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Username Post: 427 BBC racing combo experts        (Topic#198237)
Vettes82 
Lurker
Posts: 7

Reg: 08-04-08
09-06-08 11:00 AM - Post#1516461    

So for the long post. I am looking for real world experience or knowledge for 427 BBC combos that work. I recently purchased a 69 camaro stricly bachhalved drag car with 29.5 x 11.5 slick and glide with brake and 8" 4500 stall converter. No issues with spinning.I will give the specs and info. I put the car on a chassis dyno 2 weeks ago and got the fuel curve and ignition dialed in. The car made a peak 450 hp at 6500 and 400 tq at 5800. The car weighs 2950 with me in it and is running 10.80's. I would expect more from the combo though.

427 mark iv 4 bolt
3.76 steel crank
6.135 h beam rods
aries pistons
solid roller 269/277 @.050 698/700 lift 108 lobe
roller rockers with girdle
merlin iron rect 320 cc heads 2.30/1.88 valves 119 chamber
2" hooker comp open headers
weiand 2" single plane open plenum intake
850 holley double pumper
dual snorkle ram air intake inlets replace headlights
msd dist, wires, coil and 6a plus box

I cannot verify the cam, pistons and compression ratio since I did not build the engine but I was told it was 12.5 to 1. My issue is that I would expect well over 500hp with this combo and that compression at the wheels. My suspicion is it is closer to 10.5 to 1.

Let me know if I am in left field or if you see issues with the combo.

 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 16106
grumpyvette
Age: 66
Loc: FLORIDA USA
Reg: 03-16-01
09-06-08 12:46 PM - Post#1516510    
    In response to Vettes82

first ID point out that 450 rear wheel hp is aproximately 530 flywheel hp,
Ive built dozens of BBC combos and getting 500hp from a 427 is not all that difficult, but the very first thing you need to do, when checking for problems is to VERIFY exactly what your currently working with, in parts and compression,ITS rather pointless to try to suggest parts changes without knowing what your currently useing, you need to know your compression ratio, cam timing and if the valves and rings are working as designed,and theres nothing mechanically wrong with the current combo,a leak down test and verifying your ignition curve, and air/fuel ratio are necessary, before you go swapping parts blindly I also would suggest that the cam may be too large in durration if the compression is as low as you suspect at 10.5:1 and the dual plane intake may be a better match to your current combo, yes IM sure theres guys screaming (DUAL PLANE.IS HE NUTS!)but on a 427 with 320cc ports, a good dual plane like the EDELBROCK RPM air gap,(sometimes with a GOOD 2" 4 hole carb spacer) tends to work very effectively up to the 6500rpm range your testing in and produce better average torque., as it tends to boost the flow speeds in those fairly large port cross sectional areas
btw whats your rear gear ratio?
fuel pressure?
carb jetting?
whats the cars header collector dia. and length?
and anything else you can tell us?
" " IF YOU CAN'T SMOKE THE TIRES FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK !"


Edited by grumpyvette on 09-06-08 01:14 PM. Reason for edit: No reason given.

 
Vettes82 
Lurker
Posts: 7

Reg: 08-04-08
09-06-08 01:24 PM - Post#1516517    
    In response to grumpyvette

The a/f ratio, jetting and timing was verified when doing the dyno tuning. The jetting is 76 front and 80 rear now. The rear was 88 and was way to fat. Again this info was verified with changes and dyno runs. The exhaust is 2" OD hooker tubes with 3.5 x 27 collector. No extensions on currently but have 3.5" x 18" extensions that I will be installing before next trip to the track. The gear is 4.56 launching at 4000rpm flashing to 4500. I know from the dyno runs that I need to go to a 5500 stall converter to get into the meat of the rpm band. At 4500 it is making 330 tq and 275 hp at wheels, at 5500 it is making 390 tq and 400 hp at wheels. That would help my 60 ft times but doesn't resolve the issue of the low numbers on the dyno. Fuel pressure is 6.5 constant using cell with sump and holley black pump with 1/2 line. I am shifting at about 6800-7000 rpm which is where the numbers stop dropping rapidly on the dyno. Unfortunately without dissasembling the motor I cannot verify the internal parts such as pistons, cam, compression. I did a compression test but without opening the carb plates or loosening the valve train and got 175 cranking psi.

 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 16106
grumpyvette
Age: 66
Loc: FLORIDA USA
Reg: 03-16-01
09-06-08 01:35 PM - Post#1516527    
    In response to Vettes82

those tq numbers tend to make me think your running lower than a true 12.5:1 static compression or the cams a bit longer in durration that ideal for the compression ratio, and like I said above I think youll be better served with a dual plane intake.
where are you located? if your close by Id be glad to help test and verify your parts sellection in the current combo.
your combo seems to be fairly well thought thru, but I suspect it could benefit from those changes
what was the total ignition timing set at? what rpm was the advance curve set to max out at?



heres some useful info

http://victorylibrary.com/mopar/cam-tech-c.htm

http://www.crower.com/misc/valve_timing_cha rt.html...

heres some differant calculators

http://www.kb-silvolite.com/calc.php?action=comp2

http://www.wallaceracing.com/dynamic-cr.php

http://www.smokemup.com/auto_math/compression _rati...

http://not2fast.wryday.com/turbo/compression/cra nk...

" " IF YOU CAN'T SMOKE THE TIRES FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK !"


Edited by grumpyvette on 09-06-08 01:52 PM. Reason for edit: No reason given.

 
fritz1990 
Senior Member
Posts: 6397
fritz1990
Age: 52
Loc: Kansas
Reg: 02-16-03
09-06-08 03:30 PM - Post#1516571    
    In response to grumpyvette

What Grumpy says, but I would do a leak down first. This would let you know what kind of shape the engine is in.

Regards, Jeff
1998 K1500 6.5 Coal burner
1965 C10 with 498 BBC AFR Heads
1964 C10 Ran 348W for 6 years, now SBC.

Corvettes owned: '74 '77 '78 L82 Silver Anniversary, 2002 LS1

Don't have a nervous come together!

http://picasaweb.google.com/fritz199090


 
Vettes82 
Lurker
Posts: 7

Reg: 08-04-08
09-06-08 05:24 PM - Post#1516617    
    In response to fritz1990

I am located in Gainesville, FL. The guy I bought the car from was built for the pinks all out here in April. The engine was just built and only made 3 runs at pinks before I got the car. The guy appeared to know what he was doing. I just think that the compression ratio he gave me does not jive with the amount of horsepower it is making. The timing is locked down at 38. We tested between 34, 36, 38, 40 and 42. It lost horsepower below 38 and only gained 1 hp above 38. So we set it at 38. I am not sure about running a dual plane. I think it would definately help in the tq department but would start chokeing around 5500 rpm. Maybe I am wrong but isn't the Weiand intake designed for 3000-7500 as well as the cam and since I am launching the car at 4500 I would be out of the designed range for the dual plane. Not to mention I will probably go to a 5500 stall converter to get into the usable power band of the engine. The cam is designed for 12-1 or more compression. That is why I keep thinking the compression is low as well. Am I wrong in thinking this motor should be in the 600 hp plus range and torque around 550 or am I just fooling myself. By the way thanks for your input.

 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 16106
grumpyvette
Age: 66
Loc: FLORIDA USA
Reg: 03-16-01
09-06-08 05:45 PM - Post#1516625    
    In response to Vettes82

the dual plane with a 2" 4 hole spacer should pull too over 6500rpm
600hp at the rear wheels may be pushing it, (expectations) but you should realistically get 500-520 rear wheel hp reasonably easily, Ive built several 13:1-13.7:1 427-454 full race engines that got to over 550 rear wheel hp with solid roller cams similar to what you posted.
btw you probably want to maximize the hp, and a 4.25" stroker in that combo with about 12.7:1 cpr with that cam would significantly boost results, and I would not swap to a 5500rpm stall converter, ID find and fix whats holding your current combo back or stroke it not try to compensate for a low cpr and too much durration in a cam
" " IF YOU CAN'T SMOKE THE TIRES FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK !"


Edited by grumpyvette on 09-06-08 05:49 PM. Reason for edit: No reason given.

 
Vettes82 
Lurker
Posts: 7

Reg: 08-04-08
09-06-08 06:38 PM - Post#1516668    
    In response to grumpyvette

So is it your opinion that my thought process is well founded and that the combo and the dyno numbers dont match what a 12.5-1 motor should be making. The numbers I stated above of 600 plus hp and 550 tq is what I was thinking the motor should make at the flywheel if the motor is truly a 12.5-1 motor. I just wanted to make sure my thought process is correct before I pull the heads and verify the compression. If the compression is low as I suspect I will have the heads and intake shaved to get my compression around 13-1. I believe there is enough meat on the merlin heads to do it providing there isn't a piston clearance issue. But lets say I get the compression to 13-1 and the cam is what I stated and I change to a dual plane intake, are you thinking that will lower the range of the rpm band by 1000 rpm making it more ideal for my 4500 stall converter. I have thought about the 4.25 stroke but I did not want to do a complete rebuild at this point. Also, I have a question about carburetors. I have been told by several people that I need a 1050 dominator carb. One of those being Patrick at pro systems carbs. I think that is a lot of carb for a 427. What do you think?

 
motorman 
Dedicated Enthusiast
Posts: 5170

Loc: south western pa.
Reg: 01-25-00
09-06-08 09:33 PM - Post#1516749    
    In response to Vettes82

find someone with a "katech whistler" to find out the CR without tearing down the engine. most race that have a CR rule have one. http://www.katechengines.com/corporate_services/wh ...
retired race engine builder,former NASCAR tech inspector. new corvettes owned 1959,1962,1963,1964,1965, 1966,1997,1999,2002,2005, 2008 plus 30+ other chevy cars and trucks along the way. 2008 corvette sold and waiting on a C-7.


Edited by motorman on 09-06-08 09:41 PM. Reason for edit: No reason given.

 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 16106
grumpyvette
Age: 66
Loc: FLORIDA USA
Reg: 03-16-01
09-07-08 07:09 AM - Post#1516904    
    In response to motorman

yes I think the cams either too large or the compressions too low for the cam, given the limited info and results ,yes I think youll be better off with a edelbrock dual plane and a 2" 4 hole spacer under the carb


a cam like this with that 427 and a dual plane would be more realistic,(based on the VERY LIMITED info and assuming the cpr is closer to the 10.5:1 you think it is
http://www.crower.com/misc/cam_spec/cam_fin der.php...

its usually smarter to build a combo to maximize the area in the torque curve in the rpm band your car opperates in rather than build only for peak hp numbers
" " IF YOU CAN'T SMOKE THE TIRES FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK !"


Edited by grumpyvette on 09-07-08 10:16 AM. Reason for edit: No reason given.

 
jimmmy57 
Contributor
Posts: 362
jimmmy57
Loc: Australia
Reg: 03-08-08
09-08-08 03:36 AM - Post#1517533    
    In response to Vettes82

Grumpy has a point about the manifold.
I put a GM performance dual plane manifold on a 600hp 468 with oval port heads and it was an improvement.
Not sure if it made more peak hp but put the 3100 pound car into the 9's
Worth a try, I reckon BB Chev's like 1050 carbs aswell
Jimmy

"I've told you a million times, , Don't exagerate"
http://www.picturetrail.com/gallery/view?uid=1087 1...


 
Vettes82 
Lurker
Posts: 7

Reg: 08-04-08
12-09-08 03:25 PM - Post#1581200    
    In response to jimmmy57

Ok Grumpy and other motor heads. I am back with more info and need some help. First of all, after more tuning I have gotten the car to run a best of 10.27 at 131 in cold dry air. With the temp in the low 60's it runs low 10.30's. I pulled the engine out to calculate compression. The bore is 4.310 with the pistons .012 in the hole and a .039 felpro gasket. The pistons are Arias part 282101 which are apparently pretty old pistons. I contacted Arias and they said the pistons are 427 closed chamber pistons and should have a dome volume of 41cc's and dome height should be .680. I measured the dome height and came up with .475. Does anyone have a spec sheet on these pistons to verify? Arias did not seem positive about the info because they had bad record keeping. I guess the pistons could have been cut by the previous owner but do not know for a fact. I measured the cc volume with the piston in the bore and came up with 90cc. I subtracted that from 112 which is what I believe the volume should be with a flat top piston. I cc'd the piston twice to verify my 90cc number as well. That only gives me a dome of 22 cc. I measured the cc of the heads and came up with 121 cc. If I plug that in I get a compression of 9.16. Is my math wrong or what? I don't see how a 9-1 motor with stock merlin heads and a 252/262 duration roller cam with 677/712 lift and a holley 850 in a 2950 pound car can run 10.30's. Someone please help me with my ignorance.

 
Hotrodrobert 
Forum Newbie
Posts: 87

Age: 67
Loc: Charlotte,NC area
Reg: 01-30-08
12-13-08 10:02 AM - Post#1584028    
    In response to Vettes82

You really need a set of pistons. The combustion chamber shape of open and closed heads is a lot.
If you want to use your pistons and will angle mill those heads at least .100", you will get quite a perfromance increase. If you do, be sure the guy doing it can mill the intake surface as well and use the thick ilntake gaskets, check clearance on the ends of the intake to the block. Be sure to check the valve to piston clearance but I think you will be good.

Edited by Hotrodrobert on 12-13-08 10:04 AM. Reason for edit: more info

 
greg_moreira 
Very Senior Member
Posts: 3264

Reg: 10-06-03
12-13-08 11:54 AM - Post#1584086    
    In response to Hotrodrobert

Did you stop the pull at 6500....or did you go beyond 6500 and find that 6500 is where peak power was?

That compilation of parts points towards a good bit more than 6500. 2 inch headers, 320cc rectangles, those cam specs, only 427 inches.... I could go on!

The carb is on the small side also for the type of rpm you should be seeing.

Moving on....even if the compression is wrong, I do agree with you that the power should deliver a little better. Here is the thing though...10.80's is fairly stout. What was the MPH? Knowing the MPH along with weight will tell use more than your ET and your dyno session did. What kinda rpm were you turning at the stripe along with that MPH(as well as gear ration and rear tire height)? Those figures will tell if the rpm actually jives.

Bottom line is...if you leave the combo as is, it would benefit with compression(if your assumption is right), more carb, and surely more rpm. Even before any changes whatsoever...you need to experiment with more rpm if you trust it to hold together. Dont count out your fuel system being up to the task though once you really start leaning on it. What does the fuel system look like?

If you wanna keep those revs around 6500 to 7000....it wouldnt be hard to engineer a smarter combo thats also more mild in terms of rpm requirement.




 
Vettes82 
Lurker
Posts: 7

Reg: 08-04-08
12-13-08 07:05 PM - Post#1584317    
    In response to greg_moreira

Greg, not sure if you read the last post I made on 12/9 but the car is running much faster now. Made some minor changes to how I launch the car and I added 18" exhaust extensions which believe it or not gained 3/10's and 2 mph. I have verified the compression as well. The compression is 9.7. I hate to replace the Arias pistons since they are so nice and cost about 900 bucks but I want more compression so I ordered Ross pistons that will be 51cc and will use a sce copper .021 gasket to get my 13-1 compression. I think the cam will work much better with the higher compression. We did one dyno pull to 7500 and the others to 7000. I agree that the motor will need more carb. I am guessing that the extra compression should get me in the 9's. We will see.

 
greg_moreira 
Very Senior Member
Posts: 3264

Reg: 10-06-03
12-14-08 12:14 AM - Post#1584439    
    In response to Vettes82

Glad to hear it came around a bit! Also nice to hear that our suspicions were correct! Reguardless of the issues....it had more in it!

As far as the current compression goes...based on the way your doing your math, youve gotta factor in gasket thickness as well as gasket bore.....and leave some room for error. In other words, the dome can be more than you figured depending on all things.

I did miss your most recent post....however I was gonna speculate 10.30's as is if all was dialed in well. Guess I was fairly close!

Here is one thing I missed though....originally you said it was a 269 at .050 cam. Your most recent post says 252 at .050. Did I miss something? Or.....did you change? Also....your timeslip confirms the power you make more than the dyno. In other words...your closer to where you wanna be than the dyno told you cause thats real stout!

Lastly...LISTEN to Patrick at pro systems! He will not steer you wrong. And even if it dont work right at first, he will help until it does! I woulda figured at least a good 1000 cfm carb with the cam specs you initially reported. And even with the 252 at .050 cam....a stronger HP style holley will benefit over the 850DP.

Compression alone will not make 9's....but compression and carb and tuning and more seat time will!

 
Vettes82 
Lurker
Posts: 7

Reg: 08-04-08
12-14-08 04:06 PM - Post#1584787    
    In response to greg_moreira

Initially I reported the cam specs the guy that sold me the car gave me. After tearing it down I found that he was a little off. The last post is the correct cam specs. I did figure in gasket thickness and gasket bore in my compression calculation. The cam says it is designed for a minimum of 10.5-1 compression. I figure with a 3 point compression increase, the cam should work much better. I am guessing around a 50 hp increase from the compression. We will see.

 
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