Hi everyone. I just went to the track this weekend. I hadn't been to the track in months and just had shoulder surgery on my right arm and its a manual. Needless to say, shifting hurt like hell (so I was granny shifting) and I was hitting the revlimiter in 4th while trapping, but I did run a 12.385@113.47. 60' was a 1.826, 1/8 was a 7.995@89.79.

Here are my issues that I suspect to be the problem with my mph/launching abilities:

1.) 11.5" Slicks (hoosier QTPS) on some 8" Iroc Z rims (hey, they were free!)
2.) Stock Throttle Body
3.) Shorty headers with 2.5" y (no cats, cut-out)
4.) Knock sensor that STILL wont work (5 deg of timing pulled at every rpm) I have made many posts about this problem... I have replaced the wire, the sensor, and no matter what I do it still reads 5-7.5 deg knock.
5.) My mail-order tune was for 90 octane, and high altitude (now I am on 93 octane and low altitude).
6.) Stock transmission/DS (If I got a built auto, I probably wouldnt have the problem of hitting rev-limiter at the trap).
7.) Gears... my 12bolt has 4.10s in it, and I could switch to fix the trap issue.

I am sure there are more I am forgetting about, but those are the main things I see limiting my trap/ET. Which do you guys think would help the MOST as fixing all of them could easily be $4k. I was a broke college kid when I made this car, and I finally have a well paying job. They will probably all be fixed within the next year or so, I just want the 11's that are due for this car. It has seen too many 12s in its day. Thanks for reading/helping!

 

First, the knock sensor isn't the issue, you need to install an "LT4 Knock-Module" in the PCM to help the retard issue. And make sure the tuner factors than in during the tune.

Long-tube headers make more HP than shorties.

With your 383, you can take advantage of a 58mm T/B.

Your gears and slicks are good, but your 60fts need to be in the low 1.60s.

WD

 

You have a knock retard problem, that is limiting HP.

You picked a set of heads with limited porting (level 1), then put them on an engine larger than they were intended for. And you don't have the supporting mod's that the porter recommends with the heads, including a 52mm TB and 1-3/4" LT's. I would have spent the $$$ on the heads and the supporting mods, rather than invest big $$$ in the rotating assembly (unless you are going to a big shot of nitrous in the future).

You say with 4.10's and 27" tires you are hitting the rev limiter at 113.47 MPH in the traps. My calculator for an M6 indicates that would be about 5,800 RPM. Is your rev limiter really set that low? Why do you think an auto in 3rd (1:1) would not hit the rev limiter, while your M6 does in 4th (1:1)?

 

Thank you both very much for the quick replies. I can always count on you 2 to help . Ok, I have the LT4 knock module in the PCM, and I am having issues finding a knowledgeable dealership in this town. I know there are a lot, but every one I have called so far tells me they need my VIN to tell me what parts I need... well that is just plain stupid. For one, its a 95 block, with OBD1, and a 96 style opti... all messed up haha. I am about to call Dal in Florida to send me a LT1 Knock Module.

I would much rather fix the knock issue first. I tried tightening the motor mounts like you suggested previously injuneer, but with 1 arm I could not get them to budge at all, not even a little.

Also, I did not invest big money on the rotating assembly, it was bought used with the block for 1200$. I got a great deal, and probably need new pistons as they were all used. They checked out fine, and since it runs at least SOMEWHAT good, I am pretty sure they are still good. If anything, there may be some piston wobble, and if this is the case, a new set of pistons MIGHT fix my knock issue if it is nothing else.

The tires are 26" tires. I am not literally slapping my rev limiter, as I have not touched it once since I built the new motor. I am just scary close to it. I am shifting at 6500rpms, and passing the traps right around 6500rpms.

I do need to launch better, and I know in time I will get that down again. I am used to launching at high altitude with a lot less power (or at least it feels that way).

I agree I need more heads. I personally think new heads, headers, and TB are all needed as long as a dynotune. The cost just adds up quick haha. I would hate to invest all that money, then blow the transmission and/or driveshaft (both stock).

I do have a 125 shot kit in my garage, just know I will break some stuff with that. It almost feels like a good idea to me to put in a built auto, new heads, and driveshaft next to get it dialed in (once I fix knock issue).

What do you guys think? That is like 5k right there though... which will take me a bit to save for.

 

Just skimmed through your post and I see you want an LT1 knock module. I have my old one I can send to you for cheap if you'd like.

Are you hoping to narrow down your retard to a certain area? If you need that sensor, feel free to PM me.

 

i have 4.10s and can get just about 100 out of third so i don' t see how you are only getting 113 out of 4th.. granted i have a zf6 not a t56 but there is no difference between our 4th gears so you have something wrong. your tach might be off or something cause if you were at 6500 in 4th off the top of my head i would imagine you would be at like 125+mph.

 

OK... I plugged 26" tires into my T56 spreadsheet, and you are running 6,000 rpm at 113.5mph. My spreadsheet also confirms if you were at 6500 rpm you would be at 123.5 mph. Something doesn't add up. Is it possible your clutch is slipping badly?

As far as the knock retard, you are saying you have no code (DTC 43) and are you sure you have the OBD-I knock sensor (4.5kOhms)? I'm sure you told me the answers a while back, but my memory is not what it used to be.

 

what does the knock sensor do why do you need the lt4 whats the diffrerence in the 2 i also have a 383 stroker engine and i guess i have the same knock module does it really make a difference?

 

Sounds like we have found the issue!! I feel stupid, but I think I remember (now) that there is a difference between OBD1 and OBD2 knock module, I have the OBD2 LT4 knock module in there now, your saying there is an OBD1 lt4 knock module as well? I changed to the OBD1 conversion when I built the new motor, so that very well could be that problem!! I will cross my fingers.

I am almost positive the clutch is NOT slipping at all really. I mean it is possible, but it definitly doesnt feel like it is slipping at all. That is confusing me. Sounds like i need to figure out what is going on there. 123 mph would be a great end to 4th gear, that would mean with the nitrous I should be near rev limiter, not without.

Someone please clarify the LT4 knock modules being different ( i think I read they have different resistances long ago ). I will be calling Dal in Florida on monday if this is the issue.

Is it possible my tachometer is F'ed? I could always get a new tachometer to verify, but what little data logging I have done has not shown that the tach is off by much. Granted, I cant take it to rev-limiter with my computer in the car. Looks like I may have to though. Sounds like I need a lap-top mount in the car now.

 

Well, every parts department I ask now 1.) has no clue what a "knock module" or PMOD chip is, and 2.) says I need to look up my part by VIN.

When did this VIN crap start happening? I cant even get a generic part number any more without a vin? Well, the only person I talked to who knew what a knock module said that there is no difference between the OBD1 and OBD2 knock modules.

What is the resistance part that is talked about some places? Is that for the sensor or the module itself? I really would like to get this figured out, thanks for your help.

 

They only built the Corvette LT4 in 1996. So there is only one LT4 Knock Module. Everything I have ever seen first hand indicates there is no difference in the way it functions in an OBD-I PCM. I base that on my own experience, including watching the knock retard real-time with my ScanMaster.

However... I have seen a few people here claim that they had knock retard running the LT4 KM in the OBD-I PCM. Putting your stock LT1 knock module back in would answer that question.

The "resistor" is related to the knock sensor not the knock module. There is a difference between an OBD-I and an OBD-II knock sensors. If you try to run an OBD-I PCM with the 100kOhm OBD-II knock sensor, you have to do the internal resistor mod to make it work. If you don't you will get DTC 43 for the knock sensor fault, and the PCM will constantly pull timing, in a variable amount.

 

Ya, thanks. I cleared that up in my head after I posted. Thanks for clarifying though. It sounds like I will get that LT1 km bought tomorrow and see what happens. Worth a try at least.

So about the mph (6500 rpms in 4th at ~113.5 mph)... anyone have an explaination OTHER than a slipping clutch? I was running the slicks at 13psi, other than that there isnt really anything to tell about that. The clutch has never felt like it is slipping, but it is 6 and a half years old with over 25k miles on it. I have never even thought it was slipping though.

 

TO GO FASTER:
Fix that knock sensor, thats costing you hp and prolly really f ing your tuning because of the timing.
Next get a pcm tune thats for low alt. and 93 octane gas, more hp that your loosing thats an easy fix.
Third, get some pacesetters lt's with true duals, those shorties are killing you. Along with that stock tb. Another no no with 33 extra cubes.
Four, gears-stall-correct tire height.
Five, get some bigger heads on that thing, le1's are not for a 383. Send them back for more port work, more cc.
Well in cheapest to lots of loot heres your order of what i would do in your shoes. Just the first two should get you into the 11's. And the next two a lil deeper into them. good luck. (i going nuts on my car too, out of college with a real salary)

 

Thanks for the reply. I have been tracking down this knock problem for over a year now. No one has a damn clue what I am talking about when I bring it to any shop, as well as online most of the time. Injuneer has been trying to help me for the whole time, but like he says, he is not here so it makes it a little tougher. I have the tuning software and am very interested in buying a wideband o2 logger, but I don't want to learn to tune without a knock sensor... doesn't sound smart. Hopefully this knock issue gets fixed quickly and I will do the tune myself.

 

Ever thought about having the sensor tuned out?