Lynn E. Hanover

I have two Daryl Drummond engines I use in my race car. They are now obsolete and I am going to have to build up a more powerful engine. Our problem is that the rules require that we use 38MM chokes in a Webber 48IDF carb for a bridge ported engine or 40MM chokes for a street ported engine.



The current engines both were built with 84 style cast iron with very mild reshaping of the port runners, and a large "J" bridge port.



Daryl says that there is not a better combination, or need to go to cast iron with bigger runners because of the restrictive choke size. Our best power is 245HP at 9,400 RPM. His current engines have much more power and still use the small cast iron but he is now turning them well over 10,000 RPM.



There is another view on the engine construction where others use a combination of cast iron that include turbo end housings that I identified and probably center cast iron with the largest available port (runner opening) size, whatever year and model that might be.



At least two of the cars running the bigger port runners are much faster the us. One was on the pole for the national championship race two years ago. I suspect that is the way to go cast iron wise.



What is the current thinking on large verses small runners. What HP would be available from a big street port with 40MM chokes, verses a bridge port with 38MM chokes.



Underpowered in Ohio.

Lynn E. Hanover

SomeGuy_sg

no idea , but the 38mm webber does sound better. cause porting on a rotary is like playing with wild cam and timing on a pistion . you would lose low-end but you are racing so that would not matter much.........just my .02

j9fd3s

the turbo end plates have larger runners, but the center plates are a little smaller because of the injector bosses. the fd plates are yet again larger, and the cosmo plates even bigger than that.



what kind of rotors are you running? the 89-91 non turbo are lighter and have 9.7:1 compression, and the rx8 ones are cheaper, lighter and are 10:1, another guy on here put rx8 rotors into a pp motor and found 25hp

l8tbrak

Ito will probably know for sure but Drummand is correct about the choke down/ restriction of the 38MM. However the timing and volume in the primaries is where a lot of ground can be made up. The flow after the restriction is most important. The difference would be likeshooting a spit ball through a straw or through a paper towel holder. The paper towel card board can have more volume and potentially more power but your source of air is resticted, while using the staw you get more volecity and usable air volume. (but in reverse since a motor is a air pump).

The higher compression rotors would be a plus. Also the 84 side housing should be from the 12A which has pretty good size. I dont think it would have been the 13B that year. Then you must consider ( I forget) the housing o rings. They changed in 86 but the fd is back with the o ring in the cast iron. The best years were the 73-74 13B because of the large stock casting of the runners.

Dont forget they may be using a ultra light rotor set like PR Motorsports did.

they are good only for one season though.

Last but not least contact Mandeville or Downning Atlanta. They would know whats going on because Mazda sends them stuff to develope. (Renisis)

Lynn E. Hanover

The engines are 12As and came with lightened rotors. They are the leading pocket style because they are lighter in stock trim. The actual compression ratio I don't know.



Any idea exactly what year and model number end plates I should use. What center section has the biggest ports? Year and part number?



I know I will have to make a new manifold.



Thank you.



Lynn E. Hanover

l8tbrak

Contact Steve Sanders at MAZDA Comp. or any of the guys. They will know that answer and will be more than happy to help. Look at the thread here on NPabout contigency program.One thread has Hyper link to MAZDASPEED and their number.



you shouldn't have to make a new manifold because you will have the same bolt pattern UNLESS it a 3rd gen side housing. i am not sure on that, maybe some would if the manifold bolts in the same places in each side housing.Racing Beat should have that covered should you need to change.



73-76 13b center but any can be ported large enough.

camocarl

Larry, Are those Drummond motors you say are underpowered for sale? Thanks, Camocarl@aol.com

howracer

i have to admit the GT3 in the title of your post grabbed my eye. then i read your post about your "obsolete" Daryl Drummond engines.... what??????



i ran GT3 from 83 to 89 when there was actual competition in the Cendiv (any of 10 cars could win every race) and the runoffs were run at a real racetrack, Road Atlanta. Roger Mandeville built my engines for the first 3 seasons and Daryl Drummond built them for the last 3 years. and yes, we ran 38 mm chokes just like you.



it is my opinion that no one builds a better GT3 motor than Daryl.



if Daryl is telling you that he is happy w the bridgeported/38 mm setup in your motors versus a 40mm raceport configuration i would suggest you believe it.



running his motors i consistantly trapped a best in class 143 mph at the bottom of the Road Atlanta straight at 10,000 rpm in top gear. i finished 2nd, 3rd twice and 4th twice at the runoffs in GT3. while a number of years has passed the primary competition is still running the same 4 valve motors and making about the same hp. your 245 hp is hardly obsolete let alone un-competitive. who drives the car? i don't see any National points associated with your name in 02 or 03.



i have a Drummond Enterprises dyno sheet i recently dug up to show Judge Ito from 3/25/89 that shows 254 corrected hp at 9000. the Judge was quite impressed w 254 hp from a NA 12A running w 38 mm chokes. that (dry sumped) motor at one time or another held lap records at every Cendiv track, sat on the pole in 7 of 12 races, won the June Sprints at Elkhart Lake and beat the '89 National Champ Jim Dentici (Mugen Honda tube frame) twice, his only 2 losses that year. Daryl knows his stuff.



so i had 9 more hp than you. that's not alot of additional hp. i suggest you get tuning on your chassis and listen to Daryl. Daryl wrote the book. i think that Camocarl has the right idea as to wanting to buy your Drummond motors.



i am just slightly sorry for the partial rant but Daryl is a friend and a fabulous engine guy and the concept of someone who can't even spell Weber correctly building a "more powerful engine" than Daryl and labeling his engine "obsolete" when he is telling you it isn't.... well.. i do wish you good luck.



howard coleman

camocarl

Drummond builds a good motor with good HP. There are few people that I trust with a race motor, and one of them is Daryl. He has built motors a very long time and knows his stuff.BTW Daryl reccomends not turning these motors over 8000 rpms.

howracer

when scca changed the choke size down to 38 mm Daryl changed his motors to turn more rpm to make up for the increased restriction. Daryl said that 7000 to 10,000 was the only range for the engine. that's why i went to an adjustable ratio gearbox so i could come out of the slowest corners at each track at a minimum of 7000. my dynosheet shows 247 hp at 10,000 so the motor held up pretty well at high rpm. perhaps Daryl was referring to a non-drysumped motor.

howard coleman