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OK, I have a 350 sitting in my shed, and am planning on doing a rebuild. Take a guess on the Horsepower/Torque if i; Bored it .03" over, ran 9.5-10:1 compression, used the edlebrock performer RPM Manifold, and cam Int. .488", 234 degrees. Exaust .510", 244 degrees, ported the heads and manifold, used 1.6:1 roller rockers, and topped it all off with a 750cfm Rochester carb, and SLP headers through flowmaster exaust. Horsepower at the crank...
[This message has been edited by icenine9 (edited July 01, 2001).]
Basically talking Edelbrock's Performer RPM package. Don't use 1.6 rockers, use 1.5's. Chances of getting the stock heads, ported or not, to respond above .500" lift aren't good. Don't port the intake, its great as it is. You won't make it better, only worse. Depending on how well (not to be understood as how big) you port the heads, 370-400HP. Probably towards the lower end like 380HP. This is with open exhaust. I would recommend a slightly smaller cam for a better street engine, and a newer design than Edelbrock's cam. The XE274 is a good substitute for Edel's cam. 230 degrees and much better profile. Torque with Edel's cam should be in around 380ft-lbs and about 400 with the XE274. Overall though sounds like a good low dollar performance engine.
What heads? That's one of the single biggest variables, but it doesn't appear in your list of parts. If they're any kind of GM heads other than FastBurns or Bowties, you won't come anywhere close to the RPM package rating; the heads are what makes the package.
I agree with GP's cam selection. I used to have that XE274 cam, it ran real good, one of the best I've had. It ran alot better than the 282 solid that it replaced. The Eddie cam is a very old lobe design with too much "advertised" duration for its .050" duration, and not enough lift for really good-flowing heads. I'd bet that if you took the RPM package and substitued that cam using a set of 1.6 roller rockers (I'd suggest the Comp steel ones for a street build), you'd beat the package by 25-30 HP and maybe more torque than that.
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"So many Mustangs, so little time..." ICON Motorsports
<font face="Verdana, Arial" size="2">Originally posted by RB83L69: I'd bet that if you took the RPM package and substitued that cam using a set of 1.6 roller rockers (I'd suggest the Comp steel ones for a street build), you'd beat the package by 25-30 HP and maybe more torque than that.
Not necessarily. Like the other post said, on some stock heads the increase in rocker ratio won't really make much difference (although it won't ever hurt performance), while on better ones, they can be significant.
What stock heads?
There's a HUGE variety of "stock" 350 heads; that covers everything from 140 HP 350 2-barrels in 76 Impalas, to 375 HP LT1s in Z28s. 350 heads have had combustion chambers with volumes everywhere from 58cc to 76cc.
My comment was based on the Edelbrock Performer RPM heads that are part of the RPM package, not stock ones.
Without knowing what heads you are using, it is impossible to make a guess as what the engine's ouptut will be. No amount of bolt-on exterior stuff will make up for heads that don't flow, or that are mismatched in some other way to their surroundings.
What heads have you got?
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"So many Mustangs, so little time..." ICON Motorsports
I don't have the budget to get a new pair of heads, unless they cost $400, so if anyone has a better alternative than porting and polishing, lets hear it.
Several GM 350's have made better than 350HP with stock unported 2.02/1.60 iron heads. GM even had a few oddball truck 400's that made high 300's with the 882 heads. Make sure the heads do have 1.94/1.50" valves. I don't remember if an '86 350 would have the larger valves but its worth double checking. Best bang for your buck heads are the Vortecs. They are right around $400 a pair and are only a shade below the Edelbrock's in performance. Thats an assembled head but as it comes it won't handle a large cam. The only pitfall I am aware of is that it takes a special manifold that is more expensive. At least take a look at it before throwing money on these heads.
Go to this page below and check out the second article there specifically. It is the CHP Goodwrench buildup where they ported the smogger 1.94/1.5 iron heads and put in a decent cam and tested the engine. Those heads should perform very similarly to your heads. Result: 336 hp and that's with a pro doing the mild porting. Also check out what the engine made in the later updates to this article with the Vortec heads...
Like I said I think you'll be doing good to get over 325-330 hp w/ those heads.
1) 8.4:1 CR, another 1 to 1.5pts will give a solid increase.
2) They used the XE268, this is still smaller than the Edelbrock cam or the XE274. Again worth a little power.
3) They gained 26HP by increasing the compression ratio 0.6pts AND a very mild port job. This is not a fair comparison, 0.6pts itself was probably worth half of that.
4) They used the Edelbrock Performer manifold. While its a good manifold additional power will be realized with the Performer RPM.
Plugging all this in to Desktop Dyno 2000 with 10:1 and the XE274 I get about 365HP. This is with unported regular old iron heads. Depending on how well he does the porting 370-390HP should be reasonable. Which if you will recall hits right about where I said. As an additional note, if I kill the compression to 9.5:1 and then 8.5:1 I get 355HP and 335HP. So that jump from 7.8:1 to 8.4:1 while porting the heads could have been most of the 26HP increase. I'm not sure he really helped do anything but take out gross casting errors and put a good valve job on the heads. That is one of my biggest sources of irritation in the engine world. "Porting" covers knocking out casting flash to opening the ports to 250cc. So when people say they ported the heads you don't know if they flow worse, better, or drastically better than stock.
At first the engine build ups do sound the same but when you look across a handful of minor differences it adds up. Nothing major, but enough to cover 30-40HP. Unfortunately the door swings both ways. A few minor changes the other way and you drop 30-40HP.
Sorry about the double post, but i did some searching on the net and found my casting numbers at www.Nastyz28.com The heads on my 350 seem to have come from a 305 (1986-91 10110810 305. Intake 1.84" Exaust 1.5001" - EFI,swirl port, stat wgn)
[This message has been edited by icenine9 (edited July 06, 2001).]
Well in that case, they are garbage. They don't get much more anti-performance than that. You are wasting whatever money you put into this motor thinking it's going to run hard, if you use those. That would be, as they say (and they should know) penny wise and pound foolish.
Get some other heads. Remember, nothing else you do can make up for a bad set of heads; there's no such thing as some cam or something "compensating" for heads that don't flow, or that you're going to bolt on some collection of external pieces like ignition parts or the like that claim to be worth 5, or 15, or 8, or however many horsepower, add the "gains" up, and magically overcome a set of crap heads. It doesn't work like that.
The only way to release energy is to burn gasoline molecules. With a given bore and stroke and compression, torque = the number of gasoline molecules you burn per revolution of the engine, and horsepower = the time rate at which you burn them. The only way to burn gasoline molecules is with air. Therefore the only way to acheive a high time rate of burning them is by a high time rate of moving air in and out of the motor. That's another way to say FLOW.
So, to come back around to your original post, you'd be lucky to crack 300 HP with those heads. I saw in another post where you were asking about cranks; forget about a bunch of that. Spend your money where it will do some good, which is on a set of heads; even with the entire Edelbrock package and its 420 HP, the stock bottom end is fine, except that a set of forged pistons and better rod bolts would be a good thing.
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"So many Mustangs, so little time..." ICON Motorsports
Now that using the heads on the engine are out of the question, what do you think about using (L31 Vortec Similar to 'Vette LT-1' Cast Iron, 170cc intake runner, 64cc combustion chamber, Intake Valve 1.94", Exaust Valve 1.50")
