18 degree Head 434 SBC Combinations

[Wolfplace]

Hi Jason,
Haven't done any big inch 18deg stuff but it does seem way down from the numbers
Got a 332" 18 deg one that was over 670 at about 8600. Don't remember the torque but I have the numbers on the computer & you have probably seen some of the crate engine numbers I've posted off my dyno just for comparisons sake a few times.
So,,, these are probably pretty conservative compared to some numbers you will see

[steelcomp]

Jason,
I just posted up a build that a friend of mine's doing...similar to yours, but 440ci, and with the 227 AFR's. Don't know his cam specs, but hoping to draw some attention here. I'm looking for some of the same info.
For what it's worth, I agree with fatman about the springs...they seem a little light for what you have.

[pont2000]

Jason,
I've gone over all your numbers,,,,,,I might be wrong, I don't think you
have enough air for that min csa at the pushrod.
Depending on how good the manifold is I guess a loss of around 10%.
That is around 311 cfm at your lift at 75* ATDC.
Not enough velocity and low VE.
The motor tried to make max power at 620fps about 6600rpm, only had
around 558fps enough for 5900rpm.
This is a big motor, lotsa stroke big friction and windage issues.
Must flow intakes with the manifolds.
Don't open up the p/rod pinch.

dumb aussie

[jdperform]

I built a 4.00 x 4.125 18deg brodix block motor 4 years ago. Alky injection with 1- 5 1/2 butterfly set up on top of a bowtie manifold similar to a toilet but a little bigger. 5 stage pump .780 & .730 at the valve. 15.8 cr. Ex Craftsman truck heads. Motor made 830 / 665. 2600 lb car runs 1/8 5.45 / 5.52. 1/4 sometimes 8.55 or so 160 to 164mph. The heads seem to run out of air above 7500 or so. I am going to put a smaller cam in it to get the torque up a little and see what happens. I don't know about the csa I do to many motors to spend that kinda time. Thats why I pay the head porters to figure it out. I got a good price on these heads thats why I used them.

[358T]

Below are a couple of engines that I can't give you any dyno numbers from but can give the ET's, mph's and weights. You could guestimate power from that.

Combo#1 This engine powered a 1625lb dragster to a best of 7.95 at 165mph in 400ft air
-4.125 bore
-3.875 stroke
-6" steel rod
-Brodix 18XSP (out of the box)
-Brodix port matched intake
-2" headers ( 30" primary, 3.5x10 collector)
-Comp Roller Cam 308/313, 275/280, .701/.701 108LSA
-1.6 rockers
-13.8 CR
-Alky injected
-Wet sump oiling and no vacuum



Combo#2 This engine has powered a 1730lb dragster to a best of 7.85 at 170.5mph in 1100ft air. Would run high 7.7's at 171 if in air below 300ft.
-4.125 bore
-4.00 stroke
-6" steel rod
-Brodix -12P SP heads (ported) ~2.65mcsa (these are 15* heads)
-Brodix Intake (port matched)
-2" headers ( 30" primary, 3.5x10 collector)
-Comp Roller cam 312/325, 279/286, .704/.660 108lsa
-1.55 rockers
-14.3cr
-Alky injected
-Wet sump oiling and no vacuum


Both of these engines are shifted at 7200 and are geared, convertered and tired to cross the 1/4 stripe at 7100rpm.

Scott

[Fatman]

Jason,
I've gone over all your numbers,,,,,,I might be wrong, I don't think you
have enough air for that min csa at the pushrod.
Depending on how good the manifold is I guess a loss of around 10%.
That is around 311 cfm at your lift at 75* ATDC.
Not enough velocity and low VE.
The motor tried to make max power at 620fps about 6600rpm, only had
around 558fps enough for 5900rpm.
This is a big motor, lotsa stroke big friction and windage issues.
Must flow intakes with the manifolds.
Don't open up the p/rod pinch.

dumb aussie

pont2000
Can you (or any one else) please explain how you came about these numbers and maybe the theory behind it all.

Thanks

[Jay Allen]

How much smaller is the cam that Jay recommended?

Its only smaller in seat time. The Lobe Area is actually CONSIDERABLY larger. The engine will have a much broader power band. Plus, one thing that the software simulaters cannot see is the benefit of cylinder pressure. Jason did not have a lot of cylinder pressure and the engine would not have accelerated very well. That has changed. Even though it is an average of 20tq and 24hp downtrack side by side it isn't even in the same ballpark. Not too mention that 24 average hp is a ton.

If you look at the lobes he had, they are aggressive, very aggressive. I feel as though the engine had so many valve train problems that the engine just parked. But I was not there. I do not really know. I was attempting to make an educated guess.

Jason, be sure to install the camshaft using the lift at TDC method.

Thanks.

[Fatman]

jay

If his lobes were very agressive, doe that make yours more agressive again, having shorter seat timing but more lobe area?

Any particular reason that you recommend lift at TDC for installation and not Intake centerline.

Thanks

[SStrokerAce]

Thats what I would think

[pont2000]

I'm new to this forum, browsing for some time and doing heads and engines for 25 years.
The condition where a motor stops making power with to much velocity in the inlet port of a NA engine is quite true, between 620 and 690 fps in the running engine, Larry, Darin , Alan Lockeed and others have documented this on a number of occasions.

Jason unashamedly posted the details of his chev in the hope of finding some answers. I don't claim to have all of them but I did notice some problems.

Heads flow tested on a bore plate larger than the bore in use, could be worth 8-10 cfm.
Heads flowed without the manifold in place (including spacers and carb),
production manifolds can loose up to 12% in the 350cfm range.

Min csa is about the most popular topic on this board, it's size and position
is an important part of engine performance.
I guess the best place is at the vent ring just under the seat, but for most small blocks it's to large and outside the rpm range of it's intended use or the valve train. So the push rod position is a logical place and provides a good balance of air flow and cylinder filling although generally not as powerful as at the seat ring.

Now at 75-76* atdc max piston speed, a net lift of .670'' with the manifold in place, I guestimate at 310-311cfm available to the engine.
Jason's 2.66 min csa at the push rod (from Larry's and others formular) and 2.94sq'' at the vent. seat ring gives us an average port velocity at 28''
of266fps.(not spot checked with a balanced pitot, another story)

266fps relates to around 532fps in a running motor and using the formular (B*B*S*.00353*RPM)/CA=FPS we come up with 5700 rpm.
Not enough flow(velocity) to fill the cylinder much past this point, in fact the motor made peak power at 6300, and low VE power.

The key is to get as close (in this style engine) to 620fps average velocity close to the valve at a csa relavant to where you want your peak HP to be.

So Jason try to find a sheet metal ram with to good 750 carbs and stay at 2.66sq'' with a bit more inlet lift and more ex duration(time needed on ex)and your piece will perk up quite a bit.

dumb aussie

[Jason G]

Thanks for all of the replies guys. It is greatly appreciated.

358T, Thanks for posting your combos and performance. That is the bottom line. How it gets down the track.

Pont2000, thanks for the input. I had intened to flow the entire induction system, but ran out of time. Just getting the heads to flow what they do was a task. I had to get the engine together and on the dyno prior to the arrival of a new baby. It was either get it done or miss a good part of the season. The intake is fairly heavily ported. I would be surprised if it loses 12% flow. It is possible though. Here are some before and after pictures.





While the 2.66 CSA at the pushrod pinch may be adequate in SIZE the shape showed to create issues on the flowbench. The pinch protrudes into the port significantly and is causing separation effectively reducing the actual usable CSA. At the time, I was planning on running stud mounted rockers and therefore couldn't do anything about it. When I go back into the engine at the end of the season, I plan to spend some more time on the heads and intake. There is more there.

Here is the plan:

While I would like to get this thing straightened out quickly I'm more interested on what the true cause is. Because of this, I'm only going to make one change at a time and note the effect.

1.) Install new valve springs with the current cam (~270 psi on the seat / ~ 750 psi open) and install the engine and run it on the chassis dyno to determine a baseline and re-evaluate where peak power is occuring with the new valve springs. Hopefully there will be some added power and an increased power band. Then I'll dial it in on the track to establish a baseline there. I hope to be to this point by the end of March. Waiting on my "custom" headers to come back from being modified. 5 tubes hit the chassis and have to be moved. Hopefully that won't drag out and delay things further.

2.) After the car is dialed in at the track, I will swap cams for a comparison. I have no doubt in my mind that the new cam will improve performance. 20 lb-ft/24 HP average increase is a BUNCH to pick up from a cam swap. I will go back to the chassis dyno as well as compare on track performance. For anyone looking for a more optimized cam for your combo, I highly recommend giving Jay a call. He is great to deal with and I appreciate his efforts. I wish I would have listened to some friends and given him a call from the begining. I may have been asking why did it "only" make 730 HP @ 6800 RPM instead of the 672 HP @ 6300 RPM that it did. Depending on what the track shows, I may pull the engine out of the car and put it back on the dyno next winter prior to freshen up to evaluate the apples to apples difference on the dyno.

Jay mentioned installing the cam at TDC because he has checked it on the Cam Doctor. There is no guessing where the CL of the lobe is that way.

3.) On freshen up, I will re-evaluate the heads and intake and make a few other minor changes as well.

Any other comments or recommendations are welcomed.

[steelcomp]

I'm also curious as to why the TDC installation with the cam. Having never used a CamDoctor, is that the only available reference? I know that with asymetrical lobes it's difficult to go by lobe c/l, but why not install by the event?
Thanks.

[Jay Allen]

From .050 to .200 my lobes are easy does it. His from .050 to .200 were just causing catostrphic harmonics. In terms of lobe area, a little bit of lift goes a long long way.

The lift at TDC is far more accurate and easier *IF* you know lift at TDC. If you do not know the ACTUAL lift at TDC -AND- the ACTUAL I/C you are looking for, then lift at TDC is useless. I have some software that piggy backs my Audie Pro stuff. Even if you have never done it this way and you screw up, it takes maybe 10 minutes. Plus, if the cam wasn't on a Cam Dr or an Audie system, how do you know that the cam is actually right? Thus when you use the I/C method, in reality, where is it?

[steelcomp]

From .050 to .200 my lobes are easy does it. His from .050 to .200 were just causing catostrphic harmonics. In terms of lobe area, a little bit of lift goes a long long way.

The lift at TDC is far more accurate and easier *IF* you know lift at TDC. If you do not know the ACTUAL lift at TDC -AND- the ACTUAL I/C you are looking for, then lift at TDC is useless. I have some software that piggy backs my Audie Pro stuff. Even if you have never done it this way and you screw up, it takes maybe 10 minutes. Plus, if the cam wasn't on a Cam Dr or an Audie system, how do you know that the cam is actually right? Thus when you use the I/C method, in reality, where is it?

Thanks Jay, I agree. I may have worded my question wrong...why not install by the events (not event) meaning open and closing events? I understand that the the lobe c/l is about impossible to know, since it's seldom @ max lift anymore. I understand your explaination. Thanks again.

[SStrokerAce]

From .050 to .200 my lobes are easy does it. His from .050 to .200 were just causing catostrphic harmonics. In terms of lobe area, a little bit of lift goes a long long way.

Too fat at .200".... how many times I see that as a problem. Mostly a problem when it comes to the .200" duration related to the .050" and max lift.... that .200" number can be big if you have enough lift to handle it.


Jason G,

On looking at the intake the divider wall is MURDERED in that intake. There is more area for a nice radius there, but the fact that it's now gone doesn't help much.... that and I would expect a little bit of work on the radius of each port entry would help.

Some good examples....









Bret