Road race motor

[Frenchy]

Ok well since the dragstrip is 2.5 hours away and there's a lot of nice twisty roads around here I have been getting more and more into steering. And I've always been a fan of trying things nobody else does, I was throwing the idea of building a real high revving up top screamer. Was going to do it with a SBC just for pure cost factor, but I have a worn out 5.3 and a 4.8 shortblock that I've collected. So I was thinking put the 4.8 crank in the 5.3 block bored to 3.90 (LS1). This would give me a 313ci motor, I figured with a longer than stock rod (havn't figured out how long yet) it should be a good top end setup, and I'm talking 8500 rpm plus with a good balance job. I'd shoot for about 11:1 as far as compression goes and with appropriate heads and cam, LS6 manifold because well a FAST is outta my price range for now. And for the record this would not be going in a full size truck, thinking Mazda2200 or a Toyota, something like that.

Thoughts? Opinions?

Edit. This little beast has a bore/stroke ratio of around 1.3:1, guess which engines are also like that? Z/28 302, Ford 289 and Mopar 340. They're all proven high end beasts.

[sprayedenali]

I guess canadians can do something right...

That sounds like it would be badass

[IXLR8]

A motor that makes all it's power at a very high rpm is usually not a desirable thing. Most motors that are built this way are done so because of displacement rules for the class you're racing in.

A motor built for very high rpms will use an expensive valve train that will require regular maintenance to keep the valves under control at max rpm. Not something you'd really want in anything less than an all out race car. A valve train like that on the street would be devouring itself on a regular basis with a hefty price tag. You'd be looking at lots of valve spring changes. And you'd probably need to run a nice high dollar aftermarket rotating assembly that may turn into a lump of twisted metal at any time. RPM kills motors. They say the stress on the bottom end of a motor increases at the square of the rpm.

In most forms of racing it's easier to be quick with a motor that makes a broad power band with good peak power. For instance, in road racing a broad power band will pull you out of a corner without requiring the driver to find the perfect gear in the trans every time.

If you have no rules to follow, you'd probably want a light weight motor with lots of displacement and a broad power band with good peak power. This usually translates to the largest reliable displacement that will fit in your engine block and/or a very well thought out turbo.

Light weight and big power is what everyone is looking for of course. You won't usually find light weight with big power by taking displacement out of your motor. Rules are usually what forces racers to do that. Yes, the 302 Fords and Chevys came about due to rules. In almost all forms of racing if the racers were allowed to they would run more displacement in their motor. Of course there are limits to each design where a particular bore/stroke combo yields the best results, but that's not really what I'm trying to focus on here.

If you're on any kind of a budget, in the end, a larger displacement motor that makes big power at a reasonable rpm is much more friendly to your wallet and easier to win races with than a small displacement motor that has to rev to the moon to keep up.

Just my .02

[Frenchy]

Oh yeah I'm well aware of all the downsides. Like I said I'm just a fan of doing stuff nobody else does, and I learn by doing, I can't sit and read books on how to get the perfect combo. I guess I should clarify, I'm not actually building a motor for road racing. Just one in the style of it, small displacement and lots of rpm. This is just fun to me. Besides if it doesnt run like I want, 4" crank and I have a 382.

[pl4yboy]

The 5.7 block with the 4.8 crank like we talked about sounds tits to me. Throw it in a baby car/truck with a 6 speed and a power adder and you've got a BEAST of a roll racer or road racer.

[topfueljim]

The 5.3 and 4.8 blocks are exactly the same castings. The only difference is stroke. Bore whichever is in better shape. I've daydreamed about doing something very similar. I understand the attraction of a small, high revving motor. Go for it!

[kyhunter89]

you build the motor, and ship it down here, i'll put it in a 240sx and tell you how your idea worked...

[molitor]

nah nah nah, put that 4.8L crank in an l92 block... big cubes, short stroke, you'll make 8k rpms, but you'll also make a lot of power on the way up.

[Frenchy]

I would, if I had a L92 block. Working with what I have in my shop as I type this, but if I get decent results, building a badder aluminium block version isn't out of the question. It's going in a stripped out Mazda 2200. In front of a TH400 for now until I can find a T56