I was planning on removing the non-original 350 and tranny from my daughters 74 convertible this weekend in preparation for starting it's conversion to an LS3 ... until I discovered that ...

Surprise! The L82 block and M21 tranny are original. Now I'm torn.

I'm not shooting for any NCRS Flight awards but it's still meaningful to say that the car has the original L82 and tranny so I figured I'd do my due diligence and see if it can still meet my needs or at least have someone tell me I'm stupid for considering it.

My requirements are:
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I want 350+ RWHP with mufflers, sidepipes and no cats
I don't want to deal with zinc additives (no flat tappets? dunno)
A certain amount of lope is desirable but it needs to idle well and have good street manners.
The heads need to be compatible with one of the main street EFI units
It needs to have enough vacuum to handle the accessories



Suggestions?









1974 Chevrolet 350 L82

Existing problems:
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260 RWHP
Leaks oil from rear seal, valve covers, oil pan and oil pressure sender
Leaking EFI intake manifold
Tranny side plate is missing a screw and leaking oil
Bell housing is broken
Speedo cable doesn't attach to the tranny speedo gear
Motor mounts are shot
1st gen EFI doesn't self learn and I don't have the skill to adjust it

What's in it:
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Already bored .040 over, 357 CI

Edelbrock Intake - EFI Pro Flo Multiport (1st gen) #3500

Edelbrock Cam Kit #7102
Operating Range 1500-6500 RPM
Duration Advertised 308° Intake/318° Exhaust
Duration @ .050" 234° Intake/244° Exhaust
Lift @ Valve .488" Intake/.510" Exhaust
Lift @ Cam .325" Intake/.340" Exhaust
Lobe Separation Angle 112°
Intake Centerline 107°
Intake Timing @ .050"
Open 10° BTDC
Close 44° ABDC
Exhaust Timing @ .050"
Open 59° BBDC
Close 5° ATDC
Vacuum @ 1000RPM Idle 11"

Edelbrock Performer RPM Heads #6073
Combustion chamber volume: 65cc / 70cc
Intake runner volume: 185cc & 195cc
Exhaust runner volume: 65cc
Intake valve diameter: 2.02"
Exhaust valve diameter: 1.60"
Valve stem diameter: 11/32"
Valve guides: Maganese Bronze
Deck thickness: 9/16"
Valve spring diameter: 1.46"
Valve spring maximum lift: .575"
Rocker stud: 3/8"
Guideplate: Hardened steel
Pushrod diameter: 5/16"
Valve angle: 23°
Exhaust port location: Stock
Spark plug fitment: 14mm x .750 reach, gasket seat

Manley Ultra Lite Pistons #49533
Manley Sportmaster Rods #14103

 

From what you listed I would say that is just too much cam for that engine. It probably suffers from a poor acceleration off the bottom until at least 3500 RPM.
I know nothing about the EFI you have, or any for that matter.

If it's only getting 260 at the wheels with a manual trans then that's maybe 350 gross HP at the crank.

You can get a gen 1 to produce more power, but you need the right heads, intake, fuel delivery, exhaust and cam to do it.

That engine may be capable of more HP at 6500 RPM but it may be limited by the EFI or the intake or exhaust.

I have a 350 original bore with AFR 180's, ported performer 2101, modified Q-jet carb and roller cam with 270/270 219@.050 duration cam on a 108 LSA making 14" of vacuum at 800 RPM. Power is in excess of 400 HP, probably around 430-440 HP. Idles well and pulls like no tomorrow at WOT. As a bonus it gets 18 MPG on the highway and 16 MPG in mixed driving with a 3.55 rear diff and a TH350 with 3000 stall converter. I also run hooker side pipes. So what you want can be done.

430 with a manual trans assuming a 20% loss from crank to wheels would put you at 344 at the wheels. This is assuming a M21 can take that kind of power. That I don't know.

 

IMO C3s lose a lot from Engine dyno to wheels. I copied a pretty standard build that was expected to be 475 flywheel. It made 327 RWHP. I felt pretty bad till one of the magazines had both figures. A 383 making 425 on an engine dyno put 285 to the wheels of a '72 (through a Munice IIRC)

 

You're right they do lose a lot. I think a couple of guys here have shown engine vs chassis on a manual to be in the 20 to 24% loss IIRC. On an automatic more in the 30% range.
425 to 285 would be a 33% loss. If the loss is that big on a manual trans I would go looking for problems with the installation that are causing some losses. Things like exhaust and intake installation issues.

 

Bear with me, I'm a novice at cam and head profiles. What makes that an aggressive cam? I thought LSA of 112 with 234/244 was considered a mild cam? Or are you saying it's too much cam for the heads?

The EFI does come with it's own manifold so there is no telling how well it flows cause it's an old design. Exhaust shouldn't be an issue, I'm running with hooker headers into 3 inch unbaffled side pipes. The restriction should be non-existent however the scavenging is probably non-existent as well.

What is the lift on your cam?

 

One variable is the different types of dynos that are used. Dynojet vs. Mustang Dyno for example. The same car will get two completely different RWHP ratings based on which dyno is used. The same may be true with engine or lab dynos?

Other factors include what accessories are on the car. All cars will have an alternator & water pump, but once you factor in different variables like A/C, PS, Fan Clutch, Electric Fans, Headers (size), Side pipes, Mufflers, Manual or Auto, etc., the same 425hp (gross) engine will have different RWHP based on the combinations above.

The percentage % of loss will be different too based on engine performance as well. A plain jane 300hp engine may be a perfect fit for factory exhaust manifolds (100% efficiency), but a 500hp engine may lose 30% using those same factory exhaust manifolds.

In short, looking at various dyno numbers on the internet and then trying to compare them with yours or against each other isn't very scientific, there's too many unknown variables.

With my car, trying to be as scientific as possible, I had my engine run on a lab dyno before and after rebuild, and I also run the car on the same dynojet before and after rebuild. That way I was comparing apples to apples.

 

I'm not going to say understanding cams is easy, it is and it isn't. To get it just right is not easy. To get close is achievable for a guy who studies and accurately chooses a cam for the intended purpose. And then there are the large cam company recommendations.

The latter I found to vary greatly and generally be inaccurate.

The cam specs are going to vary with several other variables. Which heads and how much they flow is one important variable. The Intake exhaust ratio is often used to determine if a split on the cam is required and how big that split is. If the IE ratio is 75% or better generally speaking then a minimal spit or no split is used.
Heads that have better flow capabilities without enlarging the intake tract volume can utilize a lower duration cam due to the efficiency of the head. The opposite is also true. Poor flow=more duration to crutch the head.
Long duration is also used to achieve higher RPM goals. This is at the cost of low RPM performance for a given displacement.

For a street driven car a 308/318 with a 234/244 @.050 duration is fairly large, might be ok for a 383 but large for a 350 unless high RPM use is the goal vs low to mid RPM street use.
Also notice the difference between advertised and duration @ .050. If you subtract the two on the intake you get 74. This is known as the cam intensity. 74 is low intensity and will result in the valve being open during the overlap period for a long time resulting in low vacuum, and poor low RPM performance with it's late closing during the compression stroke.
An intensity in the 60 to 50 range would be more desirable, and on a roller cam.
I got recommendations for cam reading if you want.


I would agree, low restriction with minimal scavenging, at least at low RPM. Some scavenging may be taking place higher up in the RPM's. That said over scavenging is just as bad. Scavenging becomes less important with a good flowing exhaust port on the heads.

.549

Can't say enough about a roller cam. It's really the only decent option with the quality of flat tappet cams these days.

 

leave it alone if it runs smooth and uses little oil. Sell it and buy one of the zillions of cars out there already converted to LS engines .

 

I guess I've gotten tired of trying to address some internet "facts". I agree with you that there is too much variations in dynos and engine configurations to attempt to have a narrow range of conversion percentages. Load vs. acceleration chassis dynos can have very different results as well as correction/standardization factors. When I dynoed my '69 the operator saw my disappointment and asked if I wanted to do a run with bigger number.

I believe the biggest reason for typical 30% reductions from engine dynos to chassis is the configurations of engines on dynos. I've never seen an aftermarket engine build attempt to replicate in-car conditions. Most reported engine builds are looking for "Hero" numbers. It's pretty common to see no accessories (electric water pumps) and definitely feeding room temperature air (not 180 F as most older cars will actually ingest). Timing and A/F are often set for a big top end pull but not really safe for in car/on road conditions.

There is not of reliable info published on engines with both measurements but 30% or more seems common from what I've found. I don't have the engine numbers but for the two cars I've built engines for and chassis dynoed the spread looks large. I followed a published build for a 505 HP stroked SBC. In a '67 Camaro (TKO600) it made 348RWHP on a Dynojet. It made one strip pass with a trap speed around 111 but it was coasting for the last 300 feet or so (the owner said he had to back off for some reason).

I think newer cars add to the confusion. When advertised numbers represent "installed" configurations the rear wheel numbers are much closer. My Viper is rated at 450 but it is not a surprise to see a stock GEN II report 425RWHP. What's typical for a 650HP Z06, 550-575RWHP? I think this percentage is sometime applied inappropriately to projects.

 

Just do the LS3 conversion; sell the L82 and use it to help fund the LS3 incidentals.


The L82 has already been bored and 40 over at that. You'll have to deal with the rear main seal leak and although you can get some great heads and a roller cam all the incidental costs to converting one of these things to a roller cam add up faster than you think. -Then you'd have to deal with paying someone by the hour to tune the Gen1 Edelbrock EFI. (The roller cam with good heads can get you your low end torque back, hit your HP goals, and get rid of the zinc requirement, but the LS3 heads will still get you more airflow, probably more low end torque, and definitely hit your HP goals and save you 100lbs of weight plus you'll end up with a modern and well known fuel injection setup.)

Someone will be happy with that L82- it's already at many people's target perf level and it's got an EFI system that currently works with it.


Pull the engine+trans and while it's out and easy to work on replace all the seals so there's no oil leaks and just sell the sucker and don't look back. (This is coming from someone who is keeping his L82, has already bought the roller cam and lifters, and new heads, and is putting a new EFI system on it.) -If I didn't have a single family, numbers matching car with only 14.9k miles; it would all get pulled and LS swapped and the LS swap would probably be cheaper in the long run.


Adam