6T5RUSH

Hi Folks,

This may be a little long so bear with me but I'm firm believer in having as much information out there to get good advice/experience from you folks.

Obviously, I spend most of my time over on the C2 section but I thought I'd post up what my neighbor has in front of him to you folks here who have more insight on this particular drivetrain.

Some facts:

'80 'Hello Yellow", L48, 4 speed with factory air. Car now has over 100K miles on her.

We're not shy about wrenching and since his purchase of this Vette (his first) over 3 years ago, we have pulled the complete rear suspension out and rebuilt it to factory (new control arms, strut rod bushings, brakes as well as a complete rebuild of the factory (weak link) 3.08 posi. While-I'm-At-Its took over and he also replaced the radiator, condenser and completely rebuilt/replaced the air conditioning on her, along with all new vacuum lines.

New repaint last year...same color "Hello Yellow".

More recently he had the stock heads just rebuilt to factory ('bout a year ago).

The only other change made was converting to a true 2 1/2" dual exhaust system with Dynomax mufflers (Corvette Central). Again, he's running the factory 2" manifolds and stock snorkel and Quadrajet. Visually stock with exception of L82 valve covers.

Complete interior replacement (Corvette America).

Tranny and clutch are original.

Dilemna(sp?/opportunity:

He has first dibs on a set of Dart Iron Eagle, 180 runner heads with Crane Gold Roller Rockers (1.6). The price is right...FREE. They were originally on my 327 then moved over to my son's 327 '68 Camaro. Son is going the LS1 route. Also, he may be able to purchase the Edelbrock Intake, Edelbrock Carb (may be better to use the factory Quadrajet instead...your advice is welcome here) AND there may be a chance to bolt on a set of ceramic coated headers...again THAT would be a big maybe and I recognize it would be a departure from the "stock" appearance. Just thinking the headers with his true dual exhausts would take advantage of these Dart heads WITH the proper bump stick.

He plans on pulling the motor and trans and go through the tranny (syncros at a minimum) then maybe do a stock rebuild of the lower end. Keeping in mind he's not tracking the car and is looking for streetability, nice manners and driveability with factory air. Kinda' looking for the "best of both worlds"...a little more lively without sacrificing A-B type driving.

I and he realizes to get a more lively jump around town with the right combo, he should lose the numerically low rear end. But that is a killer as the money was spent and she's tight and right.

Since he wants to have a more spirited driving experience and doesn't plan on 6,000 rpm shifts AND possibly keeping his 3.08 posi in place (remember it was professionally rebuilt just 2 years ago), what particular bump stick would work well with these Dart heads. Understand, money is an object so short of a complete transplant to a 400 small block motor necessitating a numerically higher and stronger rear end, what would make sense...a good marriage with his combo?

Again, factory 4 speed, keeping the 3.08 posi, Dart Heads and the right bump stick to keep the driving experience lively up to say 5,500 r's.

You know, as I'm writing all this, maybe he should just mothball the stock block and get a generic 350 with a better bottom end (read that stronger, with flat top pistons)...this is me just thinking out loud.

Here's a flow sheet on these Dart Heads that Jeff Kobylski, Modern Cylinder Head, RIP Jeff, did for me a few years ago.

Appreciate any and all insights on this. We know once the motor is out he'll probably rebuild it and put her back in (would be the cheapest way to go given his desired way to use the car).

Your thoughts? Again I do appreciate your insight and experience on this particular drivetrain.

Thanks in advance!

Post away!!

Jim
In God We Trust!

6T5RUSH

Should have mentioned I did do a search for L48 Upgrades and there is a lot of topics on this but didn't see anyone posting where they kept the 3.07/.08 (not sure) posi to do this.

Jim
In God We Trust!

63mako

What chamber size? 64cc, 72cc. Header size? 1 5/8, long tube?

garygnu

consider the comp cam ex268h cam.a good mild street cam with good torque .get some long slot rockers .

iokepakai

Ok ,been down this road with my 76 L48 3.08 rear gear.Did the top end upgrade,first with a flat tappet cam(big mistake to try and save $$).Performance was better but still lacked that quick take off.This was due to the sorry gearing of the TH350 auto trans and 3.08 rear gear.Not wanting to change rear gears and longing for a manual trans with OD.I swapped in a Richmond 6spd trans.The gearing on the 7021626AA trans compliments the 3.08 rear gears.Great take offs and OD too! Have since pulled the flat tappet cam and went with a hyd roller,awsum bottom end torque...Like a new motor,and MPG's increased also.You can do all kinds of motor mods to that L48 but you'll need to improve the gearing to get the benefits.Now if you build a bigger motor that's another story.I felt it was more cost effective to change trans,& keep the gears and motor..I'm very happy with this combo and plan on running it till the ol L48 gives up.Compression is still good and no oil consumption..The way she's running now and with the OD I expect her to last another decade..
Difference between roller and flat tappet cam lobes.
[IMG][/IMG]
TH350 old -ROD 6spd.same length no mod to driveshaft needed except TH400 yoke.
[IMG][/IMG]
Looks factory:
[IMG][/IMG]

6T5RUSH

63mako, the heads are 64cc. The headers are 1 5/8 but not certain if they are long tube headers. They are currently on my son's '68 Camaro so fit may be an issue (interference with frame or steering box etc... Think they are Doug Thorley Headers.

Here's a pic of those heads after Jeff did his magic on 'em:

qwank

if the headers are for a Camaro they will not fit the Corvette

6T5RUSH

garygnu,

I've seen that cam, the X268, recommended in other build threads here. He's looking to get more oomph in the 1,500 to 5,500 curve. Thanks Gary!

iokepakai,

Nice! I am with you on the overdrive conversion as I swapped out my wide ratio Muncie (2.56:1 1st gear) for a Keisler SS700 wide ratio (2.66:1 1st gear with a .68 overdrive). I'm running a 327, solid lifter, flat tappet cam that loves it upstairs (6,500 shifts no problem). the sweet part is even though I've got a 3.73:1 posi, at 70 mph she's loafing at 2,200 r's. But I digress here as you and I can spend other people's money big time.

My neighbor's situation is he wants to keep his 3.07/.08 rear gears AND his 4 speed. As it is she really has good cruise/trip manners. He's just looking for more snap without snapping stuff (LOL!). Your idea of a hydraulic roller has merit but I think there's some up front costs going that way. Just not sure what that is.

Jim
In God We Trust!

6T5RUSH

Thanks gwank! Is it interference with steering box/frame etc...?

6T5RUSH

iokepakai,

Forgot to ask. What specific flat tappet camshaft did you have that you were disappointed in? Was it a factory grind? I'm using the factory LT1 from 70-72 and their intake.

63mako

http://www.summitracing.com/parts/hr...make/chevrolet
Will work with the 4 speed, dart heads. 1.6 rockers, Felpro 1094 gasket. If it was an auto you would need a smaller cam. Great flow on those 180 heads! This cam will make full use of them and meet your operating range wanted. 1500-5600 RPM. Will need springs, pushrods, cam button. A few hundred extra spent here now is the cheapest horsepower you will ever buy.

Jebbysan

The heads are great....looks like he CNC'd the chambers.....you should get a nice bump in compression with these.....

I had no idea Jeff had passed on...I knew him. I lived in New Baltimore and worked at Lukovich Racing engines.....RIP.

The mainfold and carb setup is great...I would lean toward a XE274...the 268 is good...but I like the 274's idle better and it compromises very little as far as Torque on the bottom....it also is a .490 lift cam...which works well with those flow numbers...help take advantage of the increasing flow.....

The kicker is that all of this is nothing without a good set of long tubes to round it off......

Comp makes an investment cast roller rocker that is ver reasonable...I recommend these....I have used three sets and they are good pieces.

I also recommend a Hex-a-just Cloyes setup...and degree the cam in at 106 intake centerline.... This is not completely necessary...but helps the mid-range....

The Q-Jet works VERY well on a Performer....no problems there.
Try to find a L-82 Air cleaner.....

Nice package.....

Stay warm my Michigan brothers.....

Jebby

6T5RUSH

63mako,

Thanks! Jeff really new his stuff. Performed his magic on many heads from all over this country. Truly a gifted, talented guy. I'm sure he's up in that sky somewhere racing today.

Do appreciate your package approach to this L48 upgrade. Don't have any personal experience with hydraulic rollers. So this kit plus springs, pushrods, cam button and gasket set will put him in a driveable, good street manners motor.

Just spoke with the owner and he's now saying he wants to look at a used 350 short block, using that as his mule to "play".

I know I started this thread with the idea of rebuilding his existing 350 but this might take a new direction.

His stock L48 motor has about 8.5:1 compression, if that. He is able to burn 89 octane.

At what point in this build would the crossover compression be where he would have to switch to 93 octane?

Thanks for the input on this. Keep 'em coming!

Jim
In God We Trust!

6T5RUSH

Hi Jebby,

See you've made the move to a warmer? state. Good for you. Yeh, I was surprised as you on Jeff's passing. He really knew his stuff when it came to headwork.

So are you saying the Edelbrock intake and Edelbrock carb or better to use his existing factory intake and Quadrajet. Whoops, you said use the Edelbrock intake and the QJet right?

Is the XE274 also a hydraulic roller cam?

So long tube headers are a must to complete this package.

Thanks Jebby!

6T5RUSH

Anyone care to comment on the point where you need to run 93 octane.

"At what point in this build would the crossover compression be where he would have to switch to 93 octane?"

Thanks again on all this input. Much appreciated!

Regards,

Jim
In God We Trust!

63mako

You can run 11 to 1 on 89 octane with a big enough cam. Dynamic Compression Ratio is a major factor that determines what octane is required. The key is matching the cam, compression, intended use, other engine specs, weight and gearing to all work effectively in the correct DCR range for your combination and needs. It is not the total picture but a big part of it. Too little DCR reduces cylinder pressure to the point you lose power but it will run on very low octane. To much DCR could push octane requirements to 91, 93 or up to race fuel depending on 2 factors, Static compression and intake valve closing point also factoring into it but to a lesser degree is gearing, quench, operating temperature, timing curve and A/F ratio. The cam I recommended should run on 89 fine with proper tune. The gasket is part of the package to optimize quench. The combination will be a very good match in all catagories. Decent intake and headers are a basic requirement of any performance build. The quadrajet properly setup is all you will ever need.

Jebbysan

Yes....the Q-Jet-if in good shape-is a great choice....
The XE274 is available in a Hydraulic Roller....and is a great cam in a roller....I have this in my 85' 383 El Camino and it pulls like a freight train.....
But......HR stuff is pricey....retro fit lifters are $400....plus the necessary pushrods (Trend/Diamond on 14 mile ) and required valve springs are a consideration as well as someone setting up the thrust for the cam because it requires a roller button.

You should first have a spring checked for tension...that would be make or break for me....it will help you decide which way to go.

Not so much warm here now....33 degrees outside....

Born in Pontiac....raised in Clarkston....
I put the packages at Lukovich together....from 350's to 632 Big Chiefs.....designed cam profiles and induction packages as well.
Jeff did a lot of Big Chief Pro Stock style stuff for us.....quiet guy but extremely methodical.

Is that your 65'?
Just traded my 66' for a 69' 427 with Trips

Best,
Jebby

6T5RUSH

63mako,

Your insight and comments are much appreciated. Thank you again for your recommended package.

Thanks again to all of you for your input here.

Time to get with the owner and see how he wants to get where he wants to go.

I'll be checking this topic from time to time and will certainly post up his decision/approach.



Regards,

6T5RUSH

Jebby,

I DID read of your trading up to that big block. Good for you. There's nothing like cubic inches is what they say!

Ain't it nice to have Trend local here in SE Michigan. Just walk in, give 'em your measurements and walk out with the exact type push rod you need for your build. Kinda' wish I had LICS or WILCOX close by too...spoiled huh?

Jeff got my stock 461 heads to flow almost as well as these Darts. He knew FLOW!! The shocker was Jeff was only 40 years old...damn cancer!!

Stay warm Jebby and keep that blowing snow and ice going east and not north!!

Regards,

Jim
In God We Trust!

Jebbysan

Those 461's will never flow what my 462's did....ask the guy in Chicago.....he got a good car!
I had 230 on the intake......no disrespect......the Serdi 5 angle was the key

Peace!
Jebby