General engine tech -- Drag Racing to Circle Track

Moderator: Team

Post Reply
Old School
Posts: 315
Joined: Sun Feb 13, 2005 11:27 am


Post by Old School » Mon Feb 27, 2006 10:58 pm

I recently had a customer bring in an assortment of parts to be assembled into a 632. After trial fitting I have come up with several "issues" that maybe someone with more experience can help with.
The combo is a Dart big M 10.2 block with 4.84 bore spacing. Callies 4.75 crank with Miller 6.7 rods, JE pistons. Heads are a set of maybe early 90's Pontiac 10093378 pro stock heads. Valve size are 2.48 intake, 1.9 exhaust. Head bolt holes have been sleeved for porting. Intake is sheet metal that was acquired from an entirely different engine but for the same style head. Camshaft is 288-312 @.050 .510 Intake lobe .477 exhaust lobe on 114 ls. Rockers 1.8 int, 1.7 ex. Cam is ground on .875 CORE standard BBC bearings. Engine will be used on a dragster. Rpms from 5500 to 7800. Problems are as follows:

The intake valves rub the piston reliefs everywhere. I can use .030 offset head dowels to move the valves away from the adjoining cylinder wall but that will require redrilling the head bolt holes and the sleeves. The sleeves now measure .460 ID and opening to .500 should take care of the .030 offset dowels. The head studs will almost start in the threads as is. I can machine the piston valve reliefs a little larger and take the offset into consideration. The intake valves have about .015 from the lap line to the outer valve edge. Reduce the size of the valves to 2.460 or so??? The bowl is already 91% of the 2.48 valve. Any other suggestions????

The pistons he has are for the Pontiac 427 heads and are 18 degree. The 378 heads are 15 degree as best I can measure. I have flycut one piston and roughed in the appoximate shape the valve reliefs need to be. From first appearance it seems this will probably work????

The cam lobes slightly touch every rod on the 2-4-6-8 side. The touch is so light the engine can still be rotated. Removing .030-.040 from the rod should provide enough clearance. My problems is with the anemic shaft diameter. Will flex and bending be an issue that should be addressed with a larger core that will magnify the rod/lobe interference???

Offsetting the heads also cause alignment problems with the ports. I will try to straighten everything up and use Z spar the fill any anurisms.

This is not my normal type of engine build. Hopefully some that has worked through the same problems can offer some help I have not thought of. I recently read in some forum that "God hates 632's"- I know why. Thanks in advance for any help.

bill jones
Posts: 2484
Joined: Sun Sep 05, 2004 6:38 pm
Location: salt lake city, ut

Post by bill jones » Mon Feb 27, 2006 11:26 pm

-One thing that is important is to make sure you check all the interferences---in particular the rods to the cam lobes-----with the entire engine assembled with the REAL valve springs you intend to use.
-The Jesel belt will stretch about 6 degrees either direction when loaded- berfore the cam starts to move--so you need to degree the cam to get the valve to piston clearances right---AND---to get the rod to cam lobe clearances right.
-And you also need to run the crankshaft backwards and check the clearances as the lobes dig into the rods either direction.
-You also need to check every cylinder for valve clash during overlap---here again in a race ready condition.
-I have seen enough variation there that I'm sure you will see descrepancies among the 8 holes.
-I have had to slightly cut the margins back----on an angle to allow the valves to pass each other without touching.
-You might want to install the cam and the heads with the valve train----leaving the crankshaft out of the engine-----and install about 4 dial indicator on the cam shaft before you install the valvetrain----then pay attention to how bad the cam becomes a worm from the pressures against the lobes when you rotate the cam and the valve train.
-One other little problem could be inside the offset Jesel rockers.
-I have found broken cage ends that normally secure the thrust of the needle bearings.
-This allows the needles to work inward and bind up etc.
-I have taken to making up exact length spacers to slip in there as i'm pressing in new Torringtons-----so that those cage ends have some support and can't just break away.
-Getting the pushrod lengths exact means that you should check all 16 to make sure they are dead nuts---as you'll be needing 3 different lengths of pushrods.
-Then these pushrods are so huge that you have to make sure they fit down inside the roller lifter without binding up on the inside of the lifter body----and that pushrods actually fit along the pushrod wall of the ports---and the valley headbolt bosses have to be clearances good too.

Posts: 2009
Joined: Tue Oct 12, 2004 1:19 pm
Location: Dillsburg, PA

Post by airflowdevelop » Mon Feb 27, 2006 11:44 pm

I was told a long time ago, that you are not building a real motor unless you need a 4" angle grinder to clearance.....I don't know how true this is, but welcome to my world! What application is this for? If it is a S/C or Top eliminator car, these guys think they can run stuff for ever, so you want extra clearance!

What clearance do you like between valves? I have heard some guys running as tight as .005". That seems very tight considering valve guide wear and heat expansion.

(sorry to HiJack thread)


Post by rmcomprandy » Mon Feb 27, 2006 11:48 pm

On the bottom end, steel rods are pretty much a bolt-together but, those Miller aluminum rods have NO clearance anywhere; especially at the bottom of the bores and camshaft so a lot of rod material has to be ground away to clear. Grinding the rod OR use a small base circle camshaft, pick your poison. GRP rods have a little more clearance however, they need some clearancing, too.
Check for exhaust pushrod interference at the valley wall of the BLOCK as they sometimes interfere a little there with the 15 degree Pontiac heads or 14 degree DART's.

Old School
Posts: 315
Joined: Sun Feb 13, 2005 11:27 am

Post by Old School » Tue Feb 28, 2006 12:26 am

The seat pressure will be 310-330. Open pressure will be about 900 at .870 net lift. How much camshaft flex/bending twist is acceptable? The customer wants a chain in the engine instead of a belt drive. To add to this the engine will be a wet sump. I know that some horsepower is given up but this is the parts we have to work with. I did a BBC with the Big Duke heads and used 3 different length pushrods. I don't know where I got the idea but I was thinking the Pontiacs only had 2 different lengths. The intake rockers are not offset like the Big Dukes were. So will I have 8 exhaust one length, 4 intake one length, the other 4 intake another length? Thanks for the previous replies.

Engine will be for a Quick 8 races in our area. Car need to run at least 4.20's at 1850 lbs with driver. May need some nitrous.

I have to use the Miller aluminum rods. The camshaft is already a small base circle that is of concern. As you mentioned the rods hit everything. After carefully clearancing the block for the rods the pistons rock pretty bad at BDC due to the clearance and the subsequent skirt out of the bottom of the cylinder. I know a taller block would be better but this is what we have. I have talked to a few other shops in our area and they say it will work but the piston skirts will have rock "lines" but should stay together. A lot of "shoulds" with this combo.

Thanks for the help from everyone.

bill jones
Posts: 2484
Joined: Sun Sep 05, 2004 6:38 pm
Location: salt lake city, ut

Post by bill jones » Tue Feb 28, 2006 1:23 am

-Some time back I posted some results about how close you could run valves to each other---did some tests where I heated the valves and measured the diameter change.
-Steel valves grow a lot and Ti valves don't grow much---but I don't exactly remember the numbers.
-I would not run .005" at the overlap clash point unless you forced both valves towards each other pretty good at the clash lift point and I would only then consider that .005" if it was Ti valves.
-That's why I cut the margins on an angle---because when you blue the edges and rub'm together at the clash point you see that the valves hit at the top edges of the margins until you cut the angles on the margins.
-I would much rather have .020" clearance after forcing the valves towards each other---especially with steel valves.
-I can't say what is acceptable as far as camshaft deflection as I haven't tested one of these lately.
-I first tested a flattappet cam in the late 1960's and I was very enlightened that deflection was a big deal so I just live with it.
-The way I first found out about the cam deflection was I had installed one head and adjusted all the rockers on that head dead nuts---then installed the other head----and came back and double checked the first head and they were all over the place.
-So I did the dial indicator test and found out about the deflection---and that was only 300# open pressure on a 1/2" lift flattappet cam.
-I was thinking about the pushrods and rockers with big chief heads---and I don't exactly know what the difference is between the pontiac heads and big dukes and big chiefs.
Last edited by bill jones on Sun Mar 05, 2006 12:05 pm, edited 1 time in total.

Posts: 421
Joined: Fri Nov 19, 2004 12:29 pm

Post by ChrisU » Tue Feb 28, 2006 6:00 am

Just an opinion, but I'd try and talk him into selling that block and getting a raised cam deal...

That small cam is going to twist enough with that spring pressure that you should be checking VtoP in every cylinder and you might end up cutting the rear pistons differently than the fronts... depending on how tight you make it.

How many rpm do you plan to spin it? I've found RPM combined with big spring pressure is the nail in the coffin for cams like that. might break, might not. It's a grenade with the pin pulled...

Lots of folks out there doing it but I just dont like that scenario, especially when your reputation is on the line.

Again, just my opinion.
Uratchko Racing Engines

Ron C.
Posts: 601
Joined: Fri Feb 04, 2005 12:54 pm
Location: Visalia, Calif

Post by Ron C. » Tue Feb 28, 2006 1:11 pm

I've built and raced a 632 so I've worked through some of the issues you've encountered. Your on the right track in fly cutting the piston rather than moving the head. The rod clearance issue is the standard deal. clearancing the block bottom and notching the rod for cam will work OK. You can send the rods to Miller or MGP to be notched if you want. It's a standard deal for them.
The real issue in running the 632 and making good power is piston speed. It's off the chart at 8K were I ran mine. It's much higher than even Pro Stock engines today. That big piston and long stroke really pounds the oil in a wet sump. At least talk him into an external pump so you can cover the oil. Definitely run a good vacuum pump. The cam is also an issue. You'll need more lobe seperation to make good power in the upper RPM range. At least 116. And I would bump the seat spring pressure up to 350 and run the NexTek springs. That's my advice anyway.......
Have fun......check everything for clearances.
Ron Clevenger
Creekside Racing Ministry
John 14:6
Ron Clevenger
CSU Gas Dominator ProCharger nonintercooled
Top Eliminator West http://www.topeliminatorwest.net
Steve Morris http://www.stevemorrisengines.com
6.49@219mph (still tunning)

Old School
Posts: 315
Joined: Sun Feb 13, 2005 11:27 am

Post by Old School » Sun Mar 05, 2006 9:41 am

Thanks for all the suggestions and help. I have been finishing up some other work and have just now had time to get back to the 632.

I am still concerned with the closeness of the intake valve to the cylinder wall. I would like to move them at least .030. This will take a lot of work with the intake and head bolt holes. Looking at Reher-Morrison Super Series engines I see they have 2.45 valves in a 4.6 bore with the 4.84 bore spacing. Does anyone know if the heads are offset with dowels or any other method??? Are they on the stock dowel location??

The customer is willing to have another cam ground. The small base core is the best for rod clearance but it makes me nervous just looking at it. What would the best core size for both clearance and durability, keep in mind this is the std. Chevy bearings???

I am feeling a little better about this engine, but when we mocked up the heads/intake I discovered I will be have to make a 3/8 inch spacer plate between the heads and intake. As an experience older engine builder told me 20 years ago "If it bolts together, it will probably be down at least 150 horsepower" Thanks to everyone

Posts: 2443
Joined: Sat Feb 14, 2004 4:04 pm
Location: Abbeville, LA

Post by maxracesoftware » Sun Mar 05, 2006 1:00 pm

Looking at Reher-Morrison Super Series engines I see they have 2.45 valves in a 4.6 bore with the 4.84 bore spacing. Does anyone know if the heads are offset with dowels or any other method??? Are they on the stock dowel location??
632 cid in Dave Beeson's Camaro
its has 14 degree Dart-Olds on stock dowel locations
i started off at 2.400/1.900 valves
then 2.420/1.900,
then 2.450/1.870,
then finally as it is now => 2.500/1.830 on 4.600" Bore
each and every time, there were gains in both HP/Torque
.5435 Ratio = 2.500/4.600
early 90's Pontiac 10093378 pro stock heads. Valve size are 2.48 intake, 1.9 exhaust
the Dart-Olds compared to your 10093378 Heads as for
valve tilt , angles , and spacing ?? i don't know/remember exact differences between those 2

with the Cams we use, i setup Cyl-Heads to have a bare minimum
of .420"

the .420" is measured by opening up the Intake Valve to .420" Lift
and then by hand opening the exhaust valve towards max lift
and see if it hits the Intake Valve at .420" Intake Lift

if the exhaust valve hits the Intake Valve at anything "LESS"
than .420" Intake Valve Lift, then i mill Exhaust Valve's margin
at an angle to help clear, and if that's still not enough, i turn down the
Exhaust Valve OD + remill margin at an angle

i'd like to see .450"+ , but .420" worked so far

Dave Beesons Camaro 632 cid
http://www.maxracesoftware.com/Dave_Bee ... Street.jpg

Flowmaster Nostalgia Pro Street

Round 1
MIKE RADNIS 0.17 7.781 174.41
BARBARA NESBITT 0.412 7.837 176.01

DAVID BEESON 0.052 13.407 65.54

DON RAYBURN 0.048 7.847 173.92

TONY NESBITT 0.071 7.555 181.96

DAVID BEESON 0.084 7.551 180.43
DON RAYBURN -0.009 7.856 172.56

TONY NESBITT 0.011 7.577 182.95
MIKE RADNIS 0.358 7.742 175.66

DAVID BEESON 0.071 17.416 53.03
TONY NESBITT -0.208 7.551 183.1

just finished and Dyno tested another 632 cid in same Nostalgia Pro Street class, has Dart-Olds 2.500/1.820 valves on stock dowel locations,
made approx +60 more HP (1604 HP w/Nitrous) than Beeson's 632 Nostalgia Pro Street

if you enough Valve-to-Valve clearance at OverLap Period,
i'd try to keep your 2.480 intake valve and not turn it down,
if the Cyl-Head is valve jobbed + ported correctly , it can use that 2.480
Meaux Racing Heads
MaxRace Software
PipeMax and ET_Analyst for DragRacers
PipeMax v3.98   http://www.maxracesoftwares.com/forum/v ... f=14&t=249

Old School
Posts: 315
Joined: Sun Feb 13, 2005 11:27 am

Post by Old School » Tue Mar 07, 2006 11:07 pm

if you enough Valve-to-Valve clearance at OverLap Period,
i'd try to keep your 2.480 intake valve and not turn it down,
if the Cyl-Head is valve jobbed + ported correctly , it can use that 2.480
Meaux Racing Heads
MaxRace Software
ET_Analyst for DragRacers

Thanks Larry for sharing the results and increasing the valve size from 2.4 to 2.5.

I am sure the head has been professionally worked. Whoever did the work is much more talented and experienced than myself. The throat diameter is 2.27. As best I can calculate that should be an area of 3.95 with the 11/32 valve stem accounted for. The tightest cross section area I can measure is 4.56 at the pushrod pinch. Rather large but the calculations I am getting says this should be sufficient up to about 7900 rpm in the 632. Someone please correct me if this is incorrect????

I depressed the intake valve .450 and then opened the exhaust valve to the closest point I could find in the overlap crunch. Had about .018 clearance between the two valves. The valves are titanium-hopefully this will be enough or should the exhaust be cut down some??? I have not yet checked with the springs assembled as Bill Jones suggested. That should wait until the cam profile and lobe separation arrives. I hope to do that soon.

The customer has headers 2 3/8 x 28" with 4 1/2 collectors 10" long. Close???

Again, thanks to all for advice given.

Post Reply