1993 LT1 Rocker Arms 1.5:1 vs 1.6:1

[Brian Smith]

Gang, I'm looking for some collective wisdom here. I know old school small block Chevys pretty well but know little about the LT1. My limited research indicates that stock rockers are 1.5:1. Has anybody installed the 1.6:1 aftermarket rocker on a bone stock LT1? What warnings could you offer? Piston interference?

What benefits in terms of horsepower/torque could one expect. I would like to quantify the horsepower/dollar ratio.

Given that a set of such rockers with roller tips are available from Jegs for $189 list what can I expect by increasing the lift and some duration by increasing the lift by doing this?

What are your suggestions? What are your experiences? Difficulty won't be an issue but lack of measurable results will be. Guide me boys if you will!
I wait to learn at the old Corvette hands knees! (No age shot intended as I am nearing sixty!);help

 

[Curious George]

Hello and welcome...
I installed 1.6 roller rockers (Summit private label set) on my '92 and did not have any piston to valve clearance issues. The LT1 has "guide" plates, so you do not need self-aligning rockers. The 1.6's gave me a little bit of increased "pep", but not too much. For $189, it was definitely worth the labor if you are going to DIY. To get maximum benefit, you should re-tune your PCM, but that may not be in the budget. On computer controlled vehicles, every modification should be followed by a "tune" to get maximum benefit. Even though most computers can compensate for minor modifications, this increases their overhead... the less the computer has to adjust, the better the car will run. I know this sounds counter-intuitive, but it is true.

CG

 

[vetteoz]

The LT1 has "guide" plates, so you do not need self-aligning rockers. The 1.6's gave me a little bit of increased "pep", but not too much.

I believe you will find the LT1 has self aligning rockers and the " guide" plates are only there to aid assembly at the factory.They are not hardened as regular guide plates are.

 

[TWISTERUP]

I did the 1.6 "self aligning" rockers and LT4 springs. The LT1 springs are not at coil bind w/the 1.6s but I had read they would be "close" and I had over 70K miles at the time, so I replaced the springs also. The cam specs of the later LT1 and the LT4 were very close the main difference was the added valve lift w/the 1.6s on the LT4. It's said you pick up 15-20 hp...I didn't do a before and after "dyno test". I also did a "retune"... as was mentioned above. The rockers are a mod which IMO wake the LT1 up more so at higher revs...I'm glad I did it

 

[Brian Smith]

Thanks guys. I presume by"tune" you mean to dump the CPU by disconnecting the battery to force a fuel map and ignition relearn.

 

[CAJUN C4]

I believe you will find the LT1 has self aligning rockers and the " guide" plates are only there to aid assembly at the factory.They are not hardened as regular guide plates are.

I Agree.You need Self Aligning Ones.You'll wear out your push rods & Guide Plates. They both must be Hardened if you use Non-Self Aligning ones.
15 H.P. Increase is Correct.

 

[TWISTERUP]

Thanks guys. I presume by"tune" you mean to dump the CPU by disconnecting the battery to force a fuel map and ignition relearn.

There are many companies that tune/reprogram the ECM/PCM to better use mods that have been made (cam,intake,porting and better exhaust etc.)....the "tune" alone will usually add a few ponies even on a bone stock LT1. Two companies that come to mind are PCMforless and Madtuner.com....there are vendors here on this forum that "tune". Some members will likely chime in with some good and/or bad experiences they have had with different tuners.

 

[surfer93]

If your only mod is RR's, I would not think you would need a tune, as your are only going to see any difference at WOT.
The 92-93 speed density computer do not handle mods very well, but this one is only at WOT.

One note, if you are going to get the ECM tuned. Then get Datamaster or some other software analyzer first, that way the tuner can better adjust the ECM, because every car has its quirks.

 

[Curious George]

I believe you will find the LT1 has self aligning rockers and the " guide" plates are only there to aid assembly at the factory.They are not hardened as regular guide plates are.

Thanks for clarifying that point. I try and make sure I post facts and not misinformation. (already too much of that on all the forums)

CG

 

[Curious George]

If your only mod is RR's, I would not think you would need a tune, as your are only going to see any difference at WOT.
The 92-93 speed density computer do not handle mods very well, but this one is only at WOT.

One note, if you are going to get the ECM tuned. Then get Datamaster or some other software analyzer first, that way the tuner can better adjust the ECM, because every car has its quirks.

In my experience, any modification you do to increase HP will benefit from a tune. Whenever you increase airflow through the motor without retuning, the computer is constantly trying to adjust for a lean condition. Newer, late model computers are much faster than mid to late 80's / early 90's computers, but the issue is really not the speed of the computer. There are certain latency issues that have to be factored in. For example, O2 sensors can only read the air/fuel mixture so fast, the computer then has to calculate the correct air/fuel mixture based on multiple sensor information. All this takes time.

If your "tune" is as close to Stoic as it can be, say in open loop, the computer has less correcting to do (in closed loop) and your vehicle will actually run better. Some guys intentionally force their cars to run "open loop", all the time, because they say it runs better.

CG

 

[surfer93]

In my experience, any modification you do to increase HP will benefit from a tune. Whenever you increase airflow through the motor without retuning, the computer is constantly trying to adjust for a lean condition. Newer, late model computers are much faster than mid to late 80's / early 90's computers, but the issue is really not the speed of the computer. There are certain latency issues that have to be factored in. For example, O2 sensors can only read the air/fuel mixture so fast, the computer then has to calculate the correct air/fuel mixture based on multiple sensor information. All this takes time.

If your "tune" is as close to Stoic as it can be, say in open loop, the computer has less correcting to do (in closed loop) and your vehicle will actually run better. Some guys intentionally force their cars to run "open loop", all the time, because they say it runs better.

CG

You are correct, if there is more air flow from idle to WOT, but there is not. The only difference will be seen at WOT and the ECM does not do any adjustments at WOT. Therefore a tune is not needed, it would be helpful no doubt, even a tune on a stock engine will help a little.

Also, you will see a 8-12hp gain, but it will only be at high RPM's, it will not be across the entire power band.

 

[JAKE]

Thanks guys. I presume by"tune" you mean to dump the CPU by disconnecting the battery to force a fuel map and ignition relearn.

No, that's not how it's done.

The programming in the car's computer needs to be changed; re-programmed to change fuel and timing maps, etc., that are programmed into the computer from the factory. Cost varies, but I paid $175

Merely disconnecting and re-connecting the battery won't get it done.

I haven't come across anyone having a piston to valve clearance problem running 1.6 RRs on a totally stock engine. In fact, I'm running 1.7s

Considering the cost and labor involeved, FULL roller rockers are the only way to go in order to get max benefit from the mod.

Most recommend changing valve springs too, but some keep their stock springs. However, that's NOT the preferred way. Most of the benefit of moving to 1.6 RRs shows up in the mid-range and up. 1.6s give around .030" more valve lift and 2-3 degree more effective camshaft duration.

One last point: Even though stock rockers are advertised at 1.5 ratio, when measured they generally check in the 1.4x ratio range.

Jake

 

[TWISTERUP]

In my experience, any modification you do to increase HP will benefit from a tune. Whenever you increase airflow through the motor without retuning, the computer is constantly trying to adjust for a lean condition. Newer, late model computers are much faster than mid to late 80's / early 90's computers, but the issue is really not the speed of the computer. There are certain latency issues that have to be factored in. For example, O2 sensors can only read the air/fuel mixture so fast, the computer then has to calculate the correct air/fuel mixture based on multiple sensor information. All this takes time.

If your "tune" is as close to Stoic as it can be, say in open loop, the computer has less correcting to do (in closed loop) and your vehicle will actually run better. Some guys intentionally force their cars to run "open loop", all the time, because they say it runs better. Quote CG
Bingo-I agrree 100%-Nail on the head--the 1.6s allow more air in from idle to WOT--i can't think of any internal engine mods that JUST affect WOT----and a WOT switch and nitrous doesn't count as a internal mod LOL

 

[JAKE]

My son's stock 1996 LT1 643 heads don't have guide plates of any type. Not even the ones so often referred to as factory installed for assembly purposes. None.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!

 

[Curious George]

My son's stock 1996 LT1 643 heads don't have guide plates of any type. Not even the ones so often referred to as factory installed for assembly purposes. None.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!

I have been thinking about this... Can anybody explain why my '92 LT1 would have "assembly guide plates", if this is indeed what they are. And if so, how long did GM use these? As mentioned by "JAKE", his '96 did not have them nor have any other LT1 motors I have seen pictures of on the Internet have them. As far as I can tell, the motor was not modified, in any way, before I bought it. Bone stock from the looks of everything I have found so far.

When I removed the OE stamped rockers they were self-aligning.

CG

 

[vetteoz]

Can anybody explain why my '92 LT1 would have "assembly guide plates", if this is indeed what they are. ....

Maybe GM found some staff that could install the rockers without them as most backyard mechanics do or the bean counters found out they could save $1.50 a engine without them
As noted ; they perform no operational part if self aligning rockers are used

 

[JAKE]

Also, when I pulled the stock 96 LT1 engine from MY 96 Vette it didn't have anything that even resembled "guide plates" either. So neither my son's 96 LT1 Vette nor my 96 LT1 Vette had them. I don't know when or why GM stopped using them though.

As far as rockers, it isn't piston to valve clearance that's the issue, it's the springs. As you probably know, going from stock rocker arms (which are supposed to be 1.5s but, when measured check in at 1.4x) to 1.6s valve lift increases on the order of .030"

May not seem like a lot, but the stock springs, which probably have many thousands of miles on them, are tired. Now, once you begin to take advantage of the additional mid-range and high RPM improvement the 1.6s provide, well, you probably can see where this is going.

Best advice is to install new springs to be able to take full advantage of the rocker arm swap. I'm also a STRONG advocate of getting away from S/A rockers and moving to non-self aligning rockers - calling for "real" guide plates and hardened pushrods. After all the posts and photos I've seen of S/A valve train failures I made that move on both of the 96s.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!

 

[JAKE]

I went back and re-read your original post, so here's some more info.

I reseached a LOT of rocker arms when I was building my 388 and when I swapped heads, cam and rockers on my son's 96. LOTS of noise complaints from guys running Pro Mags and Crane GOLDS but none of Scorpions. So Scorpions are the way I went on both engines.

Flatlander racing has them, full roller versions, for $222.00 a set which you can contrast with the $189 figure you posted. I went with Non-self-aligning, 1.7/1.7 ratio on my engine and 1.7/1.65 on my son's (packaging error I chose to live with) and I went with the 7/16" versions on both engines, requiring 7/16" studs which are a simple screw in swap. I went with 1.900" tall ARP studs to give the poly locks more thread engagement and dual springs.

When I measured, using an adjustable pushrod, his engine called for stock length pushrods, I went with TrickFlows and the rockers fit under his stock valve covers without any modification whatsoever.

However, my engine, with AFR heads and having taller valves, called for 1/4" GM licensed ProFrom valve covers to clear the poly locks. The rockers, themselves, cleared the internal webbing of the covers, but the poly locks were too tall to clear the underside of the stock 96 valve covers.

Of course, GM changed the webbing inside the valve covers over the years, so depending on which ones you have, your experience may be different.

Rockers are as quiet as stock and not a single problem with them.

Magazine dyno results generally give a power improvement of mid-teens which is concentrated in the mid/high RPM range. One swap showed more but mid-teens seems to be the norm.

I should mention, too, that one article showed a power LOSS, but when the magazine tech builder checked he found they had a geometry error that had been missed. There was no re-run after the error was corrected though. Most guys report a power increase too, though.

Bottom line, it's a WIN-WIN situation if done correctly, choosing all the recommended parts and checking the geometry.

Hope this helps.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!

 

[Brian Smith]

Thanks Jake. Very informative and complete in perspective and detail. My stock 1993 Coupe LT1 should have the same power plant as your 96 right? I will start my quest for the RRs you mentioned. I presume there is a way to determine whether these potential clearance issues could be identified before dis-assembly is started. Any measurement reference points to determine lock nut/valve cover clearance issues? Sure would like to pull the current valve covers and confirm fit before the old rockers are removed. Good to get quality feedback from another Texas boy! I'm in Flower Mound.

 

[JAKE]

Yes, our power plants are basically the same. GM did make some changes over the years; Opti, Crank Position Sensor, probably cams, PCM, etc. but nothing too dramatic.

You can go to Golen Engine's website and there's a photo there of the webbing and the areas that need to be removed for clearance. Our covers had different webbing than shown in the photo though so none of that grinding was called for with my son's.

Some guys go with narrow body rocker arms, which Scorpion sells too, but they're about $30 or so more per set. I believe Crane and CompCams use to sell narrow bodied full RRs but one member posted recently that he couldn't find them when he did a search. IIRC he was looking for 7/16" narrow body full rockers though. I suspect a call to either company or SummitRacing/Jegs could turn them up though, maybe sitting on the shelf in inventory.

Other than comparing your cover webbing with what's shown on Golen's site, I don't know of any way to get an accurate measurement without actually bolting on the rockers to see if or where you'll have interference. Would be nice if you could.

As I wrote about my engine, poly lock height was my issue, but I had to have the rockers installed order to find that. My son's stock covers dropped right in place and I didn't even have to resort to a thicker valve cover gasket for any needed clearance - they simply bolted in place.

If it's only the webbing causing the clearance issue, that's a pretty simple fix. The webbing is easy to grind away.

Let me know if I can help further.

Jake

West Point ROCKS! Nation's TOP COLLEGE per Forbes Magazine!! Graduation Day Parade 20 May 2010!!!