1970 LS-7 engine

[Justin S.]

Re: 1970 LS-7 engine

Patrick,
Was it the seemingly small (to me) differences between the aborted Corvette LS-7 and Chevelle LS6 the reason it wouldn't pass emissions testing?
I have a hard time understanding that if it was the case

[Patrick B.]

Re: 1970 LS-7 engine

Patrick,
Was it the seemingly small (to me) differences between the aborted Corvette LS-7 and Chevelle LS6 the reason it wouldn't pass emissions testing?
I have a hard time understanding that if it was the case

We may never know. The Corvette staff certainly thought it would eventually be offered in the 70 model year. It was not cancelled until June. Maybe they just ran out of time, and there were not going to be enough potential sales to be worthwhile by June.

[Justin S.]

Re: 1970 LS-7 engine

I ask because I read in Corvette Magazine that GM tried to reintroduce the big block in the C4 but it couldn't pass emissions.
I just don't know how they could get them to pass emissions in trucks and not in Corvettes.

[Tom P.]

Re: 1970 LS-7 engine

ANYTHING I build at my house will pass in my garage!!!!!!!!!!!!!!
As I mentioned, if I had the financial ability, I would build an all alum 496----------------preferably with a GM block and heads.

[Patrick H.]

Re: 1970 LS-7 engine

I ask because I read in Corvette Magazine that GM tried to reintroduce the big block in the C4 but it couldn't pass emissions.
I just don't know how they could get them to pass emissions in trucks and not in Corvettes.

They have different standards between cars and light trucks. That's how they were able to keep them in trucks.

[Duke W.]

Re: 1970 LS-7 engine

Ditto what Patrick said... medium duty truck engine emissions were looser than passenger cars, but I think the real reason was CAFE - corporate average fuel economy for passenger cars.

Remember the last big block was 1974, long before the C4 design process really even started. I can't say for sure, but I expect that the C4 design never anticipated installation of the big block.

Duk

[Joe L.]

Re: 1970 LS-7 engine

Ditto what Patrick said... medium duty truck engine emissions were looser than passenger cars, but I think the real reason was CAFE - corporate average fuel economy for passenger cars.

Remember the last big block was 1974, long before the C4 design process really even started. I can't say for sure, but I expect that the C4 design never anticipated installation of the big block.

Duk

Duke------


I don't think there was ever any real plan to install big blocks in a C4 Corvette. The tech center did build a big block powered C4 ("the big doggie") but I think it was more of an exercise than it was part of any real project with the intended goal of building PRODUCTION big block powered C4's.

[Duke W.]

Re: 1970 LS-7 engine

Yeah, and I think they also built a turbocharged V-6 and stuffed a Falconer small block architecture V-12 in one.

I don't think the big block was ever seriously considered for the C4 due to a combination of fuel economy and emissions, but they did assist Callaway with his turbo engine, probably because they knew there would not be enough volume to go through the process to make it a production line option.

Back when I was a Pontiac production engineer in '68 I made it a point to walk through the engineering garage every day when I had a chance. There were a couple of guys working on a Firebird for a couple of weeks. They pulled the engine and the next thing I knew they were installing a REAL L-88 crate engine. Then a set of Firestone indy racing tires on American Torq-Thrust wheels.

I finally asked them what they were up to and their reply was they were going to use the car for Trans-Am suspension development. Yeah, right! You need a L-88 and racing tires to develop a production car suspension package. A couple of weeks after they got it running I saw them on Woodward Avenue on a Saturday night.

Then there was the time that I was wandering around the dyno cells and spotted a V-8 with a set of prototype tunnel port heads. The inlet manifold was off so I could see the pushrod tubes through the inlet ports. I asked the guys about the round tubes mentioning that they had a drag coefficient of about 0.5 and a teardrop section would be less than half that, so much less restrictive. They gave me a look that said: Yeah, kid... if we want your opinion, we'll ask.

Anyway, those were the days, but that was about the end of the "toy era". After that is was all about meeting emissions and FMVSS, and the Pontiac tunnel port heads never made it to production.

Duke