Going to have the LT4 Hot Cam kit installed this friday by good local mechanic. Is there anything else I should be doing while he is in there. The Mechanic suggested new lifters, but others have told me the stock lifters will work fine. Any suggestions? And I don't have the money to do the heads right now.

 

I replaced the lifters while I did mine, but they weren't really needed. I installed an electric water pump at the same time for a total gain of 44 rwhp. The water pump is around $200

 

Hey Nathan, What model are your long tube Hooker Headers? I would like to get some myself.

 

They are either 2149's or 2151's. I never can remember, basically they are the same header, I just have the ones without the EGR provisions. I'm pretty sure it's the 2149. It's actually an L98 header, but they fit fine. There are some pictures on my website if you follow the links below.


[Modified by Nathan Plemons, 3:35 PM 7/29/2002]

 

You may want to change the fuel cut off to 6400 rpm from 6000 (or whatever is the stock LT1) in the ECM software to realize the increase power over the stock LT1 cut off.

 

Make absolutely sure they use a special water pump driveshaft seal protector when reinstalling the timing cover.

If not the water pump driveshaft seal will get kinked causing an oil leak, slow at first, and then get worse.

The protector looks like a thimble. The GM part number is in the service manual under reinstalling timing cover.(or water pump, can't remember)

 

You probably already know that you'll need a chip burned so it will idle correctly. If not, Ed Wright at http://www.fastchip.com seems to do a pretty good job. As far as fuel cut off at 6400rpm, I would not recommend it with a stock bottom end LT1. I had Ed set mine at 6200rpm to be safe.

 

If it were me, I'd try to do 1.6 roller rockers while into it, also. I've heard the combo of hot cam kit and 1.6 rr's yields a definite seat of the pants improvement throughout the entire rpm range.

 

Optispark
If it's got a lot of miles on it replace it.
Update it so that it's vented either with the kit or a new opti.

of course new plugs/wires, a lot easier to replace them now.
All new seals on the timing cover, crank, opti, waterpump drive.

New waterpump if old, before it takes out the opti you just upgraded.

 

With the LT1 engine and the LT4 Hot Cam Kit (kit meaning the combination package of the cam, springs and roller rockers) you will never get the full benefit of that cam unless you add the LT4s hollow stem valves and the LT4 cylinder heads. With out the hollow stem valves the engine will not RPM as it should. You will float the valves far lower than does an LT4 because the LT1 valves are too heavy. In fact, the valves will float before the camshaft peaks....kinda defeats the whole idea of the Hot Cam in the first place, huh.

The LT4 Hot Cam was originally developed for showroom stock road racing. Not only does it need the hollow stem LT4 valves to RPM but it needs the much better air flow capacity of the LT4 cylinder head and a low restriction exhaust system to really work well.

On an LT1 with standard valves, stock heads and stock exhaust do not expect a large power gain.

 

Sorry, but I'm gonna have to call a :bs on this one.

Sure you've got a very valid point, valve float is always a possibility. However, the hot cam is a proven performer in the LT1 engine, valve float is not really an issue. The Hot Cam peaks it's power right at 6000, reving it much past there really isn't that much of a benefit. So by setting the limiter around 6300 or so a good set of springs will easily prevent valve float.

Lightweight valves are always a good thing, but the hot cam does not mandate them.

My car was dyno proven to go from 270 rwhp and 300 torque to 313.3 rwhp and 313.3 torque with completely stock exhaust, fully emissions legal. That's 44 hp for around $600 worth of parts. I dare you to find that much performance anywhere else for that priice that doesn't come in a bottle.

I added a set of Long tube headers and kicked those numbers up to 336 and 345 respectively. The car runs 12's @ 112 mph. I think that's a pretty good performance increase, all on stock cylinder heads with stock valves.

Don't get me wrong, you bring some good points and some good concerns, but a properly set up hot cam kit doesn't run into the problems you mention.

 

Anyone who has been around here know not to use the lame LT4 springs with an LT4 HOT cam. Not only will the LT4 valves float with the LT4 HOT cam and LT4 springs below 6500 RPM, but the cheesy factory retainers are prone to breaking during valve float. More than one LT4 owner has dropped a valve with that combo. The LT4 springs are too close to coil bind with 0.525" lift. Going with Crane or Comp springs and some Ti retainers will allow you to rev beyond 6500 rpm with the heavier LT1 valves.

Eric

 

That is the first I had heard of this. I have read that all you need if you already have the LT4 is the hot cam. Everything else is there.

 

ttt
Does someone know the part number of the Comp Cams valve springs that can be used with the Hot cam in an LT4? The LT4 already has the Ti retainers and keepers, right?
:)

 

Yes, that's what "they" say. But the LT4 springs are very weak. I have a friend that actually measure 32 factory fresh LT4 springs and found 5 that didn't even have the rated spring rate. They are a great spring for lifts under 0.500 (like when someone upgrades an LT1 to 1.6 rockers) but at 0.525 and the agressive ramps on an LT4 HOT cam, they aren't really up to the task. And using the LT4 zero lash rockers only adds to the problem. I'm getting ready to install an LT4 HOT cam in my LT4 and I'm going to switch to some more standard adjustable lash rockers.

The factory LT1/4 retainers are steel, I think they're stamped. Very light but weak. I think the factory used really light retainers and weak springs to maximizes the lifter life in the standard LT4 with the stock LT4 cam.


The two options I see are the Crane 10308 spring/retainer kit (~$146) which has the Crane 1.460" double springs, 99893 springs or the COMP 987 springs. For Ti retainers I'm still looking. K-Motion has a set for 1.460" springs, they should fit the Crane 99893 springs, but I'm not sure.

BTW, MVR 155 dropped a valve with the LT4 HOT cam/LT4 springs combo. He's building a 383 as we speak/write.

Eric

 

I think you have convinced me on the springs. The question is would the stock rockers and non Ti retainers be fine for the factory redline? Plus I only take mine to the track 2 or 3 times a year and drive the car pretty mildy most of the time. I know if you are going beyond factory revs that Ti retainers are a must have item.

 

The springs I mentioned are double springs with a damper, so I don't think the factory retainers will work. Just as well. I don't know enough to say were the LT4 spring's/retainer's limits are, but you only need to miss a shift once....

Eric

 

I've been wrestling with this very issue for some time. Here are some of my conclusions...these and $0.50 will get you a cup of cheap coffee...
- This topic is like discussing religion and politics. Everyone has an opinion and different views are not necessarily wrong
- There are better spring combo's out there, and some of them have been listed.
- Most of the better combo's require machining of the valve spring seat. The stock spring is 1.32" OD. A 1.43" OD spring may fit, but it's real close.
- If you go to a different spring, you'll likely need to find new spring seats. The stock LT4 seats have a locator that won't fit "narrow" springs or dual springs with an ID of <.885". I actually bought different springs but returned them because I couldn't find a suitable seat. The GM ZZ3 valve spring spacer (p/n 10185066) may have worked, but I couldn't determine that conclusively.
- While it's true that MVR 155 dropped a valve, he's a single data point. There are several other LT4 owners using LT4 springs without issue even though their cars see 1/4 mile and/or road race use.
- Carefully consider how you'll be using the car. My approach will be to set my fuel cutoff at 6700, but I plan to shift at 6500. My GS sees about 2,500 miles/year with 6 or so trips to the track. Since my goal is just to have fun when I am at the track (I recognized long ago I'm got good enough or wealthy enough to be truly competitive!), I don't go 10/10ths / *****-to-the-wall (i.e. powershifting, etc).
- Don't confuse LT1 info with LT4. The LT4 has lightweight valves, significantly lighter than the LT1 pieces. This is one of the reasons the LT4 springs will work on the LT4 but not necessarily on the LT1 (above 6200 for any length of time).

Hope some of this helps. If money and time aren't an issue and you intend to beat the engine into the ground, I'd pull the heads and have good springs installed (along with some port work as well!! :yesnod: ) If the intended use is typically going to be easy street duty with a touch of stop light drag and track action, I'd go with the LT4 springs.

:cheers:

Jim Mason
'96 Grand Sport #007

 

Thanks for the info. I'm getting my cam kit installed monday. After reading some of the posts I tried to order the Crane Cam Spring and Retainer kit 10308 for the LT1 but couldn't get it in time. K-Motion Titanium retainers sounded awesome, but I don't want to be the test case for trying them on different springs. Since I am only an occassional weekend warrior and don't know much cars, I'll stick with LT4 springs that came with the kit.

 

I spoke with Pete at CNC Heads. It is nice that they are only 5 miles away!

He confirmed that the stock LT4 springs are not good enough for the hotcam. You can use the Comp Cams valve springs set 941 for the LT4 hotcam. Set it up with 1” 970. That puts about 120-125 lbs on the seat and 340-350 lbs open.

He says that with an LT4 you need to port the intake because there is a 12% flow restriction unlike the LT1. In fact, he insists on an intake port job with the LT4 heads he does. He says the intake alone is worth 11hp (crank I think) on a stock LT4. The better intake gasket is worth something on the high end as well.