Inliners International Forums General Discussion Engines To Lump or Not To Lump

Hi, another question from my visit with Jim at the machine shop.

As a backdrop, I'm looking for nice performance gain but no plans to race. I'd been planning on a lump-port head, because it seems the thing to do.

Jim thinks that a street machine with headers could use popping up valves one size is all that I need and that I don't need to go the path of lump porting. I don't recall now if he said intake or exhaust or both, but he said something like going from 172 to 182 but not 192. Other guys who work on a variety of older Chevy's, including the president of the local Camaro club, dislike modifications and believe that messing with original is either not necessary or asking for trouble. I think experience shows modifications work out fine if done right.

Jim also prefers to use studs in the engine with bolts to allow for higher torque reducing the risk of head warpage. Thinking about this after the fact, perhaps the studs change to a finer pitch on the nuts to allow tighter torqueing.

Of course, lumps are incompatible with stud bolts.

Since it's time to put up or shut up, what are your thoughts?

Is this a silly question to ask in this forum where everybody lump ports? Should I take this as a hint?

Thanks!
Mark

Hey shaw if you go up in valve size i would lump port it gives you a much better short side radius and really helps the air enter the cylinders

My head had some custome devided ports started out with lumps now i'm turboed so the air it just getting forced in there! But i ran arp studs in every hole except the three intake ports where the cM screws are its not so much the torque but the clamping for a stud has and yes the studs are fine thread on the side that doesnot enter the block

Fir streetability i would lump it ormaybe do that wing rhing thet do in stuchis book

1) Don't listen to that guy who says stay stock. He probably doesn't own a 250.

2) Lump it, baby! It's a mechanical means to increase flow. I see no downside. In fact I'm surprised the factory never copied the idea and made it standard considering the anemic flow of our heads.

People who say the lump ports are a waist of time need to go back to 1st grade and be fired from their job. Anyone can easily see how it makes a difference...just by looking at a stock vs with lump port picture....I mean c'mon! lol Even my machinist had enough brains to see the difference before he even saw it! Lump port that head and put some bigger valves in!!! If your not gonna overbore the engine or raise the compression I'd go no further than 1.86 for the intake valve and even leave the exhaust stock. Have the head shaved a bit for sure for a compression boost.

Alrighty, Lowboygmc, GBauer, TJ's Chevy, thanks for the vote of confidence in sticking with the plan.

The one person who really gave me pause is the president of the NWCC, has an original 230 even with the Rochester carb and powerglide transmission. (It took him a handful of Rochesters to find one that worked well) He races and is usually on the podium with that. Hard to believe that with my worn out engine. There were >100 cars at the All Camaro show. Three were L6's. One was the above, another a stock 250. It seems that if you keep the L6, there's a strong feeling around keeping it stock with stock carb, intake, exhaust. Me, I was teetering on the edge of a V8. These modifications are close enough to stock for me. I think the "keep it stock" sentiment is really the feedback I'm getting.

My other friend with a 250 w/ Holly/Clifford intake/headers runs pretty well. It's good enough, so I'm not likely to go too crazy on the rebuild.

It's time to start buying material. I'll start a complete build thread maybe this weekend.

Thanks again,
Mark

Have fun can't wai. To see how it turns out i recoment getti g leos book on inlines a crap ton of great info for stock and heavly moded engines

You're following a well worn path.

For the purist in you, it would be possible to build the engine to run really well and keep the stock look.
Cam, headwork and better compression to start.

Rework a stock intake and exh manifold, use a 292 carb.
I bet a 250 built this way could hit 225 hp and 250-275 tq.

It could be a real sleeper 6 cylinder.

For my 2 cents, order of importance.

Lump Ports
Aussie Intake W/ Holley 2 Barrel
1.800 intake 1.600 exhaust valves
Good exhaust
Flat Top pistons
Cut head for compression
Better Cam
Correct Converter (if automatic)

Stop any were down the line. But don't go stock it's a waste of money.

X2 pretty much!

MBHD

Thanks everyone for your suggestions. Yeah, I've got that book on order from Amazon! Now that the most basic research and decisions are done, it's time to start the build. So I started a different thread.

Mark

I totally agree with Tom. A lot of things could be done and keep the "stock" look. No one can see a lump ported, big valve milled head. If the cam isn't too wild, that can't be noticed either. Anyone passing by at a car show measure the carb Venturi? I think not. You MIGHT get away with a 292 manifold for the exhaust and still fool most people. Of course a 4bbl is a dead giveaway,just like headers. Some 230s and 250s have the same block casting numbers. 20 extra cubes would help too. Jay 6155

You can see the missing head bolts if lumped. I suppose you could create three plugs with hex heads that look like stock head bolts.

You can bolt in some upper lumps & turn down a head bolt to attach to a upper lump.

I made a stepped aluminum fitting, but you can use just a turned down head bolt instead.