Made a boo boo and let the muffler shop delete my cat converters Questions

[stinkydogfilms]

After having the 89 HO motor put into the 91 GM this past October, I decided to go with dual exhaust. The muffler guy said eliminate the cats. Which we did. I now have to go thru emissions and no one wants to touch the car without any converters.

1. Do I put need to put cats on both sides?
2. Which cats should I buy so I do not lose the performance I have?
3. Do I need an oxygen sensor on each side?
4. The old Lopo 302 only had 1 oxygen sensor. How do I hook up the wiring for adding a second oxygen sensor for the HO?
5. Never got around to swapping in a new computer? Will I need to change to an HO computer to read the emissions correctly?
6. Where do I get a computer compatible with the 89 HO in a 91 GM?

Car still runs great like a bat out of hell and does not miss.
The gas mileage does suck.
With the LOPO I used to get around 16-17 city freeway driving. I think I am around 10-11 now 8 months after the motor swap.

I have been away from the GM forum for a while. I bought a 1986 Subaru Brat that I have been spending time on.
I do thank you all.
Mike

[packman]

There is a HO Conversion thread stickied at the top of this forum for any questions that you have regarding your HO swap. I haven't done this swap yet, but I think the popular computer to use with this swap is the Lincoln MKVII computer. I would imagine with the dual exhaust you would have to run two O2 sensors. At least mine had two; but that was a dual exhaust on a LOPO. I have about the same gas mileage as I had before the upgrade..........when we're not getting on it to hear the sbf sing.



Packman

[tjc78]

With the LOPO I used to get around 16-17 city freeway driving. I think I am around 10-11 now 8 months after the motor swap

I don't understand how this car even runs on a LOPO computer. The HO has a different firing order, etc. Your poor gas mileage is the key something isn't right here. I would venture to bet that even after adding the cats back in your car is going to fail emissions. There are members here with HO conversions/ Explorer motors getting double your stated highway FE.

[mercurygm88]

When did they go to a single 02 on a 5.0? I know the cfi cars only have 1 but every sefi car I've ever seen including mine has 2, one in each manifold. Is this something they changed when they went to mass air in 89? Between running an HO on a lopo computer, and the missing 02 sensor that may be the key to your gas mileage issues. The only conclusion I can come to as to how your running an HO motor on a lopo computer is

A. Its not really a HO, its just an HO upper intake on a lopo.

B. Its an HO thats had the cam changed to a lopo cam.

Other than that it doesn't seem that theres any possible way you could run a HO with a lopo computer, due to the different firing order.

[sly]

you need to put cats on before the crossover of the H/X pipe. You will need to put one per side. I would suggest a universal cat that matches your pipe size (single in, single out) and most all brands will have plenty of flow for your application.

welded in would be best, but the band type clamps work as well.

here's a good selection from summit racing:
http://www.summitracing.com/search/P.../?Ns=Price|Asc

[gadget73]

the original engine had 2 sensors, or at least it had 2 when it left the factory. What someone may have done to it after that point is anyone's guess but there are two connectors and it wants 2 sensors to run right.

Use the Mark VII computer and 19# injectors. Should just plug in and run correctly. Make sure someone hasn't dicked with the injector wiring though. You can run an HO with a lopo ECM but it runs lean and has a high risk of destroying the engine from it. At low speeds if you drive like Grandma it may not be too obvious but if you wind it up at all, its going to do bad things. That loud rattle can sound that its making is your engine self-destructing. If its not rattle-canning then probably someone left the 19# injectors in, and its running rich as hell. This is reasonably safe but its hugely inefficient. way too much fuel will wash off the oil from the cylinder walls and cause excessive wear though, so thats not much good either. At least the pistons wont melt from this tho.

and yes you likely need 2 converters, one per side. In the future, don't listen to the exhaust shop idiots. Its actually extremely illegal for them to even do that, so I'm surprised you found one with idiots running it that even suggested removing the converters.

[stinkydogfilms]

The muffler guy is an old Asian man. Mr. Than "you not gonna have any cats okay"
I asked what about the inspection? He replied (pointing at the inspection shop 50 feet away from his shop) "Don't worry he will take care of you, tell him I sent you". 8 months later it isn't going to happen.
As far as I can tell it is an HO long block with the lopo intake turned around and lopo fuel rail and lopo injectors.
What is the casting number for the HO block? Is it near the starter?

[86VickyLX]

The muffler guy is an old Asian man. Mr. Than "you not gonna have any cats okay"
I asked what about the inspection? He replied (pointing at the inspection shop 50 feet away from his shop) "Don't worry he will take care of you, tell him I sent you". 8 months later it isn't going to happen.
As far as I can tell it is an HO long block with the lopo intake turned around and lopo fuel rail and lopo injectors.
What is the casting number for the HO block? Is it near the starter?

The casting is the same. It's the cams and heads that are different. Look for E7 stamped in the head... If not, then you were lied to..

[gadget73]

the block numbers are probably the same since it ought to be the same engine block. The only real difference is the cam, heads and pistons, and you can't tell any of that unless you take it apart. The HO motor does have a different ignition firing order though, so check that. If its the stock 1-5-4-2-6-3-7-8 and its not obviously running on 6 cylinders with random backfires and shit, then whatever motor you have, its not an HO. Possible its a truck motor though, some of those have the same firing order. An HO engine is 1-3-7-2-6-5-4-8.

John, do the E7 heads actually have that visible anywhere short of removing the lower intake and using a mirror? Thats the only place I know for sure they have a casting number but to be honest with you I haven't really looked for the numbers either. You can kinda tell by the plug holes, but its not completely obvious. The stock lopo head has the threads recessed in the head a bit, where the HO one does not. Thing is though, the E7 head was used on both HO engines and truck engines, so just that alone doesn't tell you a ton.

[jaywish]

Aren't the valve covers different? Maybe that is not definitive? I did not think you could have an ho with lopo covers but I do not know if you can have a lopo with ho covers. I am not 100% sure as it has been a long time since the ho went in.

[1990LTD]

see which injector type is peeking out from under the plenum.

[sly]

check the firing order. if it's 1-5-4-2-3-7-8 (note the 7-8... that's the quick check) It's lopo.
1-3-7-2-6-5-4-8 is HO

[88Vic]

I have one of these on my truck, it flows and sounds like it's not there: http://performance-curve.com/thunderbolt-spincat.aspx

Also they come in the style that looks stock.

[gadget73]

Aren't the valve covers different? Maybe that is not definitive?

well, yes and no. The valve covers will interchange no problem. Mark VII and Mustang motors did have different valve covers, but theres no reason you can't fit lopo covers on one. Hell, Ford put the same valve covers that are on the Vics on the 91-93 Tbird/Couger 5.0 HO and on the 93 Cobra engine. The aluminum ones look cooler, but they actually have less internal clearance than the boring steel lopo covers do inside and they are physically bigger outside.

[jaywish]

Thanks for the info on the covers. Hopefully we learn a bit more about everything every day.