I have a '75 350 4spd with about 70k original miles, basically all stock. I'm not in any hurry to mess with it, but somewhere in the future I may do motor upgrades or a replacement. Right now my intention is simply to keep it running well, and rebuild/replace anything that breaks with quality components. What I'm wondering, though, how far can the OEM or equivalent parts go in terms of HP? And if upgrades are required is there a sweet spot (say 350 or 500hp) before it gets crazy expensive? For now I'm paying others to do the work.

For example, one of my mufflers fell off, so I'm about to put a 2.5" dual exhaust w/ headers in. I'm now also having a fuel issue, and I'm wondering if I end up needing a new pump should I be thinking about a performance pump. Same line of thought if I ever need rear end work.

 

Unless you have a specific future plan in mind keep things simple. Fix what needs to be fixed. By a quality replacement fuel pump because unless you go bonkers with future engine choices you won't need more than a good quality replacement pump. A very good target for a drivable car is around 300 rear wheel HP. This can be achieved relatively easy with a good cam choice and a static compression ratio of around 9.75:1. To get that, flat top pistons and 64cc chamber cylinder heads. Add that to your 2.5" exhaust system, healthy intake system, and good timing and you're in business.

 

Thank you, that is exactly the kind of answer I was looking for.

 

Here is what I did with my 75 L-48. I had a consultant at Edelbrock provide me a list of parts to rebuild my top end. The problem with the L-48 is the lack of a decent compression ratio. I'm very happy with my results and recommend that you talk with Art at Edelbrock.

 

Is the compression choice mainly an issue of whether or not you want to pay for higher octane gas, and maybe a reduced service life, or are there other considerations and expenses? Does a higher compression top end generally cost about the same in parts/labor/tuning than doing the same work at ~9.5-10.0 compression?

 

Okay I have another question...

I was reading about the differences between the '75 L-48 and L-82 and read that the L-82 had stronger (forged instead of cast) internal components, but only put out about 50hp more. If you can get 300-350 net and 9.75 CR hp out of the stock L-48 with modern heads, cam, exhaust, and timing, why did the L-82 need stronger internals? Longevity? Stronger platform for hot rodders?

 

Because cast piston technology has come a long way in the last 37 years!

 

Right, but if we're using an L-48 with stock pistons and connecting rods but using a modern top end, wouldn't the stresses be even greater than the L-82? Why would the L-82 require forged internals if we can get >300hp out of the cast stuff in the L-48 (or am I wrong about this?)

Sorry, not being productive here just trying to learn something.

 

I would drive the car extensively and come up with a list of everything I want to improve. If you mod for more HP, you may need to improve cooling, handling and stopping power. You will also have to determine whether you want to keep a stock theme or a modded theme.

Doubling the HP of a car with 37 yr old parts may cause a cascade of other issues. You will also open up Pandora's Box. Modding is addictive and unfortunately expensive, but a lot of fun.

 

Here's a few simple starters. If you get into the engine, forget the original dished pistons and the stock heads aren't even good for a boat anchor. Modern heads, cam and flat top pistons for starters and you'll have a healthy engine. Yes much better than an original L-82. No offense meant to original L-82 owners.

 

Thanks for the suggestions.

I'm going to start looking at 350hp builds and 500hps builds and save up cash. I think which way it ends up depends on what breaks next and how much cash I have saved. I remember my buddy had a C5 with ~350hp and it was plenty fast.

 

Is this going to work on any block ?
I have a 76 L48 block.
Do I need a 4 bolts for that, or good/better piston rods ? (to handle the HP)

This means removing the crankshaft, so I might as well do a complete rebuild right ?

How about hydraulic lifters, roller rockers and springs ? Does it improves power , or just reliability ?

What would be the ballpark (power and cost ? )

Thanks.

 

honesttly its just stronger for hot rodding and racing... its not really needed unless your pushing over 500hp.

Somethings to keep in mind,
You dont NEED an edelbrock package or the premium prices they go for and there are much better heads and cams for much less available. if your goal is 350-375hp at the crank and 300 at the rear wheels this can be done for under a grand with new components. just pick up some economy performance heads like these,
http://www.speedwaymotors.com/Flo-Te...lug,25118.html
and a nice matching mild cam that makes its power down in the actual range you will use it most.
My suggestions would be a comp or lunati 262/268 (https://www.lunatipower.com/Product....d=2324&gid=287) which is what I used or even the 256/262 cam. if your keeping the rest of your drivetrain stock (gearing and stall converter)
my Cast engine build consists of older dart 64cc heads that flow similar to the flo tecs above and a .37 quench along with flat tops and together with the 262/268 cam the dyno200 software estimates 406hp and 417lbs or tq with a 700cfm carb and headers

 

The cast pistons in the L-48 are limiting. They can only take about 350 HP. And are of a poor design.
The crank is cast as well and can handle about 450hp if in good shape.
The con rods are good to maybe 400 hp, maybe less, but are of poor quality by today's standards.

The heads flow poorly, with extensive work, maybe 380 to 400 hp. Stock form 350 or less.

RPMs are limited by the valve springs. Stock valve springs are weak and yours are old. 5200-5500 RPM maybe.

If you plan on 350 hp or less stock components can be used. More than that and you would be better replacing most of the stock stuff.

The chassis on the Corvette is good for maybe 500 HP without extensive and expensive modifications. This assumes good tranny, rear end, u-joints etc.

So when you build your engine keep in mind the limits of the current components and the cost of upgrading to a certain HP level that will allow a reasonable level of reliability vs cost to do so.

400 HP can be done at a reasonable cost for a 350 or 450hp if you bore and stroke to a 383.

My 400ish HP 350 cost right around $4000 with all new components except the block and oil pump. That is with me doing all the work except machine shop work that I can't do.

But this book and it will give lots of good info.

 

I've been off the forum for a year or more because I've been so busy driving my vette that I haven't wanted to mess with it! After tacking the clutch job last fall I've been driving it every nice day. I keep procrastinating on the engine because it runs reliably with a new carb, and I wanted to try the timing advance guide to see if that will keep me busy for a while. I'm right now waiting for my timing gun to arrive in the mail.

I keep getting option overload. I think my plan is still to get a brand new zz4 and be done with it. But then I think why not a 383, and then why spend nearly as much on a new warrantied engine as I paid for the car, and do I want to take it off the road long enough to do the swap, and what if I run out of time before winter and forget how to put the car back together by spring...

I'm secretly hoping it implodes to force my hand. At this point I have they money saved its just hard to trade good enough for awesome and go back to driving a station wagon for a few ...weeks? It took me a month to do my clutch change because I am learning everything as I go.

I have a machine shop nearby that seems to be run by a hot rodder but I don't have the expertise to know what to ask for and I have a hard time believing it would end up costing less than a fully assembled engine.

I have a manual ST-10. btw. Seems to be in good shape.

 

I just ordered this, thank you.

 

I should point out when I made the comments above I had assumed you would rebuild with hyper pistons and not use the stock dish cast ones. Also not all cast components are the same... scat for example rates their cast cranks for up to 600hp.. main point is you dont need forged components for a 350-400hp build.