Inliners International Forums General Discussion Hi Performance Dyno day for a 250

Well, unless you are running a converter of say 2000+ stall ,low rear gear ratio,you won't mind the sluggish/mushy bottom end the Clifford intake will give you.

Also,, if you have stock compression,stock low stall converter,you will not like the Clifford intake anything below 2000 RPM, which by the way is most of your day to day driving RPM.

I did not mind using the Clifford intake,because I have a junk Darrel Young,3500 stall converter that could only muster up to 2800 & 4.10 rear gears w/higher than stock compression.
Don't get me wrong here,the Clifford intake is a better intake for higher RPM,just not off idle.

MBHD

I have had both but I didn't drive the clifford enough to have an opinion. I will say this, I rarely hit 3000 rpm and with a stick, I want the balls at 1000-2000 rpm. That will be 90% of my driving. And yes, I'm just an old fart.

On my stock tired 250, 3-on-the-tree Nova, 3.08 gear, the Clifford did lose some low end on the Gtech vs the 1v intake. Made up for it on top, result was just about even with the 1v. And, the stock 250 (or smaller) is the wrong place for a Clifford, so I don't think it's too bad considering that.

As for part throttle, well, once I got everything sealed, I can let the clutch out at idle - foot off the gas, and take off. True, I can't really floor it below 2000-2500 but it drives off idle just fine, just not as good on gas as the 1v.

I've not driven the Offy (like many others I can't afford both) so this is just a partial opinion, but I am encouraged by Tom's results with the big Clifford.

Speaking of those results:
I made Gonkulator predictions on the 292 before Tom ran the dyno. The dyno horsepower came in consistently lower than the Gonkulator by a few percent. I thought maybe it was exhaust restriction out of the dyno, but now wonder if it was internal friction in the 292, more than I expected/computed.

Because, Tom's first 250 dyno tests are coming in HIGHER horsepower than the Gonkulator, by about 7 percent so far. That 250 is doing really well. Maybe it is a nice loose build, maybe that chamfer in the bore is helping, maybe I was wrong in assuming any exhaust dyno restriction or something but the dyno tests are making me debate whether to build up a 250 or 292.

Thanks for the update Tom, we await more exciting news.

It would be nice if someone could run both the OffY and the Clifford. Maybe they could start another post with the results.



Duece,
When opening the 292 lower end up, the 2 middle cam bearings were mushroomed out. They are durabonds. So bad that the oil holes got covered by smooshed metal. When changing cams, they had to be forced out ( with hammer).
I am sure these bearings were costing power in 2 ways. One in frictional loses and second by allowing the cam to flex against the spring pressure of the valves. Thus causing irratic lift and duration.
The 292 was definately louder than this 250 and I am sure this was the noise. Probably would have gained 10 hp or more with the 292.

The exhaust for the dyno is a good loose design. Just last week a 400 SBC was done and produced 600 hp and 590 tq. It sounded sweet!

W/the 292 ,4.120" stroke you are dealing w/alot more harmonics I would think than the 3.52" stroke of the 250.

Harmonics absolutly kills power of the engine.

I did test both intakes & various carbs & raced against my friends dead consistant street car, it was not just a seat of the pants test.

I guess it's hard to imagine what I've been saying about these intakes "is what it is".

DeuceCoupe ,compared a Stock 1 bbl carb to a 4 bbl clifford & the results were the same,w.a Gtech,which BTW are pretty damm accurate.

The stock 1 bbl carb will actually take off better than a 4bbl & Clifford,,,imagine that.


MBHD

Was at the shop after work. Changed the 1.84 lump open chamber head to a 1.94 open chamber head. Got it all hooked up, valves ran and water in engine. Will fire it up on tues eve and see if it makes more power, it did with the 292, so am assuming the same here. Fingers are crossed.

This head has 1.94 intakes and 1.6 exh. Both are Ferrea. Using Comp cams new ultra magnum rockers, they are nice. This head has the HI-FLOW bolt in lumps installed as did the 1.84 head. Tom

I thought the 1.84 lump head is an open/big chamber head?

You can save some money & get just as good quality valve as Ferrea valves if you are interested.

MBHD

There all open chamber heads, its just a figure of speech im sure.

Yes, all the heads I am running are open chambers.
70CC chambers.
What brand valve are you reffering too?

I've never seen a Gen-3 open chamber head.

Panic, these heads are all around the 72-74cc range and were the production heads on most 250 and 292. The 194 casting heads are the smaller chambered ones and end up being in the 60cc range when big valves are added and surfaced a little bit.

Some casual video.

http://www.youtube.com/watch?v=5uVNQFkIZXc

Sorry, I meant that they're all quench (part of the chamber surface is flush with the gasket surface), and the bore isn't completely exposed at TDC. An example of a wedge chamber with inclined valves, but open chamber is the Chrysler B/RB 906 and 452.
Except for intentional smog (like these), some 2-strokes, and some hemis, closed is pretty much universal (and mandatory on sidevalves). All 4 valve and pent-roof I can thick of are closed, although the "closed" sections are really small.

Yes, they all have quench and are not like the 906 or 452 heads.

Ran the 250 tonight with the 1.94 open chambered lump head (70 CC). Made another 5 hp. Our weather is crap right now, with high humidity and changing temps. It also moved the rpm range slightly higher, now the dyno is set for 6500 rpm. Peak is now 6100-6200 rpm.
A 390 Holley will flow 420+ cfm also, It is now a limiting factor. On goes the 600 holley. Tom

Next things to try: Same cam/ head
Langdons cast iron headers
Weber intake/ carbs with headers
4 more cams
The crude turbo setup.

Thankyou to the guy's that are still contributing. Anyone missed by my emails, do not be shy. I have a sending list that just gets added to. And no it is not too late to help. This weekend will be a busy one. My email is tom@12bolt.com .

If the dyno guy offered his 650 DP, I would throw that in the mix as well.

My 65 SS Malibu V-8 350 SBC loved that 650 DP I put on it.
I know I said the "V" word sorry.

Sometimes what does not work on paper/calculations, actually works in actual testing.

Case in point, a female street racer/track car years ago had a 64 Nova SBC 350 w/a Weiand 150 size ? super charger. All the calculations ,blower books,B&M caculator, etc,said all it needed max,was a 750,which is what she was using (750 DP).
Well ,they had an 850 DP carb lying around & said ,what the heck,lets try it, well gues what,she ran 1/2 second faster in the 1/4 mile.

Morral of the story,,,think outside the box of time & time again proven recipes.

I was always told the 48 DCOE Webers were too big for my 254 L6,,,but with even that being said ,I ran them anyways,the Webers I ran w/12.1:1 compression was the fastest my 254 ever ran normally aspirated,period.

Heck, I bought the DCOEs for $200,,so I could not loose, even if they did not run good, I could always sell them for more than $200,right?

4 bbl carbs are a different story as compared to DCOEs,but w/all my trials & errors & R&D through the years,& even tried a Thermoquad 850 CFM carb,just to see how it worked on my 254.

Have you guys ever heard of anyone trying to use an 850 Thermoquad carb on a 254 CI L6?
I was young & foolish maybe,but @ least I tried many different carbs & a couple intake manifolds for the ultimate quest & search for the most power I could get out of my Chevy 250, +.030 = 254.

I think a 650 DP could be managable. Just a thought.



MBHD

In the video, the last pull seen was the 3rd of 4 pulls. After the 4th pull. The 650 DP was put on and tested, lost tq across the range and also down on Hp on top end. We did try. It almost never hurts to try.

Langdon cast headers are on and will be tested on Thurs even. Same cam and 390 carb. Tom

Yeah, I kinda was thinking it would loose torque & HP,but @ least you tried it.

I had the best luck w/ Carter AFB 400 & 500 AFB's,I even used a couple Carter AVS 625's,but it seemed a bit too much & could not get the secondaries to come in at just the right time.

When you get the side drafts on & working good,the torque increase should be a big amount.

Any guess on how much HP loss w/the cast iron headers?
I am guessing not too much if any by this engine build,but hey, I could be wrong.

MBHD

It would be interesting to see what a good QJet would do. Say one off a low HP 327. Adjust the air door rate and max open position to dial the airflow back. The stock eliminator guys make em fly...

Tom, do you think perhaps a 650 vacuum secondary would give better results??? They are in a sense "self regulating" in that the primary airflow creates the signal to open the secondaries....even though rated at 650 the end result could be 550-600 deoending upon the engines needs......based on efi's input: didn't G.M. put a q-jet on the pontiac ohc 6?.....time and expense are factors I know but it might be worth a try if you have access to either one......checked out the video; great stuff you're doing.....for years I've been running on seat of the pants feel and gut level intuition, good to see some hard data.....fats

The Pontiac Sprint 4bbl engine had factory installed spreadbore Q-jet carbs,I even pulled them off those cars from a junkyard.

I just heard they were 650 CFM Q-jets, but I did not think GM made A 650 CFM spreadbore Q-jet.

Maybe the old style squarebore Q-jets were that size?
MBHD

Hank and KS,
Yes I heard same about the Pontiac OHC-6, as I heard it those Qjets had a very stiff air valve so that where rated (std 1.5" Hg) the air valve was still partly shut, on purpose, so they did not flow the normal Qjet 750cfm but rather only 650cfm.

I've not heard of a 650cfm vac sec Holley, just a 600, then a 715cfm downleg (excellent carb) first used in 1963 on the 427 Ford.

I think the 650 Double Pumper is still a straight leg booster like the 600 Vac Sec, and the added 50cfm of air is likely not needed. To get dogleg boosters you'd have to go to a 700 double pumper or the 715 vac sec.

So if the 650dp didn't run as good, it is likely coming down to which carb the engine "likes" better. If it is happy with the 600, that is probably the one to go with.

I think you could do an entire dyno weekend just dialing in a carb to a given combo. Then, if you changed cam, intake, or headers, it would no longer be optimum. All you can do in a short weekend is have a carb that all the combos are fairly happy with and show good AFR. I don't envy Tom's rushed task, it is easier for me to sit here and type.

All the calculations ,blower books,B&M caculator, etc,said all it needed max,was a 750,which is what she was using (750 DP)

There are variables we don't know, but just a guess:
350" @ 90% VE, 6,000 peak power = 547 CFM @ 1.5" Hg vacuum.
10 psi boost at sea level (14.7 etc.) is 1.68:1 pressure ratio.
547 × 168 = 919 CFM.

The QJ air door (secondary air valve) rate can limit the total CFM on the back side if the spring is tight enough, but it also controls the secondary metering rod position (on a Holley, the diaphragm can be anywhere, and the PV still opens when you want), so if it's tight the motor gets less fuel. Not opening to 90° also creates a flow bias which will affect front vs. rear if the carb is positioned with shafts across the engine (like on a V8).
A TQ works pretty similar, but has an extra tuning headache: the air valve linkage is part of the choke linkage, and getting them both to work (on a street car) took several hours (Chrysler 360).
A 250 would have to turn pretty fast to get an improvement with a 650. Assuming 95% VE, even 7,000 RPM needs only about 529 CFM. If I were trying a 650 here, I'd run slightly smaller high speed bleeds to compensate for the lack of WOT vacuum rather than rely entirely on PVCR changes.

Ran the Langdon headers tonight. They sure quiet down the entire engine. Fit was great and sealed perfect. Tq was down as to be expected, but they held their own until the rpm got up there.

All I can say is they don't give up much to the headers and would be perfect for a reliable sealed exhaust on a peppy street build.

Taking a vac day for Fri. Webers are going on. Got my fingers crossed that all goes well. They tune much differently than I am used to. It will be interesting.

The turbo and a bunch of cam changes are set for the remainder of the day and Sat. Will save a big cam for last. Tom

Videos please. ;-)
The last one was excellent!


MBHD

Thanks, but that one was crued. Really works best when my daughter tapes, she knows how to film, nicely. Will certainly get more vids, I have lots from the 292 and more from the 250. Believe me they are getting taped in HD 1080P. I can't download from home. Used to when the movies were made with dig camera, these HD 1080 movies are giant in size compared to those. Tom

Ok , back from a long day at the shop.

Ran the 3 side draft setup. It was somewhat of a bear to fit it up. Hit the front header tube, also the header tube braces. Sanded the intake to fix that.

Engine started pretty good and idled high, had trouble getting a good idle. Ran some light pulls and found good tq readings and response. Decided idle was not so important and ran pulls to 6200 rpm. tq would hold 290+ for more Rpm than the 4 bbl did and saw the first 290+ hp #'s. Strangely the hp would drop about20-30 hp at the same place it did with Langdons Headers.
So we put the 4 bbl back on and duplicated the problem, after checking valve springs, ignition and compression it was found out the balancer was loose.

That is where the problem lies. Harmonics have got me by the tail. On Sat the motor is getting pulled and opened up for inspection. The balancer was wiggling and upon trying to pull it it wedged, so decided to wait till morning for a cold engine.

If needed, I have more cranks and can balance it for installation. Also have a good quality HP GM balancer. Still have alot of test planned and hate to quit now.

Well enough for today, just poured a big margurita and going to watch a movie with the kids. Tom

That's too bad the damper did not do it's job.

When I was using stock damper,my engine would only turn to 6000 RPM or so,but struggleing to get there also.

I did nothing else to my engine but install the 8" GM damper & man,what a difference! Smooth up to 6000+ RPM.
It wanted to rev much quicker also.

I later installed my Paxton supercharger blowing through 3 48 MM Weber DCOE's & it would want to go to 7500 RPM

I run a stock 8" HP GM damper. This damper totally smoothed out my engine & I turned to 7500 RPM w/it,not too wise w/a cast unit,but I did so anyways,because of no money @ the time.

I have heard good things & bad things w/fluid dampers.

My new engine will have a Vector damper.

Sounds like another test w/a good damper & Langdon headers .

MBHD
Previous quote" Any guess on how much HP loss w/the cast iron headers?
I am guessing not too much if any by this engine build,but hey, I could be wrong"

Sorry abut the trouble. How was the movie? Tom

Quite relaxing. Thankyou. My boy is 10 and said proudly it was rated R. So then we watched it. Cloudy with a chance of meat balls. I think his R rating was meant to be Really funny for kids.

Packing up stuff to take to the shop,
crank
balancer
bearings

Got my fingers crossed for the teardown/ inspection. Tom

What damper are you going to use now?

MBHD

He used a Fluidamper on the 292, maybe he'll stick it on there.

That was the damper that failed.

We took the engine from the stand and opened it up. Flywheel shook loose too. Bearings all look great but the crank snout is destroyed.
Had 2 spare cranks. Measured them both up, picked the better one, balanced it, polished it, cleaned it and put it in. The engine is now back on the dyno with locktighted flywheel bolts and a GM HP 8" balancer. It balely cleared the Clifford 2 peice cover. Had to remove 2 bolts from cover for it to clear. Ready to start on Mon. Tom

The only way I had goodluck from the flywheel bolts from coming loose was use red locktight,metal foldover tabs,then on top of that I used JB weld over the bolts & foldover tabs.

But all this shaking & coming loose was due to using a stock L6 damper,after I used the 8" HP GM damper,my engine totally smoothed out.

Yes ,if you use countersink screws on the clifford timing cover,it clears the damper.

MBHD

Tom was this the fluid damper off of the 292?

What is the 8" GM HP damper you guys are using? Is that a small block v8 part?

The 250 was using the fluidamper that was also used on the 292. The crank snout is toast. Will get pics. It tried to weld to the timing gear and crank snout.

The GM 8" HP balancer is a GM performance part for 350 SBC. It is used on all ZZ4 crate engines and is the same one used on the 1970 350 LT1. Had to recreate the timing tab as the 8" diameter was much larger than the old damper.

I know the V8 damper produces better results than the original (or none), but the actual tuned RPM doesn't align with the bad patches in an L6 except by coincidence.
How fast the motor turns only determines how many vibration points it will reach, not where they're located.
The factors that determine this are mostly crank length (number of cylinders in a row, number of main bearings) and stiffness (journal diameter, journal overlap, stroke length), and a SBC is much shorter with the same bore pitch, 2/3 the # of cylinders (+ 1 rod width, etc.) in a bank than a 250. This extra stiffness moves the RPM points wayyy up on the scale, which means the 250 will not reach most of them (and may not line up with any).
To actually predict how many do, I'd need the resonant frequency of a 250 crank in Hz (the 194, 215, 230 cranks will be almost identical, the 292 slightly lower).
Just a guess: if the 250 is 230 Hz, its critical points will be the 3rd at 4,600, 2-1/2nd at 5,520, and 2nd at 6,900 RPM (the others are weaker). Even a long, weak V8 crank (Buick nailhead) is over 300 Hz (up to 450); let's use 350 Hz which gives critical points with the 6th at 3,500, 3rd at 7,000 and and 2-1/2nd at 8,400 RPM (the 2nd is too high).
There is a nice match at 6,900 - 7,000 but it's the only one, and it depends on the data. The entire range from 3,000 to perhaps 6,700 has no matches.