Okay, I'm building my car through connections and deals... so what my profile says isnt where I'm gonna end up..

The engine I'm getting is 420 hp through a deal and I saw a dyno of it. Has the performer RPM cam and heads but apparently a "stock" manifold. I'm getting my own headers soon.

Anywho, because the manifold is not worth mentioning or just stock, my stepdad asked around and came home with a Holley Street Dominator intake manifold. I checked the # on it 300-36 on holleys site and it says idle-7200 rpms.

Now, given I have the performer RPM heads, what kind of cam could I slap on it to take advantage of flow up to 7200 rpms?

And the other thing I wonder is... it seems when I look at dynos the peak torque of a 350 is about 400 foot lbs.. so how much power could I make with that 7200 rpms ceiling?

And finally (sorry for the long post) when you get these hot engines, like the 420 hp built 350, or whatever I'd get with a 7200 rpm ceiling... what happens to torque under 3K rpms? I NEVER see that on a dyno sheet?

I know you "lose" some low end torque but what is it at, exactly? IT cant be that bad with all this displacement. Certainly not as bad as off-boost on some giant-turbo-wheel stuck on a Supra or 4banger

 

If the car has dyno'd at 420, then I'm assuming the engine is complete, so why would you want to change it?
Did the "stock" manifold go 420 hp?
Did the engine make it's peak HP at 7200?
What kind of driveline do you currently have in the vehicle?
What's the compression ratio?
At what rpm did the engine make it's highest torque numbers?
Lastly, and most importantly, how streetable do you want this?

 

ok... *sigh*

The engine I am GETTING is supposedly at 420 hp. Whatever manifold he had he kept, he didnt get the performer RPM manifold. He claims it has the performer RPM heads and cam. I'll verify this when I see it.

I was talking about a hypothetical build if I used a 7200 "redline" because the holley website said it could flow up to 7200 rpms. I was wondering how much power I could get if I went that high and got a cam matched to that, and of course got a bottom end to support it.

Also - whats the max peak torque you can get on a 350 N/A? The highest I see in dynos is about 400 foot lbs. So, if I tried to guestimate how much hp I'd make if the redline was 7200 rpms, I'd move the peak torque closer to 7200 rpms, and then do the math.

Anyone know the science behind it or any equation I could work with?

 

OK, you asked for it...............
http://www.strokerengine.com/dynoroom.html

 

Thanks for this! its a bit helpful.

One thing tho... I only see dynos from 2500 rpms and up...

I guess I'll just have to hit up a chassis dyno myself sometime.

 

A cam with a powerband high enough to spin to 7200 RPM isn't going to be suitable below 2500 RPMs anyway, so you'd need a higher stall on your torque converter.

I don't think you'll be able to get enough air through the 170cc ports on the Performer RPM heads to support 7200 RPM.

 

I have a manual transmission and planned on using one when the engine is in, so I wouldnt be there unless I was street driving. I was simply curious about what the torque curve would look like from idle to redline is all.

You did bring up a good point, though. If the heads were a restriction then the power would just go flat, wouldnt it?

 

It'd be more like if the heads didn't have enough flow, the power wouldn't be there to begin with.

Power comes from the heads, period. Figure out what the heads are capable of and pick the rest of your components to match.

 

Obviously, if no air gets in, no fuel gets in, and nothing burns, so the engine wont even start

But if I peaked out the airflow of something in the induction system of the engine, that would mean that if it can only flow so much, and kept flowing that much even if revs kept climbing - the power would go flat too, wouldnt it?

The example I'd site for this would be restrictor plates on race engines. Power peaks and holds until you over-rev and start getting valve float or the resonance works against it, giving a flat part of the power curve.

 

well, since you want to know what power you'll make at 7200 RPM, assuming that you're making 400ft/lbs of torque at the RPM... it'll be approximately 548.4 horsepower.

The formula to find out horsepower is

Torque x (RPM/5252) = HP

Find out what torque you're getting at what RPM, and you can find out horsepower. Then again, at that point, the dyno should already say, so what's the point heh.

Anyways, I'm going to have to agree with Apeiron here.. building your engine around an intake is foolish. The heads are a much more expensive/complex part. If you build your motor around where that can flow well, then you can find a cam and intake to match it.

Find out what RPMs this guy was running the motor at, ask him what intake he was using before (part numbers will help), then buy that one!

Unless you plan on completely redoing what powerband you're going to go through... which would be fine, but then you might as well just buy a bare block and rebuild the whole motor from the ground up. It'll probalby be cheaper than buying a motor because "at one point it had 420hp" .

It's just like people who go out and get a bare block, run the numbers and go "This is a Corvette block!!!!". There's nothing special about a block that was used in a corvette. That same block could have just as easily been put in an S10, or an Astro.

 

Gee, don't make it sound so hard to do.


How much power it "used to make" doesn't mean much anyway. My engine used to have 145 HP before the cam, lifters, rockers, crank, rods, pistons, intake, carb, ignition, valves, heads, block and exhaust were changed.

 

It's only hard because you're Canadian j/k j/k

Exactly what I mean. Dont pay top dollar for a "420 horsepower motor" just to completely rebuild/rework it.

 

*sigh* clarification time again... my bad.

It has the cam and heads already on it! He just kept the stock intake. Plus, we got this intake free anwyay, that flows better than stock, so why not use it?

The higher revving thing was a totally seperate question, that was hypothetical in nature. Unrelated.

I'm just gonna put that intake on the new engine cos it has a ****ty *** stock one, but has the cam and heads already.

Am I clear now? lol. Sorry I wasnt before.

 

Don't let the "idle to 7200" rating go to your head.
It's all subjective. Generally hi-rise dual plane manifolds like the Holley 300-36 and edelbrock RPM make best power from just off idle (1500) to 6000rpm.
In my opinion the RPM manifold is a better intake.

A 350 with a big cam and good heads will make power to 7000rpm but you'd most likey want to shift the car at 6000-6500 rpm.

A 350 with the RPM heads, a Holley 300-36 and the Edelbrock RPM camshaft will have a best rpm range of 3000 to 6500 rpm. It will need a high stall converter (3500rpm best) and higher than stock rear gearing. The exhaust system design is critical to get a good result.

The edelbrock heads are good in out of the box form and can be improved with further porting. A nicely ported rpm head will support about 460hp on a 350.

if you really want a 7000rpm 350, use a Victor Jr single plane intake, port the heads more and use a solid lifter cam about 250-260 duration at .050. 106-108 LSA .530-.550" lift It will have a rough idle. 460 to 480hp is not out of the question.

 

Hmm, thanks!

And, I'm just using the parts I'm getting the cheapest. Good ole beg/deal/bargain/steal motorsports at its finest

I'm not going to really go for the 7000 rpm ceiling because I'd lose low end, and I want street civility. I have a manual and 3.73's already, so thats not really an issue. I was just curious about what it would look like.

Also - does ANYONE have any idea what the dyno would be like from IDLE on one of these builds? all the sheets I see have it from 3K rpms and up, and occasionally from 2.5K rpms and up.

When I get my car built up I'm doing a dyno of it, right off idle, and finding out for myself.

 

It doesn't really matter what the numbers are like off idle, you won't be using the power there anyway.

 

I'm still curious! Plus, I might be there driving it on city streets instead of on the highway. But of course, I'd down shift if I wanted to take off. I know how to heel toe, and the syncros in the tranny are in excellent condition.

 

A dyno test will not show you what your looking for.
( How the car will drive and feel at low rpm)

A motor with a cam like the RPM cam will make less low rpm torque and have a rougher idle and lower manifold vacuum than a stock type cam will.

It will still drive at low rpm but the best power range is higher than stock (increased duration and overlap)

Once you changed a few things the car will drive fine.

You'd want a high stall converter for an automatic and higher rear end gearing. (3.73-4.10) The distributor will need to be recurved to give the proper advance curve. You want increased idle timing, about the same advnace at high rpm, but it should max out sooner. something like 24deg initial 10-12 deg advance to 34-36 at high rpm (3000) This usually involves
limiting the advance travel and changing the advance springs in a stock HEI distrubutor. You want to retain and use vacuum advance but it may need fine tuning.
The carb will need a power valve/ power step spring swap
because of the decreased manifold vacuum at idle.
it's all in the setup.

If you want to retain good cruising mileage in overdrive then pick a small cam.

 

You are changing, if I read correctly, the intake, exhaust and driveline. Forget the previous dyno run and go get one done yourself in your set-up. It will likely help you determine much more than any answers you get here.

 

my bad, I was confused, thought you wanted to take that 420hp motor and make it rev to 7000 lol.

But about running that intake... "run what yah bring, bring what yah got" I believe that's how it goes...

 

Its what I was planning on doing!

But honestly, I really did wonder what the torque curve was like idle to redline, not just 3K to redline. lol.


Right now I got the intake on my current engine thats gonna get pulled for the new one, and it made a big diff. Only problem so far is the throttle bracket, but I made a seperate post in the on-topic forum for that