F-Body Europe

Ok, so I have had my Trans Am in the shop since October working on a transplant of a 350 to replace my 305TBI engine. Bottom line-I want more Horsepower.

My mechanic searches and just cant find an LT1 or even a TPI that he is happy with while I am there. He then finds a police interceptor LT1 (different than the Fbody LT1 from what I understand) and decided to use that but make it carbed. I say ok, thats fine...figuring that when he is done it will be in the 400hp neighborhood.

Well, I called yesterday to find out that he has switched engines on me again. This would make about the sixth or seventh engine that he has tried...looks like this one would work and is working. If all goes well, my wife will have the car on Tuesday (heard this before). The guy has a good reputation, but wanted to get anyones advice or ideas.

What he says he found is a 330hp 350 from a 1971 Corvette. I did the research and that engine does exist and was the first generation designated as LT1. He put all my mods that I had on it and figures that the engine now creates probably in the 450hp range. Does this sound feasible??? In my mind I could see it, but just want some kind of reinforcement that this isnt too much to ask for!!!! Seems almost too good to be true....

Anyone have any thoughts...

Thanks,


Patrick

I would doubt 450 HP out of a old school SB. It would have to be a roller setup with alot of headwork to make those number @ the flywheel.

Do you have any idea how to convert that "old school" horsepower into the modern horsepower numbers?? I know that in the mid 70s they switched from SAE to Net HP or something, but dont know roughly how to convert it.

They are telling me that it sounds great with the cam, and yes they did do some headwork. I dont know what exactly though....since I have been out of the country havent kept up with it, trusted my wife to do that but she is not a gearhead, so kinda at a loss. I hope to call them tonight and find out more info.


Patrick

Is it a full roller engine meaning cam and lifters. what is the CR of your engine? Once you run it and get some numbers you can use the HP calculater

What do you mean by CR?? Thats a term I am either just being stupid over or just dont know....

I know that the engine actually came from a 1970 base Corvette, not the 71 LT-1 as I had originally been told on Saturday...so I have a base 300hp/380lb-ft...then my mods.

When they changed the HP ratings in the 70s how did that affect torque numbers?? or did it?? Does anyone know?? or anyone know how to convert the old hp ratings to modern ratings??

Also, does anyone out there know what a stock 700r4 can handle as far as torque/horsepower? or know where I could look??


Thanks again,


Patrick

CR = compression ratio (9,0:1 ; 10,5:1 etc ...)

The 1970 Corvette had an LT1 option comprising a 350 with high lift cam plus solid lifters producing 370 gross hp/380 lbs.ft@4000rpm but using an 11:1 CR. You'd be looking at dropping 50-60 horses to get an SAE figure.

The still optional 1971 LT1 dropped to 9:1 CR and pumped a lesser 330hp gross(275bhpSAE) and 360lbs.ft@4000 due to falling octane/lead content.

1972 was the final year for the 9:1 LT1 which produced 255bhp/280lbs.ft@4000rpm SAE

Even the big block LS5 had a weedy 270bhp SAE output in 1972 (quoted as 365 gross in 1971) coupled with 380lbs.ft torque (quoted as 465lbs.ft in 1971).

LuS1fer,

Thats some good information, however, I forgot to change my profile to reflect my newest information.....it should be changed by the time you read this.

The engine is the 1970 base engine, not the LT1 as I had surmised from an incorrectly informed mechanic.

300hp
380lb/ft

How would I correct those figures??

Not sure of the CR (Doh!!!) but will ask next time I talk to my mechanic...


Thanks again,

Patrick

I guess, more to the point, is do you take a percentage of that quoted horsepower to figure the SAE hp?? If so, then what percentage is it??

And did torque ratings drop as well?? or are they the same as they were before?? And would those drop a percentage as well??

My mechanic is swearing that the car is producing between 400-430hp, but somehow I am finding that more and more unreasonable, but I want to be optimistic given the amount of time he has had it. What would be reasonable to expect given the mods I have listed in my sig??


Thanks again everyone,


Patrick

My mechanic is swearing that the car is producing between 400-430hp, but somehow I am finding that more and more unreasonable, but I want to be optimistic given the amount of time he has had it. What would be reasonable to expect given the mods I have listed in my sig??

seems a bit steep, I could be wrong here are some key questions for a educated guess.
What is your Compression Ratio (CR)
what heads are you running valve size do you have flow #
camshaft specs Duration ,lift and lobe separation
hydrulic,solid, roller Hyd, roller Solid
is it bluprinted?
Ignition system
gear ratio has nothing to do with power but a hot cam with high gears IE 2.73 = slugish disappointing performance.

you cannot add HP numbers IE cam 35 Hapees, intake 15 hapees , headers 25 hapees this may equall 35 hapees because the cam was tested using the intake and headers also.
best way to figure HP is dyno or ET's
http://www.onlineconversion.com/horsepower.htm

Thanks again everyone,


Patrick[/quote]

Hawk,

I know you are right about how all of it fits together as far as horsepower. But the fact is that there is a lot of that information that I just dont know. Its killing me not being there to watch everything and see the transformation and hear it and test drive it and so on.

What I do know is that built the engine almost from the ground up. I also know that it has forged pistons. He has made it his pet project and apparently the guys in his shop are having a blast building it. Its a break for them from changing oil and pulling dents and those sorts of things. I pretty much gave them free license with it. But another thing I do know is that it is running a stock 700r4 and 2.73 gears. So, I know that I will be limited to what I can do until I replace those. I will need a tranny that can handle 500lb/ft eventually (better safe than sorry) and I want positraction when I replace the rear. Not sure which rear end I will want to go with though...was looking at Moser last night.

A lot of what will be left to do will have to wait til I am back in the states of course. But the engine was phase one...phase two will be the tranny/rear end, phase three will be the paint, and four will be all the fine details-console replacement, etc...


Patrick

I'm in work now so I'm having to do this from memory. The base 1970 Corvette had either an L48 or L46 producing 300 gross hp or 350 gross hp If you take around 50hp off for accessories, driveline loss, etc, you'll be in the right ball park. I don't think you can take a valid percentage as effectively it depends what accessories you're driving - pas, a/c, alternator and the efficiency of your exhaust and so on.

I'm sure the torque figures must also be affected since that can change (albeit slightly) just by adding an airbox. Adding an exhaust etc is bound to reduce the figure I would have thought and the figures quoted suggest they fall.

good luck with your build up just keep working toward your goals. 2.73's ar going to hurt your setup

OK, back home now.

Base 1970 Corvette engine was a 350 L48 - CR 10.5:1
300hp@4800/380lbs.ft@3200

Optional was the 350 L46 - 11:1 CR
350hp@5600/380lbs.ft@3600.

1971 saw the L48 suffer a plunge to an 8.5:1 CR 270hp@4800/360lb.ft@3200

1972 SAE equivalents for that L48 were 200bhp@4400 and 300lbs.ft@2800, still with 8.5:1 CR.

1973 got worse with 190bhp and 270lb.ft due mainly to regular or unleaded fuel requirements, bigger mufflers and that dreaded exhaust gas recirculation system being added.

You have a great source for information there LuS1fer!!!

Mine will be the base with the 300hp/380torque L48 as my starting point.

Talked again to my mechanic...he is having the exhaust put on there today. I know he is using forged pistons, but am unsure of the compression he is using. They are putting that info together for me and I will call them later today and find out. He will also let me know the cam at the same time.

Its using hydraulic lifters..nothing special there. Stock heads, and a GM HEI Ignition. They did a valve job on the heads though, but they were in good shape from what he just said.

I also found out that the exhaust is a custom job where he comes off the headers into a 3in pipe, then to either 2.5 or 2.75in after the cats...if I understood him. It is a Flowmaster cat-back system.

So, thats my latest info....


Patrick