LT1 Motor Upgrade


#1

I just finished putting a lot of money into my 93 LT1. I went with an LT4 Hot Cam Kit, including heads, 58mm TB as opposed to stock 52mm, 32 Lb. injectors instead of 24 lb. injectors, Edelbrock LT4 intake, Hooker shorties, Borla cat back exhausts and a K&N air filter and a new chip burned for the motor. It feels fatser than the old LT1 but not where I thought it would be. I was told that after the break in period and when the chip and motor work out any problems, I will feel a big difference. I was given all sorts of final crank HP numbers, ranging from 430-475. GM performance people rate the LT4 Hotcam kit with heads at 425 crank horse. The car feel very strong but will it get stronger? Thank you in advance for any answers. I appreciate it.


#2

It’s possible. The ECM in this car really needs to have time to adjust the trims to tune the system for all the changes you made. You made a lot of changes, but the ECM is still starting from a base set of values that are not optimum for those changes. I remember even is stock form, starting with an ECM with no memory, the engines ran crappy until the ECM had a chance to adjust the trims and tune itself. Give it a week and let us know if it worked.


#3

Thank you. I’ve only put 50 subdued miles on it so far and I felt it get a little smoother than when I first drove it. When you say ECM, can I assume you mean the computer where the brand new chip is in? My mechanic said that it will take a while before the chip adjusts for so many changes I made and that as the break-in period continues, the car will really come to life. He said what I feel today will be nothing like I feel once the break-in is complete. I hope he is correct. I spent a lot of money for this setup, promising HP of well over 400 at teh crank.


#4

IIRC The LT4 found in the Corvette Gran Sport and the SLP F-Bodies was rated at 330 HP. 425 HP may be a bit optimistic.


#5

You say “a new chip burned for the motor”, does it take all your changes into account? I’m no expert, but with all those changes it might be worth some time (after break-in) on a dyno with someone who knows how to tweak the settings for optimum performance.


#6

When sending out the request for the new chip, the mechanic had to fill out a very complete and thorough sheet that detailed everything about the car, from all the engine parts, exhaust, tranny and rear end stuff to anything else the chip burner needed to know to insure I got the correct chip. Thanks. Good question Texases. :slight_smile:


#7

Well, after all the work you’ve gone through I’d want to confirm optimum performance with some dyno time. Every combination is a little different.


#8

You are looking for 100hp over stock and the only mechanical change in the engine is a cam with a different profile?

What is the status on the rest of the engine? was it overhauled? what heads did you select? any idea on the compression ratio?


#9

A break-in period is not going to make much difference in engine performance.
Every engine is different and many times these horsepower figures (no matter what they’re for or who they’re from) are “optimistic”.

I also don’t see this kind of performance gain with the only major work being a cam change.


#10

Here is the story on the heads.

I replaced them along with the cam, TB, intake, exhaust (headers & Borla’s) new 32 pound injectors and a K&N air filter.

LT4 Aluminum Cylinder Head Assembly Aluminum performance head Can only be used on 1992-newer LT1 and LT4 engines Completely assembled with 2 00"/1 55" valves 195cc intake port 54 4cc combustion chamber No heat riser


#11

This is how GM performance arrived at their numbers. My stock LT1 is rated @ 300 crank HP. The LT4 is rated @330 but does not have the same heads I am using or the “Hot Cam”. The Hot cam is a 50 HP increase over my LT1 stock cam, as per GM. If you look at the comparison sheets for both cams. the LT 4 is much milder than the Hot Cam. Look at the heads, LT1, LT4 and the “Hot Cam” heads. they have bigger intake valves with 1.6 RR’s. If it was just a cam change, i wouldn’t expect 100 HP increase. But with heads, exhaust manifold, TB and air filter change being fed by 32 lb. injectors, i am now thinking it is possible for it to make over 425 crank HP. had it out today. Wants to go but I keep it civil during the break-in. Thanks for your answers


#12

The only real way of determining any gains would be a before and after dyno test on a unit that can measure HP at the crank.
The ones around here are chassis dynos and measure at the rear wheel.

About a year ago on one of the weekend TV car shows one of the hosts brought his '69 Chevelle SS 396 into the shop. This was allegedly the 375 HP version.
It dynoed at 223 HP.
After some modifications (intake, carb, distributor tweaks, etc.) the dyno showed 241 HP on the next go around.

The point being that the stock rating for the LT1 may be a bit of back-patting by Chevrolet and it never produced 330 HP to begin with.
I’m also skeptical (very) of a claim by GM that a camshaft on its own will give you 50 HP.

A recent performance magazine I got was referring to a car show that was held and a dyno setup was there which would allow people to dyno their cars after guessing at the HP.
Only one guy out of 10 was even close; the rest were guessing way high and none of the HP ratings were anywhere near what the factory said they were.
Granted, a transmission (especially an automatic) will rob HP but even taking that into account the HP ratings being guessed at were not even close.

Even a guy with a dual 4 barrel 426 Hemi in a Plymouth Roadrunner was putting out about 320 at the wheels. Figure in a lesser amount of power loss because of a manual transmission and the figure is still nowhere near the factory 425 rating.


#13

I’m thinking the dyno runs would be used to tweak the settings - would that be possible?


#14

Thanks Ok4450. It is frustrating trying to figure out why GM would advertise a kit that allegedly makes 425 HP, supplying dyno tests to back up their results. I called GM performance today and they swore that their total Hot Cam package, including heads is a 425 HP package. He told me to look up the difference between the original LT4 Motor and the one I purchased. There were siginificant differences between their 330 HP LT4 motor and the one I have as of today but 95 more HP??? I must admit that the car now goes sideways from a standing stop and the tires chirp in all gears. You can feel the torquiness (Made up word…LOL) of the motor and where the power band is now. At 2500 RPM, this motor wants to get up and do it’s thing. I will dyno it come summer time but if I were to guess i would say that this motor is putting out 400 HP at the crank. I figure the cam for a 40 HP increase over the stock LT1, especially since the plain LT 4 adds 30 HP. I figure the heads for another 35 HP over LT1 heads since they are 2 levels up from it. Add in the Edelbrock Intake for 5 HP, headers for 5, Borlas for maybe 10 58mm TB for about 5 HP and the K&N for 4-5. Considering it is in a 3250 pound car, that is a lot of HP. I just was hoping for more. I hope my guess is wrong. time will tell.

Bob


#15

About all I could suggest is maybe having a dyno run; even on a chassis dyno.
Around here it runs about 50-60 bucks for a dual run. One initial run and a follow-up after tweaking.

Take the rear wheel HP reading, add about 15%, and that should be close to crankshaft output.

A few yeara ago I built a small block Ford (Mustang GT HO 5.0) and put it in front of an early Ford AOD transmission.
The heads were ported, larger valves, a bit more than moderately wild camshaft, distributor tweaks, dual 4 barrels, etc. and the most HP that could be coaxed out of that was right at 223 at the wheels. Add 15% and it’s still nowhere near even 300 HP.

The number was disappointing but the results were still great. The torque curve on the dyno hits the maximum at 1800 and remains flat as a board clean through 5000 RPM.
Stomp the throttle from a dead stop and it’s just like getting rammed from behind by a truck clean through burying the 85 MPH speedometer. It just pulls hard the entire time with no let up.


#16

Speaking of Ford V8s, you’ll get a laugh out of this, OK - on another board someone claimed “I have a 1996 4.6l Cougar and installed XXX chip. I had it dyno tested and it went from 205hp and 280 ft lbs of torque to 307 hp and 448 ft lbs of torque.”

That set off my BS alarm…


#17

A few more cubes (stroker crank) will get you where you want to be.


#18

Yeah, your post about that Cougar got a rise out of me too! A 100 HP and 168 ft. lbs. of extra torque because of a chip? When pigs fly, maybe.

Hard to believe a measly chip turned a ho-hum 4.6 into a Cobra engine. :slight_smile:


#19

A few more cubes always helps but the motor has already been out, changed and put back in and the wallet is now empty…lol Besides, the crank I would need for this motor costs around $2,000 or higher. The motor is starting to come to life now. It feels like I do. I barely can see when I first awake but by noon time, well what the heck, I can still barely see…lol Okay, by mid afternoon I am ready to rock. :slight_smile:


#20

If the 375 HP on the Chevelle was the rated gross HP and you figure a 15% driveline loss, then 223 RWHP is right on the money. The LT1 and LS1 were actually conseratively rated, especially the LS1.