Friend of mine switched from a 305 to a 350, .42/.442 Edelbrock cam(204/214 dur).

Running SR Torquer 2.02 heads.

The car is an 86 IROC, originally LG4, with 700R4 and 3.08? rear gears. Whatever's stock.

Anyways, I have a 78 Corvette with a 350, stock heads and the low-end(for a vette) cam(195/202, .390/.410), and my 0-60 time comes in at about 6.4. I'm running headers and true duals, but the discrepancy between our cars is rather large.

He hits 60 in 8.3 seconds. (yuck!) I was expecting a lot more, and figure tuning's an issue. He's running 2-1-2 exhaust, stock exhaust manifolds and the CCC carb and computerized ignition. His chip, obviously, is for a 305.

The trans feels good, no slip. Rear end is questionable- it gives up traction incredibly easy. (Did these cars come stock with posi?)

I have a couple tuning questions then:
1) Is there a chip out there that'll properly set up the computer to work with a 350? (How much would that cost / where?)
2) What's the best route to go with exhaust while maintaining smog legality? I'd imagine 1 5/8" headers through 2-1-2(due to legality), but maybe upping the pipes after the first Y to 3".

Thanks for all the help you can give me. I want this guy to go as fast as he can with this set up!

 

There's not much to gain from chip tuning in a carb motor.

He needs exhaust. Every piece from the heads to the street. He should get chassis-specific headers, BUT NOT FOR LG4. The ones for something like a TPI 350 would be a better choice; along with a high-flow cat such as a Catco or CarSound, and any of the many 3" cat-back systems on the market. 2-1/2" is too small. Again, it must not be for LG4, and must not fit to any LG4 parts; anything that will fit to anything that's there, will retain the bottleneck. That's the single biggest thing holding him back now. Don't waste time or money on intake, carb, dist, etc. until the exhaust is fixed.

A better air cleaner would help. The L69 (HO) dual snorkel cold-air one is the best to get. Much better than an open element.

The next issue is his gears.... stock gears in that car were probably 2.73. 3.42 or 3.73 makes an incredible difference.

That's not the best cam in the world, but also far from the worst in this application. It should wake up that motor pretty well. With that, and a set of headers and the right exhaust and gears, he should be able to get around 230 - 240 HP out of it; enough to seriously wax alot of 350s, including any stock 70s 180 HP one.

 

Sounds good- I expected him to beat me.

My car runs exceptionally well for a "stock 70s 180hp" one.

6.4 is not a slouch 0-60 by any means.

I'll tell him to look into exhaust and I'll play with the base timing.

Thanks for the advice. I expected exhaust was a major bottleneck on this car.

-Steve

 

I have that exact combo! Well i used too. I had a 355, with the same WP S/R heads, and a cam very similar, in an original LG4 car with the 700 trans and 3.08 gears open diff. In that setup I went a pitiful 15.5. The above mentioned dual snorkel with ducts and K&N dropped that to 15.1 with some carb tuning. I'd highly recommend dropping in a set of DR secondary metering rods and adjusting the AV tension per the Tech article. The addition of headers for a 350TPI car, a 3" cat and catback netted me a 14.2. The exhaust made a HUGE difference. A small 2400 converter and a locker got me a 13.8.

 

Marc, did you keep the stock LG4 chip? What about Base Timing?

I agree that TPI exhaust is better then "carb" style with restrictive EFE valve, but might be needed to pass a visual smog inspection.

Someone was working on an AM EFE valve, might have been Hooker (?).

 

By EFE, you mean the heat riser, right?

Hedman sells an adaptor to hook the stock heat riser on my vette to the collector. I'm sure you could easily do something like that with some long vac hose.

-Steve

 

If you're in California or elsewhere that they visually proctologize your car to that extent, get the Edelbrock TES for the L69 (HO); and the cat and cat-back for that application. Use the stock EFE valve. It's CARB approved.

 

No, EFE is "early fuel evaporation".
Part of it is a butterfly valve that closes when the motor is cold (< 75? deg F.) to block the passenger side exhaust manifold outlet. This forces some of the exhast to flow thru passenger head heat riser port into a channel in the intake manifold, then out the driver side head heat riser into driver side exhaust manifold. This very qucikly warms up the intake manifold so fuel does not puddle during cold starts.
Even when it is open, it restricst the pass side exhaust.

I think you are talking about carb heat stove that warmes the air going onto the carb during cold starts.
IIRC that is called "thermvac"???
You would also need to add this to TPI manifolds to pass a visual.
Rubber hose would not stand up exhaust heat.

 

Sorry, double post.

 

Before the days of underhood emissions stickers and thermovac systems, the EFE valve was called the "heat riser" valve.

 

Again, the TES for L69 has that. They have to in order to pass CARB standards. Maybe not the highest-performance headers there are, but at least you can still drive your car legally after you install them.

You can port the heat riser valve, BTW. In fact you can almost make it equal to the diameter of the head pipe.

 

83.5 L69

Is the heat riser controlled electronically or by vacuum on the LG4? My vette is ran by vacuum, hence the reason the hose would have to be run. The stock EFE sits about 2" below the center exhaust ports, while the hedman setup I run is at the collector, probably at least 20" further away.

RB83L69

I bet you could just trash the internals of it and run it "looking like it works" to pass visual. After all, it does jack crap when it comes to real emissions.

 

Hey,
This sounds like the series of articles Chevy High Performance was doing last year. They also put a mild 350 into an LG4 Camaro and were not happy with their results.
My subscription ran out before they finished the series. Last I read they where planning on removing the EFE and installing a hood scoop/bigger air cleaner. Can anyone tell me what happened next?

 

Stock ECM and PROM. I tried a JET stage 2 chip, but all it did was cause detonation at low speeds in OD no matter what I did, so I sold it.

Base timing was 12-14 BTDC.

There's more in the combo with just timing. Just for kicks I ran a nonCC setup to see if there was a performance improvement, and there was, but that's on my current combo with a much more aggressive cam. An L69 ECM/PROM would work well, as would the GM ZZ4 pieces.

 

I switched from an LG4 to a 350 from an 87 Blazer. I need more power. I was thinking of useing a zz4 cam and changeing the computer to one GM made for a zz4 third gen conversion kit and intake manifold that they designed for use with the stock qudrajet. Is an electric fuel pump a good choice. Should i use headers for 350 TPI(will that cause any problems) or the L69? Dont they both go to 3 inch cat and exhaust, so i would need to get all new exhaust or can i stay with the 2 1/2. Thanks for any imput.