Longtubes hitting floor.. knock???
 

Ok I've tried to adjust the y pipe and such every which way and no matter what.. sometimes when I get on it they will vibrate against the floor... My question is... will this cause my knock module to sense knock and pull timing ?? I've heard of it happening but I want to know if it is a regular occurance. thanks in advance

I have heard of cases where the banging, being loud enough, can be picked up as "false knock" resulting in pulled timing. How many miles are on your car? It may be time for some new motor mounts.

The body has 128xxx.. motor 47xxx... I'm supposed to get my car dyno'd thur morning and I'm a little worried it might act funny on the dyno if it picks that up as knock.

best thing u can do right now is change ur motor mounts to poly ones if u havent.

the motor is torqueing and banging teh y-pipe on the xbrace or floor

if u cant do that and u dont want it to mess with ur dyno results try getting somthing between the banging areas to damnpen the sound......im not sure what i can use tho

i had longtubes and duals+xpipe and dumps before axle and it would hit the floor in several spots causing it to vibrate like crazy above 2000 rpms.
You might laugh, but i put the car on a lift and did a few chinups on my exhaust and it pulled it down enough where it quit vibrating:D Mine wasnt banging like yours was when the motor would torque over, though i had poly motor mounts...

LT4KM usually solves the false knock problem....worked for me as well as helped in a few other areas..

Thanks guys... anybody know where to get an lt4 module...

First, you need to tell us the year of your car..... why not add a "signature", with basic info like year, model, tranny and any major mods. 93's for example, don't have a knock module.

Easiest way to check whether anything is causing knock retard is to put a scanner on it and check the knock retard. If you aren't getting any, you don't have a problem.

Whoa, whoa, whoa. The LT4 KM is only more forgiving for the sound wavelength of roller rockers. Thinking the LT4KM will solve false knock issues with y-pipes banging and rattling underneath the car is naive. Also, what 'few other areas' did the LT4KM help with?

Put a poly motor mount in the driver side at least. My collectors are less than 1/2" from the floor and never hit and the motor doesn't even shake with a single poly mount in. I had poly on both sides, but that made the inside of the car shake at idle....changed the pass side out for an OEM one and all is fine and no motor shake now.

How hard is it to put the poly mounts in.?

Not that hard at all. Make sure you have a coule of socket extensions and a socket universal joint.
Make sure the car is securely raised for you to get under it.
Remove the motor mount bolts the hold the upper and lower part of the mount together on both sides..I beleive its a 18mm nut and a 15mm bolt head.
Place a jack and a piece of wood under the crank shaft pulley and jack the motor up about 2 inches...remove the existing upper and lower mounts...there's 3 bolts in each part (upper and lower)
Drill the rivets out of the stock mount couplers.....put the poly mount in and bolt the couplers back together with bolts supplied with the poly mounts or use your own from a hardware store...bolts go where the rivets were drilled out...
Then reinstall the mounts..6 bolts...lower the motor back down and reinstall the 18/15mm bolt/nuts on each mount...done.

I thought if you had lt's the headers had to come off first.... That is whats holding me up ..I don't want to have to take those off again ..

you do not need to remove the headers to do motor mounts, however motor mounts suck as much as doing headers... but they are well worth it... I had the same banging problems and poly mounts fixed the issue

doing motor mounts with longtube headers harder then doing them with the stock manifolds??