Sergio305

Hey Guys,

I need some advice on the best way to go about upgrading the powerplant in my '68 Vette. It has a stock 327 engine (RPO L75) with the TH Automatic Transmission. I wanted to improve the acceleration as well as overall horsepower however I do not know just how big I can go when it comes to upgrading the Camshaft and Cylinder Heads in particular. The car is for street use but I would really like to get that low to mid-range zip some of the higher torque engines have.

I was considering one of the Edelbrock Top-End Kits (#2022) but the reviews of the camshaft (#2102) in that application are mixed at best. Any ideas on a high-performance camshaft that would work well with the cylinder heads and intake manifold (Performer EPS) included in this kit??

*To complement the new heads/cam/intake manifold, I am leaning towards the Edelbrock Thunder Series AVS Carb (650 CFM) to replace my stock quadrajet, and Hooker Super Competition headers as a replacement for the old stock exhaust manifold.

Any input/experience is appreciated, I've only had my new ride for about a year and I'd like to try and do this the right way. Thanks fellas!

-Sergio

SuperBuickGuy

are you going to change the converter?
what are the rear gears?
a/c or no?
any substantial lightening?
what are your plans for the car? DD? Cruiser? autocross? track days?

edelbrock is a good system, but it's low hanging fruit - there's a lot better available, but it requires research

that said, answer the above and I'm sure lots will chime in with options.

Sergio305

SuperBuickGuy,

As of now, I have no plans to change the torque converter; stall speed on the (automatic) turbo hydra-matic transmission is listed at 2100 rpm. No air conditioning, no substantial lightening. The car is my weekend cruiser, no track days, just fun on the street.

First gear ratio is 2.48:1
Curb weight is approx. 3270 lbs.
The axle ratio is 3.08:1

Lobe Lift on the stock cam is .2600 inlet; .2733 exhaust
Engine Compression Ratio is 10.0:1


Thanks again for the help...

63mako

Change your rear gear ratio to a 3.55. 300 hp will fell like 350 HP with that change. Next step performance recurve on the distributor then headers. All these will then compliment any engine changes you would like to make and would need to be done first no matter what.

Matt Gruber

"low to mid-range zip"
this sounds like it needs a swap to a 383. Like a GM brand new engine. The lowest price GM HT383 will do the trick w/headers +curve.
3.08 will work great with all that torque. You will be happy for sure. And it works with your Qjet.

SuperBuickGuy

I agree with the replace the motor with a 383 - your problem is that no matter what you put on the top of the motor, it's still not going to perform as well as a crate 383 - and it's all about the same number of dollars spent.
- your stall, I presume aftermarket? GM stock converters stall at ~1600
- your rear gear, with the short stroke of the 327 makes it tough to get out of the hole, add to that your stall of 2100 and your motor doesn't have a chance to get into the RPM range were it'd make power
- 10.0 - has the motor been worked on? if so, I presume flat top pistons with 74 cc or 78 cc heads .... going to an edelbrock head, 68cc would make your car difficult to fuel since your compression ratio (guesstimate) would be 11.5:1 after the swap. You can make it run on that compression, but with those gears, that stall, and an automatic transmission you're just asking to have predetonation problems
- even if you go with the edelbrock kit - I'd run away from their cam, they do a great job of developing torque.... you need something that bleeds off compression (thumpr is a good example of one that would do that).

so I agree, albeit more wordily than Matt, that a 383 would give you what you're seeking.

I did make a presumption - any idea what heads are on the car now?

63mako

I like the 327. Had a built 302 and it was a rocket ship. It needs to be built right Will run higher rpm cruise. RPM is small displacements friend as is a higher powerband. Needs gears first. Lower gear rear or different trans. A 383 will give you more bottom end torque but so will lower gears. A 3.08 gear with stock convertor (stock TH400 convertor in a vette is 2000 stall) and a stock auto will not feel fast no matter what unless you go big block. By the time you get enough torque to feel fast you will run out of power at way to low of rpm. It is a vette not a big rig.

Sergio305

SuperBuickGuy: Ideally I'd like to stay with the 327 motor but simply maximize the output. For instance in comparing the base engine I have (RPO L75) with the L79 I see that the only differences are the high-performance camshaft and Holley carburetor found on the L79. According to the manufacturer's specs this gives the L79 a +50hp more.
The compression ratio I quoted earlier (10.0:1) is what GM lists for that stock engine, which I believe has a 64cc chamber volume. I'm not sure if the stall converter is aftermarket (all I know is that I have a TH350 tran.); that 2,100 stall speed figure I obtained was from the '68 Corvette Specs manual (http://corvettec3.ca/c3specs/1968.pdf). [Pg. 49]



63Mako: Ok, I'm trying to map this project out. Are you suggesting that I begin by changing the ring & pinion set before making any upgrades to the intake or exhaust system? If so, what is the lowest gear I can go with for performance without creating too much engine heat? Is the stall speed the same for a TH350 as it is for the TH400?
At the end of the day, I'd like to upgrade to: aluminum heads, better camshaft, new carb, new intake manifold, and install headers; I appreciate your tips on the suggested order of those mods, or things to consider as I go along.

Thanks guys!

63mako

3.55 is a good compromise between performance and crusing RPM. 3.73 is better performance but buzzes pretty good cruising down the highway. Or you can go with a richmond 5 speed with a 1-1 fifth gear and low 1st and keep your 3.08. This is the best single upgrade you can do to any C3.
All corvette 1968 - 1975 have a TH400 trans if it is a factory automatic and will have a 2000 RPM stall convertor.
Order of engine upgrades.
1. Performace distributor recurve, make sure it is functioning properly.
2. headers, low restriction exhaust
3. If your going in do heads, cam, intake at once. Your quadrajet is fine if it is original. Have Lars rebuild it.

Little Mouse

sergio305
The L79 327 chevy 65 to 68 had higher compression pistons 11.0 rated. A much higher duration cam with more valve lift, bigger valves in the heads with the same 64cc size chambers, high rise intake and holley carb to get to its 350hp rating at 5600 rpm. Your cam mostly because of its duration allows your engine to fall on its face at more like 4500 rpm. So theres a little more to the L/79 then just a cam and carb.

The first mistake your making is getting rid of the small front primaries of the Q-jet carb especially with a small engine. The whole reason chevy came out with the Q-jet and its small front primaries was so it could work on anything from small engines to large engines and heavy cars from impallas to lighter corvettes, two speed powerglides to three speed autos with gearing of only 3.08.

Assuming your shortblock is in real good shape so its even worth spending money on rather then building a stroker. I would do a modern cam with duration in between the 300hp and 350 hp chevy rated engines with considerable more lift. Then a modern head with no bigger then 180 runner or even smaller like 170 runner vortec. You said you want low to mid range, this also means you want small primary headers for a 327 kept at lower rpms. I would do no bigger then 1 5/8 primary.

One of the better ways to die could be on top of a hooker but the headers IMO have always been way overated. Come to think of it lars was recently sent two hookers that were supposed to lie down the side of his C2 that did there job screwed him up but somehow with his skills he turned them back to repenting of there sins. Regardless of brand use a small primary.

As mako said gearing is your friend with small engines you will have to make up your mind how much freeway work the car will see. If its almost always an in town car throw some gearing in the back end. I'm not an auto person but a well made well matched converter could be a real help.

gcusmano74

Speed costs money. How fast do you want to go?

1) Decide on a budget for your upgrades.

2) What kind of car do you want? How will you use it? Street, race, daily driver, occasional parade, whatever? Do you care about fuel consumption?

It's easy to spend a bunch of money on a car, and make it different. Not always so easy to make it better.

CaseyJones

I'll have to agree with what is being offered to you. I strongly suggest changing the rear gear ratio to a 3.55, put a performance curve in the distributor, add a set of small diameter long tube headers, leave the QuadraJet, add a performance air cleaner, and then drive the wheels off it until you can afford or choose to switch out the 327 for something bigger. I built a 355 with a good modrange cam, big valve heads and 10.5 to 1 compression that feels really good running around town and cruising without a big gas mileage penalty. You have a lot of options so plan carefully or you'll build a car you don't want to or can't afford to drive as much as you would like.

Matt Gruber

How many cars do u have? Easy to build a fun weekend toy. As long as there is another car for long trips/work/etc.

Rally68

I have the same setup as the OP with a fairly tired original/stock 327 & Q-jet. I swapped my 3.08s for 3.73s and recurved my distributor, and the car is a blast to drive now. It will be a beast when I have the $$ to do carb/heads/cam

63mako

There you go.

Sergio305

LittleMouse: Thanks for your suggestions. Question: Doesn't the small front primaries on the Q-Jet inhibit the acceleration? Are you suggesting to tune it to a bigger size once the other modifications are made?

Mako63: Thanks again; I need some help in understanding how much putting a performance curve in the distributor will help me. How difficult is this/cost? Just want to gain some reference before I bring it up with my mechanic who does good work (he owns a '65 himself) and charges very reasonable rates.

gcusmano74

The small primaries on a Quadrajet improve the throttle response and fuel consumption. The secondaries only start to work at near WOT/high RPM. On a street car, 95-98% of the time you run on the primaries alone. A Qjet is rated at 750 CFM when the secondaries are wide open. Send yours to Lars for a rebuild, if you like.
While testing the primary jetting on my ('74 smallblock) Qjet with the secondaries locked out, I was able to easily bring the car up to an indicated 100 MPH on the speedo (on an empty stretch of interstate highway).
Check the advance curve of your distributor. It is absolutely worth the trouble.

Little Mouse

Sergio305
The small front primaries are a plus for you with the 327 regardless of trans even more with the auto. Lars could give you good advice on a tunning setup for your 327 or you could simply send it to him. Someone side stepping a clutch at well past 4000 or a very high stall, primary not important but your not going to do that. Begining to see why the small primary can help you. If you don't want the Q-jet holley makes two 650 spreadbores.

Of course with small engines if you want best power your forced into both gearing and high rpms. But i read what you said you still want a good cruiser not some wild eyed hot rod.

I hope that people don't think i do hookers from my previous post. Someone told me once lying on hookers is a good way to die. It just struck my funny bone i remembered it lol. It fit well with telling you hooker headers are no worse but really no better then anyone else's. Anyway with low to mid range as your goal along with auto trans and some form of resonable street gearing pick one of the 1 5/8 headers. If my memory is holding without looking it up hookers super comps use 1 3/4 primaries.

Regardless of what you do even with slightly less compression then the L/79 with both modern heads and cam your going to be well past any power the original L/79 ever really made.

But if you really want to completely help yourself and you have other cars to drive you need as a minimum 3.55 or more in the back end. I personally would do 3.73 then later plan on an overdrive trans. Like i said if everything you do is intown as much gearing as your willing to do is your friend assuming your keeping the 327 or even with bigger engines. Building or buying a 383 can get pricey because at that point you begin to want all the good parts, machining costs. L/79s as an examlpe used forged parts your 327 is using cast parts crank, pistons. For what your wanting rpm wise if everything is in good shape cast crank and pistons will work fine.

63mako

The original distributor curve is horrible. It is set up to be safe, bring power in slow and be emmisions compliant but leaves a lot of power, throttle response and fuel mileage on the table. Your mechanic will likely set the initial timing at the recommended in the book and walk away unless he is "old school" and understands the drawbacks of the factory timing curve. A performance distributor curve will have more initial. have a total of about 36 degrees all in @ 2500 - 3000 RPM instead of the 4500 - 5000 factory setup and total with vacuum will be around 50-54 @ 3000 RPM steady no load cruise. It will also not ping. This is a fine line and will vary with each engine. Best bet is doing it yourself after doing enough study to understand what you are doing and shooting for. Here is some info.
http://forums.corvetteforum.com/c3-tech-performance-3/
E mail Lars for his latest distributor recurve papers weather you do it yourself or have your mechanic do it. Parts are about $10 and it will take 1/2 hr to an hr to dial it in. Here is Lars E-mail address.
v8fastcars@msn.com

Sergio305

Little Mouse: If I were to go with the Hooker Super Comps (1 3/4 primary), would that make peak power arrive at a much later RPM?

Based on the suggestions of many (including some of the guys on this post) I will likely bring it into the shop sometime next month for:

1) The distributor recurve
2) Lower gear ratio of 3.55 or 3.73 (I am still undecided...not quite sure by how much the 3.73 will increase the RPMs at idle and whether I'd be stressing the engine too much if I were to take it on the freeway).
3) & 4) Edelbrock Performer EPS Intake Manifold + Headers (long tube or shortys?)

I'd like to do the intake manifold and headers now and then wait to do the cylinders heads and camshaft...what do you think?
Lastly, how would my 3 speed automatic react to a change to something like a 3.73 gear ratio?


Thanks All!