Thanks, Scott. I have heard that about the Vortec heads, too. I just wanted to come in as close to that as possible so that I don't limit flow at the valves if I can help it. As billla points out, I have kinda painted myself into a corner as far as my selection of intakes.

The GMPP catalog reports that the Vortec heads will allow a cam with up to 0.475 lift. I am really banking on that being accurate although I trust billla more than a catalog. Are you recommending a cam with less than 0.450" so that I have more than 0.025" clearance or just in case the head has less valve lift than advertised?

 

It's fairly easy to do even on the car if you need to - just need a fitting to use air to hold the valves up and an on-the-car spring compressor - not a big deal.

My guideance regarding the cam is just that I think it's an odd pick for the application to some extent. I would tend towards one of the CompCams Xtreme Energy "4x4" cams around .450 lift for this application.

 

I do appreciate the guidance. In fact, I could obviously use more. I looked over the numbers after the guy at the shop told me his recommendation for the cam I though it looked pretty good. I have read a few papers on cams and I understand the philosophy and calculus behind the equations but that doesn't mean much in real world application and experience comparing different profiles.
Is the 0.008" difference that critical or is it the other specs on the cam? Again, sorry for my ignorance and thanks for your guidance!

 

I have heard folks say .480 is the limit for stock vortec heads, but I have also heard many people say that, because of production line variances, on any randomly picked stock head, you might find the limit to be anywhere from .450 to .480. I think a .450 lift cam will come as close as can be to guaranteeing that the combo will work with no problems. Also, I think there are lots of cams meant to work in the rpm range that you are shooting for that have less than .450 lift. I am now looking at cams myself, after talking with Billla, he convinced me to do the cam swap along with the head swap. If I remember right, you are doing a 383, right? Remember that the cam recommendations are usually meant for a 350 CI engine, a 383 can use juuuust a liiiitle more cam than a 350.

Billla says you can get more available valve lift from a stock vortec with a simple valvespring change, I was not aware of that. I know there is a tool to make the boss smaller, and a tool to make the valvespring pocket larger, so it seems like you have alot of options once you have chosen the vortecs. They are a great, cheap head, one of the best deals going, but once you start putting money and effort into them, they start to lose some of their luster. It's bad enough that you need a different intake manifold, and you're gonna need center bolt valve covers. It doesn't take a whole lot more money to get to the point where you could get better heads for the same price. My advice: find a cam with less than .450 valve lift that will do the job for you, and run the vortec heads bone stock. You can get a cam and lifters kit from Summit Racing for about 100 bucks, so don't let the fact that you already have a cam affect your decision. Take your big cam, and if you can't get your money back, cover it with some sort of preservative and keep it out in the garage as a conversation piece. Maybe someday you or a friend will be able to use it for something. Good luck with whatever you decide,


Scott

 

http://www.carcraft.com/techarticles...ade/index.html

Centerbolt valve covers can be found very, VERY cheap on eBay - like often for $20 or less from take-offs.

 

Thanks for the link, it's a very informative article, The OP should especially find it interesting. And I know that you can get the center bolt valve covers pretty cheap. Sometimes you can get the centerbolt valve covers for free, if you have a buddy who gets some aftermarket ones and is willing to give you his hand-me-downs. All I'm saying is, 20 bucks here, 30 bucks there, 50 bucks here, 70 bucks there........it adds up. And if you put too much money into the vortecs, you can end up at a point where you could have just bought a better head for the same money or less. I mean, take your 600 dollar vortecs, and put 300 bucks into them. For the same money, you can buy a pair of E-Street heads. The Vortecs are great heads, and they're a great deal, but I wouldn't put a whole lot of money into a pair of them. Maybe a little bit of money, but you have to look at your options and decide if it's really worth it. Boy, Billla, you were right when you said that selecting heads can be a crazy process!!! And here I am, muddying up the water for myko.

Ya know, now that I have taken a better look at his cam, it looks an awful lot like the L82 cam, maybe a little milder, not quite as much duration. Maybe it would work well with a Performer and a pair of stock vortecs? And it is only .008 of an inch, he could have a good chance of getting away with it without having to mod the vortecs. It's easy to say "I'd go for it!" when it's someone else who has to deal with the consequences of it not working, but.........I would definitely think about it.

Oh, man, there I go again, muddying up the water! Ya know what, just ignore me, listen to Billla, he's forgotten more about building engines than I'll ever know. He will steer you through the troubled waters, I'll try to just stay out of it. Good luck with whatever you decide to do, Myko!!


Scott

 

I think we both agree that billla knows a frightening amount about everything Corvette but I also appreciate your input. In this case muddy water is actually helping me see more clearly. I know that this is a fairly big cam for my purposes but I am hoping that it isn't overboard and provides the power I want, the idle I would like, and the vacuum I need.

I am looking into what it will take to machine the boss myself. I like the idea of the conical springs but a set would run my total up to the price of the modified heads. I know where this is going... I am soon going to wish I would have just listened to billla and gotten the 8060A kit; but then I wouldn't have gotten all this education!

 

After looking into the 1980 spec manual more closely I found that the stock AT has a 3.55:1 rear diff and the MT has the 3.07:1. AFAIK I have a stock rear diff and the HydraMatic with gear ratios as listed above. The TMH350c has the lockup converter and can be identified by the wire attached in front of the shifter linkage.

Are there any changes, tweaks, upgrades, or overhauls for the tranny or converter while I have the engine out? I likely won't do much more than a low level transmission servicing (flush, seals, etc.) if it is felt to be necessary. Again, I ask mostly for knowledge so feel free to suggest anything. I also like to hear the "...if you want a cheap way to increase torque" or "... you are going to need a _____ if you want to run 10s" theories that you guys know about and I come here to learn about!

 

A detailed comparison of the Vortecs and the E-Streets is worth looking at. We've covered some of this via PM, but I thought I'd post here as well.

To begin, as I've said a number of times here and elsewhere "upgraded" Vortecs don't make a lot of sense to me as there's little flow gain between around .450 and .500...so unless someone has to do an upgrade due to their cam choice it's not smart money. Just pick a cam with around .450 lift and be done - ideally a near-roller profile to make good use of that mid-range flow.

Comparing the flow data, we see that the Vortecs outflow on the intake side through .400 lift...which is why they're such great street heads. They also do this with a slightly smaller runner size, which means better intake velocity. On the other hand, the E-Streets have a better intake/exhaust ratio, a somewhat better chamber and they're aluminum...all good. The price differential is about $300 or so...which is about a wash if you have an existing performance manifold. I like the E-Streets a bunch for a mild street build.

Head selection isn't a black art, but it starts with selecting the flow required to make the required power, then seeking the smallest runner consistent with that flow...and then apply budget to get the best chamber and I/E ratio you can get. Still leaves a number of choices (chamber size, etc.) but it narrows the field a bunch.

 

You should be able to determine the gear ratio by looking at the stamping on the bottom of the diff housing.

You could invest in a torque converter, but it's not really required at this build level. It does make a difference - you just have to decide if you have the budget I think someone noted here or on another thread that the "little things" add up pretty darn quick if you're not watching every penny.

I always say the most expensive phrase in any mechanical endeavor is "While we're in there..."

 

Heck no, Scott - dive in All good perspective!

 

 

I am pretty sure that there was only one differential gear available for the 1980 model year, 3.07. And I want to say that the th-350C transmission was only installed in cars destined to be sold in California, so if you really do have a th-350C, check to see if you have a california car, because they all came with 305 engines. (The only year a Corvette was ever available with a 305) I only say this because if you are planning to turn your existing motor into a 383, it won't work if it's a 305, as the 305 has a much smaller bore than the 350. It would work out to be a 334, I think. Heh, heh, is the water muddy enough yet?


Scott


Scott

 

I can't find the link to the .pdf file of the actual spec sheet but this link has two rear axle ratios listed, too.
http://auto.howstuffworks.com/1980-corvette1.htm

I do have a 350 in the car now. The short block that I took to the builder was also a 350 so I'm sure I am okay in that department.

As for the TH350c, my interpritation is that it was a modification that occurred midway through the production year. It wouldn't make sense that they would put a torque converter on the 305 but not a 350.
It also makes sense as my VIN is very late in the series. But if I am wrong about the TH350c being on the 350 with AT let me know b/c that would be the first indication that I may have a CA car!

 

Oh, man!!! Howstuffworks? I have never seen a howstuff works page that didn't either have glaring errors or just gross oversimplification, or both. here is a link to a great site where you can find a factory booklet that has so many different specs, it's ridiculous. I'm serious, stuff like the crankshaft revs per mile, how many feet the piston travels in a mile, stuff that I can't figure out why in the world anyone would care about, but is still kinda cool to look at. Enjoy.

http://www.gmheritagecenter.com/gm-h...tion-kits.html


Scott

 

OK, I've calmed down a little from the whole howstuffworks thing, and just want to say that if you are sure you are dealing with 350 engines, that's good to hear. If you see that pigtail for the electrical connection on the transmission, it's got a lockup converter, allright. I have had my '80 'vette for about 3 1/2 years now, and I have yet to find anything that will definitively tell me the real deal on the th-350c transmissions, all I really know for sure is that my car doesn't have one, kinda wish it did.
It's a funny thing about the '80 california 'vettes. Chevy only made somewhere around 1500 or so 'vettes with the 305 engines, because they were the biggest engine that they could get to pass emissions for california that year, so they are kind of rare, but you never, ever, ever, hear someone bragging about their "rare 305 'vette", in fact, they are actually not considered a very desirable car.


Scott

 

Yeah, I knew I was taking a risk citing that site. I had looked at the exact specifications document as you linked a while ago but again, couldn't find it recently. I have it downloaded now and will study it closer. I was definitely wrong. Only 3.07 for the 1890.

I have heard and read that the TH350 is a very strong tranny and that the 350c is an improvement on it. And I haven't heard anything good about a CA vette, either. Maybe there are a bunch of them still sitting in garages with numbers matching because they aren't any fun to drive?

Mike

 

As far as I know the the C on the end of th-350C just means it has a lock-up converter. You can put a pretty good amount of power thru a th-350 without breaking it, but they aren't indestructable.


Scott

 

I have stock vortecs on my motor with the L82 cam with the performer eps intake 750 edelbrck carb. motor is a 350 bored .60 over with 9 to1 pistons with stock rockers with a 4 speed with 3.36 gears. it ran 13.16 in the quarter with a 1.96 60 foot at 105 mph with a better take off it will be in the 12s easily. I love my vortec heads they are completely stock out of the box.

 

A 13 second flat, over a hundred in the quarter, sub-2-second 60 foot time car ain't nuthin' to sneeze at, brother! Sounds like a pretty mild combo, too, I think the OP could duplicate it pretty easily.


Scott