FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: Joe-JDC on February 27, 2019, 10:38:46 PM
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We all know that if you put a camshaft in a 352 FE with 230* @ .050", it will be fairly lumpy, but in a 390, not so much, and in a 428 CJ, even less. So my question to all you math geniuses and those with engine programs, have you ever seen a correlation with the same cam in different cubic inch engines? The reason I ask is this, If I have a 302W cubic inch engine and a 383W(351 with 3.75" crank) cubic inch engine of same family, and the 383W makes 540 hp with a 248/252* @ 050", @6500 rpm, what will be the affect if I install that same camshaft with comparable heads, intake, headers, etc.? Where will the hp and tq band move to? Ideas? Joe-JDC
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I hesitate to reply because it sounds like a can of worms, but I am happy to put myself out there if it gets the discussion started. :)
From what I have seen with engines of different displacements with the same induction, the rpm change is almost directly proportional to the displacement change. It is more complicated than that, for sure. A larger engine has more ring drag and possibly heavier parts, while a smaller engine has less cylinder displacement per unit of time (at the same rpm).
So, figure the percent change in displacement and that is roughly the change in rpm. Going from a 383 to a 302 is roughly a 20% drop so the rpm will increase by roughly 20%. 6500 to 7800. It really is that simple if you look at displacement over time, which is just displacement combined with rpm.
JMO,
paulie
check out the Boss 302 and Boss 351 in this article. Same cam and essentially the same induction.
https://www.hotrod.com/articles/hrdp-1001-muscle-car-engine-shootout/
edit: also check out the Chevy 327 and 302. Basically displacement is the only change.
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Joe, I'd expect the horsepower peak to move up about 1000 rpm.
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Sounds like we need another dyno test! :)
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I've used the same parts on two different engines many times, but I don't think I've ever dropped 75 cubes before.
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O/T but I had forgotten about that old article. I drove a pal's near new 100% stock '71 351 Boss Mustang back in the day and that car was about the fastest I'd ever driven or encountered. And that was against all kinds of big block cars!
I hesitate to reply because it sounds like a can of worms, but I am happy to put myself out there if it gets the discussion started. :)
From what I have seen with engines of different displacements with the same induction, the rpm change is almost directly proportional to the displacement change. It is more complicated than that, for sure. A larger engine has more ring drag and possibly heavier parts, while a smaller engine has less cylinder displacement per unit of time (at the same rpm).
So, figure the percent change in displacement and that is roughly the change in rpm. Going from a 383 to a 302 is roughly a 20% drop so the rpm will increase by roughly 20%. 6500 to 7800. It really is that simple if you look at displacement over time, which is just displacement combined with rpm.
JMO,
paulie
check out the Boss 302 and Boss 351 in this article. Same cam and essentially the same induction.
https://www.hotrod.com/articles/hrdp-1001-muscle-car-engine-shootout/
edit: also check out the Chevy 327 and 302. Basically displacement is the only change.
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Well, I am in the process of building an engine that is in complete new territory for me. I have built many small blocks over the years, and this one is a head scratcher on camshaft selection. I have several companies that suggested camshaft specifications, but I am not happy with what is being suggested. Seems wrong, but I have been fooled in the past with what works vs what seems like it should work. If anyone has a program that can give that kind of advice, I would be glad to correspond by private messages. Thanks, Joe-JDC e-mail joe dot d dot craine@gmail.com
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Joe, shoot me an email. I'll help you out. brent@lykinsmotorsports.com
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Joe ,
I agree with Brent. The power band will raise at least 1,000 rpm and below that the power will be FAR less than with the smaller 302 cam. I ran 289's from '66 on and went from solids to rollers during that time. (there were no hydraulic rollers back then) . The Mustang I was racing back then was a stick and with the larger cam I needed more gear and more starting line rpm to go faster. Shift point rose to 8,000 as well Brent has a ton of dyno experience with cam changes . I was a poor guy and has to use the track to see if I made an improvement.
Randy
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I will say that I don't like using things like "lumpy" because dilution due to overlap doesn't really go away in a linear basis with cubes
However, I can absolutely agree that the curve shifts in some sort of pattern with displacement, it's basic airflow, although how hard it pulls on the intake changes somewhat.
I'd defer to Brent or other small block guys on the specific question, but my gut is if all is the SAME, smaller engine, slight decrease in HP but it will have to spin another maybe 800-1000 to do it in your example. However, if the heads and intake are even a little different, game's off
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Ok, here is some data for thought.
289 heads flow 170/130
302 E-7 heas 169/135
302 Boss 285/190
351W 175/135
351C 290/190ish
GT-40 302W 179/145
AFR 165 250/170
AFR 185 290/190
AFR 205 312/220
AFR 225 330/228
NEW AFR CNC 340/230
TFS TW 283/205
TFS R CNC 340/236
TFS HP 225 340/238
I could go on, but all these heads will fit on a 289-302-351W style engine. I have had them on just about every conceivable type of build over the years, and had some really strong 306W style engines with heads that flow up to 340cfm on the street. I never felt a loss of power or torque, but now I know there was a lot to be gained by using a much smaller port and higher velocity that I used to play with. The engine I am building is 302-303 cubic inches, and heads will flow only 260 cfm with 10.5 compression, and max lift of .600". Not worried about the rpm, but it will have a rod ratio of 1.94 which should rpm quite easily. Joe-JDC
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Ok, here is some data for thought.
289 heads flow 170/130
302 E-7 heas 169/135
302 Boss 285/190
351W 175/135
351C 290/190ish
GT-40 302W 179/145
AFR 165 250/170
AFR 185 290/190
AFR 205 312/220
AFR 225 330/228
NEW AFR CNC 340/230
TFS TW 283/205
TFS R CNC 340/236
TFS HP 225 340/238
I could go on, but all these heads will fit on a 289-302-351W style engine. I have had them on just about every conceivable type of build over the years, and had some really strong 306W style engines with heads that flow up to 340cfm on the street. I never felt a loss of power or torque, but now I know there was a lot to be gained by using a much smaller port and higher velocity that I used to play with. The engine I am building is 302-303 cubic inches, and heads will flow only 260 cfm with 10.5 compression, and max lift of .600". Not worried about the rpm, but it will have a rod ratio of 1.94 which should rpm quite easily. Joe-JDC
Joe, 2 questions
1 - Are you willing to share specific details on the new build?
2 - What were all the cam specs and the overall build on the 383W? I could easily plug in everything and change cid to 306 along with rod length, etc and see what happens
The electronic programs are just trending ools, they aren't great, but it's so darn easy to plug in and then cut/paste the curves
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https://steviescrazygarage.com/
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The 383W has a Comp Cams solid roller, I will have to find the cam card, but it was ~248/252 .612" lift/112 LSA. EFI in '86 Fox GT. Runs strong on street and idles fair with the 112 LSA. The question above will be non-specific about this engine, just trying to get a handle on choosing a camshaft for a much smaller engine. I have several Comp roller camshafts in hyd and solid roller for the SBF. Several Motorsports cams, also.
Joe-JDC
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It will just depend on where you want it to peak and what kind of horsepower you're wanting. There could literally be a 50° swing in duration depending on your goals.
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Everything else constant, with the same cam......200 rpm increase for every .200 change(decrease) in STROKE. Then throw in the shorter rod. I say the torque peak will go up by 600 rpm and the power will peak about 800 rpm higher.
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So all this is meaningless unless the new engine uses the same cam and induction. It ain't happening. Joe is smart enough to get a new cam to match the new combination. It is still fun to talk about.
JMO,
paulie
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Everything else constant, with the same cam......200 rpm increase for every .200 change(decrease) in STROKE. Then throw in the shorter rod. I say the torque peak will go up by 600 rpm and the power will peak about 800 rpm higher.
Ok, but the rod ratio is 1.94 not 1.67(3.75" stroke x 6.25" rod). You can get a 5.7" rod to work with a 302 3.000" stroke for 1.9 rod ratio. Joe-JDC
So if I want to keep the torque peak and horsepower peak at the same rpm, what do need to do to the camshaft specs? That is the real question.
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Joe ,
Maintaining the same rod to stroke ratio on the smaller engine will KILL the bottom and mid range power even MORE. Rod to stroke ratio affects piston speed off of TDC and back onto it. A larger engine has ( simple physics) a harder "pull" ( vacuum) on the cylinder head than a smaller CI engine. That "can" create a situation where the head is more than the cubic inches "need". A good example id the Boss 302. In stock form it has a near "ideal" 1.75 rod to stroke ratio. Those who subscribe to the :out of context" quote from Smokey Yunick (rip) that you have to use the longest rod possible in a race engine , or those that think the "dwell" time at TDC makes huge power increases are dillusional when it comes to that engine. Why? The head is as big as a 396-427-454-502 big block Chevy but is on a 302 ci short block. A short rod to stroke ratio increases the piston speed off of TDC ( but no affect on maximum piston speed) making the head think the engine is bigger ( harder "pull" , vacuum again) as the initial piston speed mimicks that of a larger engine.
The popularity of 4.250 stroke crankshafts for FEs has led to BIG torque numbers over a large RPM range because the big cubic inches have the head "bordering" on being too small. 50 years ago a 600hp "true 427ci" Tunnel port was a race only , radical engine. Now days a 482ci Tunnel port is perfectly streetable
I used the "302" Ford X cam "big " for a 302 in a 408ci 351W and it is actually mild enough to use a stock , low stall . C4 converter . In a 302 , I would have to put the trans in neutral at a stop light unless I had a 3,000 or more converter.
Sorry if I said a bunch of stuff you already knew , no intent to irritate you.
Randy
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Randy, I made a quick graph to try and understand what you were saying here. Becomes pretty clear once you put it into a picture. Figured I'd share in case some other guys find it interesting too. I ran this simulation at 6000 rpm.
(https://i.postimg.cc/8CSg4sCv/Document1.jpg) (https://postimg.cc/FYD6sr3F)
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The only place I have experienced rod ratio being a player has always been where the ports were too big to start with for the cubic inches. Most engines that I have dealt with over the years that made incredible horsepower/cubic inches had the longest rod possible to allow right at a 1.000" pin height. We have guys that have 400 cfm sbf heads that use a 6.000" rod in the 8.7/9.0/9.2 decks, and they generally run through the lights at 8200-8400 rpms. Rod length will definitely affect total timing for best results. The number one reason I use the longest rod is to reduce piston side forces on older thin cylinders. The longer rods seem to keep the rings square better and the pistons can be lighter making for an overall reduction in balance weight. JMO. I have read all the pros and cons on both, and my personal preference is the longer rod whenever economically feasible. Joe-JDC
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In a drag race scenario I agree. I have had situations on engines that turn corners where rod length made some serious differences. When the cubic inches increase and the heads are "moderate" , the long rod slows down the piston speed to allow for more valve opening and less restriction when the piston does get moving , which in turn makes more power.
The only negative to a super short piston is the lack of skirt material . Despite the lesser loading on the cylinder wall , there simply isn't mush skirt there to handle the load.
Randy
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Short answer might be 8-10 degrees @0.050" for every 50 cubic inches.
JMO,
paulie