All,

I was looking for some suggestions (aside from just buying a new crate engine or similar) to get more HP out of the car. It sounds like it should go fast but it really doesn't have much get up and go. I have looked at the full drop in engine option but also wanted some options that can just give it some extra HP until I decide to make that investment.

Below is the basic setup of my car, what would you guys do that could add some decent HP?

My Cars Config:
68 Vette
350 small block (replaced by previous owner)
6 speed transmission
NO side pipes, but dual exhaust out the back
4 Barrel carb (with Electric Choke)

Things I've read that may help:
- Would adding side pipes help with the air flow? (which ones would you suggest that would be an easy bolt on?
- Is there a simple air intake kit that will help?
- Do y'all buy into the electric radiator improvement?
- Other?

Thanks.

 

I too have a 68. If you are looking for more wheel spin and the illusion of alot of horse power llok at torque mulipliers as well. The 6th speed is great as it will give you a lower first gear multiplied with the rear end ratio. If you have a 3.70 or 4.11 your car will feel like it has a ton of horsepower when its just the torque multiplication. Its when you get into the higher gears and RPM that the horsepower comes into effect. So lower horsepower will have your feeling like its landing on its face after the launch.

Now depending on the year and the state you may not be able to do many mods without violating local smog laws.

What i did was to get a good dual plane intake that will still allow you to get an air cleaner under it. Dual planes made to match you current carb with a half to one inch open spacer will give you a good overall mixture. A good drop base cleaner with a 3 inch filter will still allow it to breathe. Then you need great flowing heads. The heads are the single best thing you can do to help a stock lower end. It will be easier to get the air mixture to your cylinder while giving it a little more compression. Spend a lot of money on the best heads you can afford. AFR 185 are some of the best on the market for a stock or slightly larger than stock motor. Look for 64cc combustion chambers, they will help bump the compression up a bit to help a smog motor.
Next would be a good cam. A roller conversion is expensive because of the roller lifters. A flat tappet is the next and only choice but you havve to pay attention to the breaki in oils and use a high ZDDP oil for the rest of the engines life. I suggest a roller cam and finding the best roller lifters you can sell a kidney for. If you cant afford those look at a 1.6 ratio rockers. IT will give the cam about .20 inch more lift and a tiny bit more duration. You may need new pushrods so you will have to measure on that end

getting the air out your exhaust is the next big step. IF you can afford them get long tube ceramic headers. If not go with long tube headers and remove the factory shipping paint and repaint them after test fitting them if massaging is needed.. If you run exhaust to the rear try and go 3 inch all the way out.It will help alot. Do not go smaller than 2.5 iches. If you can find side pipes used then go with those as they are mostly 3 inch all the way through depneding on the baffles you put in them

getting air into the carb. IF you can afford a cold air intake do it. Its worth the HP to do it

for cooling go with a good aluminum readiator and electric fans with a good fan controller. You will save 20 hp over a stock fan....

If you like shows go to motortrend on demand and get a subscription. Then watch engine masters and they will explain alot of this and why it works. Theres some fun shows on there to like roadkill and hotrod garage.....

 

Pics and details of your 350?
TKO 6 speed? Do you know the rear gear?

Jebby

 

Hi
4bbl carb
Ede Perf Rpm manifold
Cylinder heads ideally AFR195 Comp version hp and tq will be reflected by head choice
Hyd roller cam
exhaust
4into1 with side pipes
programable ignition advance

Cooling
Elec fans and alloy radiator will improve performance = reliability for high hp level
***Quality** brand copper rad and viscous thermal mechanical fan with shroud for mild application is ok

 

The under car exhaust is better for performance than a sidepipe system. Sidepipes are used for looks and sound but they rob HP.

Tuning and optimizing what you have now should be first. The distributor needs to be recurved to improve performance.

It would help to know more detais about what you have now. The numbers stamped on the block right in front of the passenger side cylinder head would be good to know. Carburetor would be good to know. A picture of the engine would help.

 

Thanks all. I'll look to get some of that additional detail this weekend and post here (i.e. pictures, the transmission gearing, etc.). Appreciate everyone's input and suggestions.

 

Thats not true.
Long tube 2.75 sidepipe headers to a 3 or 4 inch pipe with a straight thru baffle will be better than any 2.5 system that makes all those extra bends under the car. Now if you had a 3 inch system to some straight through mufflers it might be close but the side pipes would be hard to beat. A quick BING and no results for 3 inch stock bent system so that means a totally custom bent system.

 

This true to a point......when you start getting up there in flow and power the sidepipe tubes are way too long......and a good undercar system will make more power. Just look at all of the GM test vehicles and racers as well as private cars that had the collector up inside the engine compartment with one large 3" tube as opposed to the Hooker system which has the collector behind the front wheel......

Jebby

 

I see your point on race cars but making a 3 inch system fit under the car with all those bends is not going to be the same as a race car that dumps out straight piipes in front of the rear tires. And those side pipes do look really cool. I've been trying to find an actual Dyno result on that. I myself still have a 2.5 inch factory style 69 side exhaust behind Hedman headers which was a huge improvement over the rams horns to the same pipes but not as good as those hooker style pipes. And that is purely cosmetic choice on my part but....Eventually it will become twin 3" glass pacs under the covers on each side or Sweet Thunder C2 3 inch tubes. I may just be a cosmetic question when the OP gets there as well becasue it may be a percentage gain and not a determined gain. As long as he goes to long tube headers that is..

A question for the OP or a new thread is how much horsepowerr for the street do you really need before your are just a numbers *****.... I have just over 500 HP through calculations at the crank. Next year I'll find out how much on a chasis Dyno. Im sure its only around 300/ 350 at the tire but its more than enough to get me in trouble. So how much will satisfy the OP?

 

I have a ‘68 with a 350 as well and a 4 speed and I was thinking the same thing. The car is quick but not as fast as I would expect. I was also thinking about a drop in crate motor but may just modify what I already have.

 

Modifying what you have can be less expensive, but knowing what you have will help guide you in the right direction of what you can do. Pulling the valve covers will give you access to the cylinder head part number so you can figure out the combustion chamber size. The front serial number plate should have a engine code on it as well that may give you an indication of what the motor was built for. If the chamber is big like 72cc or larger then a 64cc or smaller aluminum head will help with compression. If you can get it up to 9.5:1 or higher the you can figure on how big a cam it can handle. The heads and the cam will be a big improvement over stock as well as a new intake and headers. All of these could be reused if you decide you want to pull the bottom end and up the compression. The cams lifters have to go back in the same hole they came out of if they are flat tappets. Some people may frown on reusing a cam but if its low miles its not a big deal.

If you go the crate motor route, make sure it has really good heads and go with a roller cam. If I could afford them I would go with AFR. AIM for a 400 hp motor or higher

 

Which 6-speed transmission?
What rear gear ratio do you have?
What is the exhaust configuration? Headers or manifolds? Size of piping?

 

I am going to add this. The sidepipes could be better than the under car exhaust, but it really depends on the engine combo. There is a lot of engine information like valve size, camshaft duration, header pipe size, collector size, and length of exhaust that go into the optimal exhaust system. If you get this information wrong, the exhaust pulse will exit at a bad time. This will not impact overall WOT power, but can kill mid range torque.

 

I bought a ZZ4 GM Performance Parts catalog engine. Added the recommended Holley carb and added a HEI distributor (mechanical tach drive modified). The engine, supposedly 415 flywheel HP, just didn't seem to perform well. Took it to a speed shop with a dynomometer cthat I remembered as the place to go in the 70's if you had a "muscle" car. Turn's out the man's son was now running the business. Talking to him, the elderly man who founded the business walked out....he was the person who really had the knowledge of working with Holley carb's and vacuum/centrifugal advance distributors. Two days. later, I drove my 68 ZZ4 powered car away......it was a different car. The power was there.

 

All these are valid suggestions however. You apparently have no reference points. You know at least the block was changed but you don't know what's in it. You also have no performance data as a reference. That makes it hard to know what to tell you. Everything is a WAG.

 

Without knowing anything more than the information provided initially, I have to wonder if the person who replaced the engine created a significant mismatch between the cam and the compression ratio. Too much duration with too little CR will create a real dog even if the rest of the parts are fine. It's not easy to reverse engineer a cam but you can might get an educated guess on CR if you know what heads you have. If the previous owner used stock heads with a 74cc combustion chamber, likely you have a 9.x:1 CR. If you have a nice 'lopey' cam, the previous owner may have over cammed the capabilities of the heads. If this is the case, a simple cam replacement for $200-300 can make an old dog feel like a totally new engine.

 

If the engine in your car was replaced with a 2-barrel 350 out of a '73 Impala Station Wagon and given a "Performer" 650 cfm 4-barrel, your car will be a dog. You need to determine what you have in your car before you can decide to do any "upgrades." If you, in fact, have a low-compression, small-valve, '73 Impala engine, you have a whopping 145 horsepower, and installing headers or exhaust isn't going to do a damned thing for you (you will have 0-60 times of 16.2 seconds). If you have a 370 horse LT 1 that's a dog, you have a completely different problem. You need to check to see what engine/heads were installed in your car to determine your baseline. Did the previous owner install one of those horrible "Performer" carbs on it? What do you have for ignition system?

Depending on what was installed in your car, you may have a 145-horse hopeless case that needs to be replaced, or you may have a fantastic engine that just needs to be properly set up and tuned. Go do some detective work first.


Lars

 

Sounds like Bob Jennings, his son Nick?
Son quit and went to work for Spangler(?)
Used Bob many times over the yrs, current distributor was done by him before he closed. EFI phased him out.First dyno run ever was on his Clayton piece.

Remember Ed @Camonics cams in north hollywood?
Slovers porting same area I believe? both popular with the Saugus Speedway crowd....Ed liked single pattern cams I believe. Still have a grind or two of his written down.
All old guys, 1 man operations who could really make a car run. Street racing scene was awesome back then in the SFV. Man I got in so much trouble...