Would this car be faster with a Performer RPM Airgap?
I have an extra Performer RPM Airgap on the shelf here and I was thinking of throwing it on the Buick. It has a Victor Jr. right now but seems to make most of its power under 6000 anyway. The only time it makes good power over 6k is with the nitrous flowing. If I could pick up some low end power that would be great for off the line. With the Victor the power band seems short. Would I be wasting my time trying this intake?
Here is the current setup:
1984 Buick Regal
Forged flat top pistons w/2 valve reliefs
Engine Quest Heads. 200cc intake runners, 64 cc chambers
Crower Solid Roller 00426S grind
ADV Duration 288/290 Lift .570 .584
Duration @ .050 250/252
108 Lobe Center
.026/.028 Valve clearance
Comp 1.5 Stainless Rockers
Victor JR intake
Holley 750 Double Pumper with Proform main body
Hooker headers, small primaries, 3" collectors
3" dual exhaust w/x-pipe, no cats, mandrel bent
700R4 Trans -built
JW Custom 4000 Stall 10" w/full size lockup plate.
Car weighs 3390 lbs
150 hp nitrous for special occasions
Watch this, very good info.
Does the 4000 stall converter actually stall at 4000 rpm??
If it does I would think the RPM wouldn't help you at all, the big claim to fame with dual plane intakes is the power they make below the torque peak is greater than a single plane, but if you are launching at 4000 rpm you are only roughly 500 rpm from peak torque already,...and soon past that just as soon as the car moves 20 feet.
I'd be looking somewhere else than the intake, it should pull right up to the 6800 rpm area and still pulling hard with no problem. Should have a power peak around 6500-6600 rpm, with a likely best shift point of 6800-7000 rpm. if it dies off before that something is holding it back
Have you tried a 1" or 2" spacer on the Vic Jr?? They tend to like one.
Full length headers in at least 1-5/8" primary size, and not shorty's??
You sure the fuel system is up to the task?? Ever checked full pressure at WOT high rpm in high gear??
The converter does flash pretty close to 4k and they are full length headers. I datalog my fuel pressure and a/f ratio and they are always dead on. The nitrous side does have it's own fuel pump as well. I have a 1/2" spacer on it right now(nitrous plate), but I could add more. I really thought this cam would scream past 7k, but it just doesn't. I called Crower and their only suggestion was a bigger cam. Overall it runs flawlessly, it just doesn't make the power where I expected it. I've ran it with different carbs, open exhaust, etc and it always runs the same.
What is the spec's on the valvespring you are using??
What size air cleaner??
What ignition?? Timing spec's??
Have you tried tightening up the lash .006-.008" tighter to see how it reacts??
The valvetrain is all matched crower stuff. Below is the cam card. With all the problems of solid rollers going flat I've been afraid of changing the valve lash from the cam card spec. The air cleaner is the typical 14x3" K&N. Ignition is a MSD Pro-Billet HEI with a 6AL box. Timing is 20 degrees initial plus 16 degrees advance.
Part Number/Work Order Number 00426
Engine Application 262-400 CHEVY
Grind Number 288R
ADVERTISED CAMSHAFT SPECIFICATIONS:
INTAKE: Duration: 288º Lift: .570 Clearance Hot: .026
EXHAUST: Duration: 290º Lift: .584 Clearance Hot: .028
The specifications listed above are based on a rockerarm ratio of 1.50 IN
RECOMMENDED VALVE SPRING INFORMATION:
Part # 36390-3 Single Dual X Triple
Approximate spring pressure: valve closed: 115/125 LBS.
valve open: 340/350 LBS.
I use Crower also, have for a long time.
Something just doesn't seem right when I look your cam and spring up in their catalog. When I search on their web site for your cam card, I get the info you posted, as far as cam specs, and spring specs and part #.
When I look in the Master Catalog, the spring listed on your cam card seems to not exist, no springs with a number even close to that. Now, there is a 68390X3(a similar #) which may be a newer # for the same spring, and it's listed specs match what your cam card says,... but this spring is not listed for use with the roller cam you have, it is a solid flat tappet spring, and the specs reflect that.
I looked up their solid roller cams for 2 pages up and down from what you have...and ALL of them take more spring than what your cam card says...leading me to believe the cam card is a mistake or misprint or mis-filed info on their site. Every one of the Catalogued solid rollers they have (including yours)for an SBC is listed as using one of three springs, all of which are 50+ lbs seat pressure and 100+ lbs open pressure higher than what your cam card says.
When you posted up the cam and spring info, this is the same as the first thing I thought...That 125 lb seat/350 lb open is a solid flat tappet spec, and way too low for a solid roller...makes me think "no wonder it won't rpm". That is the same spec as the spring I used on 3 different Solid flats , #00322, 00350, and 00356; one in a 383 and two in a 400SBC(in fact these are listed to use the 68390X3 spring...tell you anything?!).
Springs listed for their SBC solid rollers are #68385X2 at 187 lb seat/445 lb open, #68705 at 185 lb seat/511 lb open, and #68804 at 235 lb seat/582 lb open(high rpm spring)....and the first two are right in line with where iIthink you should be using before I even looked them up. My initial thought was 190-210 lb seat/500-550 lb open would be correct, and it is what I am using in several roller engines(except I use PSI Max-Life rem-process polished springs).
With a roller cam, you don't have to worry about the cam going flat like a flat tappet does, so you can tighten the lash without problems. Rough rule of thumb is .008-.010" tighter max, and .004" looser max, and see how the engine responds to the change - engine liking tighter indicates the need for a larger cam and liking looser means smaller cam would be better. I don't think this will tell you much with weak springs though.
I am completely convinced you don't have enough spring if the spring you listed is the spring you are using. Roller is the opposite of flat tappet...a roller cam is more easily hurt if the spring pressures are too low rather than if they are too high. Too low with a roller and the roller looses contact with the lobe going over the nose, and when it comes crashing back down to the lobe it pounds the roller wheel and needles leading to failure. Far better to slightly overspring a roller than to underspring it, underspring a solid roller is bad news.
I think you are running into valve float is why it won't rpm.
You are very observant! When my machinist saw the cam card he had said the same thing that the spring pressures seemed very low. I called Crower and they told me that the pressures listed were actually at the cam lobe and you have to figure in the rocker ratio. So if you multiply those numbers by 1.5.... We are right where we should be. I believe they list the numbers at the cam in case someone is running an extreme rocker ratio. When my machinist installed the springs he did check the pressures and said they were fine with those springs. Driving the car it just doesn't feel like enough cam to pull much past 6,000.
What is the NA ignition timing curve like, and are you positive the TDC line is accurate on the damper/tab?
For ignition I'd recommend the MSD Digital -7, yes it's damned expensive but it offers advance selection by each transmission gear ratio. The 700R4 starts with a very deep low then has a big jump to second finally ending in an overdrive. Frankly I don't see this as a drag race box as the low to second jump is too great and you don't need overdrive 4th. But working from what's there, the jump to second and up causes the engine to loose a lot of mechanical advantage, this drives a way different advance curve for those upper gears than in first. First can use a lot of advance without detonation, as the tranny upshifts mechanical advantage is lost and the tendency to detonate increases if the advance system is one rate and amount fits all gears. The D-7 gets around that problem letting you keep the engine just under the detonation limit in each gear. Right on that limit is where the max power is being developed, one step beyond first causes a huge loss of power followed by a ruined day, under that limit costs power and races. It's a fine line between success and disaster.
Compression with the cam you need has to be high, at issue here is the Dynamic Compression Ratio (DCR) this is a computed effect on the cam's closing point for the intake valve which in essence makes the stroke look shorter resulting in a loss of apparent cylinder displacement which against the compression volume lowers the Static Compression Ratio (SCR). You want to shove the DCR to about 9 to 1 with premium pump gas. This can be more like 9.3 to 9.5 with race gas over 100 octane. Here's a calculator:
http://www.kb-silvolite.com/calc.php The result of getting the DCR up will drive back on the SCR, the static may well need to be 12 to 1 or better with this cam, I haven't looked up the specs to run it myself but you need to get your timing card and go through the math drill.
The victor is a mighty good manifold for what you're doing, the short upper rev range is as much the cam, compression, and timing as it is the manifold. This is a bear to hear, but the intake manifold is very much a tuning tool. It's not uncommon to keep several designs and a selection of spacers in your tool box.
If you have to compromise around the detonation limit, its less expensive to power output to give a little on compression than to back off the timing, keeping in mind that this limit is different in different gears.
For a transmission I think a built TH350 or 400 would be better, this would probably result in a change to a steeper rear ratio, but final drive ratio's are just another expensive tuning tool where you have to play around to find the best solution, but at 3400 pounds the Buick is pretty porky, so some stiff gears are in order to get this thing launched. You also want to hit the traps about the peak power RPM and be able to wind through that in those final 100 feet without the engine power flopping over too much.
125 lbs on the seat and 350 lbs open is too weak for a 6000 + RPM engine.
Crower may have screwed up on the cam card, but my machinist did check the pressures and they were good for a solid roller- regardless of what goofy numbers the card says. I had ordered everything directly from Crower per their recommendations. I will have to check what part number springs they actually sent just for the heck of it. If I was floating valves I would expect to be able to hear some change in the engine, but in reality it runs flawlessy at high rpm. If I was floating valves I also think it would have grenaded by now :thumbup: I have driven this car a lot.
Posting your actual spring spec's would help end some confusion.
I agree the "pressure at cam lobe" info is bogus. Besides, when figured through the rocker ratio to get spring pressure at the lobe it would be higher at the lobe than it is at the valve.
Even Crower lists this cam as 3000-7000 rpm powerband, 7500 rpm max, for 350-400 cubic inch engines....so something is holding it back. May not be the springs, but there is definitely something. For comparison I looked through all of Comp Cams grinds within a few degrees of the same and near same lifts -street, drag, oval...and all have the same powerbands as your Crower.
I came up with very near 11-1 compression(10.8 to 11.1) based off 383 cube, flat top 2 valve relief piston, and 64cc head and depending on piston to head clearance.
Not slammin' on you, just something isn't quite right, it should rpm and make power to 7000 without problem. It has piqued my interest.
I do appreciate all the help! To clear things up I am going to recheck the springs at the machine shop on Saturday. I am also going to try to dyno the car this week as well so I can see the power drop off on paper. I called and emailed Crower today about the cam card discrepancy and they haven't got back to me yet. I do believe that something isn't right as well....
Static compression is 10.8 and DCR is 8.5. The ignition is a MSD Pro-Billet HEI and a 6AL box. I think it should be enough spark for over 7k rpm. Best 1/4 mile has been 12.6@107. I ran this car with 3.73's and 4.56's before settling on the 4.11 gears. 1/4 mile times were almost the same, but I like the 4.11's the best on the street. I'm not against milling the heads to get more compression if needed. I'm running an o-ringed block so I can't go any thinner on my head gasket which is a .041". I do run 100 octane unleaded most of the time.
|All times are GMT -6. The time now is 10:48 PM.|
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.