Okay, there is this thread where a TPI vette with full exhaust, SLP intake, and 1.6 rockers put down over 55whp, granted at 6krpm, simply by siamesing 1" into the stock lower manifold.

Here's the original post:

Now for a 305, the gains won't be as impressive and the shift points in an auto car are lower than 6k. But that can be changed with a chip burn.

Again I am just looking at the numbers. Let's say I do this mod along with the plenum porting, would SLP siamesed runners be overkill for a stock setup?

I plan on 3.42's, headers, cam, and heads eventually.

 

RPM Stk 1"cut 2"cut
3,400 210 200 188
3,600 220 210 200
3,800 230 220 210
4,000 240 230 218
4,200 245 235 225
4,400 227 237 230
4,600 247 240 233
4,800 243 240 233
5,000 233 237 230
5,200 220 233 222
5,400 200 225 212
5,600 180 215 200
5,800 160 205 187
6,000 135 190 173


this table shows that cutting the lower manifold hoelps not at all

 

No offense but did you read that correctly?

The 1st row is stock, the 2nd is w/ a 1" cut, and the 3rd is 2" cut. At 5400 rpms is where it really takes off. And at 6k it's 55hp more than w/o a cut in the manifold. But maybe I'm missing something here.

 

I think that table shows that he should be shifting no later than 5500RPM anyway... BTW, you can't change shift points with a chip burn...

 

the max hp for the stock is 247@4600rpm
the max hp for the 1"cut is 240@4800rpm
the max hp for the 1"cut is 233@4800rpm

if you gear and cam for where the intake works best your performance will be better. yes they do have gains over stock, however the optimum range for max HP for all 3 of these models is between 4500 and 5000 rpm. now if you change cam and head desing with headers you will be able to move that range up or down.

 

Right, I wouldn't do that until a head/cam swap anyway. How would I be able to stay in the power band, manually shift the auto?

 

TCI shift kit. you actually modify the valve body in the trans

 

Recalibrating the transmission governor will allow you to change your shift points...

 

You dont look at peak HP, but the average over the RPM ranges the car will see during a run, if 1/4 mile times are what you are interested in.

The 1" cut fared best on that guys car.

 

what I am doing to mine is leaveing the base alone . I did cut into the runners( edlebrock...better than SLP ) 4" . I did this in an effort to raise the top potential of the intake to about 5500 , just to match the powerband of the ZZ4 camshaft . I have pics if you want

 

depends on his gearing and torque converter and where the cam comes on. my point is its a total package and you should plan that way.

 

Of course, but looking only at peak HP will get you nowhere fast.

 

Well, like I said above, I will do that after I do a cam/heads swap. However, it was rather impressive to see the gains at 6000rpm over a stock setup. It's not peak hp but 55hp over at a certain rpm as gotta be pretty substantial, right?

Crazy, naiive question....what if I did that base mod and simamese runners, would 3.73's do good? I mean the gears would run out of steam really quick on a stock setup, but with something simamesed base and runners?

 

I'm interested in pix, I have edelbrock runners and I'm thinking of doing something like that also, I have a feeling once I get this engine up and running, I will have too much low end torque, and I will need more upper horse...

Did you run the runners before opening them up? Did you loose any lower end?

 

I cut about 3 in down in to my ed. runers and lost about 40 cfm on the flow bench. YES I lost 40 cfm. It was a real pain to weld it back up. THINK TWICE!!!