Question: Best intake port size / flow for this engine?

[macx]

I guess I should have just said best port flow, not size.

Any idea for the optimum intake port flow for a mild cam
(206 @ 050 & .435 lift) to support about 320 hp
at 4500/5000 rpm on a 9-1 cr 350 inch engine?

I'm trying to figure which of 2 heads will not leave any
power on the table at 4500/5000 rpm, but without getting
too big of a port - capable of too much airflow - so the flow
slows down at lower rpm so it won't fill the cylinder properly.
Torque & throttle response at 1600 to 1800 rpm will be very important
for this car's gearing on the highway. That'll be freeway speed.

I've looked and can't find any calculators or formulas for that -
of course there are quite a number of variables.

I'm looking at a couple options that are good quality heads
and within my budget -

One head flows about 210 and the other flows about 185 at .435 lift.
They both have 170cc intake runners and are Vortec style heads.
The bigger head flows about 235 at .500 so isn't really that big of
a head - a typical 1.9 valve Performer flows about 215 @ .500.
The engine will be real mild, though, and never see the high side of
5500, if not 5200 or so. Peak hp will be at 4500 and peak torque
at 3000 per the Cam Quest dyno program in Comp Cams website.
Building for good mileage for long trips, with 3.31 gears, 200-4R and
27" tires on an 81, so need good low rpm torque. BTW it's Pro Jection
efi on a Performer intake, not carb'd.

Would 185 restrict it at 4500/5000, or would 210 be too much
for 1600-1800? Which would be better and why - if you have
any more of an idea than I do. Or maybe that's so little difference
it doesn't really matter?

Appreciate any thoughtful, informed SWAG estimates!
Of course with suporting info / theory / what have you.

Even some actual experience, maybe even on a similar engine,
would be just super.


Thanks!

 

[Crimson Thunder]

If both heads have the same size intake port then go with the one that flows better. What heads are you looking at? What cam are you installing?

 

[macx]

First, this is a work in progress - the research that is. That is where I am at right now.

I was referring to the Summit Racing Vortec cast iron head at $309 assembled, which I have read and seen by looking at pictures is very much like Dart heads in the comb chamber, and the slightly more expensive RHS cast iron Pro-Torque Vortec style heads. Summit tells me they flow ~232 @ 500 lift, and that I could get them milled .018 to get the 64cc chamber I need for 9 to 9.1 cr. Course then I'd have to take them apart etc. The RHS are a little more but in the same ballpark. I was also looking at another one, can't remember, maybe a 65cc runner Dart, but it was 210 flow at 500, which was the smaller of the two I was talking about in the original post.

Last night I came across EQ cast iron Vortec heads in an article in Popular Hot Rodding on a budget build. They were really enthused about them as they have corrected some of the shortcoming of the oem Vortec heads, and are reportedly sanctioned as an oem replacement in IMCA circle track racing and are quite popular.

Vortec Small-Block Build - Popular Hot Rodding Magazine

They are cast in Australia and finished in the US with good valve train components. Available at a comparable cost (mid $600 for an assembled pair with standard components) to the Summit heads, and flow a little less than the Summit's (230 range but at 600). And no milling, and with hardened exhaust seats.

That article also surprised me at the cost of a Vortec roller shortblock "core" which they bought "on the market" and which just might prompt me to recalculate my budget a little to accomodate a roller cam. But that is still under study and consideration.

There are limited places that carry the EQ heads assembled, actually found them on fleaBay! That's where I found about the article.

Here's a link to some good info on them. I read in a post on some forum that the 170cc 1.94 valve Vortec EQ heads had a rather small exhaust port to intake port size and flow percentage, but the larger ones have a much better ratio. That shows up in the link here. That would then need a split pattern cam with a bunch more duration and lift, maybe use 1.6 rockers on the exhaust.
EQ Cylinder Heads @ Rogers Performance That makes me maybe reconsider the Summit heads, for a few $ less, too.
But here's what some circle track guys say
http://www.circletrack.com/techarti...gine_tips/oil_fiter_cutting_vortec_heads.html
but they're maybe not using the ones with the small exhaust port? Doesn't say. I think I'd ask and verify b4 I bought any of the EQ's.

Before I found that article and was resigned to a flat tappet cam, I did quite a bit of research and pretty much narrowed it down to one of 2 Comp Cams. I looked at Lunati, Crane, GM, and a couple others, but noticed that Comp has generally a narrower degree spread between 050 & 006 lifts which will help a little to trap more compression pressure - I'm going to have to run 91 octane if I use my stock dish piston shortblock cuz I can't get any quench unless I replace pistons, so might as well get the best low rpm torque biased combo I can.
Also the Comp cams have a decently early intake closing ABDC which is a big one for low rpm torque, and they have the necessary cam timing events to allow efi with 02 sensors.

Bear in mind that if I retain my existing stock shortblock without doing any freshening, for budget reasons, I want to keep the revs in the low 5k range max. Also with 3.31 gears, 27" tires, and a 200-4R I'd be running 1600 at 56 mph and 2200 at 80, so really will need good solid low end torque to get decent throttle response and uphill torque without downshifting.

The cams I'm currently considering are both efi & computer compatible per Comp (I'll be using my 670 cfm Pro Jection with an extra 3 lbs of fuel pressure which, per Holley, should support around 325 hp max).

First is XE-249-4, 206-212 @ 050 with 434/444 lift, the other is XE 256-H, 212-218 @ 050 with 449-456 lift.

Per the dyno program on Comp's CamQuest program, with my engine info pretty accurately represented, the 249 read out was 315 hp at 4500 & 405 tq (surprised me) at a low 3000, with 327 tq at 1500. That really would fit my rpm / torque needs nicely, altho of course
would probly run out of breath just over 5k, which I guess would be OK and in line with my goals.

The 256 read out was 330 peak hp (15 more hp) at 5000 (500 rpm higher), 402 tq at 4500 (also 500 higher) and 313 tq at 1500. The main difference would be that both the hp and tq peaks would be 500 rpm higher, with pretty equal max torque and just 15 more hp on the longer cam. The 256 would have about 15 tq less just above 1500 but with over 300 lbs should still be fine on 55-60 mph roads.

I had originally started looking at the XE268H, then the XE262H, but found them to be quite a bit weaker on low rpm torque, so kept lowering my sights until I got to the results for these 2.

I know those figures aren't going to be real accurate, but are at least representative and can be realistically compared with the 268 & 262 results from that same dyno program with the same engine info plugged in.

Also keeping in mind my efi will support around 325 hp max, that 249 might just be the ticket, esp with the good off-idle torque and the faster rise in the torque curve at low rpm.

If I end up getting a roller core like the build in the PHR article, then I'll have to start over on cams, but would look for the same basic results regarding rpm / torque curve. It would of course be fun to have a little more hp and extended rpm range, but I've got to remember to stay within what my efi will support. No matter how much fun, it would be cost prohibitive to go with i.e. the neat FAST EZ EFI system or something similar.

Yeah, kind of long winded and lots of detail, but that's half the fun of planning an engine. Also the better informed I am the closer it will come to my goals.