket bell housing, Nitrous Outlet Plate Kit or boost, drag pack, speaker upgrade, roll cage, other hopes and dreams :P

 

OP

You have a good list of parts, my $02 on your ?'s

stock TB is fine

headers are good

stock fans/radiator are fine assuming they are both in prime operating condition

stock DS will be fine to drive around with. If you run steeper than 3:73 gears a larger diameter better balanced one (Dennys) is recommended more to keep vibrations away. If you drag the car with high RPM clutch dumps than 1350 yokes and a better rear end.

I would use a high zinc content oil like Valvoline VR1 or Joe Gibbs 5-30 for initial engine break-in vs just conventional oil

The 20 min at 2k rpm even running a hydraulic roller cam is what I do. More to keep oil pressure up while you monitor for leaks and use a IR temp gun on the headers to confirm temps are reasonably uniform. Drain the oil which will have all the assembly lube and minimal debris in it. New regular oil and go drive doing the engine load process to set rings. Drive in low gear to 35 mph and let engine brake to 5 mph, repeat several times. Increase to 45 and repeat, increase to 55 and repeat several times and you are good. Then go drive "normal" (read don't baby the car)

I would however swap to 7/16" studs & RR if the 3/8" parts are new and you can exchange them

Have the PCM tuned for your set up before starting motor or the car will run like a$$. Mail order is fine. You can do tuning tweaks after once you do some data logging. IMHO a "good" tuner ill nail it from the start

If you do not have larger injectors, you may likely need them. 30 to 36 lb

The LE H/C using the Lunati spring is solid

 

I would step up to a 52mm throttle body. Did LE open the intake manifold bores to 58mm? You don't need a 58mm TB, but the 52mm is good for up to 500 flywheel HP, based on measurements taken on an engine dyno with my build.

 

On the 93 z28 I have it has a forged bottom end, but stock cam, heads and intake. (At the time time my oldest son was 17 and driving it, he wasn't use to cars like this so it was toned down until later on)

Mods on it are BBK headers, 3" single exhaust, MSD blaster coil, 160 deg thermostat and mail order tune. It's a A4 car, 3.23 gears.

Using the stock style LT1 radiator with this engine it runs fine around town. It's a small home town, but when I go to a bigger city in a lot of slow moving traffic and lots of red lights the temps will start to climb. Once I get moving again it's fine. I do have the manual fan switch override, so with both of the fans going. This was in summer. I can let the car idle in the yard with just the fans for 15 to 20 minutes just letting it run from a cold start and it hasn't tried to get up on the temps. But right now it's cold outside so it has plenty of cold air coming in.

 

Gears are 4.11's with a Strange 12 bolt. What makes you recommend Denneys over another brand? I won't be doing clutch dumps during break in, no. Later, yes.
Does the 20 minute at 2000rpm not impact the ability to seat the rings?
Unfortunately the studs and rockers were one of the items purchased a while ago and not returnable. Do you think the 3/8" are going to get it done but the 7/16" are just more peace of mind or is there more to it than that?
I plan on getting a mail order tune from Moe Bailey, I have heard good things so I expect his tune will be pretty awesome.
I already have 36lb injectors

 

LE did open the intake bores up to 58mm along with cleaning out the inside really well. If I was looking at doing a 150 shot of nitrous (wet plate kit) in a year, does the 58mm become necessary then? I did have the rings gapped appropriately for the nitrous.

 

Thanks for the feedback on the cooling! I did notice that when I reinstalled my AC system two years ago the car held a higher temp, around 190F even though it has a 160F thermostat. Beforehand it would stay at 165F to 170F. I don't have a manual fan switch though.

 

OP
I can elaborate on my previous comment on keeping the stock 48 mm TB.

If you have the ability to scan IAC counts and are mechanically inclined a larger TB, 52 IMHO would be fine, would be better in the overall picture of going with a cam assuming you are also doing all the other "supporting" mods (heads, headers, injectors fuel pump, etc) which it appears you are. My initial impression was you were asking about a cam only on a stock motor

Aftermarket, larger, TB's will require some "adjusting" which can certainly be cumbersome when starting a freshly built motor especially one with a larger cam. They often don't idle because they don't have the IAC air passage the stock one does so you either do the "crack the blades open more" mod or "drill mod" which require IAC & TPS readings to perform accurately and is a scan, adjust, scan, adjust, etc. process. Not something you want to be doing IMHO starting a fresh motor. Remember you need to bleed the cooling system also so that is all part of this 20 min dance.Your tune will need to be for a larger one if that is what you do and Moe will know those adjustments for the tune. You will need to make the physical adjustments to the TB. Might want to start the car initially with the 48 then swap over to the 52 or 58 once the motor is settled and rings set as again you will be either adjusting the throttle stop screw and modifying the TPS (slot holes) or the "drill mod". IMHO the drill mod is the way to go but again it will take the ability to scan IAC counts. You DO NOT blindly drill a hole without knowing first what your IAC counts are and after the initial 1/8" hole you scan again and drill 1/64" bigger if the IAC counts are still high. All of this takes time and not something you want to be fussing with on initial start up or ring set

There are different opinions on the 2k rpm for 20 min initial start. Originally with flat tappet cams this was critical but with hydraulic roller cams that is not really necessary. "I" do it because that is what my engine builder advises and, IMHO, those 1st 20 min are all about checking for leaks, monitoring engine temp and oil pressure while looking from above and under the car as it fast idles at 2k rpm. The 2k rpm keeps oil pressure up. After the 20 min and oil change then I go out for a drive and set the rings with the accelerate/decelerate method I mentioned earlier. It loads the pistons both ways and has worked for me. If you feel everything will be 100% right on initial start (read that is not always the case) up and immediately want to go for the drive to set rings fine but minimally you need to let the engine get up to full operating temp first

 

Thanks for elaborating!

I do have scan software, yes. Do you think boring out the original throttle body to 52mm avoids the calibration problems associated with aftermarket throttle bodies?
Would it be bad to get a tune for a larger throttle body and then run the smaller one during break in or is it better to get two different tunes?

It seems like leaving it at 48mm is the easy route that minimizes complications during initial start up. I suppose the trade off is that at some unknown higher rpm the throttle body could be flowing more air if it was larger, probably costing a little hp and tq.

Your explanation of the break in makes a lot more sense now.

 

With the 48mm TB, I would estimate that above 425 HP at the flywheel, there would be a restriction that would affect power due to increased pressure loss. The issue is not airflow volume. That is defined by the volume of the cylinders and the RPM. The issue is the mass flow of air. As pressure loss due to flow restrictions increases, the density of the air drops, there are less “pounds” of air entering the cylinders, which means less fuel can be burned = less BTU’s produced to drive the piston downward.

We broke my engine in on an engine dyno, so RPM was not an issue.... the dyno can be programmed to control that. Started with a Holley 58mm TB, no problems. Also never had an idle issue or IAC count issue with the aftermarket TB. Although again, not a comparable setup. The engine was almost totally controlled w/ an aftermarket engine management system, but retained the factory PCM for idle speed control (the MoTeC ECU could not control a stepper motor IAC, only a pulse width modulated IAC).

As far as the addition of nitrous, with a wet plate system, airflow through the throttle body is minimally affected, since MASS (fuel and N2O) is added behind the TB. I spray a dry 300-shot in front of the throttle body. The vaporization of the N2O cools the air, reducing it's volume, and has no effect on the 58mm TB flow limit.

 

OP

If you can find a service that bores out a stock 48 to 52 than that TB would be more plug & play. IDK who does this anymore. Many years ago David Kudos did mine. Depending on the cam, and tuned idle rpm for that cam, the motor may have idle issues because IAC counts are pegged at 160. This is why you need scan ability to read IAC counts. They want to be 30-35 at idle with motor at operating temp. Using a stock re-bore you "may" have to enlarge the existing 1/8" hole. You would increase hole in 1/64" increments and scan again. Yes 1/64" will make a difference so take baby steps....pretty hard to "undrill" a hole to big.

There would not be any problem in my opinion of running the motor during initial start up and break in with a 48 if it had a 52 or 58 TB tune. It may even idle OK with a 58 given a tune for a camed motor typically has "desired idle" rpm set about 825-850 rpm which is higher than stock and given you would use a washer or something to crack open the blades some to keep the motor at 2k rpm during the initial start up window the "idle" problem would not really be a issue under that situation. Once you do go for a drive though with a 58 that the pcm was not tuned for or does require a "mod" you may have to feather the gas to keep it running but otherwise it would under acceleration

There are "better" aftermarket TB's than others. Not sure which one floats to the top these days. ASM has been regarded as better. More in terms of build quality. yeah it is higher $

Fred, Injuneer, is way more versed in these LT1 motors than I especially regarding tuning issues. Sounds like your current build and future expansion plans a 52 minimally would be needed

 

I was considering machining the throttle body myself and machining new throttle body plates... Might just stick with a 48mm until I have some miles on the setup and everything else is working smoothly.

 

Moe can revise your tune for a 52 or 58 when you make that change after getting the new build sorted. I know you can bore a 48 to a 52...don't think to a 58 as I suspect that is a different casting

If you have the skills and machinery to bore a 48 to 52, do that

 

I think I'll pick up a spare stock one and bore it out in case there are any complications.

Do you guys think running a wideband O2 sensor to monitor AFR is necessary or not really?