Hey all, I got approval from the boss to get a performance top end kit for the 75 (L48 350). I am looking at the Edelbrock 2099. Since this comes with a new intake manifold, I plan on replacing my stock Q-jet with Edelbrock 1406 and a new air cleaner assembly. Is there anything else I should take into account?

I have the stock mechanical fuel pump so I'm not overly worried about it.
I have to take measurements with the stock hood to try and see what clearance I have. I would rather not have to replace the hood, but anything for squeezing more horses out of the L48.

 

I have a similar car 1975 4-spd L48 stock. Previous owner gave with purchase an edelbrock 1406
carb and weiand aluminum dual plane intake as he was acquiring items to install before sale. I have been hesitant to do the switch as the car runs real nice, but I would like more zip from the 350 as well. Interested to see how yours works out.

 

I would get the Edelbrock AVS2 650 (model 1906) over the 1406. It also looks like the 1406 is out of stock.

As for hood clearance you should be good if you get a drop air cleaner.

 

Is your 75 stick or auto? I'd want to know the powerband of that cam so its not over your TC stall RPM.
Another thing to keep in mind, this 435hp kit will find any weak links in the rest of your drivetrain so make sure it is in good condition.

FAST

 

Jim,
A lot of Edelbrock parts are out of stock right now, but that gives me time to save and plan.
With a 650 CFM carb, I imagine it'll put more stress on the fuel system. Going with a 650 CFM would be great for track days, but I think it would make fun drives harder since it'll have less low end torque and HP. Or am I missing something?

Thank you!

​​​​​​

Fast,
The 75 is an auto (unfortunately), but it went through a fresh rebuild a few years ago. I haven't touched the differential at the back, and the documentation I have from the previous owners doesn't mention anything as to what they may have done, so I would go with the assumption that it is stock along with all of the axels. Something worth looking at before I dump this kind of money into it. This would have definitely been an oversight so thank you!

 

For the entry cost of $3,836.90 I just don't see going from 165 to 435 hp by bolting on a bunch of aftermarket parts onto a stock 75 Chevy bottom end.

 

Entirely possible and happens all of the time. You have to remember that if you plucked an L-48 350 out of a 75' Corvette and stick it on a dyno with headers, it will make 240-250. Cam and intake will get ya to 340. A pair of heads are worth the extra 100.....more so here because the roller cam is more efficient......

My problem with this kit is the heads.......most of you know I am very partial to Dart, and the 180 Pro-1 would kick the E-Tec 170 heads ***......more overall power everywhere.
My second choice would be the Trick Flow 175 DH head with a 60cc chamber.

At any rate......a 600 cfm Edelbrock carb is too small for a 430 horsepower engine IMHO......the AVS2 750 will be much closer to optimal jetting out of the box but I my first choice of carb would be a 750HP Holley if you do not need a choke.

Jebby

 

The stock Q-jet flows more air and is easier (and much cheaper) to tune than the 1406.

And what is wrong with your aircleaner? The temperature of the air entering the carburetor is directly proportional to the power produced. The commonly used formula is 10-degrees = 1%. A factory aircleaner with ducting, pulling 80-degree outside air can possibly provide 10% more power than an open-element system, which is ingesting 180+ degree underhood air.

I looked at the kit you listed, and it says "rolling thunder" hydraulic roller camshaft. 1. I see 3 different "rolling thunder" cams listed by Edelbrock - which one is it? 2. I did NOT see where the lifters are included - are they an extra-cost item?? 3. If you provide your own lifters, then HOW can the kit provide pushrods? Different brands of lifters can have different dimensions - I've seen a 0.300" difference between different brands for the same motor.

I am not a fan of such "kits". I think you'll spend similar money with something custom tailored to you exact needs/wants.


I'm guessing you already have some good headers and a low-restriction exhaust - because you are NOT going to get close to the advertised performance unless you do.

 

For $3,500 you can do much better...

I just recently bought everything your considering myself but the intake because I already have a polished rpm equivalent I bought 6 years ago.
I bought an quick fuel 680vs carb from holleys reconditioned section on their website with came to just under $300 shipped. I bought a comp retro roller 270 cam for $280, lifters for $120 (rock auto) and howards pushrods for $40. as far as heads, I bought the same casting AFR sells as the enforcer line only with the stock sized 11/32 valve guides vs afrs 8mm version this is where im going low budget with about $650 invested in assembling them and doing some port cleanup. If you wanted to you could buy the loaded AFR version assembled by AFR for around $1200-1400. The flow numbers for these chinese AFR's are much better than those ETec heads.. the smaller chamber heads like jebbysan mentioned would give you even more compression and performance with your dished pistons.

For that kit you are paying top dollar for marketing and kit convenience IMO. The performance level of much of whats in that kit is nothing special.

 

I must be way behind the times if a set of headers will make 75hp.

 

I think you were comparing 160 RWHP and jebbysan seems to be talking about an engine dyno measuring the engine and not with the loss of the drivetrain.

 

The original 165hp rating was measured on an engine dyno too.....but with all accessories, manifolds, **** timing specs and one hell of a cork pellet type cat.....the 2-1-2 with cat is up there with some of the most terrible exhaust systems known to autodom.....
So yes, headers, duals, real timing specs and no accessories and you have another 75hp.....
The 165 rating had nothing to do with how bad the engine was as to what the engine had to breathe through.....they were sad, sad times......
The 72’ L-48 made 200hp....it was the exact same engine, nut for bolt....but with no cat and duals.....and it makes 240-250 on a dyno with headers and a curve too.....it just does.
The L-82 makes 315-320 and the LT-1 is the loser at 360.....the LT-1 never made the rated power. All of these ratings are through headers with proper timing....and are the only rating that matter IMHO....


Jebby

 

On a fairly mild Pontiac 455, I gained 45rwhp (peak compared to peak) by swapping from the factory log exhaust manifolds, to a set of Tri-Y headers. Same pipes & mufflers behind the collectors.

I then replaced the pipes & mufflers with a full 3" system. All the keyboard "experts" swore that I going TOO big and power was going to drop. I'm planning on going bigger on power down the road, so I figured "what the heck" and did it anyway. Power again increased, all across the board. At 4500rpm, the total gain was close to 75hp at the wheels. I can speculate that with a more radical motor, the gains would be substantially greater.

 

This is great! And unfortunate that the runs started relatively "high" in the powerband. Despite many internet warriors' opinions, long-tube headers will actually help pick up power in the low range over any manifold or shorty header setup.

I agree with a lot of the sentiment in this thread.

1. Exhaust is the greatest power per dollar of anything you can do to a 70's smallblock, particularly late-seventies. The exhaust manifolds are AWFUL. Period.
2. Changing carbs will not net you any power, assuming yours is tuned well. The Q-Jet is technologically superior to an Edelbrock. Q-Jets are a many year newer design, and the late 70's QuadraJets benefited from lots of refinement over the early ones. The M4Ms have adjustable APT settings for cruise and generally don't have any of the leak problems earlier Q-Jets had.
3. There are a ton of better heads out there. I'm partial to AFR and would recommend a set of 195 Eliminators with a good roller cam and an intake like the Edelbrock Perf RPM. If you're sticking with the Q-Jet, get the Perf RPM Q-Jet. If not, a holley or TBI setup on a Perf RPM Air Gap is the way to go. It looks like the kit has an RPM Air-Gap, so that's definitely a plus. I just don't love the rest of the setup all that much.

 

I recently saw a set of edelbrock heads flow tested I didn't pay attention to the model but the flow numbers didn't impress me. The operator said edelbrock needs to update alot of stuff.
The dual snorkel air cleaner issue is ridiculous. You need airflow first then work on cooling the air charge.

 

Just My $0.02 - but a couple of things to think about....

1) HP is made by airflow. The heads, the intake and carb, and the exhaust all have to flow well to make power. The cam basically determines where the engine's torque peak will be, and to a degree - the shape of the torque curve.

2) While it is very tempting to drop on a good on a good set of heads, pop in a decent cam, bolt on a nice set of headers and top it all off with a good intake and a carb - remember that if it's all being attached to a stock bottom end - your fun may well be short lived. The factory took weight out of OE blocks in the mid 1970s because the extra strength just wasn't needed with the power that those mid - late 1970's engines were making. Same thing with forged cranks, and forged pistons... Start making cylinder pressure, and spinning the engines, and some of the weaknesses in the factory bottom ends (including cast pistons, marginal rod bolts, cast cranks,and lighterweight blocks) are likely to show up. I'm not saying it'll break on the first test ride, but if you use the power you now have available - it's just a matter of time before you find the limitations in the other parts....

3) Probably THE most important thing.... IF you make significant changes to the engine, once you're done - get your car to a dyno facility, and get the carb and distributor tuned. Yes,, you can tune the car at the strip - but it's So Much easier when you're getting real time feedback on what the Air Fuel ratio is, and if you can play with Ignition advance and retry the run in a few minutes rather than waiting two hours. I've seen a number of cases where SIGNIFICANT jetting changes are required to get the kind of power out of an engine that it is capable of. One of the reasons that Holley sells a lot of the pricier carbs is that experienced tuners know that having the ability to adjust air bleeds and play with the Power Valve Channel Restrictions allow them to set up the carb to do what's needed throughout the engines operating range - not just at WOT - max power.

 

Thanks! The relatively (to the rest of the powerband) "high" rpm start was due to the stock transmission downshifting when I tried to start any lower. I could have disconnected the kickdown cable, but didn't want to risk losing the tranny to lower line pressure (old tranny).

To keep this thread on topic, I'll share another dyno graph - this one from a '72 El Camino. When I got the Elky, it had a 1406 on a Performer EPS, a set of unknown brand headers, HEI, an old school single-pattern Comp 268Magnum, and a 2.25" dual exhaust. I installed a wideband O2 sensor, and the 1406 was pretty much off everywhere. Before any tuning, the motor was making a bit under 190hp at the wheels. After working with the carb and playing with the timing, I got it to 213rwhp.

I then added a FAST EZ 2.0 efi system. I first tried to get it to work with the HEI, but that was futile. It was a chinese HEI, and the tach signal so noisy (even with a filter) that the tach reading was all over the place, causing erratic performance. So, I added the FAST Dual Sync distributor, and it made an amazing difference. Back on the dyno, I was able to tune the AFR, the total timing, and the timing curve as well. Power jumped to 229rwhp.

Next, I found a set of the larger chamber Edelbrock E-street heads for $700 shipped, on eBay. Never used. A cylinder head porting buddy of mine gave them a look over - rehoned the guides, back-cut the intake valves, and installed better seals. I installed the heads with no other changes, other than head bolts and pushrods to correct the geometry. On the graph below, the bottom graph is with the stock heads (but with the cam, headers & efi mentioned above). The middle graph is with the EFI set the same as with the original heads, but with the E-streets in place. The top graph is after I played around with the timing settings. The E-streets wanted a bit less total timing, and REALLY liked the total timing coming in at an earlier RPM, which is the "bump" in power you see in the midrange. [note: the dyno's tach lead was bad at that time, so I could not get TQ or RPM readings] Also to note, ALL these dyno runs were done on cheap 87 octane.

 

perf top end kit for a low perf 350. first thing you gotta decide is if you are staying with that dished piston 350 rotating assy.you put cam-heads-intake-headers on that short block you are gonna add around 100 hp. THEN you are gonna want the NEXT 100 hp which requires more displacement, and more airflow. so the cam is now too small. the heads too small. carb too small. shouldn't have bought those cute shorty headers... and now you are replacing everything you just bought.

 

L-48 is a two-bolt cast piston, cast crank rotating assembly. This kit is completely wrong for that short block. You are starting with 8.5:1 (or lower compression). Then you want to add a smaller carb. Remember, the techs at Edelbrock just want to sell parts. They dont have to drive your car later.

- Headers are always good.
- Mild cam (~216 or so at .050" lift)
- Edelbrock Performer manifold (more to save weight than anything else)
- Recurve distributor
- Have Lars retune the Q-Jet

I did this on my '75 L-48 and it made a huge difference. Made the car much more fun to drive. Probably ~350 at the crank. Plenty.

Edit: Kit you linked to also has a Hydraulic roller camshaft. That means retro-fit roller lifters ($$$), new timing chain, cam button, and heavy cover. (I did this on my second rebuild of my motor). I love Edelbrock's page on the kit.

Horsepower Possible 435 HP

 

long tube headers and a true dual exhaust. get larger than the 350 needs. no such thing as too little exhaust back pressure. are you in a state that still emissions inspects 75"s? if so, your options are limited. but duals with dual cats would be a big help. that can full of pills in your exhaust stream is the worst part of your power train and the biggest power loss. followed closely by an ignition curve (badly) designed to provide better emissions at idle since idle is where they all were tested.