Inliners International Forums General Discussion Blown and Injected Lumps needed for low RPM turbo motor?

Thinking about my objectives. Looking at low RPM (4500) low pressure (8psi max) motor. Will lumps make that big a difference with the motor being force fed? I can do lumps but seems like a bit of a waste for the application.

Second related question. Are the rocker stand / valve centerline angles shown in Leo's book correct? If I bother to do lumps I'll do some of the other prep work on the way by.

As always, thanks for the guidance.

That's a long lived debate right there. If you made a list of mods to do to the 6 cylinder and get the best bang for the buck, a camshaft change would likely be first, followed by increasing the valve size. The dyno tests we did a few years back showed the lumps to not really produce the increase in power for the effort and money spent versus the same head with just the bolt bosses removed, and really, at the end of the day the return in investment(HP) is what it's all about for most people. So for your forced induction app, many will say yes do it, but after seeing first hand what they give in return, I would say probably not. Remember, many racers won many records without lumps even when their competitors used them. The choice in the end is still yours. Not trying to be pro or con, just stating the results as shown from dyno testing many combinations.

As for the valve centerline info, what are you needing to know specifically....?

Which engine and what will it be used for? The dyno results I've seen start a around 2,500 rpm. For higher rpm big valves, lumps, and port work make a difference on a natural aspirated engine and I suppose on a blown all out race motor.

Almost all the information and parts discussed on this and other sites I've found lean very heavily toward race & hot street applications. I'm putting together a "truck" 292 and am not planning to remove the the bosses but rather reshape then. For low rpm there seems to be adequate volume for up around 4000 rpm. Velocity at low rpm falls off with bosses removed, lumps, and big valves. Now this is for an unblown engine. If you are stuffing the cylinders I'm not sure any of it matters for a 4500 rpm limit.

You probably wont get the full benefit of being forced induction if you leave the bolt bosses in place.

At this point I'm thinking just cleaning up the ports would be OK for my application. I will probably port the throats for 1.8 and 1.6 valves, pretty easy to drill out for bronze guides at the same time. Looking at the drawing the valve axis is tilted relative to the block face of the head, and there is a 0.5 degree difference from valve guide to rocker stand axis, pretty easy to flip and adjust to do rocker stands for screw in studs. If I was doing lumps I would set it up on a knee mill to hog out the bosses, but that whole thing is in a different axis.

And again I appreciate all the help and input! These are a little more sophisticated than my 1941 Allis Chalmers!

Yes, the rocker stud and valve guides have different angles. Machine shops use rollover fixtures that the head sits on to pickup those angles for machining....

I would also do as Beater suggested since you aren't going to remove the bolt bosses!

D13,
Lumps work at all RPM's. They also raise the velocity into the port and across the valve. You can see a restriction in the port with lumps if throwing massive boost at it. But you would need to be in the 450-500 hp area for that.

CNC You did not perform any of the Dyno tests that were done. All were done by Me and help from the local inliner guy's. You did help some with planning. Not financially either. Either way,We did test a performance cam and a head prepped with 1.94/1.6 valves, with and without lumps. The lump head had more TQ across the entire RPM range.

Have covid this week and am feeling better today.

Your right, when I say or said we, I am meaning collectively as a group, because it was a pretty large group that participated both financially and with knowledge and input.

Glad your recovering well, a lot have it in my area.

Tlowe used a sawsall to remove the bosses and my instructions from PES said to use a hammer. Removing the bosses is not high tech.


I donated to the dyno tests. It was a very interesting & productive time here. The problem for me is that by nature the dyno pulls started at near the top end of the rpm range i'm looking at for my truck engine. Nothing above 3,500 rpm is important to me nor is what it takes to get power up there or above. Idle to 2,500 & cruising at 2,000. From what I have seen & read a near stock head, in my case a 194 head, will have adequate flow and removing the bosses will will result in a loss of velocity at the lower end. I'll do some reshaping as shown in pictures Twistedsix sent. If it doesn't work I have other heads. With boost it's probably all different and I'd need expansive pistons. Other than the cam this uses parts I have laying around

Is there a link to these dyno test results?

I lost my copies when my old laptop crashed. I think tlowe still has them. He did the tests and supplied the parts tested. Some of the results have found their way into posts here.

Is any of this "dyno testing" information for sale? Is it something that can be made for sale? Maybe even to help fund the cost of operating this forum?

Here is a link to the dyno tests thread. It has everything but the final writeup. Those of up who donated got them but mine were lost in a computer wreck. I said in the thread that I was printing them. I'll have to take another look.
LINK

Sorry for driving this thread off-topic!

Thanks for the link! I found that same one last night. I also found this one:

Dyno day for a 250

I've got both of them in my watch list to pour through (there is a LOT of stuff there).

David

There also is an earlier thread about a 292 dyno session as well....

Late to the party on this one but if you are still curious, you might try to track down Leo Santucci. He had a sissal head that was lumped for a turbo application. The lumps were done in epoxy. There is a photo of that head in his book. Interestingly enough, I currently own that head. He would be the one to ask whether the lumps helped in a turbo application.

Leo is a great guy. He has helped me out a lot on my 6-71 blown 292 build. he always calls me back if I miss him. He sometimes has to reel me in a little bit. He doesn't just tell what I should do but explains to me why and gives me options.