anyone tell me the pipe sizes on a 91 305 stocktpi,need to change cat,not sure what size y-pipe and intermediate pipes came on car stock, not sure of inlet or outlet pipe dimensions,also what should i buy for a replacement cat?how much money?

 

A '91 305 TPI has a horrible little 2 1/4" cat.

If you are going to replace it, I'd try to spend the least amount possible. If you do not need a direct fit, look for a Magnaflow/Carsound unit like a 94015. It should be in the $60 range.

If you need a direct-fit, look for a Maremont 28925 that runs a little over $100.

Edit: I just looked at the information under your username. Are you sure that you do not have dual cats? I thought most of the '91-'92 T-5 305 TPI cars with 3.42 gears also received the G92 package.

 

only 350 cars recieved 2 cats

 

Not true. 305 TPI dual cat was an option. That's one of the differences between the 205 HP and 230 HP versions (G92/N10).

 

how do i tell if its a direct fit or not?bare with me this being my first camaro,its a learning experience for me this is all new to me,but yes i have a single cat on a 91z28vert,305 lb9 tpi,iam guessing if its factory original its probably direct fit yes?what is the difference between the two direct verses not direct?

 

Direct-fit means that it bolts in just like stock, i.e. same dimensions and fitment.

The opposite would be a universal fit. The pipe inlet/outlets have the same diameter and flanges, but the length of the converter may not be not the same as stock.

The 94015 I listed has a 16" overall length. The stocker is closer to 21" long.

I should probably also include the Catco 4115, Dynomax 15735, and an unknown brand 50110 as replacements too.

 

ok, good now i know for sure

 

so your saying you pickup 25 horsepower with the dual cats?

 

No, about 10. The cam was worth the other 15.

 

i got it

 

No disrespect five7, but I thought the general consensus and overall proof was that all SD ('90-'92) LB9's and L98's received the same camshaft, GM #10111773. The same part number is used for both the LB9 and L98 in the Parts and Illustration Manual.

I thought the 10088155 peanut cam went by the wayside after 1989.

The terrible LG4/LO3-style exhaust placed on the SD 305 TPI's really did choke them down by 25hp.

I finally found one of the threads that I remember covering the subject, Peanut cam theory disproved!!! Everyone check this out!.

 

jade grey your the man

 

Sorry im quite sure the cam is different, as I do own one of the handful of 92 G92 spec 5 speed cars. I've had a 305 tbi longblock in it, and a non G92 tpi 305 longblock, soon enough i'll be ordering the GM correct cam for the G92 pkg and we'll see if there are any actual differences during the install.

And yes 90-92 G92 305 cars got dual cats, the 145 speedometer, the oil cooler, and 3.42 posi disc axle.

 

And for the record cuda's car didnt come factory with the 3.42's. If he's really got em they were installed later, and it came with a single cat.

 

Z28R_icer, I would be interested in finding your results when you compare the non-G92 SD 305 cam to the one you'll be ordering.

When I remove my 305 in favor of a larger motor, I will have the stock cam in my car spec'd. Hell, next time I have my valve covers off maybe I'll borrow a dial indicator and see what lift I have.

My pasted link in the my post above does not work. I doubled-up the http. Here's the correct link, Peanut cam theory disproved!!! Everyone check this out!. From the thread I linked, moderators like Kevin91Z, Ed Maher, and iroc22 seem to favor the position that the camshafts were the same.

And yes, I had figured since cuda69 had a single-cat T5 305TPI that the 3.42 gears were not original. His first post sent question marks up in my head that's why I edited my question immediately. I'm just trying to help the guy find a replacement cat.

 

you say 3.42s but the first owner told me i had a 3.43 gear,whats the difference who is right?which i know was installed later not factory,i dont have my option sticker somebody bought a knew console cover and must have thrown out the original sheet,which sucks,but i have been able to gain a little info with the vin#can you tell much or do you need to look at rearend? <vin#1g1fp33fxml134616>,you guys can fight it out,peace

 

i ment to ask you,which cat would be the least restrictive,and get me the best flow,for, i dont know, lets say 75.00 dollars or so,need to dump this factory unit soon

 

There were no "3.43" gear ratios made for the 10 bolt nor the 9 bolt which were the thirdgen axles, if its a 10 bolt and truely does have a 3.4x ratio its a 3.42, if someones swapped a whole 9 bolt under there and its a 3.4x ratio then its a 3.45.

 

i got it

 

Your RPO codes are probably in the locking storage compartment in the trunk, not on the console lid. The RPO code corresponding to your original rear gear ratio starts with a "G". If you had (have) a 3.08 then the code is GU4. If you had (have) a 3.42, then the code is GU6.

I'm still not sure from your statements whether you know if the gears were changed by the original owner or not. Do you know what rpms you are at when in top gear at 65mph?

How are you ascertaining that your factory cat is bad and needs to be replaced?

If you are staying with a 2.25" cat I would not sweat the performance aspect much. I would just get a replacement.

A direct-fit would be easiest because the outlet flange is the same as stock, but the cost is going to be near $100. The Magnaflow/Carsound direct fit part # is 93456. BTW, the stock outlet diameter is 2.5" to match the size of the intermediate pipe.

 

He couldnt have got 3.42's from the factory, that would require the car to be a G92 pkg, and for that to happen it would require being a hardtop and not a convertible.

 

I'm sorry. You are right. You had already established that fact in this thread. I keep forgetting that 3.42's in a V8 car only went with the G92 package 305 in 1991. So his RPO tag if intact should list a GU4.

 

[QUOTE]Originally posted by Jade Grey
Your RPO codes are probably in the locking storage compartment in the trunk, not on the console lid. The RPO code corresponding to your original rear gear ratio starts with a "G". If you had (have) a 3.08 then the code is GU4. If you had (have) a 3.42, then the code is GU6.

I'm still not sure from your statements whether you know if the gears were changed by the original owner or not. Do you know what rpms you are at when in top gear at 65mph?

How are you ascertaining that your factory cat is bad and needs to be replaced?

If you are staying with a 2.25" cat I would not sweat the performance aspect much. I would just get a replacement.

A direct-fit would be easiest because the outlet flange is the same as stock, but the cost is going to be near $100. The Magnaflow/Carsound direct fit part # is 93456. BTW, the stock outlet diameter is 2.5" to match the size of the intermediate pipe. [/QUOTEiam going about 2600rpm in 65mph,maybe a little more,this car was sold as having stock posi and 3.43 gearing,as for the rpo theres nothing in the trunk drivers side lock box looked several times i clean the car on the reg.the cat has been 4x4ing not buy my choice either,it has two deep dents in the cover,i know its been smashed in,also my y-pipe looks original its very burnt

 

i went back and looked at the flyer from when i bought car off craigslis ,and the owner did say it was 3.43s posi that was stock,not 3.42s so,i clear that up ,sorry,

 

Right, but there were no gears ever even produced for a thirdgen that were 3.43 ratio, the only 3.4x ratios were 3.42 and 3.45, neither of which did your car roll off the production line with.

 

3.43 is simply a typo in his sales flyer, most likely.

In what gear? If you are in fourth (1:1) gear at about 2600 rpm at 65 mph with 26" tall tires, then you have a 3.08 rear.

 

sorry i would be in 5th going about2700,maybe more, i need to check for sure,i let you know next time i go out

 

[QUOTE]Originally posted by cuda69

Quote:

Originally posted by Jade Grey
Your RPO codes are probably in the locking storage compartment in the trunk, not on the console lid. The RPO code corresponding to your original rear gear ratio starts with a "G". If you had (have) a 3.08 then the code is GU4. If you had (have) a 3.42, then the code is GU6.

I'm still not sure from your statements whether you know if the gears were changed by the original owner or not. Do you know what rpms you are at when in top gear at 65mph?

How are you ascertaining that your factory cat is bad and needs to be replaced?

If you are staying with a 2.25" cat I would not sweat the performance aspect much. I would just get a replacement.

A direct-fit would be easiest because the outlet flange is the same as stock, but the cost is going to be near $100. The Magnaflow/Carsound direct fit part # is 93456. BTW, the stock outlet diameter is 2.5" to match the size of the intermediate pipe. [/QUOTEiam going about 2600rpm in 65mph,maybe a little more,this car was sold as having stock posi and 3.43 gearing,as for the rpo theres nothing in the trunk drivers side lock box looked several times i clean the car on the reg.the cat has been 4x4ing not buy my choice either,it has two deep dents in the cover,i know its been smashed in,also my y-pipe looks original its very burnt

i just got back from a ride and in 5th gear i was running between 1900 and 2000 rpms,going 65mph,not the 2600 i guessed earlier,

 

Your overdrive should be .75, so that's sound like you have 3.08 gears since 2600(rpm's in 4th) X .75 = 1950.

 

that would be in fifth gear,not fourth,or does it need tobe read in fourth gear?

 

iam going 65mph in 5gear,and doing about 2000rpms,not four gear

 

Let me say it this was way.

4th gear, 65mph, 2600rpm, 26" tires = 3.08 gears
5th gear, 65mph, 1950rpm, 26" tires = 3.08 gears

The only reason that I mentioned 2600 rpm was that I was referencing my figure in my earlier post.