How do you think this will run?

John

John

Active Member
I'll admit upfront that I know of using DCR to select components but didn't study it and learn it - I did ask plenty of questions online and from friends who know more than me for help choosing components.

So here's what I have for my 355 SBC build.

Comp XE274H
Brodix IK180 heads
Edelbrock Victor Jr intake
Holley 750 (vac secondaries)

The car (truck) is a 1979 2wd Blazer, TH350 tranny, 4200 lbs dry. I'm still gathering parts, these are the "rest of the plan but not at the house yet" stuff.

TCI 2400 stall convertor
Eaton posi/3.73 gears
1.6 (full roller) rockers
Hedmann 1 5/8" primary, 2.5" collector full-length headers
2.5" exhaust with some variant of the 2.5" straight-thru Magnaflow mufflers

Last but not least, a NOS 150 shot.

I plan on pulling my engine whole and saving it for another project on down the road. To complete this engine, I'm going with a shortblock from cmengines.com with forged TRW's and a requested compression ratio at 10:1.

The goal is to have a great cruise-in special and occasional driver. I *might* go to the track, depending on how brave I feel. I've never run the 1/4 mile and I'm not pouring money into this old truck just to wreck it there. But I might run it. From everything I've read, and that all the experience I have to draw on, the combo should be good for mid-12's.

Critique?
 
http://www.compcams.com/Technical/DynoS ... 10_001.asp
xe274.JPG


heres what comp cams suggests that cams power curve tends to look like, but your cylinder heads are significantly better and your 1.6:1 ratio roller rockers and other components will also tend to boost the results even BEFORE you use the 150hp nitrous, boost.
as your goal is a good street performance combo, ID say you selected most of the components very well,
the 2400rpm stall converters the only rather obvious mis-match, in my opinion, ID suggest a 2800rpm stall converter, MINIMUM if you want to maximize the power curve., and a rocker stud girdle sure won,t hurt to add rigidity to the valve train, and ID suggest installing that cam 4 degrees retarded to lower the effective dynamic cpr.
you should rather easily exceed 420 fwhp off nitrous and 550 fwhp on the giggle gas, making that a far faster than average truck for its engine size & weight

low-to-mid 12s at about 109-110mph should be attainable, on the giggle gas

obviously open headers or a 3" exhaust with an (X) pipe would be an advantage when nitrous is used and don,t forget you'll need an ignition retard controller to drop the ignition advance back about 2-3 degrees per 50 hp shot worth, of the nitrous when the nitrous is used to prevent detonation damage, from the far higher cylinder pressures

viewtopic.php?f=55&t=59&p=72&hilit=nitrous+tips#p72

http://www.msdignition.com/Products/RPM ... icles.aspx

viewtopic.php?f=70&t=2798
 
Thank you, sir. I have a few questions, naturally. ;)

First, the converter. Comp recommends 2200+ for that cam, I fudged up to 2400. You recommend 2800 and I trust your judgement. But I've never run a convertor that loose on the street. My only concern there is the converter being so loose the car is not fun to cruise. In normal driving will a 2800 stall act much different than 2400 stall?

What is the end result of installing the cam four degrees retarded and lowering the DCR? Is the DCR too high for pump gas, or ?

About the 3" exhaust, will it noticeably hurt the torque and street manners? I don't plan to spray this car much so I'd like to keep as much mid-range torque as possible.
 
I read up on DCR and used some of your charts and calculators linked. So with that cam I need a SCR 9.25 to 9.5, with 9.5 SCR I'm getting 8.0 DCR, about in the middle of the recommended range.
 
Thank you, sir. I have a few questions, naturally. ;)

First, the converter. Comp recommends 2200+ for that cam, I fudged up to 2400. You recommend 2800 and I trust your judgment. But I've never run a converter that loose on the street. My only concern there is the converter being so loose the car is not fun to cruise. In normal driving will a 2800 stall act much different than 2400 stall?

the whole object of a higher stall speed converter is to allow the engine to operate at a higher AVERAGE rpm so the car spends more time in the most efficient rpm range of the engines power band AND, to allow it to compensate some what for the longer duration cams lower off idle torque by allowing the engine to quickly ramp up to a more effective rpm range.
remember the HIGHER AVERAGE, RPM that the higher stall converter allows the engine to operate at and to increase the AVERAGE available TORQUE that's available to move the car, remember with that cam your not going to be making good off idle torque in fact till about 2400rpm youll find its not going to run and pull smoothly with a load, but with that rear gear ratio youll spend little time below 2400rpm if you drive even slightly aggressively.
why not call SEVERAL stall converter suppliers and ASK THEIR OPINIONS????

READ THESE

viewtopic.php?f=71&t=555

viewtopic.php?f=71&t=2794

viewtopic.php?f=71&t=435

viewtopic.php?f=71&t=2400

viewtopic.php?f=71&t=1715

What is the end result of installing the cam four degrees retarded and lowering the DCR? Is the DCR too high for pump gas, or ?

IT lowers the DCR , moves the whole torque curve about 200rpm higher and tends to boost the average hp slightly, keep in mind this matches the slightly higher rpm range suggested for the converter stall

About the 3" exhaust, will it noticeably hurt the torque and street manners? I don't plan to spray this car much so I'd like to keep as much mid-range torque as possible.


it will tend to reduce the back pressure and increase the noise, but in a properly designed exhaust it has very little if ANY effect on lower rpm torque
read

viewtopic.php?f=56&t=495

viewtopic.php?f=56&t=2870

viewtopic.php?f=56&t=1730

viewtopic.php?f=56&t=260

viewtopic.php?f=56&t=1166
 
I have no problem running a 3" exhaust. What do you think about primary header tube size? I can get very good headers with 14 ga tubing, 3/8" flanges, with 1 5/8" primaries (what I planned to run) but can step up to 1 3/4" primaries for the same price.

I was thinking the cam and heads would prefer 1 5/8" but I'm open to suggestions.

As far as lowering the DCR a touch, I can get my short block with 9.25:1 or 9.5:1 SCR, either would lower the DCR into the range you recommend.

I have a friend that races NHRA stockers and super stockers and has for a long time - he uses TCI converters and can make a call and get one based on my engine specs and I might even save some money.

I really appreciate the help!
 
I've been meaning to add the rear tire and keep forgetting to. I'm going to run 325/50/15 BFG drag radials - 28" tall.

Thanks.
 
John said:
I have no problem running a 3" exhaust. What do you think about primary header tube size? I can get very good headers with 14 ga tubing, 3/8" flanges, with 1 5/8" primaries (what I planned to run) but can step up to 1 3/4" primaries for the same price.

I was thinking the cam and heads would prefer 1 5/8" but I'm open to suggestions.

As far as lowering the DCR a touch, I can get my short block with 9.25:1 or 9.5:1 SCR, either would lower the DCR into the range you recommend.

I have a friend that races NHRA stockers and super stockers and has for a long time - he uses TCI converters and can make a call and get one based on my engine specs and I might even save some money.

I really appreciate the help!
Click to expand...


youll be better off with the 1 5/8" for daily use,as they should produce a bit more low and mid rpm tq, when you run nitrous the smaller headers may be a slight restriction, but you'll run nitrous maybe 1% of the time a best.
the 9.5:1 cpr will be a better match to that cam and pump gas,
the 2.5" exhaust will be quieter, but its almost sure to restrict peak hp, (especially on nitrous)
your headers,primairy length and diam. and header collectors,your cam timing ,compression ratio,and displacement, not the exhaust pipe diam. after the collectors tend to dictate the torque curve
 
When I say 1 5/8" primaries and 3" collector, I'm only looking at long tube headers.

Paul, I really appreciate the time you take to help me get my combo dialed in good. And you're right, I want the combo set up for best performance off the nitrous - as you said it'll only be used sometimes, so whatever the spray adds will be appreciated for what it is when I activate it.

I checked out your links, the MSD timing controller is a steal of a deal and I've added it to my parts list. Thank you, sir.

Edit to add, I'm going with a 3" exhaust now. If its not going to hurt NA performance that's great and I really don't care if its louder. ;)
 
Another question. This has always been planned as a 350 build. I was on the website last night where I plan to buy my short block and noticed they have 400's. What's the pro and con of going 400 vs. 350?
 
John said:
Another question. This has always been planned as a 350 build. I was on the website last night where I plan to buy my short block and noticed they have 400's. What's the pro and con of going 400 vs. 350?
Click to expand...

the main reason most people don,t build 400 sbc engines is the comparative rarity of decent 400 sbc blocks vs the far more common 350 blocks
the 400sbc has a larger bore, that requires a slightly smaller sealing surface between cylinders and the 400s have no coolant flow between the cylinder walls where the casting is Siamesed, this has the effect that steam holes must be drilled in the cylinder heads, to match extra holes that are drilled in the 400 block deck, if low rpm use like street driving is intended.
but in exchange your looking at gaining about 50hp/50 ft lbs of torque, from the larger displacement, with roughly the same parts used, in the engine builds.
now you can compromise and build a 383 with the 350 bore (plus .030)and longer 400sbc 3.75"stroke vs the 350s 3.48" stroke but the 400 is a great place to start and built correctly its mostly a big jump up over a 350sbc.
in an ideal world youll use an aftermarket DART block with its significantly thicker and stronger block when building a 400

read these threads

viewtopic.php?f=57&t=2991&p=7851&hilit=steam+holes#p7851

viewtopic.php?f=51&t=715

viewtopic.php?f=51&t=47
 
Grumpy, reviving an old thread here. Had to put the project on hold but is finally ready to finish the engine/drivetrain at least. I've ordered a 383 short block set up to yield 9.5:1 SCR with my 64 cc heads and they'll send the headgaskets needed or at least tell me what thickness they need to be. About installing the cam 4 degrees retarded, does this cam come with 4 degrees advance ground in?
 
John said:
Grumpy, reviving an old thread here. Had to put the project on hold but is finally ready to finish the engine/drivetrain at least. I've ordered a 383 short block set up to yield 9.5:1 SCR with my 64 cc heads and they'll send the headgaskets needed or at least tell me what thickness they need to be. About installing the cam 4 degrees retarded, does this cam come with 4 degrees advance ground in?
Click to expand...

youll need to degree the cam too verify if its advanced or retarded, I like to install cams at split overlap or strait up and most cams come out of the box set up to be 4 degrees advanced if installed in the common DOT-TO-DOT instal.

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Will do, I'd already planned to degree the cam. How much carb spacer would you run? There's only a $2 price difference between 1" and 2" phenolic spacers.
 
John said:
Will do, I'd already planned to degree the cam. How much carb spacer would you run? There's only a $2 price difference between 1" and 2" phenolic spacers.
Click to expand...


ID sure try the intake first with NO spacer then try with a 2" if a spacer helps at all its usually due to increased plenum volume and distance increase between intake runner entrances and the carbs venturies, reducing the abrupt change in flow direction, both tend to be greater and smoother with a 2"

read these
viewtopic.php?f=55&t=4362&p=11450&hilit=carb+spacer#p11450

viewtopic.php?f=55&t=1038&p=10808&hilit=carb+spacer#p10808
 
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