Hi !

I wonder if somebody can help me with this. You´ve probably answered this question before!

What is the difference between these two engines:

a/90 IROC Formula Trans Am M5,A4 LB9 V8 9.3:1 5.0 (305) 210@4400 285@3200 TPI 3.08 ---- 2.73

b/90 IROC Formula Trans Am M5 LB9 V8 9.3:1 5.0 (305) 230@4400 300@3200 TPI ---- 3.42 ---- ----

It seems to be the same engine, why is it 20 hp more in one of them?

With regards Birgitta, Sweden

www.freewebs.com/renovering/ (in swedish only, sorry)

 

I believe they put a different cam in the manuals. That gives you the extra power.

Lou

 

Possibly G92 RPO option.

 

dual cats

 

What 91305z said...... dual cats

 

Ok, another stupid question. Which one have dual cats?

 

The one with the higher horesepower number. The RPO code for dual cats was N10 if I remember correctly.

 

Ok! Thanks everybody!

 

Yes, N10 dual cats and the Cam was different, starting in 1990 there was a choice of cams on M5 LB9's... the dual cats would not substantiate a whole 20 HP on its own. I believe the hotter cam may have been a part of the G92 option...

From 1987 - 1989 it was more straight forward, LB9-A4 peanut cam, LB9-M5 better cam. But from 1990-1992 the M5 came with the peanut cam or the L98 cam.

hope that helps...

John

 

Good info, John, thanks.
Any idea where I could get a good M5 cam for my LB9? I just dropped a T-5 into my car.

Lou

 

I would get an SLP cam, they are probably cheeper. And you can get them a little hotter..

the GM part number for the L98/ M5 LB9 cam for 1990 - 1992 is 10111773


SLP cams
51002 Pretty much the same as the cam above, a little more lift tho , I have this cam.
51006 This is a good streetable cam, It will give you a little lope at low idle ( I wish I would have gotten this one or the next one),
51010 I believe this is the cam used in the Firehawk... 'nuf said.


John

 

My '85 Z28 LB9 had what I've heard refered to as a "pre-peanut cam". Was this the same cam available for the later manual equiped cars?

 

20 hp usually means the dual cat option

 

(Bangs head on desk)

Put Dual cats on any car and you will not notice a 10% increase in power... It is the CAM. You will notice it there A LOT more.

John

 

No, The 1985 Cam used solid lifters, where starting in 1987 all V8's came with roller lifters.

HOWEVER, the specs are similar.

John

 

Hmmm, thats interesting because I have a 1990 LB9 A4 and the part # for my camshaft is also 10111773, I just got off the phone with my local GM dealer and they confirmed that the part # for both the automatic and the 5 speeds are the same(at least for 1990 cars).Could the combination of the dual cats and the 5 speed prom account for the difference since the camshafts are identicle?

 

Unfortunately those cams aren't on SLP's site, so they may no longer be available. Sometime soon I'll call them and verify as I plan to do a swap in the spring.

 

I think you mean flat tappets, they were hydrolic too.

 

Ok, Flat Tappet, Your right, they were still Hydrolic lifters... My Bad...

John

 

WOW, I actually got that information from THIS site... You are correct tho, I looked in the Parts & Illustration catalog.

Still I contend there had to be more than just Dual Cats to make 20 extra HP... The G92 rear axel and a different chip could make that kind of difference... But in actuality a different rear axel may be faster, but the HP does not change, its kind of like playing with the numbers...

I drove a 1991 or 1992 T/A 5.0 A4 Convertable, What a DOG!!! I could not believe how slow that car was,

And obviously a Cam could compensate for that kind of added power.

 

My theory is that the extra ponies are in the prom and the combination of the less restrictive exhaust and the manual gearbox allowed GM to program the chip with perhaps a more agressive fuel curve, or longer injector pulse thus delivering a little more fuel. Remember back in the eighties the auto manufactureers had to adhere to C.A.F.E. ratings (corporate average fuel economy). I believe the average of all cars manufactured by a certain company had to total no less than 25mpg. So if the Lb9 with the slushbox could only manage 24mpg, but the 5 spd could get 29mpg with the same peramaters in the prom why not bring down the average fuel economy a little and up the performance to pretty close to the 5.7. Thus you give those who want the 5 speed what they want because they knew they couldn't warranty the 5sp behind the 5.7.So maybe the 5sp prom added 10 more flywheel hp and when coupled with the less restrictive exhaust another 10 hp could be attained.

 

Yeah, I should have known that.