1968 Pontiac GTO

[Stan Weiss]

Originally Posted by DeuceCoupe

"The 366 HP 'Ram Air II' had a hell of a lot more than only 6 Horsepower more than the '360 HP Ram Air I'"

I'm still learning and Gonkulating these combos but no doubt about THAT.
So far the Gonkulator is telling me that (refreshingly) the 400 GTO engines tended to be rated pretty close to their actual gross HP (iron manifolds, open exhaust, 60F 29.92 dry sea level air, no accessories).

Note that under that standard Gross HP definition of the 1960s, Ram Air adds ZERO gross HP - since all engines are dyno rated with 60F air into the carb. Ram Air adds NET HP, which is not how they were rated in the 1960s.

Of course that Gross HP varied a little since so many cams were used.
So far, a certain rough set of numbers comes out of the Gonkulator. These are NOT factory ratings, they're computed from my own Gonkulator model, based on flow, dyno data, etc. About +/- 3% typically.

335hp 066cam, log exhaust
340hp 067cam, log exhaust
344hp 068cam, log exhaust

347hp 067cam, HO/RA exhaust iron
358hp 068cam
370hp 744cam

394hp Ram Air II (041cam, heads, RA exhaust)
424hp Ram Air IV (041cam, 1.65RR, heads, RA exhaust, alum intake)

Note I can't distinguish between the RA1 and RA3 - is that about right?
RA1=360hp, RA3=366hp, but are the head flows etc really any different?
Comments welcome on all this!!

"Note: The #96 casting heads are considered to have the best exhaust ports of the 400 heads."

Well we can't ask Paul about that comment but he must have got it from somewhere. I've searched quite a bit for cylinder head EXHAUST FLOW - very hard to find especially on the #96 RamAir II heads.

I'm trying to compare factory exhaust flow, from the D-Ports vs RA2 vs RA4 (and even 455HO and 455SD) heads. Anybody know?

It has been a number of years since I gave Dwight / Class Racer Info a number of files of flow data, so I don't know if this data is there or not. Also you need to be careful with flow data. I believe this exhaust flow data is without a pipe.



Pontiac 96 '71 Flowtech - Steven Magnotti
2.11
0.10000 - 76
0.20000 - 135
0.30000 - 177
0.40000 - 199
0.45000 - 204
0.50000 - 206
0.55000 - 208
0.60000 - 210
1.77
0.10000 - 50
0.20000 - 95
0.30000 - 128
0.40000 - 148
0.45000 - 153
0.50000 - 161
0.55000 - 164
0.60000 - 166


As far as Ram Air. That is correct you will see no difference on the dyno. The amount of HP increase from Ram Air will be a function of how fast / MPH the vehicle is going. The increase is not linear so @ 200 MPH it will be much greater than at 100 MPH and at 50 MPH almost nothing.


Stan


PS - Let me just add what I think you can see (positive intake track pressure) from a "Good" Ram Air setup.

50 MPH - 0.0444 PSI
100 MPH - 0.1776 PSI
200 MPH - 0.71 PSI

[DeuceCoupe]

Stan,
Thanks for that - I had looked in your database (which I use a lot) already, but arent those the 1971 #96 heads, ie casting 481196, 96cc stock?

The RA2 #96 are casting 9793596, 71-72cc stock, those are the ones I can't find. I'd GUESS the exhausts are close to the RA4 heads but can't find any numbers.

For sure on the "Ram Air" - I find about a 4% plus-up just for the cooler air works well, if it's a good system- just as those smogger IMCO Snorkel things can heat the air up a little, even when the flapper is open. The late-60s-up IMCO snorkels cost about 2% power from testing I've done.

And of course the "ram" effect, if any, depends on where & which direction the scoops are. The Cobra Jet shakers look totally cool (got my 1st one at a swap meet for $20) but dont get much ram, if any. I suspect the grille and cowl systems have a little edge there, even for "sensible" speeds like 100mph or so.

Thanks again for your head flow database it does the community a great service.