I am preparing to build an engine with my father and had a couple of considerations and concerns I wanted to inquire about.
Sorry if these sound a little stupid, but they will help me choose the components for my engine more effectively.

Aside from the beat to death vette, I also have a Chevelle. In all the years I've worked on my Chevelle, my goal was always more torque. Torque is how I explain that seat of the pants ride you get, tires buring, front end lifting power. My chevelle was a 396, currently SLOWLY building a 454.

In my fathers case, we're looking to put together a small block good for drag racing down at the track, and good for a little light to light fun.

BORE V. STROKE

We have always fallen back on more horsepower, more importantly torque. So planning for this project the first idea was to jump to a 383 Power from 3000-6500 RPM. The Corvette already is loaded up with 3.73s, 700R4 (2800stall), and a 144 Blower. But I never thought of the possibilites of an engine that makes power a little higher up. For example, what would an engine with a huge bore and a small stroke do for me?? Supposedly they will rev faster and higher and make power up top in the power band. Does this benefit the 1/4 racer at all? How does it even feel.... pull hard down low, pull crazy up high.

Any information or input you give is appreciated. I thought it would be something to consider???

Dan

 

You'll get differing views, but I'll always recommend stroking and punching for the most cubes you can get. Typically, limits to RPM present in the valve-train, not the rotating assy. All things equal (top end, fuel delivery, exhaust) more cubes will win the race,..i.e, 350 vs. 383 or a 454 vs. 496, though with the strokers you lose ideal stroke/bore ratio (whatever that is,..ask 6 people, get 6 answers).

In fact, look at the concrete rippin' LS7 installed in newer Z06 Vettes. It has a stroke of 4.00" and a bore 4.125" and makes over 500 ponies with 427 cubes and red-lines at 7000 officially, 7500-8000 unofficially.

Again, displacement = HP.

My opinion,
Wes

 

HOTROD mag did an article a year or two ago about this very topic. They built 3 big blocks - one 3.76 x 4.600 501ci, one 4.00 x 4.494 502ci and one 4.25 x 4.31 496 ci. They ran a couple of different cams - a hydraulic roller (218/224, .501/.501 at .050) and a good size solid roller (253/260, .734/.732 at .050) in each and the end result was that 500 cubes is 500 cubes, whichever way you get it. There's more piston surface area on the big bore engine for the expanding gasses to act on, so it's output is similar to the smaller bore engine with the longer crank arm. Torque and hp curves were almost identical. Here's a link to a discussion about it on the Chevelle site:
http://www.chevelles.com/forums/show...ht=bore+stroke
My problem with that article is that they didn't optimize heads and cams for each combo.
That said, my current build for my '81 is a 3.75 x 4.600 499 cube tire shredder. I'm going to be running a solid roller so I wanted something I could buzz to 7500 if needed. Read David Reher's article about short stroke/big bore engines in the tech article section at Reher-Morrison's site. He makes points about piston speed, ring drag and position of the piston in relation to maximum thrust on the top of the piston. I decided on my combo for a lot of reasons, not the least of which is that it'll make all the power my tranny and rearend can handle plus some and it'll buzz as high as I care to push it.

 

I read throught what was sent to me about the Chevelle forum,... just so happens I have a Chevelle also so I posted this same question their just a while ago....

I think I pretty much have my answer but whats driving me nuts is the desire to spin your engine to 10,000 RPM.

Correct me if I am wrong: First off, the more displacement the better, a 502 is a 502 no matter if its bored to death or stroked. Now in the case of the 383. This 383 with a super long stroke is going to make a hell of alot more power then Chevy's high performance 302 just based on displacement alone. Difference being that the 302 will be able to rev much higher then the 383 before exploding. Now what gets me is that (This is from what I know so correct me if I am wrong) the RPM at which your engine makes the most power is not determinded by your displacment, bore or stroke, its determined by your camshaft specifically, and also in conjunction with your heads setup which is extremely important, and your intake manifold.
So if you have a huge bore, short stroke 302 with a small cam, and a small intake manifold (sorry but I'm not ready to start thinking about numbers); lets say its making peak 300HP@5500RPM,... a 302 engine with a big stroke small bore (same displacement) with the same heads, cam, and intake I should make the same 300HP@5500RPM.

Now I understand that in order to make the two make the same HP, the components would have to be better matched to the application but this is just an example......

My question is why: What would be the benefit of spinning a motor to 9000RPM then just making the same power at 5500RPM????? Is it more fun??? Whats the deal???

Dan

 

Heres another consideration I didn't think of til just now, what has more control over your torque curve, your setup (cam, etc.) or the actual bore and stroke. I've been looking at this in means of horsepower.

Obvious answer: Its important to have as much torque and horsepower as possible but whats more important, torque or horsepower.



Sorry if I'm killing you guys.... Just stuff thats on my mind. Its hard to put a finger on this stuff sometimes.

Dan

 

To quote one of the guys on the Chevelle forum: "There's nothing like rowing thru the gears at 7000rpm". Look up some of the posts by 540Hotrod (Jim) and he'll explain some of the virtues of a high revving big block. I am well aware they require more maintenance and are more finicky, but that's something I'm willing to put up with on this engine. It won't be a daily driver, more of a Viper hunter and cruise beast. Besides, a higher revving horsepower engine is an ideal match for a lightweight Corvette.
I have another project which is a heavy truck that I'm building a 565 for with a good size hydraulic roller cam, peak power will be around 6K with a 6500 redline. It's an engine built for max torque with the long stroke and big bore. Completely different engines with different purposes in mind.
If I had a huffer to put on top of a smallblock, I'd build an LS series engine to take advantage of their breathing potential. Those little suckers make some awesome power. They're just so dang hard to dress up and make look good, but a lot of that attitude is my old school upbringing.

 

torque moves the car and horsepower keeps it moving i believe. I have a 383 in my car with just about the same rpm range u want.(3000-6600) It pulls good below 3000 rpms but when it gets up to 3k its at 5k in the blink of an eye! The cam i have is a roller cam by lunati with 290 duration and .555/.555 lift(if that helps any..) Its a blast to drive the car.

 

drag racing, it will be better to have a large bore, short stroke....high rpm's is the goal.

 

I'm not agreeing with much of this. Take a 383 vs. a 302,..same bore but the 383 has a half inch longer stroke. If the rest is equal, you'll never make more power with the 302,..even though the 302 has the more ideal B/S ratio. Plus the 383 will hit the peak HP much sooner.

If you have a block and the funds, be it SB or BB, why leave cubic inches behind?

 

It seems as though me and you should be talking because in the end I will have to build the 383 to low rpm standards..... I would like to reuse the 144 powercharger I have lying on the work bench... But i have to tell you its been driving me NUTS! I need to know what the difference is.

First off my friend has an LS1 in his 04 GTO.. That thing will pull HARD to 160 MPH. I don't know the specs of the motor but Im assuming large bore smaller stroke. Thats what I was thinking when I posted this question.....

Meanwhile my chevelle had a 396/375HP engine that was not at a lack for torque from 2000 RPM-5500. And I would blow just about anything away it seems with that car. What I could never understand and am trying to figure out is what the need is for the high RPM power. Why not run the car 3000-6500 through all 4 gears.... why from 4000-8500... Where does it benefit. If two engines are making the same peak horsepower and same peak torque, at different RPM's,.... lets say one makes it at 5000, and the other makes it at 8000, which is getting down the track first?????????????????

I guess part of the problem is that I've been in alot of torque monster cars, and nothing revving over 6500... Enlighten me,

Dan

 

73, if I used a 4.25" stroke rather than a 3.75", it would make a good bit more torque and hp, neither of which I could ever hope to get to the ground. It'll be hard enough to hook and use what I'll make with the shorter stroke engine. A good running 555 will need a 4500 series carb and I don't want to go there, either - no choke just ain't much fun in cold weather and they're tough to get to run at part throttle as compared to a 4150hp. In 9 of 10 cases, I agree with you, build it as big and strong as you can, but this is one of the exceptions. I'd rather have something that gives up some of the bottom end so it's more streetable but hangs on and makes power as far as I dare rev it. I agree with you when it comes to smallblocks, but there's a lot bigger difference between engines with 4.600 bore when you're talking 3.75" stroke vs 4.25". As far as I can tell, we're talking street engines, not drag racing. If I were building a drag race engine for a big-tired car, I'd stuff as much crank in it as I could fit, but this ride is traction limited. I know the limits of my tranny and differential and that has been factored into my combo decision. I'm not talking about an engine I plan to rev to 8K - it'll generally shift at 6K or lower but will make the occasional buzz to 7500 or so. Take a ride with someone in a light car with a strong hp engine that can handle 7500 and it might help you to understand the attraction of that type engine - it's a whole new ballgame as compared to a torque monster. We're talking big blocks, not a Z-28 with a 302 as compared to a 383 - that's a no-brainer in my book.

 

first off, LS1 are monsters with great potential. And they have the newest technology stuffed into them. And for the rest of your question...idk!, lol. I guess maybe it all comes down on the cam? Some of em make power at low rpms while others are high rpm screamers.

 

When at the IHRA championships last year I believe I saw a corvette with either a 283 or 302 (can't remember which) and if I recall he ran in the low 9 second area with the front 3 feet off the ground when he launched. It was far from stock and I don't know what his setup was, but it really surprised me!

 

Well, for me, a high revving small block let me beat, or at least keep up with the big block cars, and when I beat them, I could say "I only have a little 350".

When I bought my '69 it had a '70 LT-1 in it. I put the GM off road solid lifter cam in, a set of angle plug heads, a tunnel ram with two 465 holleys and 4.56 rear gears. This motor will touch 8000 rpm and spin 7500 all day. If you've never shifted a car at 7500+ rpm, you don't know what you're missing.

 

1. There is no good substitute for cubic inches.

2. RPM is a poor substitute for cubic inches, but it is used where it is required to make the most power if you can not max out #1.

That being said - here is the short answer regarding why we have small displacement, short stroke, high rev engines that win races. I will use the Chevrolet 302 as an example because it comes up frequently as a sucessful application for a winning track combo. The same principal works for any combination.

The 302 was built to satisfy a cubic inch displacement rule. Had to be under 5.0 liters to race against Mustangs (displacement was limited) The high RPM was used to get the most power out of a limited displacement. Short stroke is used to allow higher RPM before blowing up for any given displacement.

Remember if you can't max out #1, you keep the cubes where they are then use the formula "RPM x Torque = Power".

After that is is just a matter of degrees. Bore/stroke relationships are just very fine tuning once the rest is determined. Don't let the tail wag the dog.

-Mark.

 

As for a street engine, model a 350 with 3.48" stroke then change the stroke to model the 3.75" stroke. You will not see a jump in HP so much as you will see the torque go way up BELOW THE PEAK in the lower RPM ranges. That is why they rock on the road.

-Mark.

 

Your main problem is a 144 ci blower. Over driven to near it's max RPM it can only put out so much boost with a 350 ci motor. Maybe 10 psi. Then throw it on a 383 and your only going to get 7 psi.

You need to design the motor around the blower. 302 - 383 ci will probably make the same amount of HP with equal cam, heads, & compression. TQ will be some what higher as ci goes up. The 383 will have an advantage in the unboosted lower rpm.


The real advantage to higher rpm capable motors is that you don't have to shift as often. My Vette witha 4.11 and a 700 tranny could do about 90 mph in second gear and 140 in third. Then i could shift in to OD and really drive fast

 

This is true in F1 racing where they are limited to naturally aspirated 2.4 liter V8s. They make somewhere around 800hp @ 20,000 rpm. Pretty amazing when you consider the rules also state that they must last for 2 races.

 

I think this is the biggest problem in my understanding of the potential of high rpm engines. I've never experienced one. I always had the BBC in my car and as far as I am concerned I am content with the unmanagable torque it puts out, and shift from 3000-6000 over and over again. Unfortunately this engine is going into a Vette, and we want to do a small block, so things are a little different.
Maybe its my inexperience, but I agree with you... Why leave any cubic inches behind... more displacment more power.
What you have to also remember is that these engines are strictly RACE application only. I can't imagine how high the CR ratio of an engine like that would be. I can tell you its not running on 93 pump gas. Not to mention I'm sure it incorporated a tunnel ram, 2 carbs, and a outrageously expensive and good flowing heads, ported to the max.
This is the question at hand.... anyone have an in car video or something. What I'm thinking is whats the benefit.... you could just shift a little sooner and keep the rpms within your power band to get down the track. Besides hooking up low which is a real pain with extreme amounts of torque, what is the benefit of being able to revv the motor like crazy.... is it fun??? Laziness????

The only thing I can think is that it pulls hard down low, and as you get up in RPM it begins to pull like crazy???

I like the discussion guys... keep it going

Dan

 

I just wanted to give you guys some insight into what I'm working with.

Working with GM Goodwrench 350 w/ 4 bolt that is in need of a rebuild.I will be sending it out as soon as I find a reputable machine shop to get it punched out .060 over.

Holley 750 Double Pumper (Maybe reselling and moving to larger)
B&M 144 Blower (would like too keep and reuse but also may be selling)
Roller Rockers (brand new)
Hei Distributor
MSD 6AL

The suspension is setup for drag racing, the car was a race car before we purchased it 6 years ago. We restored it back to a street car but then got wild with the blower and a scoop and now its going back to a race/street car.

Its got a brand new Ikerds 3.73 Posi Differential
Brand New Mad Dogg 700R4 High performance High abuse transmission w/ 2800 stall converter
BFG's are being replaced with Drag Radials in the spring... (after we have fun with the old ones)

The goal is the abuse the neighbor that lives next door over. Hes got a 68 Camaro that runs low 12's! This covette looks fast, it needs to go fast. We would like to break into the 10's in the spring.

As we say in OC, were gunna do it up.

Dan