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Correct compression ratio for Cam
I was reviewing some things on my 400 x.040 build I have come to the conclusion I might have made some mistakes. Not sure
pontac 406 block flat top pistons with 4 reliefs Crower 40240 cam straight up pontiac #15 heads small valve 90cc performer intake Quickfuel carb 735 cfm stock exhaust manifolds HEI 2004r with 3.73:1 = 2.55 final gear Looking at the cam information it is recomended to have 9.5:1 compression. I don't think I have that much compression probably more like 8.75. according to Wallaces charts the block and heads are rated for 290 horse engine that does not take into consideration cam and carb. Questions 1. do the heads and cam work well together? 2. what would it take to get 350 horse power from this block? The car runs OK but gas mileage is 10 mpg. If I am going to get that kind of mpg I think I'll look at more horse power. Any constructive thoughts? Thanks greg |
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https://www.summitracing.com/int/par...0240/overview/ |
Your heads flow 182 Intake cfm @ .450" lift, that's enough for 360 hp in a well tuned motor with the needed compression for the Cam its running, that being said I have not run the numbers , but I do not think your even at 9 to one comp with your set up now.
To save your combo if it lacks snap with your rear gears you might concider running a Vari duration lifter , or advancing the Cam 4 degrees. |
I couldn't find a 40240 cam. Maybe 60240. I have a similar cam, only on a 110 lsa. I had a thread on CR for that cam. Smaller cam, good cylinder filling. Was told to use not much more than 9:1 for it. I think others will say the performer intake is not ideal. A stock intake would be better but the QF will need an adapter and still not be ideal. Mine is an RPM with 750 VS. I like the power but I couldn't say if it is 350. My mpg is likely in the high teens as a guess ( my RA4 , 10:1, 4.11 gears engine got 11 mpg city driving - calculated. This one is much better.)
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Assume you mean 60240. That cam might do OK, especially in the lower rpm range. . But, a Voodoo 262 cam should get you closer to that 350hp number.
https://www.lunatipower.com/voodoo-h...8-262-268.html A '71 400 with 96cc #96 heads was rated at 300hp, with only an 067 cam. A '70 400 with 72cc #13 heads was rated at 350hp, with that same 067 cam. So, the CR does make a difference. A '69 RA3 400 with a 744 cam was rated at 366hp. Therefore, I'd guess that your 90cc heads, with a 262 Voodoo cam, should make somewhere near 350hp. Obviously, the exact specs of the build, as well as state of ignition & carb tune will help determine max hp number. Len Williams estimates aprox 385hp for this 9.25 CR 400. http://lenwilliamsautomachine.com/400_Long_Block.html Cam specs are not listed. But Rhoads lifters are on the list. Rhoads lifters can allow you to run a larger cam, but still have a decent idle, good vac, and good low rpm torque. This might help you reach that 350hp number you mentioned, but still have a very streetable cam. Some love Rhoads lifters. Some hate 'em, & badmouth 'em every chance they get. A Voodoo cam does not need Rhoads lifters. It has been posted here many times that there have been lots of guys very disappointed with an 041 clone cam, in a street 400. So, I think it is safe to say that less than 230° intake duration @ .050 lift will be better suited for a street 400. If trying to get anywhere near 350hp, I don't see any reason to use a cam smaller than an 068 clone. The 2801 Summit is similar, with more lift. Besides the 262 Voodoo I mentioned, here are a few more that might work. Howards 410021-12 https://www.summitracing.com/parts/h...w/make/pontiac Lunati 10510312 https://www.lunatipower.com/street-m...8-276-286.html Howards 410141-12 https://www.summitracing.com/parts/hrs-410141-12 Crane 283951. This cam, with Rhoads lifters, should have a broad power range, getting you to, or very near that 350hp range, but maintaining decent low rpm manners. https://www.summitracing.com/parts/c...IaAusEEALw_wcB |
What compression is what we shoot for Static or Dynamic
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From the Crower 60240 cam card.....
"4 degrees of advance have been ground into this Camshaft" . |
2004R Gear Ratios:
First- 2.74:1 Second- 1.57:1 Third- 1:1 Fourth- .67:1 3.73 rear gear x .67 = 2.499 final gear . |
Are you going to, or can you zero deck the block? IT would help with any type of a build.
I assume stock type .039 head gaskets? I get 8.6:1 with pistons .020 in hole, 8.92:1 with zero deck |
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You got a pretty deep first gear! |
Correcting the first post...
2004r with 3.73:1 = 2.55 final gear . |
Would I get any help from these heads if I put bigger valves in?
Would it be worth it to Mill these heads? What would be a good set of heads to get me to 350 hp but still have street manners? Thanks |
Is this a fresh bore, ball and ring job, etc?
What pistons? Dual exhaust? What year make and model is it in? Holley carbs are notorious for heavy fuel consumption if not tuned well or in a good state of tune. You may gain some performance and fuel economy by tweeking your dizzy and carb. Vacuum advance operational? A heavy FOOT will kill MPG in any vehicle. I'd look at the tune, cranking compression before changing out any major components. |
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It might not be the best cam for your app but, it will work fine. I ran one of those in a stock W72 400. No problems.
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In terms of your # 15 heads I know that installing a larger Exh valve will pick you up flow nicely, but I am not sure about the Intake valve.
The thing you can count on by installing larger valves is a increase in compression . For instance a easy .030" mill on the Deck ( no need to mill the Intake flange at .030" ) knocks you off 5 CCs of chamber volume and the bigger valves like 4 CCs , so right there your down to near a 80 CC chamber Every .006" milled off gets rid of 1 CC of chamber volume. If you where to mill .045" of the head I would want to see you mill that same amount off of the Intake so that all bolts back together nice & happy! If you can hold off on making a decision until the weekend, I have a # 15 casting and I will stuff in a 2.11" valve and then flow test it to see what gives for you if you like? Also since we are taking about maybe pulling your heads for a workover, I would like to know what valve springs are on them because if they can take up to .500" lift ( stock ones can't) you can add higher ratio rockers now or down the road to that Cam and pick up more over the nose duration ( will not effect idle really) and close to .040" in lift which in itself is worth atleast 10 hp . |
If you are in just under 9 to 1 compression you have the right cam. I'd make sure to modify the heads so you can add high ratio rockers. The 60240 is an awesome cam for a lower compression 400 build. Plenty of vacuum for power brakes, strong power down low and excellent street manners. If you want to add some "spice" later on it will do very well with your set-up topped with a set of 1.65 ratio rockers.......Cliff
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Always, ALWAYS, base cam choices off of static compression, NOT dynamic. Dynamic compression can be deceiving. Two cams with the same intake closing point will show the same dynamic compression, but one may be better at cylinder filling than the other[say a roller cam compared to a flat tappet cam] thus raising the dynamic compression of the engine even though the valve is still closing at the same point. Plus I have cured detonation problems in engines by advancing the cam, NOT retarding it. So the dynamic compression thing can be real deceiving, and shouldn't be used for cam determination, IMO. |
Correct.
Cam choice can certainly make or break an engine build. Case in point. Last Saturday a customer trailers his 1970 Chevelle SS 454 4 speed car here for me to custom tune. It's a very well done restoration and I restored the carb for it. The engine was "built" for it pretty much to "stock" specs from what I was told, about 10.5 to 1 compression and custom ground flat cam close to stock specs just a little "better". So from day one the engine runs poorly, and of course everyone is blaming the carb guy, so efforts via phone calls and emails are unsuccessful so I have the car brought here. It just doesn't run for chit! "Quirky" idle, doesn't like, want or need much timing, lackluster throttle response and pings unless you pull a lot of timing out of it. So I adjusted the carb some, and difficult getting the idle speed low enough, a little control with the mixture screws but it just didn't act right anyplace. So I pull the carb and all is fine and it is set up for a pretty close to stock 454 LS5 engine. So I ask the owner if he has the cam card, and he looks around some and finds it on his phone. It's a custom grind 220/224 @ .050". Well that isn't going to make the grade in this big high compression 454 and not anywhere even close to the specs of the factory cam with it's 260 something advertised seat timing. Probably more suited for a 350 build around 9 to 1 compression....IMHO. So I remove all the idle bypass air, lean up the idle system, put it back in place and it's better for idle quality and now we can slow it down to spec, but the engine is still a turd and it even pings when you crank it with only 8 degrees initial timing in it! Moral of the story, don't put 350 size cams in big 454's, or 455's if you are building a Pontiac engine. Nothing ever goes right with that deal, especially if you are trying to manage pump gas with pretty high compression on this new fuel.......Cliff |
Stock exhaust manifolds are going to choke off your power a bit after 4,000rpm.
No need for high compression or a big cam to operate at that rpm. |
I have written 3 or 4 responses and they get lost.
The motor is already built and has 1500 miles on it. I looked up the headwork reciept and it looks like they might of shimmed the springs to find the pressure for the cam. There is no mention of new springs on the reciept. So if that is the case can I check spring pressure while on the motor? Do I need special springs to run roades lifters? And I guess there needs to b work done to put 1.65 rockers on. 2 choices 1 be happy with 10 mpg and leave alone 2 Put another set of Heads on and enjoy the horse power and 10 mpg. As Always Thanks for the constructive thoughts. Greg |
"...Do I need special springs to run roades lifters?
No. But if you're not familiar with Rhoads lifters, be advised that lots of guys can't stand Rhoads lifters, because of the "ticking" sound they cause, at idle. They bleed off some cam lift & duration at idle & low rpm, then gradually restore full cam lift at aprox 3000-3500 rpm. I love 'em. LOTS of Pontiac guys hate 'em, & badmouth 'em every chance they get. Many are quick to say something like "Rhoads lifters are a crutch. Buy the right cam & you won't need Rhoads lifters". BUT, Rhoads lifters allow you to run a slightly larger cam, but still have a decent idle, enuff vac to work power brakes, & slightly more torque under 3000rpm. This produces what is called a broader power range, than the same cam would have using regular type lifters. Steep ramp cams, such as the Voodoo series usually don't need Rhoads lifters. They are also not recommended for small cams, which already have a smooth idle & plenty of brake vac. "...And I guess there needs to b work done to put 1.65 rockers on..." Yes, need to grind out some for pushrod clearance. Otherwise, some of the pushrods will bind up against the heads, since the 1.65 rockers will position the pushrods closer to the rocker studs. |
10 mpg is way off the mark for that engine/drivetrain/vehicle combo. With a small cammed 400 and OD transmission I'd expect 15-18 city and 18-20 or so on the highway. The tune just has to be WAY off the mark or a fundamental problem someplace.......Cliff
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I have been all through this engine. Timing Initial 15 mechanical 18 All in at about 3000 rpm It is using manifold vacuum New HEI, no different on points dist built for engine 735 HR Slayer quikfuel carb all cylinders are right at 160psi And the speedometer is correct Any thoughts would be appreciated. Greg |
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The card says it has 4 degrees of advance have been ground into it. Is that what you mean? Greg |
http://forums.maxperformanceinc.com/....php?p=4304819 These guys see this with the Crower cams all the time even though the cam cards claim to have advance already built in.
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Well thats a bummer. I don't think I have it in me to pull the front off of that motor.
Cliff is that your guess to? Greg |
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This motor runs 180 degrees on a 95 degree day it has snap and will turn the tires, it cruises 75 at 2300 rpm. Runs A/C and doesnt get hot. How can you tell the cam is installed wrong with out pulling the timing cover off. I think I am in denial. Thanks Sent from my iPhone using Tapatalk |
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A few hundred dollars in porting could work wonders on a set of heads. https://headsandmanifolds.wordpress....-head-porting/ |
[QUOTE=pastry_chef;6040088]Are you running the original calibration?[/QU
I recently changed the squirter because it paused a little pulling away from stop light. But every thing else is factory. I am not a fan but it takes 6-12 months to get a good quadrajet Today I changed from full manifold vacuum on vacumm advamce to ported. Thanks Greg |
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https://www.summitracing.com/int/par...0300/overview/ Not everyone is comfortable digging into a carb but I think you'd find a few MPG with a few hours tuning. I'd install headers as well. |
So I see you have been working on this a lot lately after searching your other threads.
What is unclear is what camshaft you have in it. In another thread the 60243 Crower was listed, then a 60240? In this thread. |
Going from MVA to ported isn't going to effect fuel economy assuming the ported source is correctly located. Using ported vacuum simply means that you aren't adding VA timing at idle and coasting.
I use and prefer ported vacuum for most of my engine builds because they are higher compression with well chosen cams and will not like, want or need a butt-ton of timing at idle. Most are fine with 10-14 degrees initial timing and adding another 10-15 degrees via the VA does NOTHING for them aside from making me close the throttle plates too far at idle and not as steady in and out of gear. Anyhow, the extra fuel you are consuming has to be going someplace. Assuming the distributor is getting the job done that just leaves the carburetor, and those units are not well known for being super efficient for "normal" driving. I've spent some time with a few Holley and Holley clones, there will be significant improvements waiting for you with custom tuning. You'll need to go into the metering block and air bleeds to clean it up, changing jets and PV's will be a complete waste of time/funds........IMHO........Cliff |
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60240. |
The first 400 that was in my Ventura used the Crower 60240. Used the car back then to commute back and forth to work nearly 50 miles each way. Some city, a little steady cruising at 55, quite a bit of stop/start driving. I'd average about 15-17 depending on how many full throttle blasts I did with each tank. At that time the engine had 6X heads on it and backed by a TH400, stock converter and 2.73 gears. It ran 14.0-14.20's at the track right at 99-100mph and best ever 13.78 @ 101 mph in really good air, all runs on BF Goodrich Radial T/A's.
I've used the 60240 exclusively for all the later 400's we've done topped with 5C and 6X heads. I will say that as a replacement cam for those lower compression engines there isn't a better choice out there. I've had GOBS of those engines brought here for customer tuning, a few had the Summit 2800, 280, a couple with the 068, several used the XE262 and even a few folks had RAIV cams in them....yikes!. The XE262 cammed ones were pretty much "turds" far as I'm concerned. Lackluster power and quirky idle quality tops the list of what I found with them. The 2800 actually does pretty good, the 2801 is a slug off the line but comes on decent in the mid-range and finishes pretty good. The 60240 makes right at 12" vacuum at idle, strong power from about 2000 rpms to 5000rpms, with very strong mid-range power (for one of those low compression engines). As for cam timing, like everything else with this hobby and engine building, it should be checked/degree'd when installed. Most Crower cams I've installed have required at least 2 degrees advance, the vast majority needed 4 degrees to get them where they needed to be........FWIW.......Cliff |
The mechanical advance is in at 3000 rpm and your cruising rpm is likely lower than that with the o/d trans so you may not be getting full advance.
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The OP had asked if it's worth converting his #15 castings over to 2.11" and 1.77" valve sizes and here are the results from my doing that to my # 15 castings over the week end.
Here's some things to note about the stock set up. 1) the Intake valve seat OD is only 1.876" so there is some air flow left to be found even with the stock valve size by going out to a OD of 1.945". 2) The stock Exh seat OD is 1.620" and this is way small and could be taken out to 1.645" and in doing so you could even add a small 60 degree bottom cut. 3) The issue with doing either mod will be that you will sink each valve by some .020" which will drop off some compression. Here's the stock Intake flow numbers and in the second column the numbers for the 2.11" valve with a quick 3 angle valve job ( 30/45/60 ) done to get it into the head, and the third column is the air flow gain or loss. Flow@28" with stock 30 degree seat . .050". 41.4. 42.6= +1.2 .100". 75.9. 87.5=+11.6 .200". 139. 149 =+10 .300". 173. 174.8=+1.8 .400". 180. 179.5=-.5 .450". 181.3. 181=-.3 .500" 183.8. 185.8=+2 Now here's the stock Exh flow numbers for the 1.66" valve and then for the 1.77" valve with a 60 degree bottom cut added. The column are the same as above. .050". 22.4. 26.3=+3.9 .100". 43.8 55.2=+11.4 .200". 89.9. 112.4=+22.5 .300". 120.2. 147.6=+27.4 .400". 149.5. 170=+20.5 .450". 156.4. 176=+19.6 .500". 161.3. 180=+18.6 .550". 166.6. 185=+18.4 .600". 167.2. 189=+21.8 Average flow gain with the 1.77" valve up to .550" lift is 17.8 cfm. Exh to Intake ratio now with the 2.12" / 1.77" combo up to .550" lift is 88.9% , so this set up in no way needs a duel pattern Cam if your running even half way good Headers! The added air flow from stepping up to a 2.11" valve should be worth 3 to 4 hp per cylinder. |
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I'd bet You likely need a lighter sprung vacuum can or quicker in mechanical. With lower compression it should be tolerated well. Or cut to the chase and have a tuner tune it. |
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