302 Engine mods

[machm1970 180]

I finished the mods on my '70 302 and so far I'm disappointed in the performance, it's not really any faster than it was with the stock setup (2V).

 

Here's a list of what I have done

 

Edelbrock 2122 cam .448/.472 duration @050 204/214

GT 40 heads

Scorpion 1.7 roller rockers 

Summit aluminum intake (Their version of a Weiand Stealth)

Rebuilt Autolite 4100 carb with 1.12 venturis (off a 65 galaxie with a 352).

Pertronix ignition and coil  

3.50 rear gears

I have the timing set at 16 degrees initial

 

The exhaust is stock manifolds and single exhaust (I will be upgrading to headers and 2 1/4" dual exhaust during it's hibernation this winter). I'm sure the stock exhaust is holding it back quite a bit, but how much? 

Any other suggestions?

 

Thanks,

 

Matt

[moodster 55]

how are you comparing the performance?  

 

david

[machm1970 180]

Just the way it feels, I expected a little more acceleration and it doesn't seem any different.  

 

 

Matt

[moodster 55]

I can make suggestions but these are just my opinions really without proof.  I think your stock exhaust is holding you back a tremendous amount with that combination.  Basically you've got a cam slanted towards horsepower and heads with better flow but an exhaust that is stifling all of it.  The only other thing I notice is you seem to have a lot of advance (16 degrees).  My stock 69 302 (single exhaust also) ran best with 8 degrees of advance.  Not to say 16 isn't the right number but it just seems like a lot for that engine.  I'm betting that a dual exhaust will make a difference you can feel... if not, get more cubes and graduate to a 351 :-)

 

david

[1969_Mach1 333]

I'm sure more performance minded people will chime in.  At first glance most of your parts look good  The new exhaust will help a lot, the cam is on the small end of the spectrum for a performance motor, and I don't know about the carb.  Other things, what is the static compression ratio?  You have a lot of initial timing so I am guessing the compression ratio is fairly low, 9:1 range.  Higher compression ratios increase cylinder pressure which increases power.  But todays fuel puts more limits on maximum compression ratios.  What rear axle gear are you using?  The rear axle gear ratio makes a big difference in performance.  Lastly, this is too late, but more cubic inches always makes a big difference.  Dollar for dollar, a 351W based motor makes a lot more torque, thus power, than a 302 based motor.

 

Most of your parts seem fairly good.  If you post more info on how you want to use the car members will be better able to provide better input on cam, carb, and other parts selections.

[machm1970 180]

Basically I use it as a daily driver (on nice days) take it to shows, etc. I don't plan on ever racing it. When I rebuilt the engine last year I was trying to keep everything original (everything was numbers matching). After driving it for the summer I got a little bored and decided I wanted a little more "muscle" in my muscle car. I wish I had went with a bigger cam, but at the time I was being conservative. The guy I bought the GT40 heads from threw in the 1.7 roller rockers so I figured I would get a little more lift and duration with those. I think my lift with those is now .472/.502, so that's a little better. My car came with a 3.00 open rear end. The first thing I changed was the center section replacing it with 3.55 gears, I did notice a difference with those. I do need to play with the timing a little and fine tune it. I will be adding headers this winter, I'm just working on deciding which ones.

 

Thanks,

 

Matt  

[shaun071 62]

Headers and a dual exhaust will make a huge difference. They'll add up to 50 hp with your components.

[1969_Mach1 333]

The 1.7 ratio rocker arms will increase the lift at the valve but have no affect on the duration.

[barnett468 418]

.

ok, all the poins have been mentioned but you also didnt state what you had before or exacty what your goal is.

 

the compression was probably reduced by at least 1/2 a point when you installed those heads because of the large chambers . . more compression = more power EVERYWHERE.

 

buy hedman elite headers . . they are by far the best deal on decemt headers . . 1 1/2 or 1 5/8 are both ok with the bigger ones having a hair less bottom end and a hair more top but they are in no way near being too big and if you have a 302 and switch cams, i would use the 1 5/8.

 

the carb is likely hurting you because it does not have adjustadbe vcuum secondaries and the secondaries on thos carbs typically open a little later than they otherwise could . . a rebuilt summit 600 cfm carb is a good deal and so is a quick fuel ss600vs carb . . those secondaries on both of those are adjustable and will likely need a lighter spring . . the spring kits are available from holley for around  $16.00.

 

plug your distributor vacuum advance until further notice.

 

a standard eddy entake with possibly a 1" spacer will perform better than that stealth

 

the duration on that cam is pathetic plus its an old school slow ramp design and even though you did it a big favor buy running 1.7 rockers instead of 1.6's, it is still smaller than i would put in my grandmas car . . i would trash that cam or give it to someone and install a comp xe262h . . if its too much then install 1.6 rockers and it fix your compression and it will spin the tires.

 

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=799&sb=0

 

do a compression test with a GOOD gauge and all the plugs out and the throttle propped open . . you need to have around 170 with premium gas for decent performance . . if its 140 or less, it will always be a pig.

 

1 7/8 exhaust pipes are all you need . . anything over 2 1/4 will be way to big and will kill hp.

 

you will get a mild increase in perf with headers and dual exhaust but i will be more noticeable with the new comp cam

.

[moodster 55]

barnett brings up a really good point I hadn't thought about... any idea what the difference between the chamber size on the GT40 head and your old stock heads was?  

 

david

[barnett468 418]

.

i should add that rregardless of the combustion chamber size of the heads, the chamber on the gt40 heads is around 62 cc's and it needs to be around 57 cc's with flat top pistons for optimum perf on 91 octane.

 

also, the quench/squish clearance should be adjusted to be between  .034" and .043" with the smaller number being better.

[machm1970 180]

Before my car was completely stock, 302 2v. My goal is just to have better torque and acceleration, just a little more fun to drive. When I initially rebuilt the engine I wanted everything close to stock, thus the cam choice. This summer I got the bug to make it a little quicker and got a deal on the heads, rockers and intake. So unfortunately it wasn't very well planned out. So with my current setup the 1.7's are hurting performance? I should've changed the cam last week when I already had the heads and intake off. Right now I don't want to get that far back into it. Lots of good points, especially on the adjustable secondaries.

[Rsmach1 71]

As stated, changing over to headers and a free flowing dual exhaust, along with the summit carb barnett468 suggested will help quite a bit. Your 1.7 rockers aren't hurting performance, they're helping a tad.

 

Edit, a better free flowing air cleaner would help as well. Here is the carb http://m.summitracing.com/parts/sum-m08600vs

[Rsanter 152]

As pointed out already my first though was the loss of compression due to the swap to the GT40 heads.

Yes the GT40 heads will flow better but I can port the stock heads to do much better than the stock GT40 heads.

In fact every set of GT40 heads I have ever installed I ported first

 

Next is the exhaust, you need to step up to some basic tri-y headers. For a street driver you don't need more than those

 

Bob

[machm1970 180]

I was looking at the summit ones when they first came out, I remember they had some issues. By looking at the reviews they must've fixed them. I do like the features.

[barnett468 418]

.

the best deal on headers is thee hedman elite and the shorties will work fine for your app.

 

we already know your compression is somewhat lower than it could be, therefore there is no point in changing the cam . . basically if you are not going to change the cam and compression, you are not going to get a significant increase im powr no matter what you do although you definitely will gain some with the exhaust change but dont expect a miracle because you have four other big problems.

 

low compression, wrong intake, bad carb for the app and wrong cam.

 

the comp xe cam is already a fast ramp cam with decent lift, so using the higher ratio rockers on that particular cam may or may nor increase performance with your particular combo, especially with those heads.

[machm1970 180]

Yeah I definitely should've done some research. I used to have a '66 with a 289, I put a comp cam (I don't remember which model) gt40 heads, edelbrock performer intake, street avenger 570 carb and tri y headers. It also had a toploader and 350 gears. It was a blast to drive, I was hoping to get the same kind of feel from this set up. I will do the headers, carb and intake over the winter.

[jholmes217 65]

I haven't heard anything about your transmission.  If you have an automatic and haven't matched your torque converter to your build, it will be like a pig out of the hole.  A friend had a 396 Camaro and put a Comp 280H in the engine, but left the stock converter in the tranny.  Sounded awesome at idle, but performance sucked with the stock converter.  As already stated, the exhaust is hurting it also.

[machm1970 180]

That is a good point, it is the stock converter in the C4. The exhaust will be the first thing changed, no matter what that's a given.

[barnett468 418]

That is a good point, it is the stock converter in the C4. The exhaust will be the first thing changed, no matter what that's a given.

 

your engine will not be like a pig out of the hole with 355 gears and a stock converter and either cam although it will acelerate a little more quickly off the line with one that has a higher stall like 2000 rpm, but that still will not make your car feel much faster off the line and it will not make it feel any faster once the converter is fully engaged.

 

as it is, you can run the lowest octane gas you can find so at least you will be saving some money if you arent using ot already.

.

[moodster 55]

One last thought I had was that with the Edelbrock cam (vs stock), you're losing dynamic compression due to the intake valve staying open longer.  With that cam and iron heads you really need your static compression to be around 9.8:1 to make the dynamic compression right from what I've read.  I don't think you're close to that now.  

 

david

[machm1970 180]

I did a compression test with all the plugs out and the choke open. All cylinders were 140-145. When I got the heads I was thinking about bigger valves and hardened seats, I forgot to look at the cc.I got a good deal on the heads, recently redone, trick flow spring, screw in studs, guide plates and the roller rockers all for $300. I should've checked the cc size and had them milled a bit.

[machm1970 180]

I just made a big improvement. I took the 4100 to a local carb guru last week when it wouldn't idle. There was a plugged air bleed in the primary booster under the Welch plug. He cleaned that out and while he had it he enlarged the primary jets a little. When I did the compression check I noticed the plugs were black. I pulled the 48 jets out of my 2100 and swapped them, wow, big difference, much more responsive. Breaks the tires loose easily and gets a 2nd gear scratch. I need to fine tune everything, but things are getting better.

Matt

[Rsmach1 71]

One last thought I had was that with the Edelbrock cam (vs stock), you're losing dynamic compression due to the intake valve staying open longer. With that cam and iron heads you really need your static compression to be around 9.8:1 to make the dynamic compression right from what I've read. I don't think you're close to that now.

 

david

That cam is very mild and has a an early intake valve closing point, so it won't effect the DCR all that much compared to a stock cam.

 

Randy

[moodster 55]

That cam is very mild and has a an early intake valve closing point, so it won't effect the DCR all that much compared to a stock cam.

 

Randy

 

According to the Edelbrock cam card, the intake valve closes 29 degrees (vs 8 degrees for stock 69 302) after the piston starts to move up.  If the desired dynamic compression ratio is 8:1 then the static compression ratio needs to be 9.8:1 with this cam.  Please let me know if your calculations show otherwise because I'm open to learning from all of this. 

 

david