KRE head swap dyno results
 

Another attempt to get some solid swap numbers went to the wayside. The dyno showed 452 RWHP at 5650 RPM. But the rpms and power was jumping all over the place. After making various adjustements and 8 attempted pulls we called it quits. As soon as the secondaries opened things went goofy.
The consensus is my torque converter can't hold the power against the dyno and was slipping intermitently.
The only other parts that changed besides heads was new push rods. Timing and Q Jet rods were different.
These numbers show a 77 RWHP increase from a well ported 6X-4 head to the 310 CNC 74CC KRE D Ports dynoed on the same machine.
I wanted to swap to 1.65 rockers and see results but things just weren't working right. I have another cam to swap to this winter and am looking to still be on target for 500+ RWHP to start next season.

Hmmm, exciting and disappointing at the same time! What convertor are you running (assume a conti 10'')?

Yeah Continental 10". I have emailed them to see if it's normal for a power change of 100+ HP could do this since it was made for less power.

nice numbers ron!!! I am sure they will come up even more next year with the cam change to take full advantage of the 310 flow!

Yeah, those numbers were still with the 1.5 rockers as well.

can you post copy of your dyno printout graphs w/numbers from before to after now ?

I didn't print one from today as the needle was all over. i have the one from 2 weeks ago that we had the same problem and it showed 430. I changed rods and timing and opened the caps on the cut outs for todays pulls. I will try and post them now.

Ron H

I do not think it is your vehicle that is causing your problem. I believe that the load control on the dyno is not tuned properly and cant hold the extra load. I have run on a Mustang dyno and have seen unstable loading.
I would find a differant dyno before I would suspect your torque convertor.

FWIW,
Karguy

Yeah we tried a few things to get it to work. The dyno guy said he had a similar problem with a turbo Jag. The converter was slipping.
This is a dyno pack machine. I can't help but think it was the dyno brake not being able to hold on and was slipping causing the problems.
I can't get my scanner working hopefully I will have it by the morning.

Ron - I didn't realize you selected the 74 cc heads - what compression iron vs al.?

John

''6x heads have a 93cc chamber. KRE's are 74 cc. 9.4 to 1 to 11.1 to 1 change. 6x heads never had the crossover plugged. But I did plug the crossover on the intake.''

Brought it over from the first thread.

Ron, what's the rest of your build look like? Gotta be happy with that kind of power for sure! (Well, at least I would be)

I hate gynomometers.

I am not a huge fan of them right now either.

75 455 .030 over, Stock crank, CAT rods, SRP Pistons, U/D Solid 247/255 @ .050 110* LSA .525/.540 lift, !.5 HS roller rockers, KRE 74 cc D Ports, RPM Intake, Cliff's Q Jet, Pertronix Dist with MSD Cap and Coil and 6AL box, 2 Step , Doug's headers, Continental 10", TH400 with a kit, Ford 9" with 3.89 gears, 33 spline Moser Full Spool and Axles, 3" Pypes exhaust With Cut Outs and Race Pro Mufflers, CSR Electric water Pump, Alum Rad with Dual Fans, Centerline Auto Drags , Skinnie fronts, M/T 275/60/15 Drag Radials, QA1 Coil Overs front, Summit 3 way Adjustable rear, Calvert Racing Split Mono Leaf Springs, Slide A Links, Full interior, Full Steel except Fiberglass Hood, 8 Gal Fuel ell, Mallory 140 Fuel Pump, -8an lines, Battery In trunk, 100 Amp 1 wire Alternator.
This winter U/D 255/263 Solid 108* lSA .540/.556 cam and 1.65 rockers. Freshen bearings, rings, fill the block, maybe upgrade Rods but I think they will be OK.Add a windage tray and crank scraper, new Oil pump.
Rebuild trans and add a brake. Send in Converter to match new combo.
Completely strip car, blast, clean up rust, install Roll Bar, Paint.
Hopefully go racing in Vegas/Phoenix mid-end of March?

We have very similar combos,Im curious to see what yours dynos at with the 1.65s ,thats going to put you really close to .600 lift.

I will be if the HS 1.65 rockers are 1.72 as many have said they are. that would put me at .593 after .026 lash intake and .610 exhaust with the other cam. I really wanted to see how much more power i'd make swapping them with my current cam.

452 is good power am also interested to see what the other upgrades will do. You are running more cam that what I have now (HR288). Shame there isn't a track for you to test on also. Thanks for keeping us informed.

Tom

Actual HP...
 

Ron, I was surprised when I ran the numbers so far! Your 452 RWHP comes in at 587 FWHP! This is assuming a 23% driveline loss.

Is this correct? If so then the combo seems to be working! I'm not sure if you can make the 650HP you seek without going roller? Ron wrote... " I wanted to swap to 1.65 rockers and see results but things just weren't working right. I have another cam to swap to this winter and am looking to still be on target for 500+ RWHP to start next season." The reason I say this is 650 minus 23% is 500.5

I think it's very possible to get 600 FWHP as there are a few guys on PY getting there! Congratulations and keep up the good fight! Good luck! JD

I am calculating 18-20% loss. 510 RWHP is my goal and with 20% loss that's 612 on the engine. If it's 18% loss I would be 601.8 on the engine.
This is with an RPM intake as well.
To make more I definately would need more cam, carb and intake volume.Probably bigger headers as well.

I wish I knew....
 

I don't know for sure. But I've never heard of a driveline running an automatic tranny and 9" Ford with less than 22 25% loss. I'm not saying it's impossible just tough. As for the 18% loss I've never heard a number that low, maybe in a Jerico set up.

I'd say with the 1.65's you'll be pushing close to 600 FWHP! I'm not sure how the larger camshaft will affect the power and at what range? With your heads flowing 310 cfm doesn't that indicate power possibility up to 620 HP? Plus you said you were going to freshen the short-block this winter which should add a few HP.

I'm thinking we'll see a high 10 sec car next Spring! Running a solid 120-123 MPH! Come on Spring! JD:cool:

That is my hopes. Consistent 11.20's with a 10.99 at some point. With 5000-7000 DA 3600 lbs race weight.

Sounds like the motor liked the additional airflow over the iron heads.

the problem isn't the torque converter.

Be carefull if you go over .600 lift,the springs and retainer setup on the KRE heads are only good to .600 .

Jeff told me .610 max is safe. I won't be over that with lash. The Calc I am using is 1.72 for the HS rockers as many have suggested they are instead of the 1.65 they sell them as. With this cam I am under that. Once I do the swap i will be right there.

The engine definately likes these heads. I was out on the usual launch pad and I can run them right to 6000 and it still pulls incredibly. The 6x-4's were done by 5400, at least I ran slower ET's at the track beyond there.I am gonna swap the rockers tomorrow. No more time to wait for dyno results with the issues i have been having. Plus I have sold the 1.5's already and need to ship them out...

My HS 1.65s would usually check around 1.7-1.72.

Seems like most folks making the swap are having a signifigant improvement with the extra airflow.

We're running over .600" lift with the KRE heads. It computes out to .624" with the rockers we are using. They use Crower 68405 springs. I shimmed them a bit for the HR cam, pretty sure I added a set of .030" shims, bringing them down to about 1.670" installed height. I checked them right before installing the new cam, as they had been in service for over a year. They checked the exact same pressure(s) as a new set, so we shimmed them up and put them back in service. The HR cam may be harder on them than the old flat tappet cam at .530" lift? So far no issues.....Cliff

thats true, but thats trading power curve to higher rpm levels over cast iron heads,meaning lower rpm velocity & drivability sacrifice for a street car !

i had asked earlier for a post of dyno printout overlayed each other before & after dyno pulls ,but we don't have it yet posted.

I ordered a set of the bare ones CNC ported to 325 cfm. It is my intentions to port them a little further and use 5.230 length intake 5.215 exhaust valves. The valves will also receive a 30 degree back cut to enhance flow a little more using a 45 degree seat angle. Installed height of the springs will proberly be in the 1.950 to 2.000 range to accomodate a .700+ lift cam I will swap in later, current cam .667 lift solid roller. Its good to hear about all the success you guys are haveing with these heads, I just want to push them to the next level and see if they can perform as well as a set of High Ports. Don Jonson of DCI Motorsports will be doing the flow work on them, and Rick Gable of Gable Machine will be cutting the seats and valves. After they are done and on the car then will be a trip to the dyno for some tuning. Curently I am running a set of race ported #48's, and the car runs a strong 10.70 all day long. Maybe these heads can get me into the low 10's. I'll keep you posted heads should arrive sometime this week.

Dino- when did you place the order?

Harryk- Not necessarily as the kre d-port has the more effic chamber and I would guess better velocity than a similiar cfm e-head.

I ordered mine last thursday from Kevin at Tin Indian, he is local to me and will deliver them to my door. He sent me an Email stateing that I should have them this week. He's a good guy to deal with, he was very patiant with me as I could not make up my mind as to weather have them do the valves. I choose to do them as I wanted Manley valves, NexTek springs, titanium retainers ect... But I have some other plans for them, as I want them to flow good with velocity not just volume.

HarryK -Cliffs uses the SAME rpm range and went faster. I think he has stated several times there is no loss in streetablity in his car. 60sman (I think) went faster on his car. Ron's is pulling higher because the cam now is the limiting factor not the D ports. A 10% increase in rpm, Like going from a 3.08 to a 3.42 gear. Does that make it non streetable?? How many guys have made that gear change? If you think a 6000 is too high for a street car what new car do you drive? Even 5.3 Chevy trucks pull to 6000. Now if it jumped to 6500 or 7000 yes that's more of a change from 5500. Some of the NHRA stocker D ports spin their non ported D port motors close to 6500-7000, because of their cam not the head.

I have two cars at the house a 81 with a 400 ported iron heads small cam. My 78 with a 455 and "big" ported E heads that had a HP peak at 6200. We can hop in either and I guarantee the 455 is more streetable on the bottom end. Looking at the dyno sheet I'll bet it has more torque down low rpm than many more "streetable" cars.If it has 480 ft lbs at 2500rpm how can you say it loses streetablity??

Also depending on the iron head's porting job they could have the same cc in the port than the KRE heads. Larry Navarros have 185cc if I remeber correctly. Also the higher cfm flowing KRE heads ccs are getting pretty close to a similar flowing E head so much for the theory they will have better velocity because they are smaller.the non ported ones are 185cc advertised not the ported ones. And Cross Sectional Area is now what is considered more important than ccs for determining torque rpm peak.Pushrod area or valve throat at the short turn are gerneally those areas, Pete McCarthy even used that area as his window area to work on.

The KREs definitely have a better chamber for effeciency that an E head or an iron head.

We've had the "streetable velocity debate" alot of times, yet many folks doing direct swaps are going faster with just as good or better 60 fts so the bottom end is there. It's the whole combination,and most are liking flow over velocity if average velocity over the entire port is even better. I don't think any one has mapped port velocity to show which head has a better overall average. A better shaped bigger port coud still keep up overall velocity of a poorly shaped smaller port. The samller port may have more in a few areas but may have mor dead spaces also. Look at Vizards map of a SBC port, alot of dead area.Too much velocity can drop fuel out of suspension etc.

this is going to be interesting discussion now at least for me ,no :fencing: ok .
Ok your saying "
Cliffs uses the SAME rpm range and went faster"
i know whole lot about his combo directly from him to compare with mine and also what were discussing here.
Cliff uses smaller hyd cam 231-239@ 50 if you didn't know ,instead of 250 -260ees numbers that Ron uses and also a head that flows ONLY 268cfm NOT 310cfm ,so the smaller cam definatley gonna produce cylinder pressure than the bigger cam to do lower rpm job in smaller head!


"The KREs definitely have a better chamber for effeciency that an E head or an iron head"
yes it sounds sound idea i agree ,but thats theory, if it has been confirmed or not, i am not sure ! aple to aple

the reason i asked for dyno printout is you can clearly see that the smaller head dyno pull will demonstrate @lower rpms more power than larger heads ,i have confirmed that in my dyno pulls and real world cars worked with .
example a stage 2 ported cast iron head flows in 240cfm will be so much crispier-razor sharp bottom end over a 310 cfm head., "AGAIN only low speed part throtle drivability" .
i am not talking about 60ft times comparison at the track when you WOT punching it . i have confirmed that 310 cfm head when you nailed it WOT will produce the good 60ft &et yet driving around it suffers,and Cliff can confirm that in my case with E heads .:(

official www.pontiacdragdays.com dyno sponsor

Harry,

Good points! Better street manners which allow the use of 3.31 gears in a rather "portly" car in place of the 4.10's that some with the big port high flowing heads must use to get that "satisfactory" low speed response!

Jim Hand

Harry-

310 cfm at what lift? 310 doesn't mean he is using all 310 cfm. If 310 is at 700 and his lift is high 5's then it might only be a 290 cfm head.

Cliff should use a smaller cam than Ron as Cliff has a head that does not flow the same.

John

Harry-

310 cfm at what lift? 310 doesn't mean he is using all 310 cfm. If 310 is at 700 and his lift is high 5's then it might only be a 290 cfm head.

Cliff should use a smaller cam than Ron as Cliff has a head that does not flow the same.

John

Jim :beerchug:
in order to comply with that thought, i had to add so much artificial power to the combo and still it aint like i want .
3.73 rear gear ,700r4 trans with our fav. Conti. 10" tq, Tribal tube-Tunnel ports try-y's,Performer rpm (stock ports),Cliffs qjet w/thin base gasket no spacers.

thats true but , Skip Fix was the one who brought Cliff's combo here to compare with Rons. were kinda :bounce:ing now .

Just because you use a higher flowing head and a biiger cam doesn't mean you are losing power on the bottom. You may lose a little or you may make more, but with the correct combination it is pretty certain you will make more power in a higher rpm range. I read all of Cliff's posts for a long time and pretty much what he has always said was, he can shift at a higher rpm and not gain anything, so why turn it harder. To me that means his car has a very flat power curve that extends well above 5500, but he has no use for that power because it doesn't make the car go quicker.

I just got back from a trip in my GTO, and I can tell you that it is plenty streetable. I have been in the car for probably 10 hrs over the last two days and logged probably 500-600 miles. I have 310 cfm heads and a 242-250 hydraulic roller. I can't see why anyone needs more bottom end power than this thing has. It is a stick car so that will pretty much let you know if you are bogging it down. Anything from about 1800 rpm and up, it just goes. If it was an automatic like Cliffs and others, it would never get below that rpm I would think.

I knew some reference to my 4.10s being "race equipment" would be made making it higher rpm. That's only roughly 10% more gear than 3.73s what ALOT of "street" guys run. They are still in the car from the 400 and roller motor. The car has seen only 2 outings and 7 runs since the new motor. The 3.42 are in the garage to be put back in when I get the time, and the A/C. From the feel of the car I doubt it will suddenly become a "PIG" and have no low end off idle power. The motor makes over 410 ftlbs @ 2100rpm! To even get the dyno load to read low rpm we couldn't do full pull. It can easily haze the street tires in first or second, so the decreased torque multiplication will improve that. Do I really need more torque at 1500, especially with a convertor that goes past that quickly. Maybe if you have a TKO stick and leave in in high gear, but that's why God gave you a gear shift.I've ridden/driven in alot of different combinations(including Jim's wagon) and know the feel of bottom end and throttle response.

By the way let's look at the rest of the pump gas "race" combo that just clicked off 10.99 @ 124.5 and drives 40 miles to car shows. 0.030 455 no stroker crank or long rods. A 239/247 flat tappet hydraulic (5 degrees bigger than Jim's) Jim's is a little bigger than Cliffs, the same on Floyd Hand used for awhile.Torker II that many feel is worse than a RPM or cast iron(Shaker hood) out of the box Holley 850(Cliff runs the same or slower with a massaged one) with a 2.75x13.5 air cleaner and Shaker base. 10" Hand convertor -out of the box-same as Cliff, Jim and Floyd and many others here.Headers 3" full exhaust with mufflers and tailpipes. Ported Eheads-has to be a race car high rpm no bottom end.

You missed my point Cliff did back to back with similar cam specs and ran faster(yes I know Cliff's combo) with the BIG heads. The extra weight of the hydraulic rollers could even be a potential detriment. He's said the car is at least as responsive as before. TCSGTO in the street section ran faster with out of the box E heads over ported D ports. Several others ran faster still in streetable range. I've always contended MOST of our street/strip Pontiacs can use more airflow and still have so much bottom end torque you won't notice. I think most of these guys are showing that.

example a stage 2 ported cast iron head flows in 240cfm will be so much crispier-razor sharp bottom end over a 310 cfm head., "AGAIN only low speed part throtle drivability" . Look at the bottom end number off the Kasse motor from last years Engine Master with the HUGE Tiger heads more bottom end than my motor! Tell me that motor didn't have a crisp bottom end and it was all over by 6500.

The variables of the different port shapes, chamber shapes don't make an apples to apples on just port ccs. A 6X-4 head has a smaller diameter chamber than a 6X-8 head why they are 93cc vs 98cc. That has to affect flow into the cylnder , quench slightly differently even if the port is the exact same. A 62 head has the same shape chamber but much shallower (.200) so even different flow into the cylinder, and has a different shape port than the 6X in the intake and exhaust floor. The we have the RAIV, and HO/SD "open Chamber shape" that os totally different. We'll leave the RAV out with its different chamber not too many to comapre with. We are stil talking iron heads with many variables (enough Pete Mcarthy had numerous articles documenting) and haven't even gotten to the different port shapes or chamber shapes of a aftermarket head.

So how can we say we are just looking at larger ports? I think that is being way too simplistic. Unless Cliff throws on some ported larger KRE heads or Jim had tested his 6X before his meticulous porting to spare ccs(something not done in most commercial porting jobs) we are not just looking at ccs we have other variables at play so no way its apples to apples. And as I stated before how do we know that a smaller poorer shaped port will have better overall velocity and cylinder filling than a slightly larger better shaped port? I still have a problem believing in a RUNNING engine we don't see high velocity in a port the size many FACTORY first gen SBC use(Vortecs) with 100+ CI more to suck on them, especially with the piston speed a 4.21 or 4.25 stroke puts on the port. The same way a Superflow 600 with more motors can flow more velocity test pressure on the same hole compared to a smaller (fewer motors) 110 Superflow. It can barely pull the cfm at 10" in a moderate head compared to 28" on the big bench on a big head.

In being around some chassis dynos a loose convertor almost negates an accurate torque number. So I don't think Ron's numbers would clarify that unless he has engine dyno numbers.

Those Crower rocker numbers 1.33 break ins 72885
stainless 0.090 offset trunnions 1.8-73689, 1.75 73688, 1.7 73687
aluminum offset trunnion 1.7 72897

Skip Fix: i admire your technical talent you are demostrating here ,but some how you are missing my point ! again & again my point is as Jim Hand called it even
" Better street manners " , you mean after all this, those big heads drive around just like small cast iron heads???? NOT RACED you keep coming back with higher rpm-race WOT scale comparison.

Skip- thats the thing it is very difficult to compare.

One engine might have x% of total tqe available at Xrpm, change the heads and the overall tque might climb but the actual tqe available at the same rpm is higher

With the head change it might be a lower tqe% at the same rpm but you can't tell because the overall tque rose. So in effect the "new" combo is flat if you could compare numbers in terms of %.

Yes my car drives similar to a smaller head car. I've had now 6 different motors different CIs with various heads cams, gears and convertors in this car. Come hop in it. we can blinfold you and ride in both TAs and see which you think is sluggish.Cliff has said his car has the same street manners. It's not just the head cc that impacts it! The higher end WOT is what everyone else says the big heads are only good for.How many guys does it take to say they are still using the same rpm range-not higher and they feel no change in low end "streetable manners"? It isn't just one or two guys.

How do you describe "street manners"?? 1000-2000rpm goose. 20-40 mph part throttle acceleration how much part throttle?Idle quality-at what rpm, running power brakes, A/C?My BIGGER RAIV iron heads on a 400 with a 304/312 hydraulic ran power brakes and A/C, was that streetable? Needed more gear than a 455 so apples to oranges. Did my 409 with a huge cam and an aluminum flywheel have a good bottom end-nope not until 2500 when it turned on.

410 ft lbs at 2000 is 410 ft lbs regardless of big heads or not, the flywheel doesn't know which it is. Can street tires tell 30 ftlbs when they are already broken loose? Yes maybe if we are towing a boat and need that greater low end from a dead stop idle to 2500, but guess how GM does that in their trucks- bigger motor with bigger heads! And how big are GM 454 heads?? The smallest oval ports are 280-290 cc for their truck torque motors!What were they thinking? Most of us aren't building truck pull motors-but even those are usually blown and on different fuel! We drive cars that go from idle to 5500-6000, and I'll bet little time is spent at 1200rpm.

The high end guys are seeing all the different variables besides ccs and using wet flow benches. They are seeing same size ports same dry flow cfm showing totally different wet flow patterns. And what we are ASSUMING with the theoretical better velocity on a smaller port is better air AND fuel filling cylinders. Yet chambers, port shape, port surface,swirl, tumble, boundry layers all affect that even on similar heads. That's why they use the wet flow to optimize the whole package.

Ponjohn you are right there are still variables, looking at average torque as well as peak or numbers at different rpm. But less variables using the same exact head type. Still look at Kaase's average torque!

for myself, street manners are the ability to start and idle on it's own in wintertime, get double digit gas mileage, run power brakes, not overheat in traffic.
most importantly, i like low end pull - if i can't drive around at 1200 rpm in traffic in top gear i won't be happy.
and that's where small heads will beat big heads - part throttle response under load; peak torque doesn't matter much if you're at 1/8 throttle chugging along.
however, this is not something you will ever see on dynos, cause most can't pull a torque motor down that low, and nobody tests part throttle on engine dynos anyway.
it's also hugely more relevant - like day and night - with stick cars vs automatics, because as noted above, torque converters cover a whole mess of bad behavior.

WOW - in winter?

You have a much wider set of "street" guidelines than I do. My car never sees rain let alone be driven in the winter. With no choke, headers and full 3" exhaust it takes a fair amount of time for it to warm up unless I let it heat soak.

I want, no detonation, not overheat and not to loadup while idleing. No power accessories on my car so a big nasty idle is ok.

I also run 4.10 gears so am I out of the street category? (prob go down to 3.73's over the winter)

John

speedshopmike, you are just off base if you think you can't do that with 300+ cfm heads. I have been driving mine around all weekend here in Kentucky and TN, with 310KREs and I fired it up on Sunday morning with a big thick frost on it and it idled fine in about 30 seconds, and I don't even have a place for a choke. (Proform body) I have cruised my car all summer hard and been stopped in traffic for hours in cruises in 90 degree+ and it sits at no more than 190. I logged almost 17 miles per gallon yesterday on the 3 hr trip home, and I can smoke the tires (295/45/18 Nittos) in second gear by just pushing the gas at 1500 rpm.

I have alot more torque than my 389s and 400s ever had with any cam grind from stock to RA IV and heads from stock to moderately ported. The bottom line is, for the street, there is no replacement for displacement. Cubic inches rule.

Harry, don't forget that with the swap i went from 9.4 to 1 with the 6x heads to 11.1 to 1 with the KRE heads. This has given me power all the way through the range. The throttle is as crispor better but I am making a bunch more torque and way more HP with these heads.
I was a bit lean with heavy part throttle and WOT. I switched to a 77 jet from a 75 jet on the primary side. I went to a .037 rod on the secondary from a .043. It is a bit fat on the light cruise with the APT all the way down but it still seems a bit lean heavy throttle and WOT I am around 13.5 to 14 A/F ratio on my Edelbrock monitor.
I did the rocker swap and it has more power above 3000 rpm for sure. I still need to tune and I detonated above 5000 yesterday and seem a bit lean still. Timing is around 30* total. I need to mark my balancer better and check it again. I don't think the MSD is helping much. I need more fuel again since swapping rockers? Plus the air is alot better now. Once next spring and summer comes around ecverything will change again.
I don't think the throttle is as crisp now after the swap. But I am fatter now cruising with the jet swap. And I still need to tune it some more to the new conditions. I think the more lift was wanted by the heads etc. My air cleaner isn't helping me.
I port matched my RPM intake to the 2.3" height and it was at the 1.18 width already. I blended it back over an inch.
I think I need to go to a single plane intake. I run 3.90 gears so a bit of torque loss will have no effect on my combo. I can't get any traction on the street anyway if i try to launch the car.
I attached a copy of the dyno sheets. they are crude. The KRE head one doesn't show much. The dyno was screwibng up. He had to ease the thriottle all the way to 5000 rpm and then punch it from there. The RPMS were jumping all over the place.
The last pulls we didn't bother printing as it was worse. Though on 1 pull it showed the 452 HP peak the lines were squiggly and actually wne tbackwards and in circles,lol.
I am going to try a different dyno for the hell of it but again I have now swapped the rockers. I don't think they made as much difference as I thought they would. But I haven't finished tuning it yet.

OK guys something I have brought up in previous discussions but no one has ever addressed or refuted- the factory did the apples to apples for us in 71-74 with 455s!

They had D port 455s and HO/SD 455s. The D ports averaged around 150ish ccs the round ports close to 180ish. They were similar compression,similar cams(unlike the RAIV 400s vs D port 400s) and iron vs iron. The round ports flowed more air(tested too many stock ones and D ports) and the increased (almost 30cc) port size did NOT turn them into high rpm race motors. They made more hp and had similar torque curves,look at the factory numbers. So how can that be possible if adding 30cc makes the motor a non streetable pig with no velocity? What's the answer guys-look at the factory specs. Airflow over loss of velocity wins out here too.

How about you fairly stock HO drivers is it a high rpm race motor with those giant heads? It's go no bottom end right??

Yea John those 4.10s make you a race car.But I do agree they are a pain on the freeway,why I'm looking at the 3.42s again.