306 combo, What to do?

I'm putting together a 306 as follows, need suggesstions on heads given my budget.

306 roller block
windage tray
Stef's pan
speed pro pistons (hypers)
comp cams 274 HR
performer rpm intake
custom Biggs 650 DP
FMS BS FW and Damper
CF DF Clutch
1 5/8 lontubes with 2 1/2 exhaust


I know a guy on another forum who is running the exact same combo with edelbrock performer RPM head (unported) making 419 FW HP. He has access to a dyno where he works so he's been able to do all the fine tuning as far as jets changes/ timing curves/ carb spacers/ etc...He pretty much narrowed it down to where it makes max HP. He is willing to give me all this information which will save me quite a bit of guesswork. The only thing different between our combos, engine wise, would be the exhaust systems.

Now, I can pick up a decent slightly used set of RPM 2.02 heads for about $900. This is what my plan was and I was also considering a small shot of nitrous, maybe a 75 or 100 shot once everything was in and working.


I have also been tossing around the idea of forgetting about the nitrous and simply spending that extra $$$ on AFR 185's instead. Of course they won't make 75 more Hp over the RPM's but in the long run I think that may be a better idea. I've never messed with nitrous but it seems like it wouldn't be worth the hassle of setting up the whole kit, messing with the fuel system, dealing with the wiring, refilling the bottle....for as little as I would use it I just don't see the point.

I guess my question is, is it worth the extra $400-450 to get the AFR 185's over the RPM's? and rule out the possibility of nitrous? Or should I just stick with the RPM's and get nitrous If I decide I want more power in the future.

To give you an idea of what I'm trying to accomplish, I am looking for low 12's, shouldn't be out of my reach N/A with the RPM's. this is with a T-5z, 4.33's, locker, on 26*10.5 e.t. streets. car is a 68' stang, weighs ~3100

Redrooster said:

I don't know the stats on the comp 274 but I do know that the afr 185 will out flow the crap out of the RPMs. The 2.02 RPM don't flow but like 220 cfm at .500. That's enough on a stock short block, but the AFR 185s flow like 265 cfm. You might give up 20-30 hp with the RPMs vs AFRs. IMO.

BTW you did not say what kind of head your friend was running.

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He is running Performer RPM Heads, that is the reason I was going to buy them. They flow very close to AFR 165's according to MM&FF. Maybe I'll just get the AFR 185's and cal it a done deal

Do you think this combo would be capable of low 12's with the 185's? N/A.

The comp 274 HR is actually an Extreme energy grind, 224/232, .555/.565

As far as headers go, I don't plan on buying new headers, at least not for a while. The longtubes I am currently running are a 1 5/8 oval design at the flange.

With AFR 185's I see this as a problem, the headers I currently have are going to be restricting the exit of the D shaped port, thus resulting in less flow. With the RPM heads this won't be a problem.

From what I've read the AFR's will need a 1 3/4 inch header, on a 302 that's a bit large isn't it? Not to mention we are talking another $400 on top of the cost of the heads.

Would AFR 185's be worth it then? Assuming I don't plan on buying new headers then reconfiguring my exhaust to bolt up to them. I think it would end up being a wash is I keep the headers I have on the AFR's, I don't see how they would outflow the edelbrocks significantly if the exit ports are restricted.

This kind of sways me toward buying the RPM heads and then a small shot of N20, together that would be cheaper than AFR's/new Headers/exhaust and still make more power when the N20 kicks in; I'm just trying to get the most bang for my buck here.

2000xp8 said:

Those numbers sound a bit optimistic to put down when it lands up on a chasis dyno. With that combo i'd be happy with 330rwhp.
It's only a 306, and from the sound of it, nothing real special. (not an insult).

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I agree, and it wasn't meant to be, he wanted realiability, and to be able to run on 89 octane, he's only running 9.1:1 compression. He's put down 12.7@105 with that combo on street tires, but he runs a C4 and I'm running a t5. He's had the ability to fine tune everything on the dyno which isn't something I can do unless I pay $100+ an hour. I'm sure those numbers were with no belt driven accessories either. If you think about all the variables that affect power (jetting, carb spacers, timing curves, total timing, plug gap) I could be at a dyno all day. All that information is already available to me, however, I may bolt on AFR's instead, but this ins't a race engine, will be 98% street driven, I wan't it to run on 89 and I would like to be able to drive it in the summer if need be, I currently have no overheating problems with the 27 by 19 northern radiator so that shouldn't be an issue either