Thread: Dome pistons match to what type heads

Tweet

I just purchased a stock 1971 chevy SB 350 with flat top pistons. What type heads would I need to mate up to those pistons. Hp is rated at 145 stock. What would be the approximate hp with an aluminum 2x4 setup and those pistons and whatever heads?
Thank you
farmerdick

First, how much compression do you want to run? Is this going to be a pump gas regular, premium, or an E85 engine. Are the block and pistons stock or has the engine been gone through recently? Unless you're just after aesthetics, might want to reconsider the dual fours, twice the expense and twice the upkeep! If this is a street engine, a quality dual plane intake with a 600 to 650 CFM vacuum secondary carb will work quite well.

Welcome to CHR:
Your comment leads me to believe that you have a two-barrel, stock 350. If it is a 1971, the good news is that it is an L65, which is not a bad little motor. In 1971, this engine was a base for a lot of GM products and typically came with 1.94/1.50 heads and 8.5:1 compression generating 245 horsepower. It was in 1973 that the L65 became the weakest 350 of all time, generating 145 hp at 4,000 rpm and 255 lb-ft at 2,400 rpm.
As it sets, 2x4 would be a disaster for several reasons however; you could do the following and have a pretty nice low-budget build that would get you 300 horsepower.
1. Buy a set of Vortec heads, +/- $500 on eBay
2. Buy a used Vortec intake manifold +/- $150
3. Buy a rebuilt Q-Jet - +/- $225
4. Set of headers to fit your rig
5. Gaskets
This is all bolt on and go and you’ll not get too far afield as this is all stock stuff that will complement this engine. If you want to go deeper and spend more money, you could replace the camshaft and lifters, but this will certainly give you a solid dependable engine that fires right up every time and give you a decent increase performance without much of a sacrifice in mileage

Again, welcome to CHR!
Glenn

Most believe 2 x 4's will loss a little horse power over a single four. However, when tuned correctly many have seen increases on a dino over a single four. Though you may need to increase the cam a little in your motor for them.

I ran 2 x 4's on a '62 vette back in the sixties and loved em, never had to fuss with them much more than a kid would anyway. I run 2 x 4's on my current ride and love em. Gained a slight horse power increase once they were dialed in and motor sounds throatier (deeper), especially when floored (lol). Have not had to fuss with them any more than I have with a single carb. Although I do get a little less mileage depending on my foot.

IMHO, the key to success with 2 x4's is getting them sized and tuned correctly in the beginning. I'm currently using the Edelbrock 2 x 4 set up. While it was a little pricy, it comes with matched carbs that are tuned pretty close out of the box, both carbs have adjustable vacuum secondaries which help tuning the motor CFM requirements. Didn't take much to dial them in, and their instruction are very comprehensive covering everything you need to know (and then some).

I got the 145hp figure from a Google search. So if it is putting out 245hp I would be happy with that. The motor came out of a station wagon. I guess I mostly was looking for "Looks" under the hood. This engine will be going in the 41` chevy coupe I just purchased and hooked to a 350 turbo automatic. My friend and I both had 61` vettes in the mid 80`s, his having a 2x4 set up and mine a single 4bbl.

Thanks everyone for the info.
farmerdick

All good advice farmerdick. Keep in mind though it’s kind of hard to build an engine in an information vacuum.

The key factor is what you want the vehicle to do when all is said and done, cruiser, race car, poser etc. Things like performance, reliability, fuel mileage, type of fuel (Regular, Mid Grade, Premium, E85), weight of vehicle, transmission type, rear end ratio, tire size all figure into the equation. Finally and likely the biggest consideration is what is the realistic budget for the project.

Many years ago I did a 350 for a 65 Biscayne I had. The car was intended as a daily driver long distance cruiser. I started by rebuilding a stock 350 short block. I had a choice of several different heads but settled on just a plain Jane set of 1.94/1.50 large chambers I had laying around. It got a PAW house brand cam (around .465/.488 280/290 as I recall) and 1 5/8” long tube headers. I started out with a single 4 barrel intake and carb and changed over to an Offenhauser dual quad intake with 600 AFBs. I actually didn’t see any seat of the pants power increase or decrease and fuel mileage stayed the same…...it was nice eye candy under the hood though. It was connected to a wide ratio 4 speed with a 3.08 rear gear and 235/70/15 tires. It ran great, was rock solid dependable and got 20+ on the highway (back in the national 55 MPH national speed limit days when everybody was really running 65).

Even though there are “better” heads out there I would still duplicate this combination again in a heartbeat especially if budget was a consideration.

Finally your question about horse power….who really cares? Unless you actually put it on a Dyno (and you will likely be disappointed) you can claim anything you like…….. hell look around some of the other forums, I don’t think there is anybody out there that are claiming less than 400 HP out of their almost stock low compression 1st gen small blocks.


.

Originally Posted by Mike P

Finally your question about horse power….who really cares? Unless you actually put it on a Dyno (and you will likely be disappointed) you can claim anything you like…….. hell look around some of the other forums, I don’t think there is anybody out there that are claiming less than 400 HP out of their almost stock low compression 1st gen small blocks.

Mike, you bring out a very good point, and spot on IMO. Unless you dyno an engine the HP and torque output numbers tossed around are simply projections. Now granted the computer programs we have today can at least be consistent in their method of calculation and approach if the input data is correct and accurate, but until it spins a calibrated dyno the numbers can be anything you want to claim them to be. And anyone who tells you they can tell you the numbers by the seat of their pants is fooling themselves (and anyone who believes them), plain & simple, again my opinion and everyone has one along with a belly button.

Very good point!!! Anyone making horsepower claims on an engine they have for sale and not having the dyno sheet to back it up is just doing some "creative" advertising!!!! IMO a rock solid 400 horse street engine is all you will ever be able to use and still be able to afford fuel for on the street!!!!!

Farmerdick, if you want real numbers and an excellent tuneup, when your engine is all done, running, and broke in properly search out a shop with a chassis dyno and run your car on it a couple pulls and adjust the tuneup between pulls!!!! Yeah, it cost another couple hundred bucks, but it's also a very good way to optimize the performance you already spent all the bucks to get!!!!!

Just spent yesterday at Nickey doing a carb on an early Camaro on a 500 hp engine that wouldn't start very well, idle or run enough to even move it from trailer to shop----------after filling the 4 holes the previous tuner had put in the throttle plates, removing big secondary power valve, cleaning all passages, re doing float levels, etc,etc,etc--put carb back on, car cranked over6 or 7 turns and fired up and idled at 850 just while we were turning it over to prime carb thru the window(no one in the seat) 3 pulls to balance primary to secondary mixtures 457 hp at 6000, 468 tq with above 400 from 2700 up


will try pic and dyno sheet posting Monday

Originally Posted by Mike P

Finally your question about horse power….who really cares? Unless you actually put it on a Dyno (and you will likely be disappointed) you can claim anything you like…….. hell look around some of the other forums, I don’t think there is anybody out there that are claiming less than 400 HP out of their almost stock low compression 1st gen small blocks.


.

I have to laugh at this one as it brings back those "oh-so-fond" memories of the sixties when pretty near everyone was running 283 or 327's with power pack or fulie heads and everybody claimed to have at least 400 horsepower! Many were setup with fender well headers and so over cammed that raw gas dripped our the collectors and the engine wouldn't idle below 1200 RPM. To complicate matters, I lived at a 5,000 plus foot elevation and that really played havoc with the normally aspirated engines.

We've come a long way...