A guide to building the lil guy. The Mighty 300

Sounds like a good approach. For right now I'd like to concentrate on sorting out the crank/rod/piston package. I'll get the # for those 305 pistons, that seems like a good starting point.

This would be for a different car that I have out in the shed. Also a MGB convertible but late model (1974-1/2) so fewer engine bay mods, just a bigger radiator I think, and maybe the RV8 headers.

The blown 340 doesn't need the TA heads. It's fast enough already. There does come a point where a car is no longer fun to drive every day, I'm trying to avoid that. Hit the sweet spot so to speak. In fact I may end up having to swap in a milder cam for the 340 if I can't find another way to reduce the idle fluctuations. But let's not go off on that tangent here, it can be another thread and I'll try to start that in a few days.

So anyway, this car is stripped down and we were planning on using it for a Chump Car racer, but rule changes and expense have stalled that project. It has a tired 60 degree V6 in it right now but no interior, no doors (just the skins are tacked on) and the plan was for a roll cage. That will probably still happen but going for the lightest reasonable car weight with the 300, something as close as possible to 2100lbs. Just something to take out and play with on nice days and maybe use sometimes as a track car.

The target with the motor is to give it a broad operating envelope with decent power, something a bit over 300hp with a nice smooth idle and able to wind to a 7K redline. I know hitting both ends of that target are a challenge, but MGB was able to do that 50 years ago with a 4 cylinder so it's clearly not impossible. (about 90hp, 110cu.in.) A lot will depend on the headers/exhaust so those will get some additional attention, and when I get to that point, a roller cam might be part of the mix.

But like I say it'll be a little while before I start. The engine is two states away at present, and right now I'm concentrating on tidying up the '71 with the 340.

Jim

 

With the car being so light and only a 300 HP goal, I don't think you need to get a 350 crank for it. Just stroke the 300 crank from 3.400" to 3.540" stroke for a set of nascar take outs, that with a set of ported TA rover heads should make well over your HP goals. With a .050" overbore and a 3.540" stroke would get you to 321 cubes, should be plenty with a car that light and only a 300 HP goal.

The $$ you save on sourcing a crank then having the mains ground down that far, use that $$ for a custom set of pistons or the AutoTech piston and ring set. You will have an easier time finding rods because you won't have to try to find take out with the .927" wristpin size, the custom or customizable pistons you can change the wristpin size to whatever the rods have.

If you send the heads to the guy Dan Jones uses to port heads, he said he can get 300 CFM out of a set of the TA Rover heads which would be enough to support 600+ HP!

With a stroked sbb 350 crank and .050" overbore would get you to around 364 cubes IIRC, will probably make more low end torque than you would want with a car that light even with a bigger cam?

If you have a lathe maybe you can try to make your own roller cam blank? Have it ground for solid rollers so it'll spin easier and more RPM. You can use sbc roller lifters, just pencil grind the slot on the tie bar longer towards the other lifter and they will drop right in. The sbc lifter bores are a little bit farther apart than the sbb engines so that's why the slot needs to be lengthened about .125", I would settle on altering a lesser expensive made in USA part.

Well, now everyone that reads this has a choice to go with sbc roller lifters and slightly alter them to work in a sbb if they want to go with a roller cam.

 

Very cool idea, would be great to see a 350 crank in a 300!

 

Hmmmm......
I think that has been done.

Lemme look...
Yep, right here "350 crank in 350".

 

Lol

 

If you make your own cam from 8620, be sure to turn enough blanks to bring the heat treat costs down.

 

I think Art still has some roller cam blanks for the Rover, those should be adaptable to the 300. Guess I'll ask him, I don't remember what he wanted for them. There are some differences in the cam snout though.

I do have a lathe so I could cut down the mains myself and send it out for finish grinding, that'd take some of the cost out. Thanks for the tip about the roller lifters, that sounds like a pretty good dodge.

Sadly, those 305 pistons (ICON IC832- STD) are not cheap enough to buy in preference to a fully spec'd custom piston. Prices I saw were over $600.

Now the deck height of the 300 is 9.543"
Stroke is 3.400"
Stroke of the 350 is 3.850"
300 rod length is 5.960"
350 rod length is 6.387"

So doing the math for zero deck, a piston with a 1-3/16" compression height and a 1" wrist pin could use a 5.93" rod. (Check my math please?)

That means that the 350 crank and 300 rods could be used if the piston is spec'd with a 1.200" compression height for zero deck. No messing with custom rods at all. BUT, those rods are cast and,

There are plenty of NASCAR rods on ebay today with a length of 6.200" at prices around $100 or less a set. Makes a set of custom pistons look a lot more affordable.

Jim

 

Just stroking the 300 crank an extra .140" for a set of the 6.200" inexpensive take outs and the AutoTech piston and ring set should hit your 300 HP goal without even trying topped off with a set of TA Rover heads, even if you de-stroked the crank that .140"!

Yeah, I've looked at those Icon pistons before, very nice but with a big price tag. The standard size for a sbc 305 is 3.736" and the standard bore size for the sbb 300 is 3.750" so you would have to go with one of the 305 over sizes.

The AutoTechs are around the same price that includes a premium set of rings. If you bought the Icons you would still have to buy rings that would be $100 to $200 range for a decent set of rings above that price. With the AutoTech pistons you need to choose your bore diameter wisely so there are good ring sets made for that diameter, that way you get better rings for the same price.

What intake were you planning on using? To spin to 7,000 you'll probably want a single plane, is that Hufftaker I think its called is it a single plane? If not you'll probably be better off making a custom intake than trying to adapt a 215 single plane intake on it because I don't think it would flow enough volume of air for over 300 cubes. It might flow enough if you decided on de-stroking the 300 crank possibly and keeping the bore as small as possible to keep the cubes down.

If you went with a 3.756" bore with the AutoTech piston and ring set there are good rings available for that size;

https://www.summitracing.com/parts/uem-3736cd8-025/overview/

With only a .006" over the standard bore size of 3.750" you can save some $$ not getting the block bored, it would only need to be honed and .004" to .006" is just right to be honed out(depending on bore wear?). You can get the cubes down to 288.967 with only a .006" bigger bore and a de-stroked crank with a stroke of 3.260". A longer rod would probably be a good idea to get some weight off of the pistons. There are still inexpensive take out available with a longer length and the good part about doing a de-stroker would be you shouldn't have any cam clearance issues at all! Even with this 6.450" rod;

https://www.ebay.com/itm/6-450-Carr...e=STRK:MEBIDX:IT&_trksid=p2055119.m1438.l2649

That would call for a piston with a 1.463" compression distance to get to a zero deck with the factory spec, actual deck height measurements will vary so order pistons accordingly. Getting the AutoTechs allows you to skip deck milling if the deck is still in good shape, no excessive pitting to use the inexpensive Fel-Pro blue perma-torque head gaskets.(unless you want more than 10:1 compression IIRC they are good to?)

If you get greedy with the cubes with such a small HP goal, your low end torque is going to be off the charts for such a light car. The tires will probably break loose way to easy at higher speeds than you would probably want them too? Even with a big cam and a highway gears in the car. All that torque is great for a car 1,000 lbs or more heavier but not so much with a car as light as you're building.

With the smaller cubes you can set the high RPM HP closer to 300 easier than with a larger cubic inch engine with less tire shredding low end torque and a useless high end HP because the tires just spin even at higher speed when the peddle is floored.(unless that's what you want?) Just like we went through with that friend of yours that was thinking of building a sbb 300 for his MG.

If you still want to be greedy and build a sbb 364 cubic inch engine, over cam the crap out of it to try and kill as much low end as you can if you want to be safely able to spin it at 7,000 RPM at higher speeds and keep the HP down at the 300 level. You will probably want it to be lower compression as well with the big cam. You won't need the TA Rover heads either, all you'll need is a set of ported '64 sbb 300 heads to get to your 300 HP goal. You'll probably be able to use 87 octane pump gas building it this way. LOL But should work how you want it to if you mis-match the parts and compression just right?

With the 289 sbb with '64 300 heads ported buy the guy Dan Jones uses so they flow 200 cfm intake would be more than enough to hit your 300 HP goal.(you would probably be closer to 400+ HP setup to spin to 7,000 building this way!) You might even have a set of those heads lying around you can use? With the cubes that small you might be able to get away with running a 215/Rover single plane with adapters and hogged out to the '64 sbb 300 ported heads port size?

If you build a sbb de-stroker you'll probably start a trend in the MGB community after they hear how good it runs in your car? You don't need the torque the extra cubes will give you, you need the high RPM HP that the less cubes will give you. Cool project can't wait to read what you decide to do.

 

If it helps, 1.425" is a more common CH for sbc's now with so many 3.750" cranks being used.
A 1.540" average CH 305 pistons could easily be trimmed down with plenty of thickness left...for a lot le$$ than custom slugs.
The dish is a good .060-.080 or .125-.140" on the round dish type.
A lot (350/383's having the same CH as 305's) were done that way before the aftermarket offered the 383 'kits', you couldn't hurt them.

[Piston material or type not specified here, just sizing.]

 

How good do cast pistons handle hitting 7,000 RPM on a regular basis?

 

Not at all anxious about the horsepower target. With decent compression and even a mild cam it should get there or close enough. I'm not even remotely concerned about dyno bragging rights, maximum output, or timeslip ET. There is NO problem with inadequate power with this engine/vehicle combination.

I'm going to stick with the stock aluminum 300 intake. I realize it's a limiting factor but it is also a low height intake, which allows the engine to fit under a stock hood. Plus, I have the intake so it's an easy choice. There is no reason why a 1000cfm TB-EFI won't work just fine with that, removing essentially all of the restriction of the carb and helping to minimize the intake restriction. It will need to be port matched of course, probably on both ends. With the carb and head restrictions largely eliminated the flow through the intake should be plenty good enough. Not building a race engine here, just a good strong street engine.

I've had good luck previously with a stock intake on a 215 I built which I regularly redlined at 7K and it pulled strongly all the way up. It had a good cam, 650cfm Holley, and slightly oversized equal length headers and header mufflers. If a stock 215 intake worked there it seems like a stock 300 intake should work here.

I think your concerns about the torque are misplaced. With my 340 (350cid) and 5psi of boost and a 3.54 axle ratio I have no particular difficulty with the car. True, you can light 'em up if you want to, but I don't see that as a negative thing. Sometimes it is handy to be able to break traction at the rear on demand.

I'm not going to destroke the engine, and I doubt I'll try to get any more than the stroke the 350 crank already has. A 350 in a car that weighs that little is quite good without going to a lot of extra trouble. Power/weight ratio should be better than 7:1 in any case. That's pretty good. It's a lot different game from putting it in a 3400 lb GS.

Also, cam/rod clearance is a concern any time aftermarket rods are used in these engines with the 350 crank. I had that problem with my 340 with the 7" Scat rods. I don't expect offset grinding would lessen the problem and it will be worse with a roller cam. If it hasn't been reported with the Hersch rods that leads me to suspect that longer rods are more likely to interfere with the cam lobes than short rods. This may mean that the 300 will be alright but I won't know until test fitting. The farther out on a limb you go, the more likely you'll encounter Murphy, so I plan to stay conservative.

So what makes sense to me right now is to use the 6.2" nascar rods (probably with the 2" big end) and then check with Diamond to see what they can do on a slipper skirt piston matching the pin size of the rods. Or I could go back to Venolia again or one of the other manufacturers. That makes the heads, the pistons, and the EFI the expensive parts of the build. The cost of those three items means that this build is likely to stretch out over several years time.

Jim

 

As long as you are good with all that low RPM torque you might as well get the TA Rover heads and have Dan's guy port them to flow 300 CFM on the intake side and shoot for 600 + HP! Building a max effort would kill off some of low RPM torque for the light car and still be able to spin at will!

You'll probably have to machine a bigger opening in the 300 intake's carb pad and perhaps weld a new crab pad on it for whatever throttle body you want to use? You can hollow out the bottom side of the intake and convert it to a low profile single plane, that will get the coolant out of the intake for a cooler A/F charge if you wanted to?

Here is the set of rods you can get;

https://www.ebay.com/itm/NASCAR-LENTZ-CONNECTING-RODS-6-200-x-2-x-929-x-904-wide/391540081506?ssPageName=STRK:MEBIDX:IT&_trksid=p2055119.m1438.l2649

They're a little pricey but there's a make an offer option for them and they have been for sale for a long time so they may take a couple hundo under asking? Start low, but remember you only have 3 tries and then you'll have to wait another month to try again. They do look like very nice rods though and they have the sbc wrist pin size. You would need a piston with a compression distance of 1.418" to get to zero deck using the 9.543" deck height number.

Give these pistons a .015" hair cut and ta da, you'll have 1.418" compression distance but still a bit pricey;

https://www.summitracing.com/parts/uem-kb186-020/overview/

And of coarse the Icon even more expensive pistons;

https://www.summitracing.com/parts/uem-ic834-030/overview/

Or with some altering maybe you can make these more inexpensive ones work?;

https://www.summitracing.com/search/part-type/pistons/bore-in/3-800-in/piston-style/dish-with-no-valve-reliefs/compression-distance-in/1-443-in?N=4294914196+4294859475+4294882387+4294790346&PageSize=100

Or these;

https://www.summitracing.com/search/part-type/pistons/compression-distance-in/1-430-in?N=4294859475+4294803672+4294859373+4294859615+4294790315+4294882387+4294880902+4294882379+4294880925+4294882360+4294803794&PageSize=100

I like the above ones because they are float or press fit wristpins with a choice of coated skirts or un-coated skirts. Either change the bushings in the rods or slightly enlarge the wristpin holes in the pistons. Which ever cost less, the new bushings or new wristpins?

So do you think you'll go with the TA Rover heads? Or ported '64 heads? There is 2oo + extra HP potential going with the TA fully ported heads than the fully ported '64 sbb 300 heads. Fun stuff.

 

...or poke the pistons out the top .015"

 

That's actually a really good suggestion for someone who is planning to use copper head gaskets, as they can be ordered in whatever thickness you like.

I think I'll stick with the forged pistons though. Hypers have gotten a lot better but they'll never be as good. And for a long stroke engine with a high redline the extra couple hundred is cheap insurance. I should be able to pick up a great set of forged rods for about $200 and expect to go that way. Using rods with a smaller crank pin should give extra cam clearance, another consideration worth thinking about.

But again (Derek) I am not building for max horsepower. Mildly tuned engines are just so much easier to live with on a day-to-day basis. And with the light vehicle I do not need to. Consider: this car with a 300hp 300/350 is comparable to a GS with a 500hp 455. Still plenty streetable but a great performer. To match the same GS with 700hp would require about 430hp out of the 300. Certainly possible but a bit less tame. Which sort of describes my car with the 340. I'm shooting for a target somewhere in the range between the two and it should be pretty easy to hit. Just for completeness, 700hp in the MG would be like 1130hp in the GS and I'm not going there. I'm too old to start a drag strip career and there could be no other justification.

So I think the plan is fairly well settled and there is not much more to do until I have the engine and tear it down. Maybe this summer. Thanks for all the good suggestions.

Jim

 

I'm not sure how the suggestions for cast pistons got mixed into my comments (if they did...unsure?).
I guess I was assuming forged pistons would be used and should have clarified that.
Just pointing out that sbc forged pistons are more prevalent and there's often a less intrusive solution to their use.
Anything that reduces cost by common parts are simplifies machining.

My contribution to the power level and long term use is that I've had very little issues with daily driving 1.25 hp/cube combos to an OEM life expectancy. If anyone is having issues with the way they run it's either a component or induction mismatch of sorts or the tuning skill level could use some improvement.

 

Derek's piston links were all hypers, sorry I wasn't clear about that. Other than the ICONs I haven't really seen a good inexpensive forged piston for the 305 yet.

My math was off I think. If I did it right this time, the longest rod that could be used with a 1.1875" compression height and 350 crank in a 300 block would be 6.430", and there are some 6.380" rods on ebay for about a hundred bucks a set. So compression heights between 1-3/16 and 1-1/2" are in the ballpark. Plenty of cheap forged rods are available in that range. Finding a cheap forged piston is the challenge, preferably in a slipper skirt style for reduced weight. It seems that has always been the issue, which is exactly why I have custom pistons in my 340.

I'm not saying I'd object to a 450 hp N/A 350 in an MGB... that might stand a chance against a Challenger Demon. But I'd rather be pleasantly surprised by the output than disappointed so my expectations are lower. (I'm still telling the guys I have "a little over 300hp" in my car. Pretty sure that's a bit low.) But unless you go to a roller cam the relationship of "the hotter the cam the faster the idle" is pretty much true. And I do like a nice slow idle in a daily driver. OEMs don't nerf engine power without a good reason.

Jim

 

Jim, the problem with the cheaper nascar take out rods is the wristpin size. If you get a set of rods with a .787" wristpin size there will NOT be enough material to remove to make the wristpin hole much bigger. Plus the rods with the smaller wristpin sizes a lot of the time they do NOT have bushings in them, they are heat treated in that area instead.

So the better option with those rods are to get the custom or customizable pistons, that's why I posted a link to the rods with the sbc pin size with bushings setup for 2" rod journals already for you. Do what gsjohnny said he did, message the seller and ask them if they are in love with the rods and plan on marrying them when they turn down your low bid! (LOL) You might be able to get them for $300 using that line?

Your going to have a hard time finding forged off the shelf pistons, let alone ones that will work with the lower priced take out rods with the smaller wristpin sizes. You may be able to make bushings(a lot of extra work) for the pistons you find to use the smaller wrist pins(and you'll still have to buy wristpins) but still they more than likely won't be forged ones unless you get the Icons?(and those would still need custom bushing so the smaller wristpin rods will work)

So you can get the $453.97 hyper pistons with the rods I posted a link for maybe for $300 so $753.97 and still need to buy rings. Or get the $100 rods and get the AutoTech piston and ring kit for $649 and save $3.97 PLUS the cost of a set of rings.

I wish there was magically an off the shelf forged piston set that would work with the less costly take out rods but I have yet to find them, if you do let us know. I have only look at Summit's list of pistons because their list is so easy to look pistons up. But they don't carry all the pistons made so you might get lucky from a different source.GL

 

It is certain that "cheap, forged, and 305" pistons don't all coincide together.
I bet some more looking would turn up a less expensive option, net.
Imports have some close alternatives but....also not cheap.

Circle track has more demand for this application. (nowhere else really runs them AFAIK)
A quick search pulls up this;
Icon IC957.030 Chevy 305 Forged. $575.

 

I was referring to forged pistons other than what's available for the sbc 305, like perhaps a Nissan or something like that name that Summit may not sell? Then again, cheap and Nissan don't go together and I don't think others do either? Perhaps an Australian engine's piston that Summit doesn't have listed?

But for it to be forged and cheap, it would have to be a Speed-Pro forged piston. If the block sonic checks good enough to go to a 3.875" bore there use to be sbc 283 and 307 or maybe Pontiac 350 or if you can find forged Jeep Speed-Pro pistons made but then the wristpin issue would still be there.

The 3.75" or the 3.8" piston range size isn't that popular, not very easy finding a piston for that size! A 4" bore would be a piece of cake though!

If you take the rings away from the AutoTec pistons you're looking at $500 for a set of those without the rings, buy the rings separately that comes with those and you would have to spend another $100 to $200 depending on what rings are available for the bore size and ring thickness you choose unless you want cheap cast iron "stock" replacement rings for around $50 or $60 on your performance pistons? So still $600 to $700 dollars would have to be spent because pistons don't run real well without rings!

 

Good point on the rings, I saw the info the second time through.
I looked into Subaru for a couple sbc and Ferd strokers but see they were expensive then too, but have some good features found on much more expensive slugs.
In no way was I suggesting an easy solution, just that there is some potential with so many hobby stock 305's and their convenient sizing.
Time being money, it's tough for any of us to search for parts for someone else's project.
All we can do is point the way.